LM3535TMX/NOPB - NATIONAL SEMICONDUCTOR

LM3535

LM3535 Multi-Display LED Driver with Ambient Light Sensing and Dynamic

Backlight Control Compatibility

Literature Number: SNVS598

LM3535

August 12, 2010

Multi-Display LED Driver with Ambient Light Sensing and

Dynamic Backlight Control Compatibility

General Description

The LM3535 is a highly integrated LED driver capable of driv-

ing 8 LEDs in parallel for large display applications. Indepen-

dent LED control allows for a subset of the 6 main display

LEDs to be selected for partial illumination applications. In

addition to the main bank of 6, the LM3535 is capable of driv-

ing an additional 2 independently controlled LEDs to support

Indicator applications.

The LED driver current sinks are split into three independently

controlled groups. The primary group can be configured to

drive up to six LEDs for use in the main phone display. Groups

B and C are provided for driving secondary displays, keypads

and indicator LEDs. All of the LED current sources can be

independently turned on and off providing flexibility to address

different application requirements.

The LM3535 provides multi-zone Ambient Light Sensing (1 or

2 ALS inputs depending on option) allowing autonomous

backlight intensity control in the event of changing ambient

light conditions. A PWM input is also provided to give the user

a means to adjust the backlight intensity dynamically based

upon the content of the display.

The LM3535 provides excellent efficiency without the use of

an inductor by operating the charge pump in a gain of 3/2 or

in Pass-Mode. The proper gain for maintaining current regu-

lation is chosen, based on LED forward voltage, so that

efficiency is maximized over the input voltage range.

The LM3535 is available in National’s tiny 20-bump, 0.4mm

pitch, thin micro SMD package.

Features

■Drives up to 8 LEDs with up to 25mA of Diode Current

Each

■External PWM input for Dynamic Backlight Control

■Multi-Zone Ambient Light Sensing (ALS)

■Dual-ALS Sensor Inputs (LM3535-2ALS only)

■ALS Interrupt Reporting

■Independent On/Off Control for all Current Sinks

■128 Exponential Dimming Steps with 600:1 Dimming Ratio

for Group A (Up to 6 LEDs)

■8 Linear Dimming States for Groups B (Up to 3 LEDs) and

D1C (1 LED)

■Programmable Auto-Dimming Function

■Up to 90% Efficiency

■0.55% Accurate Current Matching

■Internal Soft-Start Limits Inrush Current

■True Shutdown Isolation for LEDs

■Wide Input Voltage Range (2.7V to 5.5V)

■Active High Hardware Enable

■Total Solution Size < 16mm2

■Low Profile 20 Bump micro SMD Package

(1.650mm × 2.055mm × 0.6mm)

Applications

■Smart-Phone LED Backlighting

■Large Format LCD Backlighting

■General LED Lighting

Typical Application Circuit

30082468

30082441

Minimum Layout

LM3535 Multi-Display LED Driver with Ambient Light Sensing and Dynamic Backlight Control

Compatibility

Connection Diagram

20 Bump micro SMD Package

NS Package Number TMD20AAA

30082469

Pin Descriptions

Bump #s

TMD20AAA

Pin Names Pin Descriptions

A3 VIN Input voltage. Input range: 2.7V to 5.5V.

A2 VOUT Charge Pump Output Voltage

A1, C1, B1, B2 C1+, C1-, C2+, C2- Flying Capacitor Connections

D3, E3,E4, D4 D1A-D4A LED Drivers - GroupA

C4, B4 D53, D62 LED Drivers - Configurable Current Sinks. Can be assigned to GroupA or GroupB

B3 D1B / INT LED Driver/ ALS Interrupt - GroupB Current Sink or ALS Interrupt Pin. In ALS Interrupt

mode, a pull-up resistor is required. A '0’ means a change has occurred, while a ‘1’

means no ALS adjustment has been made.

C3 D1C / ALS LED Driver / ALS Input - Indicator LED current sink or Ambient Light Sensor Input

D2 PWM External PWM Input - Allows the current sinks to be turned on and off at a frequency

and duty cycle externally controlled. Minimum On-Time Pulse Width = 15µsec.

E1 HWEN Hardware Enable Pin. High = Normal Operation, Low = RESET

C2 SDIO Serial Data Input/Output Pin

E2 SCL Serial Clock Pin

A4 GND

(LM3535)

ALSB

(LM3535-2ALS)

Ground for LM3535 or Ambient Light Sensor B for LM3535-2ALS

D1 GND Ground

Ordering Information

Order Information Package Supplied As

LM3535TME

TMD20AAA

250 Units, Tape & Reel

LM3535TMX 3000 Units, Tape & Reel

LM3535TME-2ALS 250 Units, Tape & Reel

LM3535TMX-2ALS 3000 Units, Tape & Reel

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LM3535

Absolute Maximum Ratings (Note 1, Note

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales Office/

Distributors for availability and specifications.

VIN pin voltage -0.3V to 6.0V

SCL, SDIO, HWEN, PWM pin

voltages

-0.3V to (VIN+0.3V)

w/ 6.0V max

IDxx Pin Voltages -0.3V to

(VVOUT+0.3V)

w/ 6.0V max

Continuous Power Dissipation

(Note 3)

Internally Limited

Junction Temperature (TJ-MAX) 150°C

Storage Temperature Range -65°C to +150° C

Maximum Lead Temperature

(Soldering)

(Note 4)

ESD Rating(Note 5)

Human Body Model 2.0kV

Operating Rating

(Note 1, Note 2)

Input Voltage Range 2.7V to 5.5V

LED Voltage Range 2.0V to 4.0V

Junction Temperature (TJ) Range -30°C to +110°C

Ambient Temperature (TA) Range

(Note 6)-30°C to +85°C

Thermal Properties

Junction-to-Ambient Thermal

Resistance (θJA),

TMD20 Package

(Note 7)

40°C/W

Electrical Characteristics (Note 2, Note 8)

Limits in standard typeface are for TA = 25°C, and limits in boldface type apply over the full operating temperature range (-30°C to

+85°C). Unless otherwise specified: VIN = 3.6V; VHWEN = VIN; VPWM = 0V;VDxA = VDxB = VDxC = 0.4V; GroupA = GroupB = GroupC

= Fullscale Current; ENxA, ENxB, ENxC Bits = “1”; 53A, 62A Bits = "0"; C1 = C2 = CIN= COUT= 1.0µF. (Note 9)

Symbol Parameter Condition Min Typ Max Units

IDxx

Output Current Regulation

GroupA

2.7V ≤ VIN ≤ 5.5V

EN1A to EN4A = '1', 53A = 62A = '0'', EN53

= EN62 = ENxB = ENxC = '0'

4 LEDs in GroupA

23.6

(-5.6%) 25 26.3

(+5.2%)

(%)

2.7V ≤ VIN ≤ 5.5V

EN1A to EN4A = EN53 = EN62 = '1', 53A =

62A = '1'', ENxB = ENxC = '0'

6 LEDs in GroupA

23.2

(-7.2%) 25 26.3

(+5.2%)

(%)

Output Current Regulation

GroupB

2.7V ≤ VIN ≤ 5.5V

EN1B = EN53 = EN62 = '1', 53A = 62A = '0',

ENxA = ENC = '0'

3 LEDs in GroupB

23.3

(-6.8%) 25 26.0

(+4.0%)

(%)

Output Current Regulation

IDC

2.7V ≤ VIN ≤ 5.5V

ENC = '1', ENxA = ENxB = '0'

23.8

(-4.8%) 25 26.8

(+7.2%)

(%)

Output Current Regulation

GroupA, GroupB, and GroupC

Enabled

3.2V ≤ VIN ≤ 5.5V

VLED = 3.6V

DxA

mA 25

DxB

DxC

IDxx-

MATCH

LED Current Matching(Note 10)2.7V ≤ VIN ≤ 5.5V

GroupA (4 LEDs) 0.25 2.40

%GroupA (6 LEDs) 0.55 2.78

GroupB (3 LEDs) 0.25 2.41

VDxTH

VDxx 1x to 3/2x Gain Transition

Threshold VDxA and/or VDxB Falling 130 mV

VHR

Current sink Headroom Voltage

Requirement

(Note 11)

IDxx = 95% ×IDxx (nom.)

(IDxx (nom) = 25mA) 100 mV

ROUT

Open-Loop Charge Pump Output

Resistance

Gain = 3/2 2.4 Ω

Gain = 1 0.5

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LM3535

Symbol Parameter Condition Min Typ Max Units

IQQuiescent Supply Current Gain = 3/2, No Load 2.86 4.38 mA

Gain = 1, No Load 1.09 2.31

ISB Standby Supply Current 2.7V ≤ VIN ≤ 5.5V

HWEN = VIN, All ENx bits = "0" 1.7 4.0 µA

ISD Shutdown Supply Current 2.7V ≤ VIN ≤ 5.5V

HWEN = 0V, All ENx bits = "0" 1.7 4.0 µA

fSW Switching Frequency 1.10 1.33 1.56 MHz

tSTART Start-up Time VOUT = 90% steady state 250 µs

VALS ALS Reference Voltage Accuracy 0.95

(-5%) 11.05

(+5%) V

RALS ALS Resistor Accuracy

RALSA = 9.08kΩ-5 +5

RALSA = 5.46kΩ-5 +5

RALSB = 9.13kΩ-5 +5

RALSB = 5.52kΩ-5 +5

VHWEN HWEN Voltage Thresholds 2.7V ≤ VIN ≤ 5.5V Reset 0 0.45 V

Normal Operation 1.2 VIN

VPWM PWM Voltage Thresholds 2.7V ≤ VIN ≤ 5.5V Diodes Off 0 0.45 V

Diodes On 1.2 VIN

VOL-INT Interrupt Output Logic Low '0' ILOAD = 3mA 400 mV

I2C Compatible Interface Voltage Specifications (SCL, SDIO)

VIL Input Logic Low '0' 2.7V ≤ VIN ≤ 5.5V 0 0.45 V

VIH Input Logic High '1' 2.7V ≤ VIN ≤ 5.5V 1.225 VIN V

VOL SDIO Output Logic Low '0' ILOAD = 3mA 400 mV

I2C Compatible Interface Timing Specifications (SCL, SDIO)(Note 12)

t1SCL (Clock Period) (Note 13)2.5 µs

t2Data In Setup Time to SCL High 100 ns

t3Data Out stable After SCL Low 0 ns

SDIO Low Setup Time to SCL Low

(Start) 100 ns

SDIO High Hold Time After SCL High

(Stop) 100 ns

30082413

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under which operation

of the device is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed performance limits and associated test conditions,

see the Electrical Characteristics tables.

Note 2: All voltages are with respect to the potential at the GND pins.

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LM3535

Note 3: Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ = 150°C (typ.) and disengages at TJ

= 125°C (typ.).

Note 4: For detailed soldering specifications and information, please refer to National Semiconductor Application Note 1112: Micro SMD Wafer Level Chip Scale

Package (AN-1112).

Note 5: The human body model is a 100pF capacitor discharged through a 1.5kΩ resistor into each pin. (MIL-STD-883 3015.7)

Note 6: In applications where high power dissipation and/or poor package thermal resistance is present, the maximum ambient temperature may have to be

derated. Maximum ambient temperature (TA-MAX) is dependent on the maximum operating junction temperature (TJ-MAX-OP = 110°C), the maximum power

dissipation of the device in the application (PD-MAX), and the junction-to ambient thermal resistance of the part/package in the application (θJA), as given by the

following equation: TA-MAX = TJ-MAX-OP – (θJA × PD-MAX).

Note 7: Junction-to-ambient thermal resistance is highly dependent on application and board layout. In applications where high maximum power dissipation

exists, special care must be paid to thermal dissipation issues in board design. For more information, please refer to National Semiconductor Application Note

1112: Micro SMD Wafer Level Chip Scale Package (AN-1112).

Note 8: Min and Max limits are guaranteed by design, test, or statistical analysis. Typical numbers are not guaranteed, but do represent the most likely norm.

Note 9: CIN, CVOUT, C1, and C2 : Low-ESR Surface-Mount Ceramic Capacitors (MLCCs) used in setting electrical characteristics

Note 10: For the two groups of current sinks on a part (GroupA and GroupB), the following are determined: the maximum sink current in the group (MAX), the

minimum sink current in the group (MIN), and the average sink current of the group (AVG). For each group, two matching numbers are calculated: (MAX-AVG)/

AVG and (AVG-MIN)/AVG. The largest number of the two (worst case) is considered the matching figure for the Group. The matching figure for a given part is

considered to be the highest matching figure of the two Groups. The typical specification provided is the most likely norm of the matching figure for all parts.

Note 11: For each Dxx pin, headroom voltage is the voltage across the internal current sink connected to that pin. For Group A, B, and C current sinks, VHRx =

VOUT -VLED. If headroom voltage requirement is not met, LED current regulation will be compromised.

Note 12: SCL and SDIO should be glitch-free in order for proper brightness control to be realized.

Note 13: SCL is tested with a 50% duty-cycle clock.

Block Diagram

30082467

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LM3535

Typical Performance Characteristics

Unless otherwise specified: TA = 25°C; VIN = 3.6V; VHWEN = VIN; CIN= 1µF, COUT = 1µF, C1=C2= 1µF.

ILED vs Input Voltage

6 LEDs

30082419

ILED vs Input Voltage

30082420

ILED vs Brightness Code

Linear Scale

30082423

ILED vs Brightness Code

Log Scale

30082422

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LM3535

Input Current vs Input Voltage

4 LEDs

30082464

LED Drive Efficiency vs Input Voltage

4 LEDs

30082463

Input Current vs Input Voltage

6 LEDs

30082460

LED Drive Efficiency vs Input Voltage

6 LEDs

30082424

Input Current vs Input Voltage

8 LEDs

30082461

LED Drive Efficiency vs Input Voltage

8 LEDs

30082462

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LM3535

LED Drive Efficiency vs Input Voltage

Tri-Temp 6 LEDs

30082426

ILED Matching vs Input voltage

6 LEDs

30082421

Switching Frequency vs Input Voltage

Tri-Temp

30082431

Shutdown Current vs Input Voltage

VIO = 0V

30082427

Shutdown Current vs Input Voltage

VIO = 2.5V

30082428

Quiescent Current vs Input Voltage

1× Gain

30082429

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LM3535

Quiescent Current vs Input Voltage

3/2× Gain

30082430

ALS Boundary Voltage vs. Boundary Code

Falling ALS Voltage

30082470

ALS Boundary Voltage vs. Boundary Code

Falling ALS Voltage (Zoom)

30082471

Diode Current vs PWM Duty Cycle

30082453

Ambient Light Sensor Response

30082454

Diode Current Ramp-Up

tSTEP = 6ms

30082458

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LM3535

Diode Current Ramp-Down

tSTEP = 6ms

30082459

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LM3535

Circuit Description

OVERVIEW

The LM3535 is a white LED driver system based upon an

adaptive 3/2× - 1× CMOS charge pump capable of supplying

up to 200mA of total output current. With three separately

controlled Groups of constant current sinks, the LM3535 is an

ideal solution for platforms requiring a single white LED driver

IC for main display, sub display, and indicator lighting. The

tightly matched current sinks ensure uniform brightness from

the LEDs across the entire small-format display.

Each LED is configured in a common anode configuration,

with the peak drive current set to 25mA. An I2C compatible

interface is used to enable the device and vary the brightness

within the individual current sink Groups. For GroupA , 128

exponentially-spaced analog brightness control levels are

available. GroupB and GroupC have 8 linearly-spaced analog

brightness levels.

Additionally, the LM3535 provides 1 or 2 inputs (LM3535 has

1 and LM3535-2ALS has 2) for an Ambient Light Sensor to

adaptively adjust the diode current based on ambient condi-

tions, and a PWM pin to allow the diode current to be pulse

width modulated to work with a display driver utilizing dynamic

or content adjusted backlight control (DBC or CABC).

CIRCUIT COMPONENTS

Charge Pump

The input to the 3/2× - 1× charge pump is connected to the

VIN pin, and the regulated output of the charge pump is con-

nected to the VOUT pin. The recommended input voltage

range of the LM3535 is 2.7V to 5.5V. The device’s regulated

charge pump has both open loop and closed loop modes of

operation. When the device is in open loop, the voltage at

VOUT is equal to the gain times the voltage at the input. When

the device is in closed loop, the voltage at VOUT is regulated

to 4.3V (typ.). The charge pump gain transitions are actively

selected to maintain regulation based on LED forward voltage

and load requirements.

Diode Current Sinks

Matched currents are ensured with the use of tightly matched

internal devices and internal mismatch cancellation circuitry.

There are eight regulated current sinks configurable into 3

different lighting regions.

Ambient Light Sensing (ALS) and Interrupt

The LM3535 provides an Ambient Light Sensing input (2 in-

puts on LM3535-2ALS version) for use with ambient backlight

control. By connecting the anode of a photo diode / sensor to

the sensor input pins, and configuring the appropriate ALS

resistors, the LM3535 or -2ALS version, can be configured to

adjust the diode current to five unique settings, corresponding

to four adjustable light region trip points. Additionally, when

the LM3535 determines that an ambient condition has

changed, the interrupt pin, when connected to a pull-up re-

sistor will toggle to a '0' alerting the controller. See the I2C

interface section for more details regarding the register con-

figurations.

Dynamic Backlight Control Input (PWM Pin)

A PWM (Pulse Width Modulation) pin is provided on the

LM3535 to allow a display driver utilizing dynamic backlight

control (DBC), to adjust the LED brightness based on the

content. The PWM input can be turned on or off (Acknowledge

or Ignore) and the polarity can be flipped (active high or active

low) through the I2C interface. The current sinks of the

LM3535 require approximately 15µs. to reach steady-state

target current. This turn-on time sets the minimum usable

PWM pulse width for DBC/CABC.

LED Forward Voltage Monitoring

The LM3535 has the ability to switch gains (1x or 3/2x) based

on the forward voltage of the LED load. This ability to switch

gains maximizes efficiency for a given load. Forward voltage

monitoring occurs on all diode pins. At higher input voltages,

the LM3535 will operate in pass mode, allowing the VOUT

voltage to track the input voltage. As the input voltage drops,

the voltage on the Dxx pins will also drop (VDXX = VVOUT –

VLEDx). Once any of the active Dxx pins reaches a voltage

approximately equal to 130mV, the charge pump will switch

to the gain of 3/2. This switch-over ensures that the current

through the LEDs never becomes pinched off due to a lack of

headroom across the current sinks. Once a gain transition

occurs, the LM3535 will remain in the gain of 3/2 until an

I2C write to the part occurs. At that time, the LM3535 will

re-evaluate the LED conditions and select the appropri-

ate gain.

Only active Dxx pins will be monitored.

Configurable Gain Transition Delay

To optimize efficiency, the LM3535 has a user selectable gain

transition delay that allows the part to ignore short duration

input voltage drops. By default, the LM3535 will not change

gains if the input voltage dip is shorter than 3 to 6 milliseconds.

There are four selectable gain transition delay ranges (4 for

LM3535-2ALS and 3 for LM3535) available on the LM3535.

All delay ranges are set within the VF Monitor Delay Register .

Please refer to the INTERNAL REGISTERS section of this

datasheet for more information regarding the delay ranges.

Hardware Enable (HWEN)

The LM3535 has a hardware enable/reset pin (HWEN) that

allows the device to be disabled by an external controller

without requiring an I2C write command. Under normal oper-

ation, the HWEN pin should be held high (logic '1') to prevent

an unwanted reset. When the HWEN is driven low (logic '0'),

all internal control registers reset to the default states and the

part becomes disabled. Please see the Electrical Character-

istics section of the datasheet for required voltage thresholds.

I2C Compatible Interface

DATA VALIDITY

The data on SDIO line must be stable during the HIGH period

of the clock signal (SCL). In other words, state of the data line

can only be changed when SCL is LOW.

30082425

FIGURE 1. Data Validity Diagram

A pull-up resistor between the controller's VIO line and SDIO

must be greater than [ (VIO-VOL) / 3mA] to meet the VOL re-

quirement on SDIO. Using a larger pull-up resistor results in

lower switching current with slower edges, while using a

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LM3535

smaller pull-up results in higher switching currents with faster

edges.

START AND STOP CONDITIONS

START and STOP conditions classify the beginning and the

end of the I2C session. A START condition is defined as SDIO

signal transitioning from HIGH to LOW while SCL line is

HIGH. A STOP condition is defined as the SDIO transitioning

from LOW to HIGH while SCL is HIGH. The I2C master always

generates START and STOP conditions. The I2C bus is con-

sidered to be busy after a START condition and free after a

STOP condition. During data transmission, the I2C master

can generate repeated START conditions. First START and

repeated START conditions are equivalent, function-wise.

30082411

FIGURE 2. Start and Stop Conditions

TRANSFERRING DATA

Every byte put on the SDIO line must be eight bits long, with

the most significant bit (MSB) transferred first. Each byte of

data has to be followed by an acknowledge bit. The acknowl-

edge related clock pulse is generated by the master. The

master releases the SDIO line (HIGH) during the acknowl-

edge clock pulse. The LM3535 pulls down the SDIO line

during the 9th clock pulse, signifying an acknowledge. The

LM3535 generates an acknowledge after each byte is re-

ceived. There is no acknowledge created after data is read

from the LM3535.

After the START condition, the I2C master sends a chip ad-

dress. This address is seven bits long followed by an eighth

bit which is a data direction bit (R/W). The LM3535 7-bit ad-

dress is 38h. For the eighth bit, a “0” indicates a WRITE and

a “1” indicates a READ. The second byte selects the register

to which the data will be written. The third byte contains data

to write to the selected register.

30082412

FIGURE 3. Write Cycle

w = write (SDIO = "0")

r = read (SDIO = "1")

ack = acknowledge (SDIO pulled down by either master or slave)

id = chip address, 38h for LM3535

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LM3535

I2C COMPATIBLE CHIP ADDRESS

The 7-bit chip address for LM3535 is 111000, or 0x38.

INTERNAL REGISTERS OF LM3535

Address

Power On Value

Diode Enable

0x10 0000 0000 (0x00)

Configuration

0x20 0000 0000 (0x00)

Options

0x30 0000 0000 (0x00)

ALS Zone

Readback

0x40 1111 0000 (0xF0)

ALS Control

0x50 1 ALS

Version

0000 0011 (0x03)

2 ALS

Version

0000 0000 (0x00)

ALS Resistor

0x51 0000 0000 (0x00)

ALS Select

0x52

LM3535-2ALS

Only

1111 0001 (0xF1)

ALS Zone

Boundary #0

0x60 0011 0011 (0x33)

ALS Zone

Boundary #1

0x61 0110 0110 (0x66)

ALS Zone

Boundary #2

0x62 1001 1001 (0x99)

ALS Zone

Boundary #3

0x63 1100 1100 (0xCC)

ALS Brightness

Zone #1

0x70 1001 1001 (0x99)

ALS Brightness

Zone #2

0x71 1011 0110 (0xB6)

ALS Brightness

Zone #3

0x72 1100 1100 (0xCC)

ALS Brightness

Zone #4

0x73 1110 0110 (0xE6)

ALS Brightness

Zone #5

0x74 1111 1111 (0xFF)

Group A

Brightness

Control Register

0xA0 1000 0000 (0x80)

Group B

Brightness

Control Register

0xB0 1100 0000 (0xC0)

Group C

Brightness

Control Register

0xC0 1111 1000 (0xF8)

30082404

FIGURE 4. Diode Enable Register Description

Internal Hex Address: 0x10

Each ENx Bit controls the state of the corresponding current

sink. Writing a '1' to these bits enables the current sinks. Writ-

ing a '0' disables the current sinks. In order for current to begin

flowing through the BankA current sinks, the brightness codes

stored in either the BankA Brightness register or the ALS

Brightness registers (with ALS enabled) must be non-zero.

The BankA current sinks can be disabled in two different

manors. Writing '0' to the ENx bits when the current sinks are

active will disable the current sinks without going through the

ramp down sequence. Additionally, setting the BankA bright-

ness code to '0' when the current sinks are active (ENx = '1')

does force the diode current to ramp down. All ramping be-

havior is tied to the BankA Brightness or ALS Brightness

LM3535 brightness state machine to ramp the diode current.

Writing a '1 to ENC, EN1B, EN62 and EN53 (when EN62 and

EN53 are assigned to BankB) by default will enable the cor-

responding current sinks and drive the LEDs to the current

value stored in the BankB and BankC brightness registers.

Writing a '0' to these bits immediately disables the current

sinks.

The ENC and EN1B bits are ignored if the D1C/ALS pin is

configured as an ALS input and if the D1B/INT is configured

as an interrupt flag.

30082405

FIGURE 5. Configuration Register Description

Internal Hex Address:0x20

•PWM-EN: PWM Input Enable. Writing a '1' = Enable, and

a '0' = Ignore (default).

•PWM-P: PWM Input Polarity. Writing a '0' = Active High

(default) and a '1' = Active Low.

•53A: Assign D53 diode to BankA. Writing a '0' assigns D53

to BankB (default) and a '1' assigns D53 to BankA.

•62A: Assign D62 diode to BankA. Writing a '0' assigns D62

to BankB (default) and a '1' assigns D62 to BankA.

•ALS-ENA: Enable ALS on BankA. Writing a '1' enables

ALS control of diode current and a '0' (default) forces the

BankA current to the value stored in the BankA brightness

block to control the BankA brightness.

•ALS-ENB: Enable ALS on BankB. Writing a '1' enables

ALS control of diode current and a '0' (default) forces the

BankB current to the value stored in the BankB brightness

block to control the BankB brightness. The ALS function

for BankB is different than bankA in that the ALS will only

enable and disable the BankB diodes depending on the

ALS zone chosen by the user. BankA utilizes the 5

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LM3535

different zone brightness registers (Addresses 0x70 to

0x74).

•ALS-EN: Enables ALS monitoring. Writing a '1' enables

the ALS monitoring circuitry and a '0' disables it. This

feature can be enabled without having the current sinks or

charge pump active. The ALS value is updated in register

0x40 (ALS Zone Register)

•ALSF: ALS Interrupt Enable. Writing a '1' sets the D1B/INT

pin to the ALS interrupt pin and writing a '0' (default) sets

the pin to a BankB current sink.

30082406

FIGURE 6. Options Register

Internal Hex Address: 0x30

•RD0-RD2: Diode Current Ramp Down Step Time. : ‘000’

= 6µs, ‘001’ = 0.77ms, ‘010’ = 1.5ms, ‘011’ = 3ms, ‘100’ =

6ms, ‘101’ = 12ms, ‘110’ = 25ms, ‘111’ = 50ms

•RU0-RU2: Diode Current Ramp Up Step Time. : ‘000’ =

6µs, ‘001’ = 0.77ms, ‘010’ = 1.5ms, ‘011’ = 3ms, ‘100’ =

6ms, ‘101’ = 12ms, ‘110’ = 25ms, ‘111’ = 50ms

•GT0-GT1: Gain Transition Filter. The value stored in this

transition in the event of an input line step. Filter Times =

‘00’ = 3-6ms, ‘01’ = 0.8-1.5ms, ‘10’ = 20µs, On

LM3535-2ALS, '11' = 1µs, On LM3535, ‘11’ = DO NOT

USE

The Ramp-Up and Ramp-Down times follow the following

equations: TRAMP = (NStart - NTarget) × Ramp-Step Time

30082409

30082410

30082414

FIGURE 7. Brightness Control Register Description

Internal Hex Address: 0xA0 (GroupA), 0xB0 (GroupB),

0xC0 (GroupC)

Note: DxA6-DxA0: Sets Brightness for DxA pins (GroupA).

1111111=Fullscale. Code '0' in this register disables the BankA cur-

rent sinks.

DxB2-DxB0: Sets Brightness for DxB pins (GroupB). 111=Fullscale

ALSZT2-ALSZT0: Sets the Brightness Zone boundary used to enable

and disable BankB diodes based upon ambient lighting conditions.

DxC2-DxC0: Sets Brightness for D1C pin. 111 = Fullscale

The BankA Current can be approximated by the following equation

where N = BRC = the decimal value stored in either the BankA Bright-

ness Register or the five different ALS Zone Brightness Registers:

30082418

www.national.com 14

LM3535

TABLE 1. ILED vs. Brightness Register Data

BankA or

ALS

Brightness

Data

% of

ILED_MAX

BankA or ALS

Brightness

Data

% of ILED_MAX BankA or ALS

Brightness Data

% of ILED_MAX BankA or ALS

Brightness

Data

% of ILED_MAX

0000000 0.000% 0100000 0.803% 1000000 4.078% 1100000 20.713%

0000001 0.166% 0100001 0.845% 1000001 4.290% 1100001 21.792%

0000010 0.175% 0100010 0.889% 1000010 4.514% 1100010 22.928%

0000011 0.184% 0100011 0.935% 1000011 4.749% 1100011 24.122%

0000100 0.194% 0100100 0.984% 1000100 4.996% 1100100 25.379%

0000101 0.204% 0100101 1.035% 1000101 5.257% 1100101 26.701%

0000110 0.214% 0100110 1.089% 1000110 5.531% 1100110 28.092%

0000111 0.226% 0100111 1.146% 1000111 5.819% 1100111 29.556%

0001000 0.237% 0101000 1.205% 1001000 6.122% 1101000 31.096%

0001001 0.250% 0101001 1.268% 1001001 6.441% 1101001 32.716%

0001010 0.263% 0101010 1.334% 1001010 6.776% 1101010 34.420%

0001011 0.276% 0101011 1.404% 1001011 7.129% 1101011 36.213%

0001100 0.291% 0101100 1.477% 1001100 7.501% 1101100 38.100%

0001101 0.306% 0101101 1.554% 1001101 7.892% 1101101 40.085%

0001110 0.322% 0101110 1.635% 1001110 8.303% 1101110 42.173%

0001111 0.339% 0101111 1.720% 1001111 8.735% 1101111 44.371%

0010000 0.356% 0110000 1.809% 1010000 9.191% 1110000 46.682%

0010001 0.375% 0110001 1.904% 1010001 9.669% 1110001 49.114%

0010010 0.394% 0110010 2.003% 1010010 10.173% 1110010 51.673%

0010011 0.415% 0110011 2.107% 1010011 10.703% 1110011 54.365%

0010100 0.436% 0110100 2.217% 1010100 11.261% 1110100 57.198%

0010101 0.459% 0110101 2.332% 1010101 11.847% 1110101 60.178%

0010110 0.483% 0110110 2.454% 1010110 12.465% 1110110 63.313%

0010111 0.508% 0111011 2.582% 1010111 13.114% 1110111 66.611%

0011000 0.535% 0110111 2.716% 1011000 13.797% 1111000 70.082%

0011001 0.563% 0111000 2.858% 1011001 14.516% 1111001 73.733%

0011010 0.592% 0111001 3.007% 1011010 15.272% 1111010 77.574%

0011011 0.623% 0111010 3.163% 1011011 16.068% 1111011 81.616%

0011100 0.655% 0111011 3.328% 1011100 16.905% 1111100 85.868%

0011101 0.689% 0111100 3.502% 1011101 17.786% 1111101 90.341%

0011110 0.725% 0111101 3.684% 1011110 18.713% 1111110 95.048%

0011111 0.763% 0111111 3.876% 1011111 19.687% 1111111 100.000%

GroupB and GroupC Brightness Levels = 2.5, 5, 7.5, 10, 12.5,

15, 17.5, 25mA

30082407

FIGURE 8. ALS Zone Register Description

Internal Hex Address: 0x40

•ZONE0-ZONE2: ALS Zone information: '000’ = Zone0,

‘001’ = Zone1, ‘010’ = Zone2, ‘011’ = Zone3, ‘100’ = Zone4.

Other combinations not used

•FLAG: ALS Transition Flag. '1' = Transition has occurred.

'0' = No Transition. The FLAG bit is cleared once the 0x40

15 www.national.com

LM3535

30082417

FIGURE 9. ALS Control / Silicon Revision Register

Description

Internal Hex Address: 0x50

•Rev0-Rev1 : Stores the Silicon Revision value. LM3535 =

'11', LM3535-2ALS = '00'

•AVE2-AVE0: Sets Averaging Time for ALS sampling.

Need two to three Averaging periods to make transition

decision.‘000’ = 25ms, ‘001’ = 50ms, ‘010’ = 100ms, ‘011’

= 200ms, ‘100’ = 400ms, ‘101’ = 800ms, ‘110’ = 1.6s, ‘111’

= 3.2s

30082466

ALS Resistor Control Register Description

Internal Hex Address: 0x51

FIGURE 10.

•R3A-R0A are valid on both the LM3535 and

LM3535-2ALS.

•R3B-R0B are only valid on LM3535-2ALS.

•R0-R3: Sets the internal ALS resistor value

Internal ALS Resistor Table

R3x R2x R1x R0x ALSA

Resistor

Value (Ω)

ALSB

Resistor

Value (Ω)

0 0 0 0 High Impedance

0 0 0 1 13.6k 13.65k

0 0 1 0 9.08k 9.13k

0 0 1 1 5.47k 5.52k

0 1 0 0 2.32k 2.37k

0 1 0 1 1.99k 2.05k

0 1 1 0 1.86k 1.92k

0 1 1 1 1.65k 1.70k

1 0 0 0 1.18k 1.24k

1 0 0 1 1.10k 1.15k

1 0 1 0 1.06k 1.11k

1 0 1 1 986 1.04

1 1 0 0 804 858

1 1 0 1 764 818

1 1 1 0 745 799

1 1 1 1 711 765

30082465

ALS Select Register (2-ALS Version Only)

Internal Hex Address: 0x52

FIGURE 11.

•CP-EN: Forces the LM3535 to operate in the gain of 1.5x

exclusively when the Dx current sinks are enabled.

•PASS-EN: Forces the LM3535 to operate in the 1x Pass-

Mode exclusively when the Dx current sinks are enabled.

CP-EN PASS-EN RESULT

0 0 Normal Operation

0 1 Pass-Mode Only

1 0 1.5x Gain Only

1 1 1.5x Gain Only

•SEL1-SEL0: ALS Selection Bits. SEL1 and SEL0

determine how the ALS sensor information is processed.

'00' = Min. of ALSA and ALSB used, '01' = ALSA used and

ALSB ignored (DEFAULT), '10' = ALSB Used and ALSA

ignored, '11' = Max. of ALSA and ALSB used.

30082415

FIGURE 12. Zone Boundary Register Descriptions

•ZB7-ZB0: Sets Zone Boundary Lines with a Falling ALS

voltage.

0xFF w/ ALS Falling = 992.3mV (typ.).

VTRIP-LOW (typ) = [Boundary Code × 3.874mV] + 4.45mV

For boundary codes 2 to 255. Code 0 and Code1 are

mapped to equal the Code2 value.

Each zone line has approx. 5.5mV of hysteresis between

the falling and rising ALS trip points..

•Zone Boundary 0 is the line between ALS Zone 0 and Zone

1. Default Code = 0x33 or approx. 200mV

•Zone Boundary 1 is the line between ALS Zone 1 and Zone

2. Default Code = 0x66 or approx. 400mV

•Zone Boundary 2 is the line between ALS Zone 2 and Zone

3. Default Code = 0x99 or approx. 600mV

•Zone Boundary 3 is the line between ALS Zone 3 and Zone

4. Default Code = 0xCC or approx. 800mV

www.national.com 16

LM3535

30082416

FIGURE 13. Zone Brightness Region Register

Description

•B7-B0: Sets the ALS Zone Brightness Code. B7 always =

'1' (unused). Use the formula found in the BankA

Brightness Register Description (Figure 7) to set the

desired target brightness. Default values can be

overwritten

•Zone0 Brightness Address = 0x70. Default = 0x99 (25) or

0.084mA

•Zone1 Brightness Address = 0x71. Default = 0xB6 (54) or

0.164mA

•Zone2 Brightness Address = 0x72. Default = 0xCC (76) or

1.45mA

•Zone3 Brightness Address = 0x73. Default = 0xE6 (102)

or 6.17mA

•Zone4 Brightness Address = 0x74. Default = 0xFF (127)

or 25mA

17 www.national.com

LM3535

Application Information

AMBIENT LIGHT SENSING

Ambient Light Sensor Block

The LM3535 incorporates an Ambient Light Sensing interface

(ALS) which translates an analog output ambient light sensor

to a user specified brightness level. The ambient light sensing

circuit has 4 programmable boundaries (ZB0 – ZB3) which

define 5 ambient brightness zones. Each ambient brightness

zone corresponds to a programmable brightness threshold

(Z0T – Z4T).

Furthermore, the ambient light sensing inputs (ALSA and

ALSB(LM3535-2ALS)) features 15 internal software se-

lectable voltage setting resistors. This allows the LM3535 the

capability of interfacing with a wide selection of ambient light

sensors. Additionally, the ALS inputs can be configured as

high impedance, thus providing for a true shutdown during low

power modes. The ALS resistors are selectable through the

ALS Resistor Select Register (see Internal ALS Resistor Ta-

ble). Figure 14 shows a functional block diagram of the am-

bient light sensor input.

30082442

FIGURE 14. Ambient Light Sensor Functional Block Diagram

ALS Operation

The ambient light sensor input has a 0 to 1V operational input

voltage range. The Typical Application Circuit shows the

LM3535 with an ambient light sensor (AVAGO, APDS-9005)

and the internal ALS Resistor Select Register set to 0x40

(2.32kΩ). This circuit converts 0 to 1000 LUX light into ap-

proximately a 0 to 850mV linear output voltage. The voltage

at the active ambient light sensor input is compared against

the 8 bit values programmed into the Zone Boundary Regis-

ters (ZB0-ZB3). When the ambient light sensor output cross-

es one of the ZB0 – ZB3 programmed thresholds the internal

ALS circuitry will smoothly transition the LED current to the

new 7 bit brightness level as programmed into the appropriate

Zone Target Register (Z0T – Z4T, See Figure 13).

With bits [6:4] of the Configuration Register set to 1 (Bit6 =

ALS Block Enable, Bit5 = BankB ALS Enable, Bit4 = BankA

ALS Enable), the LM3535 is configured for Ambient Light

Current Control. In this mode the ambient light sensing input

(ALS) monitors the output of analog output ambient light

sensing photo diode and adjusts the LED current depending

on the ambient light. The ambient light sensing circuit has 4

configurable Ambient Light Boundaries (ZB0 – ZB3) pro-

grammed through the four (8-bit) Zone Boundary Registers.

These zone boundaries define 5 ambient brightness zones.

On start-up the 4 Zone Boundary Registers are pre-loaded

with 0x33 (51d), 0x66 (102d), 0x99 (153d), and 0xCC (204d).

The ALS input has a 1V active input voltage range which

makes the default Zone Boundaries approx. set at:

Zone Boundary 0 = 200mV

Zone Boundary 1 = 400mV

Zone Boundary 2 = 600mV

Zone Boundary 3 = 800mV

These Zone Boundary Registers are all 8-bit (readable and

writable) registers. By Default, the first zone (Z0) is defined

between 0 and 200mV, Z1’s default is defined between

200mV and 400mV, Z2 is defined between 400mV and

600mV, Z3 is defined between 600mV and 800mV, and Z4 is

defined between 800mV and 1V. The default settings for the

5 Zone Target Registers are 0x19, 0x33, 0x4C, 0x66, and

0x7F. This corresponds to LED brightness settings of 84µA,

164µA, 1.45mA, 6.17mA and 25mA of current respectively.

See Figure 15.

www.national.com 18

LM3535

30082443

ALS Zone to LED Brightness Mapping

FIGURE 15.

ALS Configuration Example

As an example, assume that the APDS-9005 is used as the

ambient light sensing photo diode with its output connected

to the ALSA input. The ALS Resistor Select Register (Address

0x51) is loaded with 0x40 which configures the ALS input for

a 2.32kΩ internal pull-down resistor (see Internal ALS Resis-

tor Table). This gives the output of the APDS-9005 a typical

voltage swing of 0 to 875mV with a 0 to 1k LUX change in

ambient light (0.875mV/Lux). Next, the Configuration Regis-

ter (Address 0x20) is programmed with 0xDC, the ALS Con-

trol Register (Address 0x50) programmed to 0x40 and the

Control Register is programmed to 0x3F . This configures the

LM3535’s ambient light sensing interface for:

•Ambient Light Current Control for BankA Enabled

•ALS circuitry Enabled

•Assigns D53 and D62 to bankA

•Sets the ALS Averaging Time to 400ms

Next, the Control Register (Address 0x10) is programmed

with 0x3F which enables the 6 LEDs via the I2C compatible

interface.

Now assume that the APDS-9005 ambient light sensor de-

tects a 100 LUX ambient light at its input. This forces the

ambient light sensors output (and the ALS1 input) to 87.5mV

corresponding to Zone 0. Since Zone 0 points to the bright-

ness code programmed in Zone Target Register 0 (loaded

with code 0x19), the LED current becomes:

Next assume that the ambient light changes to 500 LUX (cor-

responding to an ALS1 voltage of 437.5mV). This moves the

ambient light into Zone 2 which corresponds to Zone Target

comes:

This Example still applies to the LM3535-2ALS version using

two ambient light sensors. The ALS selector block makes the

front end decision as to which sensor to use.

ALS Averaging Time

The ALS Averaging Time is the time over which the Averager

block collects samples from the A/D converter and then av-

erages them to pass to the discriminator block (see ). Ambient

light sensor samples are averaged and then further pro-

cessed by the discriminator block to provide rejection of noise

and transient signals. The Averager is configurable with 8 dif-

ferent averaging times to provide varying amounts of noise

and transient rejection (see Figure 9). The discriminator block

algorithm has a maximum latency of two averaging cycles,

therefore the averaging time selection determines the amount

of delay that will exist between a steady state change in the

ambient light conditions and the associated change of the

backlight illumination. For example, the A/D converter sam-

ples the ALS inputs at 16kHz. If the averaging time is set to

800ms, the Averager will send the updated zone information

to the discriminator every 800ms. This zone information con-

tains the average of approximately 12800 samples (800ms ×

16kHz). Due to the latency of 2 averaging cycles, when there

is a steady state change in the ambient light, the LED current

will begin to transition to the appropriate target value after

approximately 1600ms have elapsed.

The sign and magnitude of these Averager outputs are used

to determine whether the LM3535 should change brightness

zones. The Averager block follows the following rules to make

a zone transition:

•The Averager always begins with a Zone0 reading stored

at start-up. If the main display LEDs are active before the

ALS block is enabled, it is recommended that the ALS-EN

bit be enabled at least 3 averaging cycles times before the

ALS-ENA bit is enabled.

•The Averager will always round down to the lower zone in

the case of a non-integer zone average (1.2 rounds to 1

and 1.75 also rounds to 1). Figure 16 shows an example

of how the Averager will make the zone decisions for

different Ambient conditions.

19 www.national.com

LM3535

30082450

FIGURE 16. Averager Calculation

•The two most current averaging samples are used to make

zone change decisions.

•To make a zone change, data from three averaging cycles

are needed. (Starting Value, First Transition, Second

Transition or Rest)

•To Increase the brightness zone, a positive Averager zone

output must be followed by a second positive Averager

output or a repeated Averager zone. ('+' to '+' or '+' to

'Rest')

•To decrease the brightness zone, a negative Averager

zone output must be followed by a second negative

Averager output or a repeated Averager zone. ('-' to '-' or

'-' to 'Rest')

•In the case of two increases or decreases in the Averager

output, the LM3535 will transition to zone equal to the last

Averager output.

Figure 17 provides a graphical representation of the

Averager's behavior.

30082449

FIGURE 17. Brightness Zone Change Examples

Using the diagram for the ALS block (Figure 14), Figure 18

shows the flow of information starting with the A/D, transition-

ing to the Averager, followed by the Discriminator. Each state

filters the previous output to help prevent unwanted zone to

zone transitions.

30082448

FIGURE 18. Ambient Light Input to Backlight Mapping

When using the ALS averaging functionality, it is important to

remember that the averaging cycle is free running and is not

synchronized with changing ambient lighting conditions. Due

to the nature of the Averager round down, an increase in

brightness can take between 2 and 3 averaging cycles to

change zones while a decrease in brightness can take be-

tween 1 and 2 averaging cycles to change. See Figure 9 for

a list of possible Averager periods. Figure 19 shows an ex-

ample of how the perceived brightness change time can vary.

30082451

FIGURE 19. Perceived Brightness Change Time

Ambient Light Current Control + PWM

The Ambient Light Current Control can also be a function of

the PWM input duty cycle. Assume the LM3535 is configured

as described in the previous example, but this time the Enable

www.national.com 20

LM3535

PWM bit set to ‘1’ (Configuration Register bit [0]). Figure 20

shows how the different blocks (PWM and ALS) influence the

LED current.

30082446

FIGURE 20. Current Control Block Diagram

ALS + PWM Example

In this example, the APDS-9005 sensor detects that the am-

bient light has changed to 1 kLux. The voltage at the ALS input

is now around 875mV and the ambient light falls within Zone

5. This causes the LED brightness to be a function of Zone

Target Register 5 (loaded with 0x7F). Now assume the PWM

input is also driven with a 50% duty cycle pulsed waveform.

The LED current now becomes:

LED CONFIGURATIONS

The LM3535 has a total of 8 current sinks capable of sinking

200mA of total diode current. These 8 current sinks are con-

figured to operate in three independently controlled lighting

regions. GroupA has four dedicated current sinks, while

GroupB and GroupC each have one. To add greater lighting

flexibility, the LM3535 has two additional drivers (D53 and

D62) that can be assigned to either GroupA or GroupB

through a setting in the general purpose register.

At start-up, the default condition is four LEDs in GroupA, three

LEDs in GroupB and a single LED in GroupC (NOTE: GroupC

only consists of a single current sink (D1C) under any con-

figuration). Bits 53A and 62A in the general purpose register

control where current sinks D53 and D62 are assigned. By

writing a '1' to the 53A or 62A bits, D53 and D62 become as-

signed to the GroupA lighting region. Writing a '0' to these bits

assigns D53 and D62 to the GroupB lighting region. With this

added flexibility, the LM3535 is capable of supporting appli-

cations requiring 4, 5, or 6 LEDs for main display lighting,

while still providing additional current sinks that can be used

for a wide variety of lighting functions.

MAXIMUM OUTPUT CURRENT, MAXIMUM LED

VOLTAGE, MINIMUM INPUT VOLTAGE

The LM3535 can drive 8 LEDs at 25mA each (GroupA ,

GroupB, GroupC) from an input voltage as low as 3.2V, so

long as the LEDs have a forward voltage of 3.6V or less (room

temperature).

The statement above is a simple example of the LED drive

capability of the LM3535. The statement contains the key ap-

plication parameters that are required to validate an LED-

drive design using the LM3535: LED current (ILEDx), number

of active LEDs (Nx), LED forward voltage (VLED), and mini-

mum input voltage (VIN-MIN).

The equation below can be used to estimate the maximum

output current capability of the LM3535:

ILED_MAX = [(1.5 x VIN) - VLED - (IADDITIONAL × ROUT)] /

[(Nx x ROUT) + kHRx] (eq. 1)

ILED_MAX = [(1.5 x VIN ) - VLED - (IADDITIONAL × 2.4Ω)] /

[(Nx x 2.4Ω) + kHRx]

IADDITIONAL is the additional current that could be delivered to

the other LED Groups.

21 www.national.com

LM3535

ROUT – Output resistance. This parameter models the internal

losses of the charge pump that result in voltage droop at the

pump output VOUT. Since the magnitude of the voltage droop

is proportional to the total output current of the charge pump,

the loss parameter is modeled as a resistance. The output

resistance of the LM3535 is typically 2.4Ω (VIN = 3.6V, TA =

25°C). In equation form:

VVOUT = (1.5 × VIN) – [(NA× ILEDA + NB × ILEDB + NC × ILEDC) ×

ROUT] (eq. 2)

kHR – Headroom constant. This parameter models the mini-

mum voltage required to be present across the current sinks

for them to regulate properly. This minimum voltage is pro-

portional to the programmed LED current, so the constant has

units of mV/mA. The typical kHR of the LM3535 is 4mV/mA. In

equation form:

(VVOUT – VLEDx) > kHRx × ILEDx (eq. 3)

Typical Headroom Constant Values

kHRA = kHRB = kHRC = 4 mV/mA

The "ILED-MAX" equation (eq. 1) is obtained from combining the

ROUT equation (eq. 2) with the kHRx equation (eq. 3) and solv-

ing for ILEDx. Maximum LED current is highly dependent on

minimum input voltage and LED forward voltage. Output cur-

rent capability can be increased by raising the minimum input

voltage of the application, or by selecting an LED with a lower

forward voltage. Excessive power dissipation may also limit

output current capability of an application.

Total Output Current Capability

The maximum output current that can be drawn from the

LM3535 is 200mA.

DRIVER TYPE MAXIMUM Dxx CURRENT

DxA 25mA per DxA Pin

DxB 25mA per DxB Pin

D1C 25mA

PARALLEL CONNECTED AND UNUSED OUTPUTS

Connecting the outputs in parallel does not affect internal op-

eration of the LM3535 and has no impact on the Electrical

Characteristics and limits previously presented. The available

diode output current, maximum diode voltage, and all other

specifications provided in the Electrical Characteristics table

apply to this parallel output configuration, just as they do to

the standard LED application circuit.

All Dx current sinks utilize LED forward voltage sensing cir-

cuitry to optimize the charge-pump gain for maximum effi-

ciency. Due to the nature of the sensing circuitry, it is not

recommended to leave any of the Dx pins open when the

current sinks are enabled (ENx bits are set to '1'). Leaving Dx

pins unconnected will force the charge-pump into 3/2× mode

over the entire VIN range negating any efficiency gain that

could have been achieved by switching to 1× mode at higher

input voltages.

If the D1B or D1C drivers are not going to be used, make sure

that the ENB and ENC bits in the general purpose register are

set to '0' to ensure optimal efficiency.

POWER EFFICIENCY

Efficiency of LED drivers is commonly taken to be the ratio of

power consumed by the LEDs (PLED) to the power drawn at

the input of the part (PIN). With a 3/2× - 1× charge pump, the

input current is equal to the charge pump gain times the output

current (total LED current). The efficiency of the LM3535 can

be predicted as follow:

PLEDTOTAL = (VLEDA × NA × ILEDA) +

(VLEDB × NB × ILEDB) + (VLEDC × ILEDC)

PIN = VIN × IIN

PIN = VIN × (GAIN × ILEDTOTAL + IQ)

E = (PLEDTOTAL ÷ PIN)

The LED voltage is the main contributor to the charge-pump

gain selection process. Use of low forward-voltage LEDs

(3.0V- to 3.5V) will allow the LM3535 to stay in the gain of 1×

for a higher percentage of the lithium-ion battery voltage

range when compared to the use of higher forward voltage

LEDs (3.5V to 4.0V). See the LED Forward Voltage Monitor-

ing section of this datasheet for a more detailed description

of the gain selection and transition process.

For an advanced analysis, it is recommended that power con-

sumed by the circuit (VIN x IIN) for a given load be evaluated

rather than power efficiency.

POWER DISSIPATION

The power dissipation (PDISS) and junction temperature (TJ)

can be approximated with the equations below. PIN is the

power generated by the 3/2× - 1× charge pump, PLED is the

power consumed by the LEDs, TA is the ambient temperature,

and θJA is the junction-to-ambient thermal resistance for the

micro SMD 20-bump package. VIN is the input voltage to the

LM3535, VLED is the nominal LED forward voltage, N is the

number of LEDs and ILED is the programmed LED current.

PDISS = PIN - PLEDA - PLEDB - PLEDC

PDISS= (GAIN × VIN × IGroupA + GroupB + GroupC ) - (VLEDA × NA ×

ILEDA) - (VLEDB × NB × ILEDB) - (VLEDC × ILEDC)

TJ = TA + (PDISS x θJA)

The junction temperature rating takes precedence over the

ambient temperature rating. The LM3535 may be operated

outside the ambient temperature rating, so long as the junc-

tion temperature of the device does not exceed the maximum

operating rating of 110°C. The maximum ambient tempera-

ture rating must be derated in applications where high power

dissipation and/or poor thermal resistance causes the junc-

tion temperature to exceed 110°C.

THERMAL PROTECTION

Internal thermal protection circuitry disables the LM3535

when the junction temperature exceeds 150°C (typ.). This

feature protects the device from being damaged by high die

temperatures that might otherwise result from excessive pow-

er dissipation. The device will recover and operate normally

when the junction temperature falls below 125°C (typ.). It is

important that the board layout provide good thermal conduc-

tion to keep the junction temperature within the specified

operating ratings.

CAPACITOR SELECTION

The LM3535 requires 4 external capacitors for proper opera-

tion (C1 = C2 = CIN = COUT = 1µF). Surface-mount multi-layer

ceramic capacitors are recommended. These capacitors are

small, inexpensive and have very low equivalent series re-

sistance (ESR <20mΩ typ.). Tantalum capacitors, OS-CON

capacitors, and aluminum electrolytic capacitors are not rec-

ommended for use with the LM3535 due to their high ESR,

as compared to ceramic capacitors.

For most applications, ceramic capacitors with X7R or X5R

temperature characteristic are preferred for use with the

LM3535. These capacitors have tight capacitance tolerance

(as good as ±10%) and hold their value over temperature

www.national.com 22

LM3535

(X7R: ±15% over -55°C to 125°C; X5R: ±15% over -55°C to

85°C).

Capacitors with Y5V or Z5U temperature characteristic are

generally not recommended for use with the LM3535. Ca-

pacitors with these temperature characteristics typically have

wide capacitance tolerance (+80%, -20%) and vary signifi-

cantly over temperature (Y5V: +22%, -82% over -30°C to

+85°C range; Z5U: +22%, -56% over +10°C to +85°C range).

Under some conditions, a nominal 1µF Y5V or Z5U capacitor

could have a capacitance of only 0.1µF. Such detrimental de-

viation is likely to cause Y5V and Z5U capacitors to fail to

meet the minimum capacitance requirements of the LM3535.

The recommended voltage rating for the capacitors is

10V to account for DC bias capacitance losses.

23 www.national.com

LM3535

Physical Dimensions inches (millimeters) unless otherwise noted

TMD20AAA: 20 Bump 0.4mm micro SMD

X1 = 1.650mm

X2 = 2.055mm

X3 = 0.6mm

www.national.com 24

LM3535

Notes

25 www.national.com

LM3535

Notes

LM3535 Multi-Display LED Driver with Ambient Light Sensing and Dynamic Backlight Control

Compatibility

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