AAT3174 Datasheet, PDF (10/14 Pages) Advanced Analogic Technologies – High Current, High Efficiency Charge Pump

AAT3174
High Current, High Efficiency Charge Pump
Application Information
Flash/Torch Control Using the RSET Pin
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).
EN
ENFL
Mode
0
0
Off
0
1
Off
1
0
Flash
1
1
Torch
Table 2: Flash/Torch Control Modes.
C₁
1µF
According to I/O port type, the following equations
can be used to calculate appropriate resistor values.
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:
600mA · 187kΩ
R₁ = _{ILED (torch)}
Next, choose R₂ based on the desired flash level
LED current:
R₂
=
R₁
·
R₁ · 600mA · 187kΩ
I_LED (flash) - 600mA · 187kΩ
The current and resistance values used in the equa-
tions come from the conditions placed on the I_DX
parameter of the Electrical Characteristics table.
C2
1µF
2.7V
to 5.5V
C1+ C1- C2+ C2-
VIN
VOUT
C_IN
4.7µF
AAT 3174
EN
EN/SET
F1
RSET
GND
COUT
2.2µF
Flash
LED
R2
R1
ENFL
Figure 1: Flash/Torch Control Using the RSET Pin.
10
3174.2006.05.1.2