TPS40077: Output is not 3.3V

Chris Jensen

Prodigy 20 points

Part Number: TPS40077

I am testing the design that was provided by our contractor of the TPS40077.

The input is 6.5V to 9.5V and is supposed to give 3.3V output, but I am only getting 1V.

over 4 years ago

0 Yuchang Zhang over 4 years ago

TI__Mastermind 18510 points

Hi, please Upload your schematic for review.

Yuchang

0 Chris Jensen over 4 years ago in reply to Yuchang Zhang

Prodigy 20 points

TPS40077.docx

0 Yuchang Zhang over 4 years ago in reply to Chris Jensen

TI__Mastermind 18510 points

Jensen,

For the schematic, please do some change to try.

By the way, what's the loading spec? and also you can try a smaller inductor if the loading is big, such as 3.3uH for 8A~10A.

Also if still not work, please catch Vin/VDBP/VSW/Vout waveforms.

Yuchang

0 Peter James Miller over 4 years ago in reply to Chris Jensen

TI__Guru 53255 points

Chris Jensen

Have you been able to make the changes Yuchang Zhang suggested?

Have they addresses your issue?

The TPS40077 controller uses the KFF pin to provide UVLO, Voltage Feed Forward and a maximum duty cycles. The low resistance on the KFF pin (10k) would create a very low maximum on-time, which is likely the cause for your 1V output.

The 100kOhm value Yuchang Zhang provided you with is for a 4.5V UVLO, since your minimum input voltage is 6.5V, you may want tp select a resistor as high as 140kOhms for a UVLO voltage closer to 6.5V. Also, since the KFF resistor programs the voltage feedforward gain, you should review the compensation design using the design tool - https://www.ti.com/lit/zip/sluc263

TPS40KType III Loop Stability kVenable_sluc263c-071312_ChrisJensen.xls

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TPS40077: Output is not 3.3V