STBP112 datasheet(10/38 Pages) STMICROELECTRONICS

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Operation

STBP112

10/38

Doc ID 023357 Rev 3

Operation

The STBP112 provides overvoltage protection for positive input voltage up to 28 V using

a built-in low RDS(on) N-channel MOSFET switch.

3.1

Power-up

At power-up, with EN = low, the MOSFET switch is turned on after the startup delay, ton,

after the input voltage exceeds the UVLO threshold to ensure the input voltage is stabilized

(see Figure 5).

3.2

Normal operation

The device continuously monitors the input voltage and its own internal temperature so the

output voltage is kept within the specified range. The internal MOSFET switch is turned on

and the FLT output is deasserted.

The STBP112 enters normal operation state if the input voltage returns to the interval

between VUVLO and VOVLO - VHYS(OVLO) and the junction temperature falls below Toff -

THYS(off). The internal MOSFET is turned on after the trec delay to ensure that the conditions

have stabilized and the FLT output is deasserted.

Note:

The STBP112 MOSFET switch topology allows the current to flow also in a reverse

direction, i.e. from OUT to IN, which can be useful for powering external peripherals from the

system connector (see the supply current in Figure 4). At first, the current flows through the

MOSFET body diode. If the voltage that appears on the IN terminal is above the UVLO

threshold, the MOSFET is (after the startup delay) turned on so the voltage drop across

STBP112 is significantly reduced.

If the reverse current is undesirable, it may be prevented by connecting an external, properly

rated low drop Schottky diode in series with the OUT pin. The voltage drop between IN and

charger is increased by the voltage drop across the diode.

3.3

Undervoltage lockout (UVLO)

To ensure proper operation under any condition, the STBP112 has an undervoltage lockout

(UVLO) threshold. When the input voltage is rising, the output remains disconnected from

input until the VIN voltage exceeds the VUVLO threshold. This circuit is equipped with

hysteresis, VHYS(UVLO), to improve noise immunity under transient conditions.

3.4

Overvoltage lockout (OVLO)

If the input voltage VIN rises above the threshold level VOVLO, the MOSFET switch is

immediately turned off. At the same time, the fault indication output FLT is activated

(i.e. driven low), see Figure 6. This device is equipped with hysteresis, VHYS(OVLO), to

improve noise immunity under transient conditions.

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