LM3537TME/NOPB - NATIONAL SEMICONDUCTOR

LM3537

VIN = 2.7 to 5.5V

CIN_A

1 PF

C1+ C1- C2+ C2-

COUT

1 PF

VOUT

MCU

SCL

SDA

HWEN

PWM 1 PF

CLDO1

1 PF

CLDO2

1 PF

CLDO3

1 PF

CLDO4

ALS

D7/

INT

CIN_C

2.2 PF

VIN_C

VIN_A

GNDs

LDO2

LDO1

LDO3

LDO4

GROUP A GROUP B

CIN_B

100 nF

VIN_B

SBIAS

AMBIENT

LIGHT

SENSOR

CSEN

1 PFGPO1

GPO2

LM3537

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SNVS634B –JUNE 2011–REVISED MAY 2013

LM3537 8-Channel WLED Driver with Four Integrated LDOs

Check for Samples: LM3537

1FEATURES

2Lighting: • LDO Input Voltage = 1.8V to VIN_A

• Overload Protection

• 8-channel Backlight Capability Combined Common Features:

• Internal ALS Engine; PWM Input to Support

CABC • Wide Input Voltage Range: 2.7V to 5.5V

• Built-In Power Supply and Gain Control for • I2C-Compatible Serial Interface

Ambient Light Sensor • 2 General-Purpose Outputs

• Up to 90% Efficiency APPLICATIONS

• Adaptive Charge Pump with 1x and 1.5x

Ggains for Maximum Efficiency • Smartphone Lighting

• 128 Dimming Steps for Group A, Exponential • MP3 Players, Gaming Devices

or Linear Dimming Selectable by Register • Digital Cameras

Setup

• 8 Linear Dimming States for Group B DESCRIPTION

LDOs: The LM3537 is a highly integrated LED driver

capable of driving 8 LEDs in parallel for single display

• 4 Programmable LDOs (300 mA/150 mA Output backlighting applications. Independent LED control

Currents) allows for a subset of the main display LEDs to be

• Default Startup Voltage States selected for partial illumination applications.

• Low Dropout Voltage: 100 mV typ. at 150 mA

Load Current

Typical Application Circuit

1Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of

Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.

2All trademarks are the property of their respective owners.

Products conform to specifications per the terms of the Texas

Instruments standard warranty. Production processing does not

necessarily include testing of all parameters.

54321

FLDO1

LDO2

VOUT

VIN_A

ALS

C2-

D7/

INT

LDO3

GND

SDA

C1-

PWM

HWEN

SCL

PGND

LDO4

C2+ C1+

SBIAS

GPO1

GPO2 VIN_B

VIN_C

LM3537

SNVS634B –JUNE 2011–REVISED MAY 2013

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DESCRIPTION (CONTINUED)

I2C-compatible control allows full configurability of the backlighting function. The LM3537 provides multi-zone

Ambient Light Sensing 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.

Four integrated LDOs are fully configurable through I2C capable of addressing point-of-load regulation needs for

functions such as integrated camera modules. The LDOs can be powered from main battery source, or by a fixed

output voltage of an external buck converter (post regulation) leading to higher conversion efficiency.

The LM3537 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 regulation is chosen, based on LED forward

voltage, so that efficiency is maximized over the input voltage range.

LM3537 is offered in a tiny 30-bump DSBGA package.

Connection Diagram

Figure 1. 30–Bump DSBGA Package

Top View

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SNVS634B –JUNE 2011–REVISED MAY 2013

Pin Descriptions

Bump Name Description

C5 VIN_A Input voltage for LED driver and sensor interface. Input range: 2.7V to 5.5V.

E5 VIN_B Input voltage for the regulators. This must be connected to the same voltage supply as

VIN_A

F5 VIN_C Input voltage (power rail) for the LDO regulators. 1.8V ≤VIN_C ≤VIN_A

B1 SCL Serial interface clock

B3 SDA Serial interface data

A1 HWEN Hardware enable pin. High = normal operation, low = RESET

B2 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 = 15 µsec.

E4 SBIAS Power supply for a light sensor. Leave unconnected if not used.

E3 GPO1 General purpose output. Can be used as a sensor gain control signal. When functioning

as a general purpose output, it is open drain and requires an external pullup. Leave

unconnected if not used.

E2 GPO2 General purpose output. Can be used as a sensor gain control signal. When functioning

as a general purpose output, it is open drain and requires an external pullup. Leave

unconnected if not used.

D5 ALS Ambient Light Sensor input. Connect to ground if not used.

F3 GND Regulator ground

A2 PGND LED driver and charge pump ground

F2 LDO4 Programmable VOUT of 1.2-3.3 V. Max load = 150 mA.

F4 LDO3 Programmable VOUT of 1.2-3.3 V. Max load = 150 mA.

E1 LDO2 Programmable VOUT of 1.2-3.3 V. Max load = 150 mA.

F1 LDO1 Programmable VOUT of 1.2-3.3 V. Max load = 300 mA.

C3 D8 LED driver

C4 D7/INT LED driver/ ALS interrupt (mode of operation is selected via register). In ALS interrupt

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

no ALS adjustment has been made.

D4 D6 LED driver

D3 D5 LED driver

D2 D4 LED driver

D1 D3 LED driver

C1 D2 LED driver

C2 D1 LED driver

B5 VOUT Charge pump output

B4 C2- Flying capacitor 2 negative terminal

A4 C2+ Flying capacitor 2 positive terminal

A3 C1- Flying capacitor 1 negative terminal

A5 C1+ Flying capacitor 1 positive terminal

These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam

during storage or handling to prevent electrostatic damage to the MOS gates.

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SNVS634B –JUNE 2011–REVISED MAY 2013

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ABSOLUTE MAXIMUM RATINGS(1)(2)(3)

VIN_A, VIN_B , VIN_C pin voltage -0.3V to 6.0V

Voltage on Logic Pins (SCL, SDA, GPO1, GPO2, HWEN, PWM) -0.3V to (VIN_A+0.3V) with 6.0V max

LED driver (D1 to D8) Pin Voltages -0.3V to (VOUT+0.3V) with 6.0V max

Voltage on All Other Pins -0.3V to (VIN_A +0.3V) with 6.0V max

Continuous Power Dissipation(4) Internally Limited

Junction Temperature (TJ-MAX) 150°C

Storage Temperature Range -40°C to +150°C

ESD Rating(5) Human Body Model 2 kV

(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 specified. Operating Ratings do not imply specified performance limits. For specified performance limits

and associated test conditions, see the Electrical Characteristics tables.

(2) All voltages are with respect to the potential at the GND pins.

(3) If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/Distributors for availability and

specifications.

(4) Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ= 160°C (typ.) and

disengages at TJ= 155°C (typ.).

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

OPERATING RATINGS(1)(2)

VIN_A, VIN_B Input Voltage Range 2.7V to 5.5V

LED Voltage Range 2.0V to 4.0V

VIN_C Input Voltage Range (Note: must stay > VOUTLDO + 0.3V) 1.8V to VIN_B

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

Ambient Temperature (TA) Range(3) −30°C to +85°C

(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 specified. Operating Ratings do not imply specified performance limits. For specified performance limits

and associated test conditions, see the Electrical Characteristics tables.

(2) All voltages are with respect to the potential at the GND pins.

(3) 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).

THERMAL PROPERTIES(1)

Junction-to-Ambient Thermal Resistance (θJA), YFQ Package(2) 45°C/W

(1) If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/Distributors for availability and

specifications.

(2) 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 Texas

Instruments' Application Note AN-1112: DSBGA Wafer Level Chip Scale Package (Literature Number SNVA009).

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SNVS634B –JUNE 2011–REVISED MAY 2013

CHARGE PUMP AND LED DRIVERS ELECTRICAL CHARACTERISTICS(1)(2)

Limits in standard typeface are for TJ= 25°C, and limits in boldface type apply over the operating ambient temperature range

(−30°C to +85°C). Unless otherwise specified: VIN_A = 3.6V; VHWEN = VIN_A; VDx = 0.4V; GroupA = GroupB = Fullscale Current;

C1= C2= CIN_A= COUT= 1.0 µF.(3)

Symbol Parameter Condition Min Typ Max Units

Output Current Regulation 2.7V ≤VIN_A ≤5.5V −7.5% 25 +7.5% mA

GroupA 8 LEDs in GroupA

Output Current Regulation 2.7V ≤VIN_A ≤5.5V −7.5% 25 +7.5% mA

GroupB 4 LEDs in GroupB

IDx 3.2V ≤VIN_A ≤5.5V

Output Current Regulation VLED = 3.6V 22.3

All LED Drivers Enabled mA

BankA current code = 1111101b, exp dimming DxA

All LED Drivers on BankA(4) scale

2.7V ≤VIN ≤5.5V GroupA (8 LEDs) 0.8 3

IDx- LED Current Matching(5) LED Current = %

MATCH GroupB (4 LEDs) 0.4 3

Fullscale current

VDxTH VDx 1x to 3/2x Gain Transition Threshold VDx Falling 135 mV

Current sink Headroom Voltage IDx = 95% ×IDx (nom.)

VHR 100 mV

Requirement(6) (IDx (nom) ≈20 mA)

Gain = 3/2 2.4

Open-Loop Charge Pump Output

ROUT Ω

Resistance(7) Gain = 1 0.5

Gain = 1.5x, No Load. Current through VIN_A 2.9 4.4

pin. Sensor Bias OFF

IQQuiescent Supply Current mA

Gain = 1x, No Load. Current through VIN_A 1.1 2.4

pin. Sensor Bias OFF

HWEN = 1.8V. All registers in factory defaults

ISB Standby Supply Current 1.2 µA

state. Current through VIN_A pin.

ISD Shutdown Supply Current HWEN = 0V. Current through VIN_A pin. 0.2 1.0 µA

fSW Switching Frequency 1.1 1.3 1.6 MHz

tSTART Startup Time See(8) 250 µs

VALS ALS Reference Voltage −6% 1.0 +6% V

RALS register setting = 00010b −6% 10.1 +6%

RALS Internal ALS Resistor kΩ

RALS register setting = 00100b −6% 5.0 +6%

(1) All voltages are with respect to the potential at the GND pins.

(2) Min and Max limits are specified by design, test, or statistical analysis. Typical numbers are not ensured, but do represent the most

likely norm.

(3) CIN_X, COUT, CLDOX, CSEN, C1, and C2: Low-ESR Surface-Mount Ceramic Capacitors (MLCCs) used in setting electrical characteristics.

(4) The total output current can be split between the two groups (IDx = 25 mA Max). Under maximum output current conditions, special

attention must be given to input voltage and LED forward voltage to ensure proper current regulation. The maximum total output current

for the LM3537 should be limited to 180 mA.

(5) For the two groups of current sinks on a part (group A and group B), 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.

(6) For each Dxpin, headroom voltage is the voltage across the internal current sink connected to that pin. For group A and B current sinks,

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

(7) Specified by design.

(8) Turn-on time is measured from the moment the charge pump is activated until the VOUT crosses 90% of its target value.

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SNVS634B –JUNE 2011–REVISED MAY 2013

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LOGIC INTERFACE CHARACTERISTICS(1)(2)

Symbol Parameter Condition Min Typ Max Units

I2C-Compatible Interface Timing Specifications (SCL, SDA)(3)

t1SCL (Clock Period) See(4) 2.5 µs

t2Data In Setup Time to SCL High 100 ns

t3Data Out stable After SCL Low 0ns

SDA Low Setup Time to SCL Low

t4100 ns

(Start)

SDA High Hold Time After SCL High

t5100 ns

(Stop)

I2C-Compatible Interface Voltage Specifications (SCL, SDA)

VIL Input Logic Low "0" 2.7V ≤VIN_A ≤5.5V 0 0.45 V

VIH Input Logic High "1" 2.7V ≤VIN_A ≤5.5V 1.25 VIN_A V

VOL Output Logic Low "0" ILOAD = 3mA 400 mV

Logic inputs HWEN and PWM

Reset 0 0.45

VHWEN HWEN Voltage Thresholds 2.7V ≤VIN_A ≤5.5V V

Normal Operation 1.2 VIN_A

LEDs Off 0 0.45

VPWM PWM Voltage Thresholds 2.7V ≤VIN_A ≤5.5V V

LEDs On 1.2 VIN_A

ALS interrupt

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

Logic outputs GPO1, GPO2(5)

VOL Output Low Level IOUT = 3 mA 0.3 0.5 V

VOUT_S VOUT_S

VOH Output High Level IOUT =−2 mA V

−0.5 –0.3

(1) All voltages are with respect to the potential at the GND pins.

(2) Min and Max limits are specified by design, test, or statistical analysis. Typical numbers are not ensured, but do represent the most

likely norm.

(3) SCL and SDA should be glitch-free in order for proper device control to be realized. See Figure 2 for timing specification details.

(4) SCL is tested with a 50% duty-cycle clock.

(5) VOUT_S = SBIAS pin output voltage. The voltage level of the GPOs depends on the sbias_en-bit: '1'; GPOs will behave as push-pull

outputs and will reference the high-side to the voltage of SBIAS. '0'; GPOs will act as open-drain outputs (default). In the open-drain

configuration, they can be high-side referenced to any voltage equal to, or less than, the VIN_A of the LM3537. Output High Level (VOH)

specification is valid only for push-pull -type outputs.

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SNVS634B –JUNE 2011–REVISED MAY 2013

VOLTAGE REGULATORS ELECTRICAL CHARACTERISTICS(1)(2)

Unless otherwise noted, VIN_A= VIN_B = VIN_C = 3.6V, CIN_A = 1 µF, CIN_B = 100 nF, CIN_C = 2.2 µF, CLDOX= 1 µF, HWEN = high.

Limits in standard typeface are for TJ= 25°C, and limits in boldface type apply over the operating ambient temperature range

(-30°C to +85°C).(3)

Symbol Parameter Condition Min Typ Max Units

LDO1

−2 +2

Output Voltage Accuracy IOUTLDO = 1 mA, VOUTLDO = 2.80V %

VOUT −3 +3

Default Output Voltage 2.80 V

Output Current 1.8V ≤VIN_C ≤5.5V 300 mA

IOUT Output Current Limit (short circuit) VOUTLDO = 0V 600 mA

VDO Dropout Voltage IOUTLDO = 300 mA 220 300 mV

VOUTLDO + 0.5V ≤VIN_C ≤4.5V

Line Regulation 2

IOUTLDO = 1 mA

ΔVOUT mV

Load Regulation 1 mA ≤IOUTLDO ≤300 mA 20

f = 100Hz,

CLDO1 = 1 µF,

PSRR Power Supply Ripple Rejection Ratio 65 dB

IOUTLDO = 20 mA

Output Voltage = 1.20V

LDO2, LDO3, LDO4

−2 +2

Output Voltage Accuracy IOUTLDO = 1 mA, VOUTLDO = 2.80V %

−3 +3

VOUT LDO2 1.80 V

Default Output Voltage LDO3 1.80 V

LDO4 2.80

Output Current 1.8V ≤VIN_C ≤5.5V 150 mA

IOUT Output Current Limit (short circuit) VOUTLDO = 0V 400 mA

VDO Dropout Voltage IOUTLDO = 150 mA 100 200 mV

VOUTLDO + 0.5V ≤VIN_C ≤4.5V

Line Regulation 2

IOUTLDO = 1mA

ΔVOUT mV

Load Regulation 1mA ≤IOUTLDO ≤150 mA 10

f = 100 Hz,

CLDOX = 1µF,

PSRR Power Supply Ripple Rejection Ratio 65 dB

IOUTLDO = 20 mA

Output Voltage = 1.20V

LDO Combined Common Electrical Characteristics

All LDOs Disabled 0.2 1µA

One LDO Enabled 70 130

Ground Pin Current (GND and PGND-

IGND Note: IOUTLDOX = 0mA Two LDOs Enabled 100

pin) µA

Three LDOs Enabled 130

Four LDOs Enabled 160

CLDOX = 1µF, IOUTLDO = 150 mA 130

VOUT = 2.8V. Enable of First LDO

tSTARTUP Turn-on Time from Shut-down(4) µs

CLDOX = 1 µF, IOUTLDO = 150 mA

VOUT = 2.8V. Enable of Each Subsequent 70

LDO after First Enabled

TTransient Startup Transient Overshoot CLDOX = 1 µF, IOUTLDO = 150 mA 30 mV

(1) All voltages are with respect to the potential at the GND pins.

(2) Min and Max limits are specified by design, test, or statistical analysis. Typical numbers are not ensured, but do represent the most

likely norm.

(3) CIN_C, CLDOX : Low-ESR Surface-Mount Ceramic Capacitors (MLCCs) used in setting electrical characteristics.

(4) Time needed for VOUTLDO to reach 95% of final value.

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SENSOR INTERFACE ELECTRICAL CHARACTERISTICS

Unless otherwise noted, VIN_A = 3.6V, CIN_A = 1 µF, CIN_B = 100 nF, CIN_C = 2.2 µF, CSEN= 1 µF, HWEN = high. Limits in

standard typeface are for TJ= 25°C, and limits in boldface type apply over the operating ambient temperature range (−30°C

to +85°C).

Symbol Parameter Condition Min Typ Max Units

SBIAS

IOUT_S SBIAS Output Current 2.7V ≤VIN_A ≤5.5V. VOUT_S < (VIN_A +0.3V) 20 mA

2.7V ≤VIN_A ≤5.5V. IOUT_S = 1.0 mA. 2.4V −5% 2.4 +5%

option selected via register.

VOUT_S SBIAS Output Voltage V

3.3V ≤VIN_A ≤5.5V. IOUT_S = 1.0 mA. 3.0V −5% 3.0 +5%

option selected via register.

Sensor Interface Quiescent Supply

IQIF No Load 35 µA

Current(1)(2)

(1) In addition to Quiescent Supply Current (IQ) drawn by the charge pump. (See Charge Pump and LED Drivers Electrical Characteristics.)

(2) Specified by design.

Figure 2. Timing Parameters

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SNVS634B –JUNE 2011–REVISED MAY 2013

TYPICAL PERFORMANCE CHARACTERISTICS

Unless otherwise specified: VIN_A,B,C = 3.6V, CIN_A = COUT = 1.0 µF, CIN_B = 0.1 µF, CIN_C = 4.7 µF, C1= C2= 1.0 µF, CLDOx= 1.0

µF, TA= 25°C.

Regulator 1 (300 mA) Output Voltage Regulator 2,3,4 (150 mA) Output Voltage

vs vs

Output Current Output Current

VSET = 2.80V VSET = 1.80V

Power Supply Rejection Ratio, VOUT = 1.20V, ILOAD = 20 mA Power Supply Rejection Ratio, VOUT = 1.20V, ILOAD = 20 mA

VIN_C is shorted to VIN_A, VIN_B Signal Applied on VIN_C, VIN_A and VIN_B Clear.

Load Transient. VOUT setting = 1.80V Line Transient Response

ILOAD 1mA to 150mA to 1mA; tRISE= tFALL= 5µs VOUT setting = 1.80V,, ILOAD 1mA

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TYPICAL PERFORMANCE CHARACTERISTICS (continued)

Unless otherwise specified: VIN_A,B,C = 3.6V, CIN_A = COUT = 1.0 µF, CIN_B = 0.1 µF, CIN_C = 4.7 µF, C1= C2= 1.0 µF, CLDOx= 1.0

µF, TA= 25°C.

Regulator Enable Response; Enable of First Regulator Regulator Enable Response; Enable of First Regulator

(1mA load, 1.80V) via Reg. Write (150mA load, 2.80V) via Reg. Write

Regulator 2,3,4 Short Circuit Current Regulator 1 Short Circuit Current

VOUT setting = 1.80V VOUT setting = 2.80V

Shutdown Supply Current Standby Supply Current

HWEN = 0V. Current through VIN_A pin HWEN = 1.8V. Current through VIN_A pin

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SNVS634B –JUNE 2011–REVISED MAY 2013

TYPICAL PERFORMANCE CHARACTERISTICS (continued)

Unless otherwise specified: VIN_A,B,C = 3.6V, CIN_A = COUT = 1.0 µF, CIN_B = 0.1 µF, CIN_C = 4.7 µF, C1= C2= 1.0 µF, CLDOx= 1.0

µF, TA= 25°C. Quiescent Current Quiescent Current

vs vs

Input Voltage Input Voltage 3/2× Gain

1× Gain 3/2× Gain

Charge Pump 1.5x Efficiency

LED Current Matching Distribution. vs

6 Drivers on Group A, Output Set to 25 mA.(1) Load Current

(1) For the two groups of current sinks on a part (group A and group B), 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.

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CHARGE PUMP

1X/1.5X

C1+ C1- C2+ C2-

1 PF1 PF

1 PF

COUT

CURRENT SINKS

GROUP B

BRIGHTNESS

CTRL = 8 STEPS

GROUP A

BRIGHTNESS

CTRL = 128 STEPS

INT

PWM

GAIN

CONTROL

1.3 MHz

OSC

VREF

1.25V

SOFT-

START

SERIAL

DATA

SDA

SCL

HWEN

CONTROL

VIN_A

1 PF

CIN

REGISTERS

POR

THERMAL

SHUTDOWN

VOLTAGE REFERENCE

WITH NOISE

SUPPRESSION FILTER

ALS ENGINE

SENSOR

POWER

1 PF

2.4V or

3.0V CSEN

SBIAS

AMBIENT

LIGHT

SENSOR

LDO 2

LDO 1

LDO 4

LDO 3

CLDO1

CLDO2

CLDO3

CLDO4

1 PF

LDO1

LDO2

LDO3

LDO4

VIN_B

100 nF

CIN_B

VIN2.7V to 5.5V

VIN_C

CIN_C

2.2 PF

RALS

GPO1

GPO2

ALS

GNDs

D7/

INT

VOUT

PWM

LM3537

SNVS634B –JUNE 2011–REVISED MAY 2013

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BLOCK DIAGRAM

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SNVS634B –JUNE 2011–REVISED MAY 2013

Circuit Description

OVERVIEW

The LM3537 is a white LED driver system based upon an adaptive 3/2× - 1× CMOS charge pump capable of

supplying up to 180 mA of total output current. With two separately controlled groups of constant current sinks,

the LM3537 is an ideal solution for platforms requiring a single white LED driver for main display and sub display

(or keypad). 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 25 mA. An I2C-

compatible interface is used to enable the device and vary the brightness within the individual current sink

groups. For group A, 128 brightness control levels are available (user defined linear or exponential dimming

curve). Group B has 8 linearly-spaced analog brightness levels.

The LM3537 provides an input for an Ambient Light Sensor to adaptively adjust the diode current based on

ambient conditions, 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). Additionally, the device provides 20

mA power supply output for the sensor. The GPOs can also be configured to serve as a gain control interface for

sensors with HW-controlled gain.

The LM3537 also integrates three 150-mA LDO and one 300-mA LDO voltage regulators, which can be turned

on/off using separate enable bits on each LDO. Each LDO operates with a power rail input voltage range

between 1.8 V and 5.5V allowing them to be supplied from the battery or a step-down converter. Furthermore,

the regulated output voltages can be adjusted through the serial bus.

CIRCUIT COMPONENTS

Charge Pump

The input to the 3/2× - 1× charge pump is connected to the VIN_A pin, and the regulated output of the charge

pump is connected to the VOUT pin. The operating input voltage range of the LM3537 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 4.2V (typ.). The charge pump gain transitions are actively selected to

maintain regulation based on LED forward voltage and load requirements.

Diode Current Sinks

The matched current outputs are generated with a precision current mirror that is biased off the charge pump

output. 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 2 different lighting regions.

Ambient Light Sensing (ALS) and Interrupt

The LM3537 provides an Ambient Light Sensing input for use with ambient backlight control. Connecting the

anode of a photo diode to this pin and configuring the appropriate ALS resistor, the LM3537 can be configured to

adjust the LED current to five unique settings corresponding to four adjustable light region trip points.

Additionally, when the LM3537 determines that an ambient condition has changed, the interrupt pin, when

connected to a pullup resistor will toggle to a '0' alerting the controller. Available resistor values are shown in

Table 1 below.

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Table 1. ALS Resistor Values

r_als[4] r_als[3] r_als[2] r_als[1] r_als[0] RALS (typ) Value Unit

1 1 1 1 1 0.651 kΩ

1 1 1 1 0 0.672 kΩ

1 1 1 0 1 0.695 kΩ

1 1 1 0 0 0.720 kΩ

1 1 0 1 1 0.747 kΩ

1 1 0 1 0 0.776 kΩ

1 1 0 0 1 0.806 kΩ

1 1 0 0 0 0.840 kΩ

1 0 1 1 1 0.876 kΩ

1 0 1 1 0 0.916 kΩ

1 0 1 0 1 0.960 kΩ

1 0 1 0 0 1.01 kΩ

1 0 0 1 1 1.06 kΩ

1 0 0 1 0 1.12 kΩ

1 0 0 0 1 1.19 kΩ

1 0 0 0 0 1.26 kΩ

0 1 1 1 1 1.34 kΩ

0 1 1 1 0 1.44 kΩ

0 1 1 0 1 1.55 kΩ

0 1 1 0 0 1.68 kΩ

0 1 0 1 1 1.83 kΩ

0 1 0 1 0 2.02 kΩ

0 1 0 0 1 2.24 kΩ

0 1 0 0 0 2.52 kΩ

0 0 1 1 1 2.88 kΩ

0 0 1 1 0 3.36 kΩ

0 0 1 0 1 4.03 kΩ

0 0 1 0 0 5.00 kΩ

0 0 0 1 1 6.72 kΩ

0 0 0 1 0 10.1 kΩ

0 0 0 0 1 20.2 kΩ

0 0 0 0 0 HighZ --

Automatic Gain Change

GPO pins of the LM3537 can be configured to serve as a gain control interface for sensors with HW controlled

gain, like ROHM BH1600-series. Please see Table 2. LM3537 changes sensor gain automatically based on

ambient light intensity changes.

Table 2. Sensor Gain Control

OUTPUT PIN STATUS

Can be set to "1" or "0" with REG 52H, bit Can be set to "1" or "0" with REG 52H, bit

autogain_en = "0" gpo1 gpo2

autogain_en = "1" (enables autogain 0 1

functionality) LOW GAIN

autogain_en = "1" (enables autogain 1 0

functionality) HIGH GAIN

Product Folder Links: LM3537

Ambient Light (lux)

Vsense

Vals_ref

= 1V

ZB3

ZB0

ZB1

ZB2

Zone 0

Zone 4

Zone 3

Zone 2

Zone 1

LED Driver Input Code (0-127)

LED Current

Full

Scale

Z0T Z4T

Z3TZ2TZ1T

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The ambient light sensing circuit has 4 configurable Ambient Light Boundaries (ZB0 – ZB3) programmed through

the four 8-bit Zone Boundary Registers. These zone boundaries define 5 ambient brightness zones.

The ambient light sensor input has a 0 to 1V operational input voltage range. The Typical Application Circuit

shows the LM3537 with an ambient light sensor (ROHM, BH1621FVC). If the internal ALS Resistor Select

linear output voltage (high-gain mode). The voltage at the active ambient light sensor input is compared against

the 8-bit values programmed into the Zone Boundary Registers (ALS ZONE BOUNDARY#0 - ALS ZONE

BOUNDARY#3 ). When the ambient light sensor output crosses one of the 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 (ALS BRIGHTNESS ZONE#0 to ALS BRIGHTNESS ZONE#4).

Ambient light sensor samples are averaged and then further processed by the discriminator block to provide

rejection of noise and transient signals. The averager is configurable with 8 different averaging times to provide

varying amounts of noise and transient rejection. 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 samples the ALS inputs at 16 kHz. If the averaging time is set to

800 ms, the averager will send the updated zone information to the discriminator every 800 ms. This zone

information contains the average of approximately 12800 samples (800 ms × 16 kHz). 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 1600 ms have elapsed.

ALS Zone to LED Brightness Mapping principle without AutoGain is shown in Figure 3 below. Here, the

exponential dimming scheme is used.

Figure 3. ALS Zone to LED Brightness Mapping

ALS Zone transitions with AutoGain is shown in Figure 4. When the light intensity increases, the LM3537

configures the sensor for low-gain mode. Transition from Zone2 to Zone3 triggers the shift to lower gain mode.

When the light intensity decreases, the LM3537 configures the sensor to high-gain mode. The trip point to this

transition is set by the ALS LOW_to_HIGH_TP register, and it should be set lower than the Zone2 to Zone3

transition, in order to have hysteresis. Zone3 to Zone2 transition trip point must be set separately for lower gain

mode, by the ALS ZONE BOUNDARY Z3_to_Z2 register. This register value should be set higher than the ALS

LOW_to_HIGH_TP. In low-gain mode the sensor will have a lower output current which helps save battery

power. High-gain mode will allow better resolution, but will result higher output current. Thus, there is a trade-off

between increased resolution and increased power consumption. High-gain mode is the default mode of

operation after enabling the autogain.

Product Folder Links: LM3537

VSENSE (mV)

1000

LOW INTENSITY HIGH INTENSITY

750

500

250

}

Z0 Z1 Z2 Z3 Z4

}

Z0 Z1 Z2 Z3 Z4

LIGHT INTENSITY INCREASES

LIGHT INTENSITY DECREASES

t0-1

t1-2

t2-3

t3-2

t3-4

LOW-to-HIGH gain

transition

HIGH-to-LOW gain

transition

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The higher X-axis is for increasing light intensity, while the lower axis is for decreasing light intensity

There are some limits in Zone transitions when the autogain is enabled, for example a direct transition from the lowest

Zone0 to the highest Zone4 (and vice versa) is not possible, because the device must go through the gain change

process first.

Figure 4. ALS Zone Transitions with AutoGain

Countdown Timer

The ALS engine includes a pre-defined countdown timer function. This function is targeted to applications where

it's favorable to only increase through the zones; i.e., the LM3537 will stick to the highest zone reached, but won't

allow transitions to lower Zones until the countdown has completed. At the end of every countdown, the timer

sets the countdown timer flag (reg 40H), and after that, any Zone transition to a lower Zone re-loads the timer

and starts the next timer period. See Table 3 and Figure 5 for details.

Table 3. Countdown Timer

Pre-defined Countdown Timer Function

TIMER[1] TIMER[0] Timer Function

0 0 Countdown timer is disabled

0 1 10s countdown timer is enabled (stick to the highest zone for 10s).

1 0 Always stick to the highest zone the ALS reached.

1 1 Always stick to the highest zone the ALS reached.

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ZONE0

ZONE1

ZONE2

ZONE3

ZONE4

510 15 20 25 30 35 40 45 50 55 60

THE END OF THE

COUNTDOWN PERIOD

TIMER PERIOD

STARTED TIMER PERIOD

STARTED

TIMER PERIOD

STARTED

TIMER PERIOD

STARTED

ELAPSED TIME (s)

THE END OF THE

COUNTDOWN

PERIOD

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Solid line shows the ALS operation when the timer is disabled. Dashed line shows the operation when the 10s timer

is enabled. Dotted line shows the operation when the device sticks to the highest zone.

Figure 5. Countdown Timer Principle

PWM Input

A PWM (Pulse Width Modulation) pin is provided on the LM3537 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 LM3537 require approximately 15 µs to reach steady-state target current. This turn-on

time sets the minimum usable PWM pulse width for DBC. The external PWM input is effective for group A LEDs

only.

LED Forward Voltage Monitoring

The LM3537 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 LM3537 will operate in pass mode, allowing the VOUT voltage to track the input voltage.

As the input voltage drops, the voltage on the Dx pins will also drop (VDX = VVOUT – VLEDx). Once any of the

active Dx pins reaches a voltage approximately equal to 150 mV, 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 LM3537 will remain in the gain of 3/2

until an I2C write to the part occurs. At that time, the LM3537 will re-evaluate the LED conditions and

select the appropriate gain.

Only active Dx pins will be monitored.

Configurable Gain Transition Delay

To optimize efficiency, the LM3537 has a user-selectable gain transition delay that allows the part to ignore short

duration input voltage drops. By default, the LM3537 will not change gains if the input voltage dip is shorter than

3 to 6 milliseconds. There are four selectable gain transition delay ranges available on the LM3537.

Hardware Enable (HWEN)

The LM3537 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 operation, 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 Characteristics section of

the datasheet for required voltage thresholds.

Product Folder Links: LM3537

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Low Dropout Voltage Regulators

The four low dropout voltage regulators are designed to operate with small-size ceramic input and output

capacitors. They can operate with power rail voltages down to 1.8V. The LDOs 2, 3 and 4 offer a typical dropout

voltage of 100 mV at 150 mA output current. The single, higher-current LDO 1 offers a typical dropout voltage of

220 mV at 300mA output current. The LDOs are enabled by the EN_LDO1, EN_LDO2, EN_LDO3 and EN_LDO4

bits (see Table 5 for details). summarizes the supported output voltages. At startup, the LDOs are off but are

preset to 1.8V (for LDO2 and LDO3) and 2.8V (for LDO1 and LDO4).

Table 4. Regulator Voltage Options

Output Voltage

LDOX_VOUT[4] LDOX_VOUT[3] LDOX_VOUT[2] LDOX_VOUT[1] LDOX_VOUT[0] (typ.)

1 1 1 1 1 3.30V

1 1 1 1 0 3.20V

1 1 1 0 1 3.10V

1 1 1 0 0 3.00V

1 1 0 1 1 2.95V

1 1 0 1 0 2.90V

1 1 0 0 1 2.85V

1 1 0 0 0 2.80V

1 0 1 1 1 2.75V

1 0 1 1 0 2.70V

1 0 1 0 1 2.65V

1 0 1 0 0 2.60V

1 0 0 1 1 2.55V

1 0 0 1 0 2.50V

1 0 0 0 1 2.40V

1 0 0 0 0 2.20V

0 1 1 1 1 2.00V

0 1 1 1 0 1.90V

0 1 1 0 1 1.85V

0 1 1 0 0 1.80V

0 1 0 1 1 1.75V

0 1 0 1 0 1.70V

0 1 0 0 1 1.65V

0 1 0 0 0 1.60V

0 0 1 1 1 1.55V

0 0 1 1 0 1.50V

0 0 1 0 1 1.45V

0 0 1 0 0 1.40V

0 0 0 1 1 1.35V

0 0 0 1 0 1.30V

0 0 0 0 1 1.25V

0 0 0 0 0 1.20V

Product Folder Links: LM3537

PASS

ELEMENT

VREF

NOISE

SUPPRESSION

VOLTAGE

CONTROL

VIN_C

VIN_B

REGULATED

OUTPUT

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The power input voltage applied between VIN_C and GND should be at least 0.3V above the output voltage of the

regulators. The bias input voltage applied between VIN_B and GND should be equal to VIN_A, and at least 0.3V

above the output voltage of the regulators.

VIN_B supplies internal circuitry. VIN_C, the power input voltage, is regulated to the fixed output voltage.

Figure 6. LDO Block Diagram

I2C-Compatible Interface

STOP AND START CONDITIONS

The LM3537 is controlled via an I2C-compatible interface. START and STOP ) conditions classify the beginning

and the end of the I2C session. A START condition is defined as SDA transitioning from HIGH to LOW while SCL

is HIGH. A STOP condition is defined as SDA transitioning from LOW to HIGH while SCL is HIGH. The I2C

master always generates START and STOP conditions. The I2C bus is considered busy after a START condition

and free after a STOP condition. During data transmission, the I2C master can generate repeated START

conditions. A START and a repeated START conditions are equivalent function-wise. The data on SDA must be

stable during the HIGH period of the clock signal (SCL). In other words, the state of SDA can only be changed

when SCL is LOW.

Figure 7. Start and Stop Sequences

I2C-COMPATIBLE CHIP ADDRESS

The chip address for the LM3537 is 0111000 (38h). After the START condition, the I2C master sends the 7-bit

chip address followed by a read or write bit (R/W). R/W= 0 indicates a WRITE and R/W = 1 indicates a READ.

The second byte following the chip address selects the register address to which the data will be written. The

third byte contains the data for the selected register.

Product Folder Links: LM3537

Bit 7

MSB

Bit 6 1

Bit 5 1

Bit 4 0

Bit 3 0

Bit 2 0

Bit 1 R/W

Bit 0

LSB

Serial Bus Slave Address (chip address)

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Figure 8. Chip Address

TRANSFERRING DATA

Every byte on the SDA line must be eight bits long, with the most significant bit (MSB) transferred first. Each byte

of data must be followed by an acknowledge bit (ACK). The acknowledge related clock pulse (9th clock pulse) is

generated by the master. The master releases SDA (HIGH) during the 9th clock pulse. The LM3537 pulls down

SDA during the 9th clock pulse, signifying an acknowledge. An acknowledge is generated after each byte has

been received. Figure 9 is an example of a write sequence to the DIODE ENABLE register of the LM3537.

Figure 9. Write Sequence to the LM3537

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Internal Registers of LM3537

The LM3537 is controlled by a set of registers through the two-wire serial interface port. Table 5 below lists

device registers and their addresses together with a short description.

Table 5. Control Register Map

Hex Read/W Default Value

Addr. rite After Reset

00 MASTER ENABLE [2] R/W xxxxx0xx group_A_en

Master enable for all the LEDs, which are assigned to group A. '1' =

LEDs ON '0' = LEDs OFF.

[1] R/W xxxxxx0x group_B_en

Master enable for all the LEDs, which are assigned to group B. '1' =

LEDs ON '0' = LEDs OFF.

[0] W xxxxxxx0 softw_rst

Writing = '1' to this register bit resets all the registers to factory

defaults. After writing, this bit is forced back to '0' automatically.

10 DIODE ENABLE [7] R/W 0xxxxxxx enD8

ON/OFF Control for D8 output

[6] R/W x0xxxxxx enD7

ON/OFF Control for D7 output

[5] R/W xx0xxxxx enD6

ON/OFF Control for D6 output

[4] R/W xxx0xxxx enD5

ON/OFF Control for D5 output

[3] R/W xxxx0xxx enD4

ON/OFF Control for D4 output

[2] R/W xxxxx0xx enD3

ON/OFF Control for D3 output

[1] R/W xxxxxx0x enD2

ON/OFF Control for D2 output

[0] R/W xxxxxxx0 enD1

ON/OFF Control for D1 output

20 CONFIGURATION [7] R/W 0xxxxxxx D7_int

Enables the Interrupt Pin. 1 = interrupt output enabled. 0 = interrupt

output disabled, LED driver operation. Reading the 0x40 register

clears the interrupt.

[6] R/W x0xxxxxx lin

Selects between linear and exponential dimming curve. Effective for

Group A only. 1 = linear dimming curve. 0 = exponential dimming

curve.

[5] R/W xx1xxxxx D8_A

Assign D8 diode to Group A Writing a '1' assigns D8 to BankA

(default) and a '0' assigns D8 to Group B.

[4] R/W xxx1xxxx D7_A

Assign D7 diode to Group A Writing a '1' assigns D7 to BankA

(default) and a '0' assigns D7 to Group B.

[3] R/W xxxx1xxx D6_A

Assign D6 diode to Group A Writing a '1' assigns D6 to BankA

(default) and a '0' assigns D6 to Group B.

[2] R/W xxxxx1xx D5_A

Assign D5 diode toGroup A . Writing a '1' assigns D5 to BankA

(default) and a '0' assigns D5 to Group B.

[1] R/W xxxxxx0x pwm_p

PWM input polarity. Writing a '0' = active high (default) and a '1' =

active low.

[0] R/W xxxxxxx0 pwm_en

PWM input enable. Writing a '1' = Enable, and a '0' = Ignore

(default).

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Table 5. Control Register Map (continued)

Hex Read/W Default Value

Addr. rite After Reset

30 OPTIONS [7:6] R/W 00xxxxxx gt

Charge pump gain transition filter. The value stored in this register

determines the filter time used to make a gain transition in the event

of an input line VIN_A step. Filter Times (typ.) = ‘00’ = 3-6ms, ‘01’ =

0.8-1.5ms, ‘10’ = 20µs, '11' = 1µs,

[5:3] R/W xx000xxx rd

Diode current ramp down step time: ‘000’ = 6µs, ‘001’ = 0.77ms,

‘010’ = 1.5ms, ‘011’ = 3ms, ‘100’ = 6ms, ‘101’ = 12ms, ‘110’ = 25ms,

‘111’ = 50ms

[2:0] R/W xxxxx000 ru

Diode current ramp up step time : ‘000’ = 6µs, ‘001’ = 0.77ms, ‘010’

= 1.5ms, ‘011’ = 3ms, ‘100’ = 6ms, ‘101’ = 12ms, ‘110’ = 25ms, ‘111’

= 50ms

40 ALS ZONE [7:6] R 00xxxxxx rev

READBACK Stores the silicon revision value. LM3537 = '00'

[5] R xx0xxxxx als_gain

Gain_status indicator: '1' = high gain, '0' = low gain.

[4] R xxx0xxxx timerflag

At the end of every countdown, the timer sets the timerflag ='1'. The

flag bit is cleared once the 0x40 register has been read.

[3] R xxxx0xxx zoneflag

ALS transition flag. '1' = Transition has occurred. '0' = No transition.

The flag bit is cleared once the 0x40 register has been read.

[2:0] R xxxxx000 zone

ALS Zone information: '000’ = Zone0, ‘001’ = Zone1, ‘010’ = Zone2,

‘011’ = Zone3, ‘100’ = Zone4. Other combinations not used.

50 ALS CONTROL [7:5] R/W 000xxxxx ave

Sets averaging time for the 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.

[4:3] R/W xxx00xxx timer

Pre-defined countdown timer function.

'00' = countdown timer is disabled

'01' = 10s countdown timer is enabled (stick to the highest zone for

10s)

'10' = Always stick to the highest zone the ALS reached

'11' = Always stick to the highest zone the ALS reached.

At the end of every countdown, the timer sets the countdown

timerflag (reg 40H), and after that, a Zone transition to a lower Zone

re-loads the timer and starts the next timer period.

[2] R/W xxxxx0xx 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 READBACK.

[1] R/W xxxxxx0x als_en_a

Enable ALS on Group A. Writing a '1' enables ALS control of diode

current and a '0' (default) forces the Group A current to the value

stored in the Group A brightness register. The als_en bit must be set

to a '1' for the ALS block to control the Group A brightness.

[0] R/W xxxxxxx0 als_en_b

Enable ALS on Group B. Writing a '1' enables ALS control of diode

current and a '0' (default) forces the Group B current to the value

stored in the Group B brightness register. The als_en bit must be set

to a '1' for the ALS block to control the Group B brightness. The ALS

function for Group B is different than Group A in that the ALS will

only enable and disable the Group B diodes depending on the ALS

zone chosen by the user. Group A utilizes the 5 different zone

brightness registers (Addresses 0x70 to 0x74).

51 ALS RESISTOR [4:0] R/W xxx00010 r_als

Sets the internal ALS resistor value. See Table 1 for details.

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Table 5. Control Register Map (continued)

Hex Read/W Default Value

Addr. rite After Reset

52 ALS CONFIG [7] R/W 0xxxxxxx autogain_en

'1' = Enables autogain for the external ambient light sensor.

'0' = disables autogain and GPO's are controlled by the gpo1 and

gpo2 -bits. See Table 2 for details.

[6] R/W x0xxxxxx sbias_en

'1' = External sensor power output enabled.

'0' = External sensor power output disbaled.

Note: '1' -> GPOs will behave as push-pull CMOS outputs

referenced to voltage on SBIAS. '0 '-> GPOs will act as open-drain

outputs (default).

[5] R/W xx0xxxxx sbias_volt

Sensor bias output voltage selection.

'1' = 3.0V output voltage.

'0' = 2.4V output voltage.

[3] R/W xxxx0xxx cp_en

Writing = '1' to this register bit enables the Charge-Pump block.

Forces the LM3537 to operate in the gain of 1.5x. This mode DOES

NOT require the Dx current sinks to be enabled for operation.

[2] R/W xxxxx0xx pass_en

Writing = '1' to this register bit forces the LM3537 to operate in the

gain of 1x (pass-mode). This mode DOES NOT require the Dx

current sinks to be enabled for operation. Note: 1.5x gain (cp_en bit)

has a higher priority.

[1] R/W xxxxxx0x gpo1

'0' = GPO1 pin state is low. '1' = GPO1 pin state is high. Effective

only when the autogain is disabled.(1)

[0] R/W xxxxxxx0 gpo2

'0' = GPO2 pin state is low. '1' = GPO2 pin state is high. Effective

only when the autogain is disabled.(1)

60 ALS ZONE [7:0] R/W 00110011 zb0

BOUNDARY#0 Sets Zone0 to Zone1 transition trip point

61 ALS ZONE [7:0] R/W 01100110 zb1

BOUNDARY#1 Sets Zone1 to Zone2 transition trip point

62 ALS ZONE [7:0] R/W 10011001 zb2

BOUNDARY#2 Sets Zone2 to Zone3 transition trip point

63 ALS ZONE [7:0] R/W 11001100 zb3

BOUNDARY#3 Sets Zone3 to Zone4 transition trip point

64 ALS LOW to HIGH [7:0] R/W 00001011 LtoH

TP Sets the trip point for low gain to high gain transition. Effective only

when autogain = '1'.

65 ALS ZONE [7:0] R/W 00010000 zb3to2

BOUNDARY Z3 to Zone3 to Zone2 transition trip point when the autogain is enabled.

70 ALS BRIGHTNESS [6:0] R/W x0111100 z0b

ZONE#0 Sets the Zone Brightness code for Zone0.

71 ALS BRIGHTNESS [6:0] R/W x1001101 z1b

ZONE#1 Sets the Zone Brightness code for Zone1.

72 ALS BRIGHTNESS [6:0] R/W x1011001 z2b

ZONE#2 Sets the Zone Brightness code for Zone2.

73 ALS BRIGHTNESS [6:0] R/W x1100110 z3b

ZONE#3 Sets the Zone Brightness code for Zone3.

74 ALS BRIGHTNESS [6:0] R/W x1110010 z4b

ZONE#4 Sets the Zone Brightness code for Zone4.

A0 GROUP A [6:0] R/W x0000000 dxa

BRIGHTNESS Sets Brightness for Group A. 128 steps, 1111111=Fullscale.

(1) VOUT_S = SBIAS pin output voltage. The voltage level of the GPOs depends on the sbias_en-bit: '1'; GPOs will behave as push-pull

outputs and will reference the high-side to the voltage of SBIAS. '0'; GPOs will act as open-drain outputs (default). In the open-drain

configuration, they can be high-side referenced to any voltage equal to, or less than, the VIN_A of the LM3537. Output High Level (VOH)

specification is valid only for push-pull -type outputs.

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Table 5. Control Register Map (continued)

Hex Read/W Default Value

Addr. rite After Reset

B0 GROUP B [5:3] R/W xx000xxx alsZT

BRIGHTNESS Sets the Brightness Zone boundary used to enable and disable

Group B diodes based upon ambient lighting conditions.

[2:0] R/W xxxxx000 dxb

Sets Brightness for Group B. 8 steps, 111 = Fullscale.

C0 LDO ENABLE [3] R/W xxxx0xxx en_ldo4

'1' = Regulator 4 enabled.

'0' = Regulator 4 disbaled.

[2] R/W xxxxx0xx en_ldo3

'1' = Regulator 3 enabled.

'0' = Regulator 3 disbaled.

[1] R/W xxxxxx0x en_ldo2

'1' = Regulator 2 enabled.

'0' = Regulator 2 disbaled.

[0] R/W xxxxxxx0 en_ldo1

'1' = Regulator 1 enabled.

'0' = Regulator 1 disbaled.

C1 LDO1 VOUT [4:0] R/W xxx11000 ldo1_vout

Regulator 1 output voltage programming. See Table 4 for voltage

options.

C2 LDO2 VOUT [4:0] R/W xxx01100 ldo2_vout

Regulator 2 output voltage programming.

C3 LDO3 VOUT [4:0] R/W xxx01100 ldo3_vout

Regulator 3 output voltage programming.

C4 LDO4 VOUT [4:0] R/W xxx11000 ldo4_vout

Regulator 4 output voltage programming.

Product Folder Links: LM3537

ILED (mA) |25 x 0.85

[44 ± {(N+1)/2.91}]

LM3537

www.ti.com

SNVS634B –JUNE 2011–REVISED MAY 2013

Current Control Registers

A0 GROUP A BRIGHTNESS

This is the LED driver current control register for Group A. The register is effective when the ALS isn't used. The

resolution is 7 bits, so in linear dimming mode the step size from zero up to full brightness is fixed (25.0mA/127)

= 197 µA. Exponential dimming scheme provides a more fine-grained level of control over low level LED

currents. Group A exponential dimming curve current can be approximated by the following equation (where N =

the decimal value stored in the Group A Brightness register):

(1)

Current vs. code is shown below.

Figure 10. LED current (typ.) vs. register code, exponential dimming curve

B0 GROUP B BRIGHTNESS

Bits [2:0] set the GroupB Brightness Levels, as shown in below:

Table 6. Group B Brightness Levels

dxb[2] dxb[1] dxb[0] GroupB LED Current (typ.)

1 1 1 25.0 mA

1 1 0 17.5 mA

1 0 1 15.0 mA

1 0 0 12.5 mA

0 1 0 10.0 mA

0 1 0 7.5 mA

0 0 1 5.0 mA

0 0 0 2.5 mA

Product Folder Links: LM3537

LM3537

SNVS634B –JUNE 2011–REVISED MAY 2013

www.ti.com

APPLICATION INFORMATION

LED CONFIGURATIONS

The LM3537 has a total of 8 current sinks capable of sinking 180mA of total diode current. These 8 current sinks

are configured to operate in one or two independently controlled lighting regions. GroupA has eight dedicated

current sinks, while GroupB has 0 by default. However, drivers D5 to D8 can be assigned to either GroupA or

GroupB one-by-one through a setting in the configuration register. With this added flexibility, the LM3537 is

capable of supporting applications requiring from 4 to 7 LEDs for main display lighting, while still providing

additional current sink(s) that can be used for a wide variety of lighting functions.

PARALLEL CONNECTED AND UNUSED OUTPUTS

Connecting the outputs in parallel does not affect internal operation of the LM3537 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 tables 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 circuitry to optimize the charge-pump gain for maximum

efficiency.

If some of the drivers are not going to be used, make sure that the enable bits in the DIODE ENABLE register

are set to '0' to ensure optimal efficiency.

THERMAL PROTECTION

Internal thermal protection circuitry disables the LM3537 when the junction temperature exceeds 160°C (typ.).

This feature protects the device from being damaged by high die temperatures that might otherwise result from

excessive power dissipation. The device will recover and operate normally when the junction temperature falls

below 155°C (typ.). It is important that the board layout provide good thermal conduction to keep the junction

temperature within the specified operating ratings.

CAPACITOR SELECTION

The LM3537 circuit requires 11 external capacitors for proper operation. Surface-mount multi-layer ceramic

capacitors are recommended. These capacitors are small, inexpensive and have very low equivalent series

resistance (ESR <20 mΩtyp.). Tantalum capacitors, OS-CON capacitors, and aluminum electrolytic capacitors

are not recommended for use with the LM3537 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 LM3537. These capacitors have tight capacitance tolerance (as good as ±10%) and hold their value over

temperature (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 LM3537.

Capacitors with these temperature characteristics typically have wide capacitance tolerance (+80%, -20%) and

vary significantly 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 deviation is likely to cause Y5V and Z5U capacitors to fail to meet the minimum

capacitance requirements of the LM3537.

Table 7 below lists recommended external capacitors from some leading ceramic capacitor manufacturers. It is

strongly recommended that the LM3537 circuit be thoroughly evaluated early in the design-in process with the

mass-production capacitors of choice. This will help ensure that any variability in capacitance does not negatively

impact circuit performance.

Product Folder Links: LM3537

LM3537

www.ti.com

SNVS634B –JUNE 2011–REVISED MAY 2013

Table 7. Suggested Capacitors

Model Type Vendor Voltage Rating Package Size

1 µF for COUT , CLDO1, CLDO2, CLDO3, CLDO4, CSEN, C1, C2and CIN_A(1)

C1005X5R1A105K Ceramic X5R TDK 10V 0402

LMK105BJ105KV-F Ceramic X5R Taiyo Yuden 10V 0402

GRM155R61A105K Ceramic X5R Murata 10V 0402

0.1 µF for CIN_B(1)

GRM155R61A104K Ceramic X5R Murata 10V 0402

LMK105BJ104KV-F Ceramic X5R Taiyo Yuden 10V 0402

C1005X5R1A104K Ceramic X5R TDK 10V 0402

2.2 µF for CIN_C

JMK105BJ225MV-F Ceramic X5R Taiyo Yuden 6.3V 0402

GRM155R60J225ME15D Ceramic X5R Murata 6.3V 0402

(1) The recommended voltage rating for these capacitors is 10V to account for DC bias capacitance losses.

Product Folder Links: LM3537

LM3537

SNVS634B –JUNE 2011–REVISED MAY 2013

www.ti.com

REVISION HISTORY

Changes from Revision A (May 2013) to Revision B Page

• Changed layout of National Data Sheet to TI format .......................................................................................................... 27

Product Folder Links: LM3537

PACKAGE OPTION ADDENDUM

www.ti.com 10-Dec-2020

Addendum-Page 1

PACKAGING INFORMATION

Orderable Device Status

(1)

Package Type Package

Drawing Pins Package

Qty Eco Plan

(2)

Lead finish/

Ball material

(6)

MSL Peak Temp

(3)

Op Temp (°C) Device Marking

(4/5)

Samples

LM3537TME/NOPB ACTIVE DSBGA YFQ 30 250 RoHS & Green SNAGCU Level-1-260C-UNLIM -30 to 110 3537

LM3537TMX/NOPB ACTIVE DSBGA YFQ 30 3000 RoHS & Green SNAGCU Level-1-260C-UNLIM -30 to 110 3537

(1) The marketing status values are defined as follows:

ACTIVE: Product device recommended for new designs.

LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.

NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.

PREVIEW: Device has been announced but is not in production. Samples may or may not be available.

OBSOLETE: TI has discontinued the production of the device.

(2) RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance

do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may

reference these types of products as "Pb-Free".

RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.

Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of <=1000ppm threshold. Antimony trioxide based

flame retardants must also meet the <=1000ppm threshold requirement.

(3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.

(4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.

(5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation

of the previous line and the two combined represent the entire Device Marking for that device.

(6) Lead finish/Ball material - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead finish/Ball material values may wrap to two

lines if the finish value exceeds the maximum column width.

Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information

provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and

continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.

TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.

In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.

PACKAGE OPTION ADDENDUM

www.ti.com 10-Dec-2020

Addendum-Page 2

TAPE AND REEL INFORMATION

*All dimensions are nominal

Device Package

Type Package

Drawing Pins SPQ Reel

Diameter

(mm)

Reel

Width

W1 (mm)

(mm) B0

(mm) K0

(mm) P1

(mm) W

(mm) Pin1

Quadrant

LM3537TME/NOPB DSBGA YFQ 30 250 178.0 8.4 2.18 2.69 0.76 4.0 8.0 Q1

LM3537TMX/NOPB DSBGA YFQ 30 3000 178.0 8.4 2.18 2.69 0.76 4.0 8.0 Q1

PACKAGE MATERIALS INFORMATION

www.ti.com 8-May-2013

Pack Materials-Page 1

*All dimensions are nominal

Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm)

LM3537TME/NOPB DSBGA YFQ 30 250 210.0 185.0 35.0

LM3537TMX/NOPB DSBGA YFQ 30 3000 210.0 185.0 35.0

PACKAGE MATERIALS INFORMATION

www.ti.com 8-May-2013

Pack Materials-Page 2

MECHANICAL DATA

YFQ0030xxx

www.ti.com

TMD30XXX (Rev B)

. All linear dimensions are in millimeters. Dimensioning and tolerancing per ASME Y14.5M-1994.

B. This drawing is subject to change without notice.

NOTES:

4215085/A 12/12

0.600

±0.075

D: Max =

E: Max =

2.529 mm, Min =

2.049 mm, Min =

2.469 mm

1.989 mm

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