PRODUCT DATASHEET
AAT3177
TM
ChargePump
High Current, High Efficiency Charge Pump with Auto-Timer
Real-Time Control of the CT Pin
Flash/Torch Control Using the RSET Pin
To achieve flash and torch mode control, the auto-timer
can be enabled or disabled in real-time. This can be done
by connecting a microcontroller or microprocessor GPIO
port to the CT pin.
An alternative method can be used for flash/torch con-
trol that eliminates the need to use the S2Cwire single-
wire interface. By using any typical digital I/O port, an
additional enable can be created (see Figure 3).
To set up flash mode in real-time, enable the auto-timer
by tri-stating the GPIO port. Do not drive the port high. It
can only be set to high-impedance so that the CT capaci-
tor can be charged and discharged by the AAT3177.
The I/O port output configuration can be an open-drain
NMOS or open-drain PMOS, but not a push-pull type. The
control will always act as an active-low flash enable or,
equivalently, an active-high torch enable (see Table 2).
To set up torch mode in real-time, disable the auto-
timer by driving the GPIO port low so that the CT pin will
be pulled to GND through the GPIO port.
EN
ENFL
Mode
0
0
1
1
0
1
0
1
Off
Off
Flash
Torch
AAT3177
EN/SET
Table 2: Flash/Torch Control Modes.
Tri-state = TMR ON
CT
According to I/O port type, the following equations can
be used to calculate appropriate resistor values.
Low = TMR OFF
0.1μF = 1 sec
For an open-drain NMOS I/O port output configuration,
the line is pulled low to GND or left floating, according to
state. To calculate the appropriate R1 and R2 resistor
values, first calculate the R1 resistor value needed for the
desired torch level LED current:
Figure 2: Enable or Disable the Auto-Timer in
Real-Time for Flash/Torch Control.
600mA · 187kΩ
ILED (torch)
R1 =
C1
1μF
C2
1μF
C1+
C1- C2+
C2+
2.7V
to 5.5V
VOUT
CIN
4.7μF
COUT
Flash
2.2μF
AAT3177
LED
EN
EN/SET
CT
F1
R2
ENCT
RSET
ENF
GND
CT
R1
Figure 3: Flash/Torch Control Using the RSET Pin.
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3177.2008.06.1.0
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
