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

100

Ω 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

output voltage regulation point. In track mode, the

regulator runs at a fixed start-up oscillator frequency.

The start-up oscillator runs freely until V

exceeds V

OUT

When V

falls below V

OUT

enabled again. Thus, in track mode, the regular loop

control of PWM operation remains off. Instead, the

regulator runs by intermittent oscillator operation.

July 2007

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© 2007 Power IC. All Rights Reserved.

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