AS1322_1 AMSCO [austriamicrosystems AG], AS1322_1 Datasheet - Page 7

• Manufacturer Part Number: AS1322_1
• Description: Low Voltage, Micropower, DC-DC Step-Up Converters
• Manufacturer: AMSCO [austriamicrosystems AG]

AS1322
Data Sheet
8 Detailed Description
The AS1322/AS1322B can operate from a single-cell input voltage (V
(1.2MHz) and current mode PWM control for exceptional line- and load-regulation. With low R
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
Note: The AS1322B does not support powersave mode and provides continuous operation at light loads, eliminating
Figure 15. Block Diagram
Low-Voltage Start-Up
The AS1322 requires V
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 V
mode, the AS1322 operates independent of V
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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Single
1.5V
Cell
low-frequency V
* Optional
OUT
SHDNN
> 2.3V, the start-up circuitry is disabled and normal fixed-frequency PWM operation is initiated. In this
- D e t a i l e d D e s c r i p t i o n
1µF
C
V
IN
IN
6
4
Powersave
IN
OUT
Start Up
of only 0.85V (typ) or higher to start up. The low-voltage start-up circuitry controls the internal
OSC
Shutdown
Control
ripple at the expense of light load efficiency.
Control
PWM
Generator
1.2MHz
Ramp
Powersave
Comp
PWM
Operation
Control
Shutdown
A
B
+
–
–
(see Figure 3 on page
MUX
A/B
Compensator
IN
, allowing extended operating time as the battery can drop to several
Slope
4.7µH
Revision 1.07
150pF
80kΩ
L1
R
C
C
C
Sync Drive
Control
2.5pF
C
P2
Σ
5).
IN
1
2
) below 1V, and feature fixed frequency
0.35Ω
SW
GND
Current
Sense
AS1322
Good
V
g
OUT
m
Amp
Error
0.45Ω
–
+
–
+
1.23V
Ref
2.3V
DS(ON)
5
V
3
FB
OUT
C
FF
*
and gate charge
Output
3.3V
1.02MΩ
640kΩ
4.7µF
C
1%
R
R
1%
OUT
2
1
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