AS1343 austriamicrosystems AG, AS1343 Datasheet - Page 9

• Manufacturer Part Number: AS1343
• Description: DC-DC Boost Converter
• Manufacturer: austriamicrosystems AG

AS1343
Datasheet - D e t a i l e d D e s c r i p t i o n
8 Detailed Description
The AS1343 features a current limiting circuitry, a fixed-frequency PWM architecture, power-OK circuitry, thermal pro-
tection, and an automatic powersave mode in a tiny package, and maintains high efficiency at light loads.
Figure 27. AS1343 - Block Diagram with Shutdown Disconnect Switch
Automatic powersave mode regulates the output and also reduces average current flow into the device, resulting in
high efficiency at light loads. When the output increases sufficiently, the powersave comparator output remains high,
resulting in continuous operation.
For each oscillator cycle, the power switch is enabled. A voltage proportional to switch current is added to a stabilizing
ramp and the resulting sum is delivered to the positive terminal of the PWM comparator.
The error amplifier compares the voltage at FB with the internal 1.25V reference and generates an error signal (V
When V
etic comparator disables the power circuitry, with only the low-power circuitry still active (total current consumption is
minimized).
When a load is applied, V
In light loads, the output voltage (and the voltage at FB) will increase until the powersave comparator disables the
power circuitry, causing the output voltage to decrease again. This cycle is repeated resulting in low-frequency ripple at
the output.
POK Function
The POK output indicates if the output voltage is within 90% of the nominal voltage level. As long as the output voltage
is within regulation the open-drain POK output is high impedance. The POK output can be tied to any external voltage
up to a maximum of 5V via a pull-up resistance R3
below 90% of the nominal voltage the POK pin is pulled to GND.
Note: It is important to consider that in shutdown mode the POK output is pulled to V
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Input Voltage
0.9V to 3.6V
C
is below the powersave mode threshold voltage the automatic powersave-mode is activated and the hyster-
10µF
C
V
EN
IN
CC
4
1
Powersave
FB
Shutdown
Control
Control
PWM
Generator
decreases; V
Spectrum
Spread
1 MHz
Ramp
3
Powersave
GND
Comp
PWM
Operation
Control
Shutdown
7
SWOUT
0.3Ω
PMOS
+
–
–
C
increases and enables the power circuitry and the device starts switching.
8
Compensator
GND
Slope
6.8µH
L
1
(see Typical Application on page
R
C
Revision 1.04
C
C
Sync Drive
2
POK
Control
C
P2
Σ
5
PGND
0.9Ω
NMOS
6
LX
V
Current
Sense
C
AS1343
V
Good
g
OUT
m
Amp
Error
–
+
–
+
10). If the output voltage drops
1.25V
Ref
1.13V
CC
D
in order to save current.
1
9
VOUT
10
FB
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Output Voltage
5.5V to 42V
R
R
1
2
4.7µF
C
OUT
9 - 17
C
).