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How does a BST pin function?


DC/DC Switching RegulatorsFunction

The BST pin is necessary for DC/DC converters with a bootstrap circuit.

A bootstrap circuit generates the gate drive voltage for a high-side N-channel driver by constructing a boost charge pump circuit utilizing switching operations of a DC/DC converter.*

  • *An N-channel driver has higher driving capability than a P-channel driver. Therefore, the driver size can be small compared with a P-channel driver.

By connecting a capacitor (CBST) between the BST and Lx pins, the voltage between the two pins is regulated to 5 V typically.

When the Lx voltage is low, the CBST is charged. Then, when the BST voltage exceeds the Lx voltage by 5 V, the N-channel driver can be driven.
Any types of capacitors are available as CBST, if the capacitance is equal or more than the recommended value.

Gate Voltage over VIN is necessary

CBST is charged when LX is Low

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