TPS54560: TPS54560 Latching when Varying Vin

Ricky Thomson

Part Number: TPS54560

Hey All,

So I've designed a circuit that uses the TPS54560 to switch a Variable Vin voltage source to and Ideal Vou of 24 volts. When the Vin is decreased to the point where Vout of 24V can no longer be achieved, Vout will also decrease linearly with the decrease of Vin. However when increasing the Vin back to a point such that Vout of 24V is possible (lets say Vin = 40V), the Vout appears to "latch" on the way back up and wont surpass approx 17V.

I've also tested this with the TPS54560-EVM board and get the same effect.

Any help would be greatly appreciated.

Cheers

Ricky

over 6 years ago

0 David Baba over 6 years ago

TI__Mastermind 40060 points

Hello Ricky,

I have forwarded your question to the Product applications Engineer who will respond shortly.

Thanks.

0 Arief Hernadi over 6 years ago in reply to David Baba

TI__Mastermind 23845 points

Hi,

Is the EVM test is done with a default BOM?

Thanks

0 Ricky Thomson over 6 years ago in reply to Arief Hernadi

Prodigy 30 points

Hey David,

The EVM board has been slightly modified to include a 33uH inductor to support the higher voltage output.

It's also worth mentioning that I only observed this when using a High power load (90 watts), when the load is drawing around 26 watts the problem doesn't occur.

Thanks

0 Arief Hernadi over 6 years ago in reply to Ricky Thomson

TI__Mastermind 23845 points

Hi Ricky,

Upon checking the datasheet, your voltages might be close to this condition.
www.ti.com/.../tps54560.pdf

When operating with a low voltage difference from input to output, the high side MOSFET of the TPS54560 will
operate at 100% duty cycle as long as the BOOT to SW terminal voltage is greater than 2.1 V. When the voltage
from BOOT to SW drops below 2.1V, the high side MOSFET is turned off and an integrated low side MOSFET
pulls SW low to recharge the BOOT capacitor. To reduce the losses of the small low side MOSFET at high
output voltages, it is disabled at 24 V output and re-enabled when the output reaches 21.5 V.

You can try to power VCC externally and see if this will improve the condition as shown on this document
www.ti.com/.../slva547a.pdf

Thanks
-Arief

Power management

Power management forum

TPS54560: TPS54560 Latching when Varying Vin