AAT3156

High Efficiency 1X/1.5X/2X Charge Pump

For White LED Applications

3156.2005.09.1.2

11

Max Current Register Settings—Address 4

Low Current Register Settings—Address 5

Disabled Current Sinks

Current sink inputs that are not used should be dis-

abled. To disable and properly terminate unused

current sink inputs, they must be tied to V

unconnected or terminated to ground, the part will

be forced to operate in 2X charge pump mode.

Properly terminating unused current sink inputs is

important to prevent the charge pump modes from

prematurely activating. When properly terminated,

only a small sense current flows for each disabled

channel. The sense current for each disabled chan-

nel is less than 120µA.

The AAT3156 is also equipped with an auto-disable

feature to protect against an LED failure condition.

Thermal Protection

The AAT3156 has a built-in thermal protection cir-

cuit that will shut down the charge pump if the die

temperature rises above the thermal limit, as is the

case during a short circuit of the V

Applications Information

LED Selection

The AAT3156 is specifically intended for driving

white LEDs. However, the device design will allow

the AAT3156 to drive most types of LEDs with for-

ward voltage specifications ranging from 2.0V to

4.3V. LED applications may include main and sub-

LCD display backlighting, camera photo-flash appli-

cations, color (RGB) LEDs, infrared (IR) diodes for

remotes, and other loads benefiting from a con-

trolled output current generated from a varying input

voltage. Since the D1 to D6 constant current sinks

are matched with negligible voltage dependence,

the LED brightness will be matched regardless of

the specific LED forward voltage (V

In some instances (e.g., in high-luminous-output

applications such as photo flash), it may be neces-

sary to drive high-V

current sinks in the AAT3156 make it capable of

driving LEDs with forward voltages as high as 4.3V

at full current from an input supply as low as 3.0V.

Current sinks can be paralleled to drive high-cur-

rent LEDs without complication.

Device Switching Noise Performance

The AAT3156 operates at a fixed frequency of

approximately 1MHz to control noise and limit har-

monics that can interfere with the RF operation of

cellular telephone handsets or other communica-

tion devices. Back-injected noise appearing on the

input pin of the charge pump is 20mV peak-to-

peak, typically ten times less than inductor-based

DC/DC boost converter white LED backlight solu-

tions. The AAT3156 soft-start feature prevents

noise transient effects associated with inrush cur-

rents during start-up of the charge pump circuit.

Data

D1-D4 (mA)

D5-D6 (mA)

10

0

20

0

30

0

40

0

5

0

0.05

6

0

0.5

70

1

80

2

9

0.05

0

10

0.5

0

11

1

0

12

2

0

13

0.05

0.05

14

0.5

0.5

15

1

1

16

2

2

Data

Max Current

1

20mA Max Scale

2

30mA Max Scale

3

15mA Max Scale

4

Low Current Mode

1

1. Low Current Mode requires the Max Current register to be set to Low Current Mode. Low Current Mode is unaffected by the settings

for Addresses 1-3.