A8435EESTR-T - Allegro Microsystems

NOTE: For detailed information on purchasing options, contact your

local Allegro field applications engineer or sales representative.

Allegro MicroSystems, Inc. reserves the right to make, from time to time, revisions to the anticipated product life cycle plan

for a product to accommodate changes in production capabilities, alternative product availabilities, or market demand. The

information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, Inc. assumes no respon-

sibility for its use; nor for any infringements of patents or other rights of third parties which may result from its use.

Recommended Substitutions:

High Ef ficiency Charge Pump White LED Driver

A8435

For existing customer transition, and for new customers or new appli-

cations, contact Allegro Sales.

This device is in production, however, it has been deemed Pre-End

of Life. The product is approaching end of life. Within a minimum of

6 months, the device will enter its final, Last Time Buy, order phase.

Date of status change: January 31, 2011

LED1

VOUT

GND ISET

LED2

LED3

LED4

VIN

C2+

C2-

EN1

EN2

C1+

C1-

CTRL

Single-Wire On/Off and

Dimming Control

A8435

VBATT

2.7 to 5.5 V

RSET

CIN

1 µF COUT

1 µF

A8435

LED1

VOUT

GND ISET

LED2

LED3

LED4

VIN

C2+

C2–

EN1

C1+

C1–

CTRL

On/Off and

Dimming Control

VBATT

2.7 to 5.5 V

RSET

CIN

1 µF COUT

1 µF

Figure 1. Typical Circuit. Dual wire control configuration: 2-bit

parallel or PWM dimming.

Figure 2. Typical Circuit. Single wire control configuration.

A8435-DS, Rev. 2

Description

The A8435 high efficiency charge pump IC offers a simple,

low-cost white LED driver solution for portable electronics

display applications. Using a proprietary control scheme (1×,

1.5×), the A8435 can output well-matched currents for up to

4 LEDs, while maintaining the highest efficiency over most

of the Li-ion battery lifetime.

The A8435 accepts an input range of 2.7 to 5.5 V and delivers

up to 30 mA for each of the four regulated current sources. The

A8435 can deliver a total continuous output current of 120 mA,

meeting the requirements of most Li-ion battery-powered white

LED backlight applications. Outputs can also be tied together

for WLED flash/torch applications.

The A8435 offers flexible options for LED current driving.

The LED current can be set by any of the following methods:

(a) choosing an appropriate value for RSET, (b) 2-bit

parallel control with 3 levels, (c) PWM control, or (d) serial

programming

The A8435 is available in a very thin profile 0.75 mm (nominal

height) 3 × 3 mm QFN/MLP-16 package (ES), fitting the needs

of space-conscious applications.

Features and Benefits

▪ Proprietary adaptive control scheme (1×, 1.5×)

▪ Maximum efficiency, over 92%

▪ 0.5% LED current matching

▪ 1 MHz operating frequency

▪ Flexible dimming control:

▫ Serial 11-level dimming, down to 5%

▫ PWM

▫ 2-bit parallel

▪ Drives up to 4 white LEDs

▪ 30 mA per LED

▪ 120 mA total continuous output

▪ Low input ripple and EMI

▪ Soft-start limits inrush current

▪ Short circuit protection

▪ Overvoltage protection

▪ Thermal shutdown protection

▪ Space-saving MLP-16 package: 3 × 3 mm footprint

▪ Very thin 0.75 mm nominal height package

High Ef ficiency Charge Pump White LED Driver

Package: 16 pin QFN/MLP (suffix ES)

Typical Applications

A8435

Approximate Scale

▪ White LED backlights for cellular phones, PDAs

▪ Digital cameras, camcorders

▪ Portable audio devices

▪ Other portable device white LED backlighting

▪ 120 mA WLED flash/torch

Applications include:

High Ef ficiency Charge Pump White LED Driver

A8435

Allegro MicroSystems, Inc.

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

Ab so lute Max i mum Rat ings

Package Thermal Characteristics

Input or Output Voltage

VIN, VOUT, C1+, C1–, C2+, and C2– pins ..................... –0.3 to 6 V

All other pins ..................................................... –0.3 to VIN + 0.3 V

VOUT Short Circuit to GND ....................................................Continuous

Operating Ambient Temperature, TA ..................................... –40°C to 85°C

Maximum Junction Temperature, TJ(max) ............................................. 150°C

Storage Temperature, TS

................................................... –55°C to 150°C

Selection Guide

Part Number Packaging* Package Type

A8435EESTR-T 7-in. reel, 1500 pieces/reel ES, 3 × 3 mm QFN/MLP-16

*Contact Allegro for additional packing options.

Package is lead (Pb) free, with 100% matte tin leadframe plating.

RθJA = 47 °C/W, on a 4-layer board based on JEDEC spec

Additional information is available on the Allegro Web site.

+–

–

+–+–+–

Fractional Charge Pump

(1× and 1.5×)

VIN

RSET

LED1

LED2

LED3

LED4

EN1

EN2

VOUT

C1+ C1 –C2+ C2–

ISET

GND

1 µF

CIN COUT

CTRL

Minimum Select

Current Mirror

Control, Clock,

and Reference

Functional Block Diagram

High Ef ficiency Charge Pump White LED Driver

A8435

Allegro MicroSystems, Inc.

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

(Top View)

Name Pin Number Function*

C1– 13 Negative terminal of capacitor C1.

C1+ 16 Positive terminal of capacitor C1.

C2– 15 Negative terminal of capacitor C2.

C2+ 1 Positive terminal of capacitor C2.

CTRL 4 Brightness control scheme toggle. For 2-bit parallel or PWM dimming, leave open or tie to VIN

(see table 1). For single-wire serial input dimming, connect to GND (see figure 2).

EN1 3

When CTRL is open or HIGH: Enable and dimming control input 1 (see table 1).

When CTRL is grounded: single-wire enable and dimming control (see table 1 and figure 2).

(Do not leave unconnected.)

EN2 5 When CTRL is open or HIGH: Enable and dimming control input 2 (see table 1).

When CTRL is grounded: this pin disables shutdown. (Do not leave unconnected.)

EP – Exposed metal pad on bottom side. Connect this to ground plane for better thermal

performance.

GND 11 Ground.

ISET 6 Connect RSET resistor to ground to set desired constant current through LEDs.

LED1 8 Current sink for LED1. Connect to VIN or VOUT if not used for LED. (Do not leave unconnected.)

LED2 7 Current sink for LED2. Connect to VIN or VOUT if not used for LED. (Do not leave unconnected.)

LED3 10 Current sink for LED3. Always connect this pin to LED.

LED4 9 Current sink for LED4. Connect to VIN or VOUT if not used for LED. (Do not leave unconnected.)

NC 12 No Connection.

VIN 14 Power supply voltage input.

VOUT 2 Charge pump voltage source output for connection to the LED anodes.

* See Application Information section for cited figure and tables.

Terminal List Table

GND

LED3

LED4

C2+

VOUT

EN1 EP

CTRL

C1+

C2–

VIN

C1–

EN2

ISET

LED2

LED1

Pin-out Diagram

High Ef ficiency Charge Pump White LED Driver

A8435

Allegro MicroSystems, Inc.

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

ELECTRICAL CHARACTERISTICS1

VIN = VEN1 = VEN2 = 3.6 V, C1 = C2 = 1 μF, TA = –40 to 85°C, typical values at TA = 25°C (unless otherwise noted)

Characteristics Symbol Test Conditions Min. Typ. Max. Units

Input Voltage Range VIN 2.7 – 5.5 V

Undervoltage Lockout Threshold VUVLO VIN falling, VUVLOHYS = 35 mV 2.25 2.45 2.60 V

UVLO Hysteresis Window VUVLOHYS – 35 – mV

Quiescent Current IQ

Switching, TA = 25°C – 2.8 4 mA

EN1 = EN2 = GND, TA = 25°C – 0.1 1 μA

Soft-Start Completion Time tSS – 2 – ms

ISET Bias Voltage VISETBIAS 0.56 0.6 0.64 V

ISET Leakage in Shutdown VISETLKG – 0.01 1 μA

ISET Current Range IISET 40 – 140 μA

ISET to LEDx Current Ratio ILEDx

/ IISET

IISET = 60 μA,

CTRL = open or HIGH

EN1 = EN2 = VIN 190 219 245 A/A

EN1 = VIN, EN2 = GND 105 121 137 A/A

EN1 = GND, EN2 = VIN 51 60 69 A/A

IISET = 60 μA,

CTRL = LOW Full brightness – 200 – A/A

ILED Accuracy EILED EN1 = EN2 = VIN, RSET = 4.3 kΩ– ±0.9 – %

LED Current Matching2∆ILED VIN =3.6 V, ILED = 30 mA per LED – ±0.5 – %

Regulation Voltage at LEDx (1.5×) VLED EN1 = EN2 = VIN – 150 – mV

Open Loop Output Resistance3ROUT

1× mode: [(VIN – VOUT) / IOUT] – 1.1 – Ω

1.5× mode: [(1.5 × VIN – VOUT) / IOUT] – 3.6 – Ω

1× to 1.5× Mode Transition Voltage at LEDx VTrans V

LEDx Falling – 100 – mV

Transition to Dropout Voltage Difference4∆Vdr Measured as VTrans – VDropout – 60 – mV

LED Leakage in Shutdown VLEDLKG EN1 = EN2 = GND, VIN = 5.5 V, TA = 25°C – 0.01 1 μA

Oscillator Frequency fosc – 1 – MHz

Output Overvoltage Protection5VOVP

Open circuit at any LED that is programmed to be

in the ON state – 5.74 – V

CTRL, EN1, EN2 Input High Logic Threshold6VIH 1.6 – – V

CTRL, EN1, EN2 Input Low Logic Threshold6VIL – – 0.4 V

Input High Current IIH V

IH = VIN –– 1μA

Input Low Current IIL V

IL = GND – – 1 μA

EN1 Pulse Low Time7 t

LO 0.5 – 500 μs

EN1 Pulse High Time7tHI 0.5 – – μs

Initial EN1 Pulse High Time7 t

HI(Init) First EN1 pulse after shutdown 100 – – μs

Shutdown Delay7 t

SHDN Falling edge of EN1 pulse – 2 3 ms

Thermal-Shutdown Threshold TSHDN 20°C hysteresis – 165 – °C

1Specifications guaranteed by design over operating temperature range, –40°C to 85°C.

2LED current matching is defined as (ILEDX – ILED(AVG)) / ILED(AVG)

3The Open Loop Output Resistance for 1.5× mode is measured with one of the LEDx pins tied to ground or open (thus its voltage is always less

than 80 mV).

4Dropout Voltage, VDropout, is defined as the LEDx-to-GND voltage at which ILEDx drops 10% below the value of ILEDX at VLEDX = 200 mV.

5Guaranteed by design.

6EN2 is not used when CTRL is tied to ground.

7Applies only when CTRL is tied to ground. See figure 3 in Application Information section.

High Ef ficiency Charge Pump White LED Driver

A8435

Allegro MicroSystems, Inc.

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

Performance Characteristics

Tests performed using application circuit shown in figure 1: dual wire control; and

VIN

= 3.6 V, EN1 = EN2 = VIN, CIN

= C1

= C2

= COUT

= 1 μF, R SET

= 7.5 kΩ, TA = 25°C (unless otherwise noted)

100

2.70 2.90 3.10 3.30 3.50 3.70 3.90 4.10

(V)

η (%)

4.75

9.8

17.6 (Full Brightness)

Dimming Level

(mA)

100

120

2.70 2.90 3.10 3.30 3.50 3.70 3.90 4.10

(V)

IBATT (mA)

VIN Rising

VIN Falling

17.6 mA

9.8 mA

4.75 mA

VIN Rising

VIN Falling

VIN Rising

VIN Falling

2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5

(V)

ILED (mA)

Efficiency versus Supply Voltage

Over Range of Dimming Levels, VIN Falling

Supply Current versus Supply Voltage

Over Range of Dimming Levels (mA)

LED Current versus Supply Voltage

Matching Between LEDs <1% Over Range of VIN

High Ef ficiency Charge Pump White LED Driver

A8435

Allegro MicroSystems, Inc.

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

VEN

Startup Response

2-Bit (EN1-EN2) Dimming Response

11-Level Single-Wire Serial Dimming

Response

IBATT

VOUT

IOUT

VEN

VEN1

IOUT

VOUT

Symbol Parameter Units/Division

C1 VEN 5 V

C2 IBATT 50 mA

C3 VOUT 2 V

t time 500 μs

Symbol Parameter Units/Division

C1 VEN1 2 V

C2 IOUT 50 mA

C3 VOUT 2 V

t time 10 ms

Conditions

EN2 = CTRL = GND, apply control

signal to EN1

Symbol Parameter Units/Division

C1 VEN1 2 V

C2 IOUT 50 mA

t time 5 μs

Conditions

EN2 = VIN

High Ef ficiency Charge Pump White LED Driver

A8435

Allegro MicroSystems, Inc.

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

Setting LED Current

The LED current level, ILEDX, is set by the value chosen for the

external resistor, RSET, which is connected to the ISET terminal.

The full current (100%) level for ILEDX can be calculated using

the following formulas:

Setting Formula

CTRL = Open or HIGH RSET (Ω) = 0.6 V × 219 / ILEDX

CTRL = LOW RSET (Ω) = 0.6 V × 200 / ILEDX

Dimming

The A8435 offers serial, 2-bit parallel, and PWM dimming

control. When the CTRL pin is pulled LOW, the EN1 pin accepts

one-wire serial pulse input both to enable the part, and to select

one of the 11 dimming levels, from 100% down to 5% (see

table 1).

With EN2 low, when EN1 is pulled high, the IC turns on. The

initial LED current defaults to 100% after softstart is complete.

The tLO must be < 500 ms to avoid shutdown. With EN2 high,

the operation of EN1 is the same as when EN2 is low, except

shutdown is disabled (TLO = ∞).

Application Information

Table 1. CTRL, EN1, and EN2 Pin States

CTRL EN1 EN2 Brightness LED Current, ILED

Open or HIGH LOW LOW Shutdown 0

Open or HIGH LOW HIGH 27% Brightness 60 × IISET

Open or HIGH HIGH LOW 55% Brightness 121 × IISET

Open or HIGH HIGH HIGH Full Brightness 219 × IISET

LOW Pulse

input

effect

Adjustable; 11 levels of dimming from

100% to 5% (see figure 3; 100% cor-

responds to 200 × IISET)

LOW LOW

> 2 ms LOW Shutdown

High Ef ficiency Charge Pump White LED Driver

A8435

Allegro MicroSystems, Inc.

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

When changing from one specific brightness level to another, the

user may not want to keep the existing brightness level stored

in memory. A simpler method is to program a shutdown and

re-enable, followed by an appropriate number of pulses (from

100%) to reach the target brightness level. The total “LED off”

time during shutdown, re-enable, and brightness programming

can be kept sufficiently short such that no delay is discernable to

the eye.

Shutdown

If the CTRL pin is unconnected or HIGH, the device enters the

shutdown mode when EN1 and EN2 are pulled LOW. When

configured to have a serial pulse dimming control (the CTRL pin

is grounded), the EN1 and the EN2 pins must be pulled LOW for

longer than tSHDN (2 ms typical) in order to enter shutdown mode.

The output is high impedance after shutdown.

Disabling Unused LEDs

If any WLED is not used, connect the corresponding pin to either

VIN or VOUT to disable it. Never leave open any unused WLED

pin. LED pins will sink 30 μA typical when connected to VIN or

VOUT and the IC is enabled.

LED3 must always be selected. For example, to drive 2 LEDs,

select LED3 and one of either LED1, LED2, or LED4.

Component Selection

Ceramic capacitors with X5R or X7R dielectric are recommended

for the input capacitor, CIN, the output capacitor, COUT, and the

charge pump capacitors, C1 and C2.

SHDN

tSHDN

EN1

100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 5%

100% 90%

tHI

tLO

tSS

SHDN

tHI(Init)

IILEDX

12345 67891011

Figure 3. Single-Wire Serial Dimming Control, at pin EN1; CTRL = LOW, EN2 = LOW.

High Ef ficiency Charge Pump White LED Driver

A8435

Allegro MicroSystems, Inc.

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

Package ES, 3 × 3 mm 16-Pin QFN/MLP

C0.08

17X

ATerminal #1 mark area

BExposed thermal pad (reference only, terminal #1

identifier appearance at supplier discretion)

For reference only

(reference JEDEC MO-220WEED)

Dimensions in millimeters

Exact case and lead configuration at supplier discretion within limits shown

CReference land pattern layout (reference IPC7351

QFN50P300X300X80-17W4M);

All pads a minimum of 0.20 mm from all adjacent pads; adjust as

necessary to meet application process requirements and PCB layout

tolerances; when mounting on a multilayer PCB, thermal vias at the

exposed thermal pad land can improve thermal dissipation (reference

EIA/JEDEC Standard JESD51-5)

PCB Layout Reference View

B1.70

1.70

0.30

16 0.50

0.90

3.10

SEATING

PLANE

0.25 +0.05

–0.07

0.40 +0.15

–0.10

0.50 0.75 ±0.05

3.00 ±0.15

DCoplanarity includes exposed thermal pad and terminals

Allegro MicroSystems, Inc. reserves the right to make, from time to time, such de par tures from the detail spec i fi ca tions as may be required to per-

mit improvements in the per for mance, reliability, or manufacturability of its products. Before placing an order, the user is cautioned to verify that the

information being relied upon is current.

Allegro’s products are not to be used in life support devices or systems, if a failure of an Allegro product can reasonably be expected to cause the

failure of that life support device or system, or to affect the safety or effectiveness of that device or system.

The in for ma tion in clud ed herein is believed to be ac cu rate and reliable. How ev er, Allegro MicroSystems, Inc. assumes no re spon si bil i ty for its use;

nor for any in fringe ment of patents or other rights of third parties which may result from its use.

For the latest version of this document, visit our website: