TPS54561: The output ripple is large

Jayden Qiu

Part Number: TPS54561

Tool/software:

Hi team,

This is FAE Jayden, ZTE is using TPS54561in their new CPE project. And they find the voltage ripple is large during the transient test. Could you help check the schematic and give some advice on their design?

Test report and waveforms:

Iout= 0A to 0.5A to 0A, cff=22pF

Iout= 0A to 0.5A to 0A, cff=48pF

Iout= 0A to 1.5A to 0A, cff=22pF

Iout= 0A to 1.5A to 0A, cff=48pF

Brs

Jayden

over 1 year ago

0 Nityanand Hegde over 1 year ago

TI__Expert 5490 points

Hi Jayden,

Let me check the schematic. Before that can you ask customer to fill below excel tool for their requirement?

SLVC452

Thanks,

Nitya

0 Jayden Qiu over 1 year ago in reply to Nityanand Hegde

TI__Intellectual 1405 points

Hi Nitya,

Sure,I'll ask customer to do that. Do you think Cff is needed for this device?

Thanks.

Brs

Jayden

0 Nityanand Hegde over 1 year ago in reply to Jayden Qiu

TI__Expert 5490 points

Hi Jayden,

The TPS54561 uses fixed frequency, peak current mode control method. For peak current mode control, generally Type 2 compensation is sufficient. We can ask customer to remove Cff capacitor and check the device load transient response.

Thanks,

Nitya

0 Jayden Qiu over 1 year ago in reply to Nityanand Hegde

TI__Intellectual 1405 points

Hi Nitya,

Thanks. They removed the cff and test, but there is little difference in both condition. Here I attach the excel tool.

ZTE's requirement is very sample, they hope the load transient is within 500mV with 2-3A Load current.

Copy of TPS54360-361FAMILY_CALC_TOOL_REVE_0911.xls

Brs

Jayden

0 Nityanand Hegde over 1 year ago in reply to Jayden Qiu

TI__Expert 5490 points

Hi Jayden,

I looked into excel tool, i don't see any deviation on the design. The undershoot and overshoot on the customer design is with 500mV of requirement and the design has sufficient output capacitor.

If customer is asking about the output voltage ripple under red marked region in below figure, then it is expected due to PSM under no/light load condition.

Thanks,

Nitya

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TPS54561: The output ripple is large

SLVC452