Operation

STBP120

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Doc ID 15492 Rev 4

3

Operation

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

3.1

Power-up

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

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. 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

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

Note:

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

immunity under transient conditions.