ALLEGRO A8434 User Manual

A8434

6-Channel High Efficiency Charge Pump White LED Driver

Features and Benefits

▪ Proprietary adaptive control scheme (1×, 1.5×, 2×)
▪ 0.5% typical WLED current matching
▪ Drives up to 6 white LEDs

▫ Main display backlight (up to 6 WLEDs)
▫ Main display and sub display backlight

▫ Main display and low-current flash/torch
▪ 30 mA per WLED
▪ 2× serial dimming interfaces
▪ 320 mA charge pump capability
▪ Low EMI design and soft start function
▪ Short circuit, overvoltage, thermal shutdown protection
▪ 0.75 mm nominal height (very thin profile),

3 × 3 mm footprint packages

Package: 16 pin QFN/MLP (suffix ES)

Description

The A8434 high efficiency charge pump ICs offer a simple,
low-cost WLED (white LED) driver solution for driving up to
six WLEDs in various application configurations, either all six
backlighting a single display, or for multiple displays, such as
four WLEDs as the main display backlight, with the other two
WLEDs used for backlighting a sub display or a low-current
flash/torch. Using a proprietary control scheme (1×, 1.5×, and

2×

), the A8434 can deliver well-matched WLED current while

maintaining the highest efficiency and low EMI.

The WLED current is regulated over the entire range of Li+
battery voltage to provide uniform intensity. WLED brightness
and on/off can be controlled for the main display and sub
display/torch through 2 single-wire serial interface pins.

The A8434 is available in an QFN/MLP-16 space-conserving
(3 × 3 mm footprint) ES package.

Applications include:

▪ White LED backlights for cellular phones, PDAs
▪ Digital cameras, camcorders
▪ Portable audio devices and MP3s
▪ Other portable device white LED backlighting

Approximate scale 1:1

T ypical Applications

V

BATT

2.7 to 5.5 V

CIN
1 µF

RSET

On/Off and

Dimming

Control

C1

1 µF

C2
1 µF

VIN

C1+

C1–

C2+

C2–

ISET

ENM

ENS

A8434

GND

VOUT

LED1

LED2

LED3

LED4

LED5

LED6

Figure 1.6 × 30 mA WLED display Figure 3. High efficiency current sink

COUT
1 µF

D1

D2

D3

D4

D5

D6

V

2.7 to 5.5 V

CIN
1 µF

RSET

On/Off and

Dimming

Control

BATT

C1

1 µF

C2
1 µF

VIN

C1+

C1–

C2+

C2–

ISET

ENM

ENS

VOUT

LED1

LED2

A8434

LED3

LED4

LED5

LED6

GND

D1-D4 Main Display; D5-D6 Sub Display

COUT
1 µF

D1

D2

D3

D4

D5

D6

CIN
1 μF

RSET

On/Off and

V

IN

Dimming

Control

VIN

C1+

C1–

C2+

C2–

ISET

ENM

ENS

A8434

GND

VOUT

LED1

LED2

LED3

LED4

LED5

LED6

V

IN>Vf

D1

D2

D3

D4

D5

D6

(max)+0.2 V, Vf = LED forward drop

Figure 2. 4 × 30 mA main with 2 × 30 mA sub display

8434-DS, Rev. 1

A8434

6-Channel High Efficiency Charge Pump

White LED Driver

Functional Block Diagram

CIN

1 μF

RSET

VIN

ENM

ENS

ISET

Control, Clock,
and Reference

Current Mirror

+

−

C1+

C1

1 μF

−

C1

Fractional Charge Pump

(1×, 1.5×, and 2×)

−

+

−

+

C2+

+

−

Minimum Select

−

+

C2

1 μF

C2−

VOUT

COUT

1 μF

LED1

LED2

LED3

LED4

LED5

LED6

−

+

−

+

−

+

GND

Ab so lute Max i mum Rat ings

Input or Output Voltage

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

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

+ 0.3 V

IN

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

Operating Ambient Temperature, T
Junction Temperature, T
Storage Temperature, T

J(max)

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

S

..................................... –40°C to 85°C

A

.............................................................. 150°C

Use the following complete part number when ordering:

Part Number Packaging* Package Type

A8434EESTR-T 7-in. reel, 1500 pieces/reel ES, 3 × 3 mm MLP-16

*Contact Allegro for additional packing options.

Package Thermal Characteristics

ES Package R

= 68 °C/W

θJA

(vendor data, on 4-layer PCB; unverified)
Additional information is available on the Allegro website.

The device package is lead (Pb) free, with 100% matte tin
leadframe plating.

Allegro MicroSystems, Inc.

115 Northeast Cutoff, Box 15036

Worcester, Massachusetts 01615-0036 [phone]

www.allegromicro.com

2

A8434

6-Channel High Efficiency Charge Pump

White LED Driver

Pin-out Diagram

ES Package

C1+

C2–

VIN

C1–

C2+

VOUT

ISET

ENS

161514

1

2

3

4

567

ENM

(Top View)

EP

LED6

LED5

13

12

11

10

8

LED4

GND

LED1

LED2

9

LED3

Terminal List Table

Name Number Function

C1– 13 Negative terminal of capacitor C1. Connect capacitor C1 between C1+ and C1–.
C1+ 16 Positive terminal of capacitor C1.
C2– 15 Negative terminal of capacitor C2
C2+ 1 Positive terminal of capacitor C2. Connect capacitor C2 between C2+ and C2–.

ENS 4 Enable and dimming control input for sub display WLED group.

ENM 5 Enable and dimming control input for main display WLED group.

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

GND 12 Ground.

ISET 3

LED1, LED2,
LED3, and LED4

8, 9, 10,

and 11

LED5 and LED6 6 and 7

VIN 14 Power supply voltage input.

VOUT 2

Connect RSET resistor to ground to set desired constant current through main and sub WLEDs.
I

LED(max)

= 220 x 0.6 V / R

SET

Current sink for main display WLEDs. If not used, connect to VOUT, but do not leave open. If left
open, the IC works in 2 × mode.

Current sink for sub display WLEDs. If not used, connect to VOUT, but do not leave open. If left open,
the IC works in 2 × mode.

Charge pump output voltage for display backlight and flash/torch LED anodes.
Connect a 1 F capacitor, COUT, between VOUT and GND (see figure 2).

Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036

Worcester, Massachusetts 01615-0036 [phone]

www.allegromicro.com

3

A8434

6-Channel High Efficiency Charge Pump

White LED Driver

ELECTRICAL CHARACTERISTICS

a

VIN = ENM = ENS = 3.6 V, C1 = C2 = 1 F, CIN = COUT = 1 F, RSET = 6.49 k,

TA = –40°C to +85°C; typical values are at TA = 25°C; unless otherwise noted

Characteristics Symbol Test Conditions Min. Typ. Max. Units

Input Voltage Range V

Undervoltage Lockout Threshold V

UVLO Hysteresis Window V

Quiescent Current I

Soft-start Completion Time t

ISET Bias Voltage V

ISET Leakage in Shutdown V
ISET Current Range I

ISET to LEDx Current Ratio for LED1 through LED6 I

I

Accuracy for LED1 through LED6

LED

LED Current Matching for LED1 through LED4

LED Current Matching for LED5 and LED6

b

c

c

Regulation Voltage at LEDx (1.5× and 2× modes) V

1× mode to 1.5× or 1.5× to 2× mode transition voltage at LEDx V

Transition–Dropout Delta

d

IN

UVLO

UVLOHYS

Q

ss

ISETBIAS

ISETLKG

SET

LEDx/IISET

E

ILEDERR

I

LED14

I

LED56

REG

trans

V

dr

VIN falling 2.25 2.45 2.60 V

Switching in 1.5× or 2.0× mode; TA = 25°C – 6 – mA

ENS = ENM = GND; T

100% setting, I

ENS = ENM = VIN – ±1.6 – %

ENS = GND, ENM = VIN – ±0.5 – %

ENS = VIN, ENM = GND – ±0.5 – %

ENS = ENM = VIN – 250 – mV

V

LEDx

Measured as V

1× mode (VIN – V

Open Loop Output Resistance

e

R

1.5× mode (1.5 × V

OUT

2× mode (2 × V

LED Leakage in Shutdown V

LEDLKG

Oscillator Frequency f

Output Overvoltage Protection (guaranteed by design) V

ENS and ENM Input High Threshold V

ENS and ENM Input Low Threshold V

Input High Current I

Input Low Current I

ENM and ENS Pulse Low Time (figure 5) t

ENM and ENS Pulse High Time (figure 5) t

ENM and ENS Initial Pulse High Time (figure 5) t

Shutdown or Dimming Reset Delay t

INIHI

SHDN

Thermal Shutdown Threshold T

a

Specifications for the range TA = –40°C to 85°C are guaranteed by design.

b

I

accuracy is defined as ( I

LED

c

LED current matching is defined as (I

d

Dropout voltage V

e

The open loop output resistance, R

is defined as LEDx-to-GND voltage at which I

dropout

SET

× 220 – I

LEDx

, for 1.5 × mode is measured when one of the LEDx pins is tied to ground or open (thus its

OUT

LEDAVG

– I

LEDAVG

) / (I

SET

) / I

× 220).

LEDAVG

.

ENS = ENM = GND, VIN = 5.5 V – 0.01 1 A

osc

Open circuit at any LED that is programmed

ovp

to be in the ON state

Input high logic threshold 1.4 – – V

IH

Input low logic threshold – – 0.4 V

IL

VIH=VIN – – 1 A

IH

VIL= GND – – 1 A

IL

LO

HI

First ENM or ENS pulse after shutdown 50 – – s

Falling edge of ENS and/or ENM – 0.5 – ms

20oC hysteresis – 165 –

TSD

LEDx

voltage is always less than 80 mV).

2.7 – 5.5 V

–60–mV

= 25°C – 0.1 2 A

A

– 0.4 – ms

– 0.6 – V

– 0.01 1 A

40 – 140 A

= 60 A – 220 – A/A

SET

falling – 150 – mV

trans

IN

– V

OUT

– V

IN

) / I

– V

OUT

dropout

OUT

OUT

) / I

) / I

OUT

OUT

–40–mV

–1–

– 2.5 – 

–5–

– 1 – MHz

– – 6.0 V

0.5 – 250 s

0.5 – – s

o

drops 10% below the value of I

LEDx

when V

= 300 mV.

LEDx

C

Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036

Worcester, Massachusetts 01615-0036 [phone]

www.allegromicro.com

4