AS1330
Datasheet - D e t a i l e d D e s c r i p t i o n
Low-Noise Fixed-Frequency Operation
Oscillator
The AS1330 switching frequency is internally fixed at 4MHz allowing the use of very small external components.
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 650mA independent of V
IN
or V
OUT
.
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 (C
SW
).
Powersave Operation
In light load conditions, the integrated powersave feature removes power from all circuitry not required to monitor
V
OUT
. When V
OUT
has dropped approximately 1% from nominal, the device powers up and begins normal PWM oper-
ation.
C2 recharges, causing the AS1330 to re-enter powersave mode as long as the output load remains below the power-
save 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 AS1330 turns on less frequently. When the load current increases above
the powersave threshold, the AS1330 will resume continuous, seamless PWM operation.
Notes:
1. An optional capacitor (C
FF
) between pins V
OUT
and FB in some applications can reduce V
OUTp-p
ripple and input
quiescent current during powersave mode. Typical values for C
FF
range from 15 to 220pF.
2. In powersave mode the AS1330 draws only 30µA from the output capacitor(s), greatly improving converter effi-
ciency.
Shutdown
When pin EN is low the AS1330 is switched off and <1µA current is drawn from the battery; when pin EN is high the
device is switched on. If EN is driven from a logic-level output, the logic high-level (on) should be referenced to V
OUT
to
avoid intermittently switching the device on.
In shutdown the battery input is disconnected from the output.
Thermal Overload Protection
To prevent the AS1330 from short-term misuse and overload conditions the chip includes a thermal overload
protection. To block the normal operation mode the device is turning the PFET and the NFET off in PWM mode as
soon as the junction temperature exceeds 150°C. To resume the normal operation the temperature has to drop below
140°C.
Note:
Continuing operation in thermal overload conditions may damage the device and is considered bad practice.
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