TPS54821: Is the low side MOSFET turned off when EN pin pulled to GND?

David Reed2

Part Number: TPS54821

I would like to know if the low side MOSFET is turned off in the TPS54821 when the EN pin is pulled to GND? The reason I ask is because I would like to use the TPS54821 to convert +12V on the PVIN/VIN pins to a programmable output voltage in the range 3V - 11.5V, but sometimes I would like to apply +12V to the output rail from another voltage source and so during this situation I would like to disable the TPS54821 (ie pull EN pin to GND). This scenario will only work if the low side MOSFET is guaranteed to be turned off when EN low, otherwise the TPS54821 ends up sinking a whole lot of current from the alternative voltage source.

over 4 years ago

0 Edwin Zang over 4 years ago

TI__Expert 6425 points

Hi David,

TPS54821 low side FET is turned off when EN pin is pulled to GND.

BRs,

Edwin.

0 Lishuang Zhao over 4 years ago

TI__Expert 7500 points

Hi David,

From TPS54821 datasheet, we can see that:

7.3.6 Safe Start-up into Pre-Biased Outputs
The device has been designed to prevent the low-side MOSFET from discharging a pre-biased output. During
monotonic pre-biased startup, the low-side MOSFET is not allowed to sink current until the SS/TR pin voltage is
higher than 1.4 V.

So if EN=Low, SS is also low, so the low-side is not allowed to sink current.

Thanks,

Lishuang

0 David Reed2 over 4 years ago in reply to Edwin Zang

Prodigy 80 points

Thanks Edwin.

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TPS54821: Is the low side MOSFET turned off when EN pin pulled to GND?