STBP120 Datasheet, PDF(10/36 Page) STMicroelectronics – Overvoltage protection device with thermal shutdown

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STBP120 Datasheet, PDF (10/36 Pages) STMicroelectronics – Overvoltage protection device with thermal shutdown

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Operation

STBP120

3.1

3.2

Note:

The STBP120 provides overvoltage protection for positive input voltage up to 28 V using

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

Power-up

At power-up, with EN = low, the MOSFET switch is turned on after a 50 ms delay, ton, after

the input voltage exceeds the UVLO threshold to ensure the input voltage is stabilized. After

an additional 50 ms delay, tstart, the FLT indication output is deactivated (see Figure 6).

The FLT output state is valid for VIN input voltage 1.2 V or higher.

Normal operation

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

output voltage is kept within the specified range. Internal MOSFET switch is turned on and

the FLT output is not active.

The STBP120 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). Internal MOSFET is turned on after the 50 ms delay ton to ensure that the

conditions have stabilized. Then, after an additional 50 ms delay, tstart, the FLT output is

deactivated (i.e. driven high). This behavior is equivalent to the startup shown on Figure 6.

The STBP120 MOSFET switch topology allows the current to also flow in the reverse

direction, i.e. from OUT to IN, which can be useful e.g. 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 50 ms startup delay) turned on so the voltage

drop across STBP120 is significantly reduced. The charger IC should not contain the

reverse diode to prevent the battery pack voltage from appearing on the system connector.

If the reverse current is undesirable, it may be prevented by connecting a 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.

Due to the MOSFET body diode, thermal shutdown protection is not functional for the

supply current.

3.3

Undervoltage lockout (UVLO)

To ensure proper operation under any conditions, the STBP120 has an undervoltage lockout

(UVLO) threshold. For rising input voltage, the output remains disconnected from input until

VIN voltage exceeds the VUVLO threshold (3.25 V typ). The FLT output is driven low as long

as VIN is below the UVLO threshold (assuming the input voltage is above 1.2 V). For falling

input voltage, the UVLO circuit has a 50 mV hysteresis, VHYS(UVLO), to improve noise

immunity under transient conditions.

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Doc ID 15492 Rev 4

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