AAT3170_08 Datasheet, PDF (9/15 Pages) Advanced Analogic Technologies – High Current LED Flash Driver Charge Pump IC

ChargePump^TM
PRODUCT DATASHEET
AAT3170
High Current LED Flash Driver Charge Pump IC
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 indepen-
dently 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 AAT3170 has a software programmable timer func-
tion 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 register 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 timing capaci-
tor, which are listed in the “Timer Register” table.
Calculate the timer capacitor value according to the fol-
lowing formula:
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.
The AAT3170 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 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 voltage will regulate
appropriately.
AS²Cwire Serial Interface
The AAT3170 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
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
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 T_LAT (500μs). Address or data is dif-
ferentiated by the number of EN/SET rising edges.
Since the data registers are 4 bits each, the differentiat-
ing 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 pro-
tocol is a burst of EN/SET rising edges, signifying a par-
ticular 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 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 T_OFF (500μs), the AAT3170 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
3170.2007.11.1.2
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