AAT3172 View Datasheet(PDF) - Advanced Analogic Technologies
Part Name
Description
MFG CO.
'AAT3172' PDF : 15 Pages View PDF
ChargePumpTM
PRODUCT DATASHEET
AAT3172
High Current LED Flash Driver Charge Pump IC
battery operating range for 1X and 1.5X modes, improv-
ing efficiency and extending battery life. Each constant
current sink is programmable through the AS2Cwire
serial interface. 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 lev-
els for the two current sinks, the AAT3172 has three
mode registers. Register 3 is the HI/LO mode register. It
sets the maximum per channel current level to either
300mA or 50mA. Each channel can be set independently
so one channel can be for flash while the other can be in
a low constant current mode.
Register 4 is the ON/OFF register. When set with 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 significantly 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 delivers a regulated
4.5V output that continuously operates 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 Register
5 with Data = 1 will reset the mode back to current
mode and the charge pump output voltage will regulate
appropriately.
AS2Cwire Serial Interface
The AAT3172 utilizes the AS2Cwire serial interface to
enable/disable the charge pump, set the operating
mode, and adjust the output current level of each con-
stant current sink. Each current sink can be indepen-
dently programmed with sixteen current levels (see
table below). AS2Cwire incorporates addressing to pro-
gram the operating modes and current level settings.
Constant Current Sink
Nominal Programming Levels
Data
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
300mA HI Scale
ISINK (mA/ch)
300
267
238
214
190
167
152
133
119
105
95
86
76
67
62
0
50mA LO Scale
ISINK (mA/ch)
50
44
40
36
32
28
25
22
20
17
16
14
13
11
10
0
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 rising 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, fol-
lowed 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 multiple 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 shutdown mode and
draws less than 1µA from the supply. Address 0 is the
default address on the first rising edge after the AAT3172
has been disabled. After shutdown, if only data is issued
with the first rising edge (i.e., 1 - 16 edges, no address
given), both current sinks will be programmed since the
default will be Address 0.
3172.2008.04.1.6
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