AS1325 데이터 시트보기 (PDF) - austriamicrosystems AG
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AS1325 Datasheet PDF : 17 Pages
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AS1325
Data Sheet - Detailed Description
8 Detailed Description
The AS1325 is a high-efficiency, compact step-up converter with 35µA quiescent supply current which ensures the
highest efficiency over a wide load range. With a minimum of +1.5V input voltage, the device is well suited for applica-
tions with one- or two-cells, such as lithium ion (Li+), nickel-metal-hydride (NiMH), or alkaline.
Figure 27. Block Diagram
+5.0V Output only
+1.5 to +3.3V or
+1.5 to +5.0V
Battery
CIN
22µF
4
10µH LX
Zero
Crossing
Detector
Anti-
Ring-
ing
Switch
2
BATT
Current
Limiter
Driver
and
Control
Logic
VREF
1
SHDNN
AS1325
Startup
Circuitry
–
+ +1.228V
–
+1.1V
+
GND 3
5
OUT COUT
22µF
+3.3 or
+5.0V
Output
6
RESETN
The input battery is connected to the device through an inductor and an internal P-FET when pin SHDNN is low. In this
state, the step-up converter is off and the voltage drop across the P-FET body diode is eliminated, and the input bat-
tery can be used as a battery-backup or real-time-clock supply.
The built-in synchronous rectifier significantly improves efficiency.
Control Circuitry
The AS1325 integrated current-limited key circuitry provides low quiescent current and extremely-high efficiency over
a wide VOUT range without the need for an oscillator.
Light Loads:
Inductor current is limited by the 0.4A N-channel current limit or by the 7µs switch maximum on-time. The lower current
limit reduces the ripple of the output voltage. At each cycle, the inductor current must ramp down to zero before the
next cycle may start. When the error comparator senses that the output has fallen below the regulation threshold,
another cycle begins.
Higher Loads:
If after the first light load cycle the output voltage has not reached its target value of 3.3V or 5.0V, the inductor current
limit is increased to 0.7A. After the P-channel minimum on-time the next loading cycle is started if the output voltage is
still below its target value. If the target value is reached, the inductor current must ramp down to zero before the next
cycle may start. When the error comparator senses that the output has fallen below the regulation threshold, another
load cycle begins (see Figure 13 on page 7 and Figure 25 on page 9).
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