TPS65295: Resistor on BST, how much current?

Boris Yost

Part Number: TPS65295

As per the datasheet and reference design, the BST pin has a 5.1 ohm resistor. The reference design used an 0603. What's the current going into the BST pin, or the power on the BST resistor? Would be nice to know for derating analysis, and whether we can get away with an 0402 in that position.

over 2 years ago

Peter James Miller over 2 years ago

TI__Guru 51315 points

Boris Yost

The current and power dissipation for the BST pin is quite low. Calculating it requires knowing a number of factors that are generally not published in the device datasheets, like the high-side MOSFET gate charge and the internal MOSFET driver resistance.

You can see a full discussion here - https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1060174/faq-tps546d24a-selecting-rboot-and-calculating-rboot-power-dissipation

That analysis is for a 40A converter with a 4.2mΩ high-side FET switching at 1.5MHz, and found power dissipation of 14mW for 4.7Ω

The 8-A TPS65295, with a 22mΩ high-side FET with similar Vds voltage rating, switching at 600kHz will have much lower FET gate charge, higher driver resistance, and is switching at less than half the switching frequency for much less boot-resistor power dissipation.

A 62mW (1/16W) rated 0402 resistor will be easily able to support the power dissipation of the BST resistor.

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TPS65295: Resistor on BST, how much current?