PS0021

Enable Input

Under Voltage Lockout

The PS0021 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 supply becomes too low (typically below 1.8V),

the PS0021 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

In track mode Vout follows Vin. Difference between Vout

and Vin is determined by the load current and the

schottky forward voltage drop at that current.

July 2007

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© 2007 Power IC. All Rights Reserved.

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