AS1329
Data Sheet - Detailed Description
8 Detailed Description
The AS1329 can operate from a single-cell input voltage (VIN) below 1V, and features fixed frequency (1.2MHz) and
current mode PWM control for exceptional line- and load-regulation. With low RDS(ON) and gate charge internal NMOS
and PMOS switches, the device maintains high-efficiency from light to heavy loads.
Modern portable devices frequently spend extended time in low-power or standby modes, switching to high power-
drain only when certain functions are enabled. The AS1329A, AS1329B and AS1329C are ideal for portable devices
since they maintain high-power conversion efficiency over a wide output power range, thus increasing battery life in
these types of devices.
In addition to high-efficiency at moderate and heavy loads, the AS1329A as well as the AS1329B includes an auto-
matic powersave mode that improves efficiency of the power converter at light loads. The powersave mode is initiated
if the output load current falls below a factory programmed threshold (see Figure 3 on page 5).
Note: The AS1329C does not support powersave mode and provides continuous operation at all loads, eliminating
low-frequency VOUT ripple at the expense of light load efficiency.
Figure 15. Block Diagram
L1
4.7µH
1
SW
1.5V
Single
Cell
6
Start Up
OSC
2.3V
–
+
3.3V
Output
VOUT
Good
VIN
A
B
A/B
MUX
5
CIN
1µF
VOUT
PWM
Control
0.45Ω
0.35Ω
Sync Drive
Control
R1
1.02MΩ
CFF*
Current
Sense
1.2MHz
Ramp
Generator
Σ
Slope
Compensator
1%
AS1329
COUT
4.7µF
+
3
PWM
Comp
–
–
–
FB
gm Error
Amp
+
RC
4
Shutdown
Control
Shutdown
80kΩ
CC
CP2
2.5pF
R2
640kΩ
1%
SHDNN
1.23V
Ref
Powersave
Operation
Control
150pF
Powersave
2
GND
* Optional
Low-Voltage Start-Up
The AS1329 requires VIN of only 0.85V (typ) or higher to start up. The low-voltage start-up circuitry controls the internal
NMOS switch up to a maximum peak inductor current of 850mA (typ), with 1.5ms (approx.) off-time during start-up,
allowing the devices to start up into an output load.
With a VOUT > 2.3V, the start-up circuitry is disabled and normal fixed-frequency PWM operation is initiated. In this
mode, the AS1329 operates independent of VIN, allowing extended operating time as the battery can drop to several
tenths of a volt without affecting output regulation. The limiting factor for the application is the ability of the battery to
supply sufficient energy to the output.
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