AAT3172 datasheet(9/15 Pages) AAT

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AAT3172

High Current LED Flash Driver Charge Pump IC

3172.2006.05.1.5

programmable through the AS2Cwire serial inter-

face. Independent current settings can be used for

a multistage flash LED control. This feature allows

users to conveniently drive separate dual flash

LEDs directly while achieving good brightness

matching. Also, F1 and F2 can be connected

together for single output configuration.

Modes of Operation

In addition to the data registers that set the current

levels for the two current sinks, the AAT3172 has

three mode registers.

mode register. It sets the maximum per channel

current level to either 300mA or 50mA. Each chan-

nel can be set independently so one channel can

be for flash while the other can be in a low constant

current mode.

Data = 1, both current sources are enabled

(default); when set with Data = 2, both current

sources are disabled. When Register 4 is set to

OFF, the device is in standby mode with signifi-

cantly reduced quiescent current.

The AAT3172 also includes a regulated output

voltage mode setting. By setting Register 6 with

Data = 2 for voltage mode, the charge pump deliv-

ers a regulated 4.5V output that continuously oper-

ates in 1.5X mode. It is suitable for driving loads

of up to 100mA. The voltage mode may be used

to drive LEDs with ballast resistors. Driving either

F1 or F2 in current mode will override the voltage

mode state until F1 and F2 are set back to zero

current by either data or mode register. Setting

to current mode and the charge pump output volt-

age will regulate appropriately.

AS2Cwire Serial Interface

The AAT3172 utilizes the AS2Cwire serial interface

to enable/disable the charge pump, set the operat-

ing mode, and adjust the output current level of

each constant current sink. Each current sink can

be independently programmed with sixteen current

levels (see table below). AS2Cwire incorporates

addressing to program the operating modes and

current level settings.

Constant Current Sink

Nominal Programming Levels

AS2Cwire relies on the number of rising edges of

the EN/SET pin to address and load the registers.

AS2Cwire latches data or address after the EN/SET

pin has been held high for time TLAT. Address or

data is differentiated by the number of EN/SET ris-

ing edges. Since the data registers are 4 bits each,

the differentiating number of pulses is 24 or 16, so

that Address 0 is signified by 17 rising edges,

Address 1 by 18 rising edges, and so forth. Data is

set to any number of rising edges between 1 and

including 16. A typical write protocol is a burst of

EN/SET rising edges, signifying a particular

address, followed by a pause with EN/SET held

high for the TLAT timeout period, a burst of rising

edges signifying data, and a TLAT timeout for the

data registers. Once an address is set, then multi-

ple writes to that address are allowed where only

data is issued.

When EN/SET is held low for an amount of time

greater than TOFF, the AAT3172 enters into shut-

down mode and draws less than 1µA from the sup-

ply. Address 0 is the default address on the first ris-

ing edge after the AAT3172 has been disabled.

300mA HI Scale

50mA LO Scale

Data

ISINK (mA/chnl)

300

267

238

214

190

167

152

133

119

105

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