High Current LED Flash Driver Charge Pump IC
matching. Also, F1 and F2 can be connected
together for single output configuration.
The AAT3170 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 200mA. 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.
AAT3170
Modes of Operation
In addition to the data registers that set the current
levels for the two current sinks, the AAT3170 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 dis-
abled. When Register 4 is set to OFF, the device is
in standby mode with significantly reduced quiescent
current.
The AAT3170 has a software programmable timer
function to automatically adjust the flash on-time
duration. This feature can be used directly to set
the flash on-time, or it can be used indirectly for
fault tolerant flash protection. When used for flash
protection, the user can be sure that the flash will
still turn off in the event of any system software or
hardware malfunction.
Write to Address 5 to enable the flash timer and
flash channels. When the timer register is
addressed and data is latched, the ON/OFF regis-
ter is automatically switched to ON, enabling the
current sinks for the duration of the programmed
time. When the timer expires, the ON/OFF register
is switched to OFF, disabling the current sinks.
The on-time T depends on the combination of the
setting of the timer register and the value of the tim-
ing capacitor, which are listed in the “Timer
Register” table. Calculate the timer capacitor value
according to the following formula:
AS
2
Cwire Serial Interface
The AAT3170 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.
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
T (seconds) = 10 · C
T
(µF)
where C
T
is in micro-farads.
For example, using a 0.1µF timer capacitor value
results in an on-time duration of one second.
AS
2
Cwire relies on the number of rising edges of
the EN/SET pin to address and load the registers.
3170.2006.11.1.1
9
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
