PS0100
Enable Input
Anti-Ringing Control
The PS0100 features an active-high CMOS input enable
pin (SHUTB) that allows on/off control of the regulator.
When SHUTB=Low, shutdown of the chip occurs and at
that time almost no quiescent current (<1µA) flows. The
output capacitor can be completely discharged through
the load or the feedback resistors for real output shut-
down. A discharge switch is internally connected between
VIN and SW. The Enable (SHUTB) input is TTL/CMOS
compatible. Connect SHUTB to VIN for normal operation.
When the inductor current goes to zero, there arises a
high frequency ringing at the SW pin. To prevent this, a
100Ω discharge switch is provided between SW and VIN,
so that this high frequency ringing is damped out.
Under Voltage Lockout
When the supply becomes too low (typically below 1.8V),
the PS0100 produces an internal UVLO (Under Voltage
Lockout) signal that disables the normal PWM operation
and enables the start-up oscillator to run at a fixed
frequency. At this stage, very few circuits are operational.
When the oscillator raises the supply to above 1.9V, the
UVLO signal is disabled and the normal PWM mode takes
over the operation of the start-up oscillator. This
mechanism protects the chip from producing false logic
due to low input supply.
Track Mode
The PS0100 is in track mode when VIN is greater than the
output voltage regulation point. In track mode, the
regulator runs at a fixed start-up oscillator frequency.
The start-up oscillator runs freely until VOUT exceeds VIN.
When VOUT falls below VIN, the start-up oscillator is
enabled again. Thus, in track mode, the regular loop
control of PWM operation remains off. Instead, the
regulator runs by intermittent oscillator operation.
11
July 2007
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