AS1322 データシートの表示（PDF） - austriamicrosystems AG
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AS1322 Datasheet PDF : 17 Pages
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AS1322
Data Sheet
austriamicrosystems
8 Detailed Description
The AS1322/AS1322B can operate from a single-cell input voltage (VIN) below 1V, and feature 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 devices maintain 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 AS1322A and the AS1322B 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 AS1322A includes an automatic 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 AS1322B does not support powersave mode and provides continuous operation at light loads, eliminating
low-frequency VOUT ripple at the expense of light load efficiency.
Figure 15. Block Diagram
1.5V
Single
Cell
L1
4.7µH
1 SW
6
VIN
CIN
1µF
Start Up
OSC
PWM
Control
A A/B
B MUX
Sync Drive
Control
1.2MHz
Ramp
Generator
Slope
Compensator
Σ
+
PWM –
Comp
–
4
SHDNN
Shutdown
Control
Shutdown
Powersave
Powersave
Operation
Control
RC
80kΩ
CC
150pF
CP2
2.5pF
–
VOUT
Good
+
2.3V
5
VOUT
0.35Ω 0.45Ω
Current
Sense
AS1322
–
gm Error
Amp
+
CFF*
3
FB
1.23V
Ref
3.3V
Output
R1
1.02MΩ
1%
COUT
4.7µF
R2
640kΩ
1%
* Optional
2 GND
Low-Voltage Start-Up
The AS1322 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 AS1322 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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Revision 1.03
7 - 17
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