PRODUCT DATASHEET
AAT3177
TM
ChargePump
High Current, High Efficiency Charge Pump with Auto-Timer
THI
TOFF
TLO
TLAT
EN/SET
1
2
n-1
n ≤ 16
0
n-1
Data Reg
0
Figure 1: S2Cwire Serial Interface Timing.
Application Information
Output Current
Flash Auto-Timer
Enabled
Data
(% of IMAX)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
100.01
89.11
79.41
70.81
63.1
56.2
50.1
44.7
39.8
35.5
31.6
28.2
25.1
22.4
20.0
0.0
Yes
Yes
Yes
Yes
No
No
No
No
No
No
No
No
No
No
No
No
Selecting a Timer Capacitor for CT
The CT pin must be configured according to the desired
flash function1. There are two options: connect a small
valued capacitor or connect the pin to GND.
Configure the timer feature for the AAT3177 by connect-
ing a small valued capacitor between the CT pin and
GND. The value of the capacitor will determine the tim-
eout duration according to the following formula:
s
T = CT · 10
µF
As an example, the result of connecting a 0.1μF capaci-
tor between the CT pin and GND will be a 1 second tim-
eout duration. Operationally, when the AAT3177 is
enabled, it will automatically disable itself after 1 sec-
ond. When using the auto-timer feature, select a CT
capacitor value according to the formula above.
Table 1: Current Level Settings.
When EN/SET is held low for an amount of time longer
than TOFF (500μs), the AAT3177 enters into shutdown
mode and draws less than 1μA from VIN. Data and
address registers are reset to 0 during shutdown.
To disable the auto-timer feature, connect the CT pin to
ground. The result will be a small bias current of approx-
imately 3μA. A large valued pull-down resistor should not
be used for connecting the CT pin to GND. The CT pin can
be connected directly to GND. If a pull-down resistor is
preferred, it should be of low value (i.e., less than 10K).
The flash timer is active for DATA values 1 through 41.
For lower current settings (DATA 5 through 16) the flash
timer is turned off to allow extended LED on time for
movie mode applications. When changing from high cur-
rent (DATA = 1-4) to lower current (DATA = 5-16) the
timer will be ignored. When changing from low current
to high current the timer will be reset and restarted.
The primary considerations for selecting the capacitor
type are leakage current and tolerance of the capacitor
value. The auto-timer duration is determined by charg-
ing and discharging the timing capacitor with a small
charging/discharging current of approximately 3μA.
Avoid leaky capacitor types as they will distort the time-
out duration. Select the capacitor value’s tolerance
according to the desired time-out tolerance.
The charge pump will be reset during current level
changes to allow the system to operate in the most effi-
cient mode.
1. Flash Timer is enabled only for the four highest current level settings (DATA = 1, 2, 3, and 4).
w w w . a n a l o g i c t e c h . c o m
3177.2008.06.1.0
9
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
