AAT3174
High Current, High Efficiency Charge Pump
According to I/O port type, the following equations
can be used to calculate appropriate resistor values.
Application Information
Flash/Torch Control Using the RSET Pin
For an open-drain NMOS I/O port output configu-
ration, 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 resis-
tor value needed for the desired torch level LED
current:
An alternative method can be used for flash/torch
control 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 1).
The I/O port output configuration can be any one of
open-drain NMOS, open-drain PMOS, or push-pull
type. The control will always act as an active-low
flash enable or, equivalently, an active-high torch
enable (see Table 2).
600mA · 187kΩ
ILED (torch)
R1 =
Next, choose R2 based on the desired flash level
LED current:
EN
ENFL
Mode
0
0
1
1
0
1
0
1
Off
Off
R1 · 600mA · 187kΩ
R1 · ILED (flash) - 600mA · 187kΩ
R2 =
Flash
Torch
The current and resistance values used in the equa-
tions come from the conditions placed on the IDX
parameter of the Electrical Characteristics table.
Table 2: Flash/Torch Control Modes.
C1
1µF
C2
1µF
C1+
VIN
C1- C2+
C2-
2.7V
to 5.5V
VOUT
CIN
4.7µF
COUT
2.2µF
Flash
LED
AAT3174
F1
EN/SET
EN
R2
RSET
ENFL
GND
R1
Figure 1: Flash/Torch Control Using the RSET Pin.
10
3174.2006.05.1.2
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
