AS1329_13 Datasheet, PDF (8/20 Pages) ams AG – Low Vol tage, Micropower, DC-DC Step-Up Conver ters

AS1329
Datasheet - 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 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 6 on page 5).
Note: The AS1329C does not support powersave mode and provides continuous operation at all loads, eliminating low-frequency VOUT rip-
ple at the expense of light load efficiency.
Figure 19. AS1329 - Block Diagram
1.5V
Single Cell
L1
4.7µH
6
VIN
CIN
1µF
Start Up
OSC
PWM
Control
A _A/B
B _MUX
Sync Drive
Control
1.2MHz
Ramp
Generator
Slope
Compensator
Σ
4
SHDNN
+
PWM _–
Comp
–
Shutdown
Control
Shutdown
Powersave
Powersave
Operation
Control
RC
80kΩ
CC
150pF
CP2
2.5pF
1 SW
–
VOUT
Good
+
2.3V
5
VOUT
0.35Ω
0.45Ω
Current
Sense
AS1329
–
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
8.1 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.
www.ams.com/DC-DC_Step-Up/AS1329
Revision 1.12
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