AS1323
Data Sheet - D e t a i l e d D e s c r i p t i o n
8 Detailed Description
The AS1323 is a compact, high-efficiency, step-up DC-DC converter guaranteed to start up with voltages as low as
0.95V, and operate with an input voltage down to 0.75V. Consuming only 1.6µA of quiescent current, the device
includes an integrated synchronous rectifier that eliminates the need for an external diode and improves overall effi-
ciency by minimizing losses
The AS1323 also features an active-low shut-
down circuit that supply current to 0.1µA.
Figure 11. Block Diagram
L1
1
4
V
OUT
Comparator
Discharge
Comparator
Voltage
C
OUT
0.95 to
1.6V
V
BATT
C
IN
3
SHDNN
AS1323
Ref
Control
Logic
Startup
System
Timing
5
LX
Comparator
Charge
2
V
SS
PFM Control
A forced discontinuous, current-limited, pulse-frequency modulation (PFM) control scheme provides ultra-low quies-
cent current and high efficiency over a wide output current-range. Rather than using an integrated oscillator, the induc-
tor current is limited by the 400mA N-channel current limit or by the 6µs switch maximum on-time. After each device-on
cycle, the inductor current must ramp to zero before another cycle can start. When the error comparator senses that
the output has fallen below the regulation threshold, another cycle can begin.
Synchronous Rectification
The integrated synchronous rectifier eliminates the need for an external Schottky diode, reducing cost and PCB space.
During normal operation, while the inductor discharges, the P-channel MOSFET turns on and shunts the MOSFET
body diode. Consequently the rectifier voltage drop is significantly reduced improving efficiency without the need for
external components.
Low-Voltage Startup Circuit
The AS1323 contains a unique low-voltage startup circuit which ensures start-up even with very high load currents.
The minimum start-up voltage is independent of the load current. This device is powered from pin V
BATT
, guaranteeing
startup at input voltages as low as 0.95V.
Shutdown
The AS1323 enter shutdown when the SHDNN pin is driven low. During shutdown, the output is completely discon-
nected from the battery. Shutdown can be pulled as high as 3.6V, regardless of the voltage at pins V
BATT
or V
OUT
. For
normal operation, connect SHDN to the input.
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