High Current LED Flash Driver Charge Pump IC
programmable through the AS
2
Cwire 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.
AAT3172
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
I
SINK
(mA/chnl)
300
267
238
214
190
167
152
133
119
105
95
86
76
67
62
0
50mA LO Scale
I
SINK
(mA/chnl)
50
44
40
36
32
28
25
22
20
17
16
14
13
11
10
0
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. Register 3 is the HI/LO
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.
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 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
Register 5 with Data = 1 will reset the mode back
to current mode and the charge pump output volt-
age will regulate appropriately.
AS
2
Cwire Serial Interface
The AAT3172 utilizes the AS
2
Cwire 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). AS
2
Cwire incorporates
addressing to program the operating modes and
current level settings.
AS
2
Cwire relies on the number of rising edges of
the EN/SET pin to address and load the registers.
AS
2
Cwire latches data or address after the EN/SET
pin has been held high for time T
LAT
. 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 2
4
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 T
LAT
timeout period, a burst of rising
edges signifying data, and a T
LAT
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 T
OFF
, 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.
3172.2006.05.1.5
9
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
