AS1322 Просмотр технического описания (PDF) - austriamicrosystems AG
Номер в каталоге
Компоненты Описание
Список матч
AS1322 Datasheet PDF : 17 Pages
| |||
AS1322
Data Sheet
austriamicrosystems
Low-Noise Fixed-Frequency Operation
Oscillator
The AS1322 switching frequency is internally fixed at 1.2MHz allowing the use of very small external components.
Error Amplifier
The integrated error amplifier is an internally compensated trans-conductance (gm) type (current output). The internal
1.23V reference voltage is compared to the voltage at pin FB to generate an error signal at the output of the error
amplifier. A voltage divider from VOUT to GND programs the output voltage from 2.5 to 5V via pin FB as:
VOUT = 1.23V(1 + (R1/R2))
(EQ 1)
Current Sensing
A signal representing the internal NMOS-switch current is summed with the slope compensator. The summed signal is
compared to the error amplifier output to provide a peak current control command for the PWM. Peak switch current is
limited to approximately 850mA independent of VIN or VOUT.
Zero Current Comparator
The zero current comparator monitors the inductor current to the output and shuts off the PMOS synchronous rectifier
once this current drops to 20mA (approx.). This prevents the inductor current from reversing polarity and results in
improved converter efficiency at light loads.
Anti-Ringing Control
Anti-ringing control circuitry prevents high-frequency ringing on pin SW as the inductor current approaches zero. This
is accomplished by damping the resonant circuit formed by the inductor and the capacitance on pin SW (CSW).
Powersave Operation (AS1322A)
In light load conditions, the integrated powersave feature removes power from all circuitry not required to monitor
VOUT. When VOUT has dropped approximately 1% from nominal, the AS1322A powers up and begins normal PWM
operation.
COUT (see Figure 15 on page 7) recharges, causing the AS1322A to re-enter powersave mode as long as the output
load remains below the powersave threshold. The frequency of this intermittent PWM is proportional to load current;
i.e., as the load current drops further below the powersave threshold, the AS1322A turns on less frequently. When the
load current increases above the powersave threshold, the AS1322A will resume continuous, seamless PWM opera-
tion.
Notes:
1. An optional capacitor (CFF) between pins VOUT and FB in some applications can reduce VOUTp-p ripple and input
quiescent current during powersave mode. Typical values for CFF range from 15 to 220pF.
2. In powersave mode the AS1322A draws only 30µA from the output capacitor(s), greatly improving converter effi-
ciency.
www.austriamicrosystems.com
Revision 1.03
8 - 17
Share Link: 