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I plan on using a TPS63061 as DC/DC to get a steady 5V from 4xAA batteries. The data sheet says:

8.3.4 Undervoltage Lockout
An undervoltage lockout function prevents device start-up if the supply voltage on VIN is lower than approximately its threshold (see the Electrical Characteristics table). When in operation, the device automatically enters the shutdown mode if the voltage on VIN drops below the undervoltage lockout threshold. The device automatically restarts if the input voltage recovers to the minimum operating input voltage.

The Electrical Characteristics table states:

UVLO Under voltage lockout threshold:
Input voltage falling | min 1.8V | typ 1.9V | max 2.2V
UVLO hysteresis:
300 mV

Does this mean that the TPS63061 protects me from reverse polarity if I place my batteries in reversed order? Which would yield -6V which would be below 1.8V and hence the under voltage lockout function would protect me?

Or do I need an additional protection e.g. using a Schottky diode or MOSFET to avoid damage to the DC/DC and other components?

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Alas, no. If you give it a voltage under -0.3V it will probably be toast.

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So yes, you need additional protection against reverse polarity.

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No, generally, DC to DC components do not provide reverse polarity protection. Undervoltage lockout prevents starting with a too low voltage for the converter to work with. Certain components can tolerate reverse voltage, but this puts stress on the component, and is not recommended by the manufacturer.

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