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TPS54821: Voltage dip when load is applied

Part Number: TPS54821

Dear Sir,

 

We are using TPS54821RHLR for generating 1.03V from 5V input, the circuit designed as per webench attached the simulation report for 8Amps requirement,

Actual board Scenario

In our design we are facing a voltage dip which generates pgood (interfaced to enable of next regulator) and shuts down the next power cycle regulator.

The voltage is dropped to 916mV (actual voltage 1.03V) which is provided to Arria10 SoC expected to take less then 5Amps,

 

Independent load test Scenario

To test the voltage drop we have isolated the SoC and provided with resistive load (0.2E) at the load capacitor. We observed dip in voltage 952mV. we need to nullify the voltage dip when load is applied, kindly suggest what needs to be taken care to minimize/completely eliminate the voltage dip.

Please note that Total load capacitor is 100uF x 2 at regulator and additional 100uF near SoC.

In our PCB we will not be able to add additional bulk capacitors. To reduce the voltage dip during dynamic load which are the other components which could be varied.

 

Kindly let us know is there any web simulation to analysis of dynamic load test for the same.

 

Schematics:

CRO Snap shot of the Voltage Dip:

WEBENCH Schematics with Report:

Best regards,

Shashi.

  • hello Shashi,

    When load is applied, output voltage does have a drop. it's difficult to eliminate the voltage dip completely. normally we think 5% of dip volage is accepted.

    what's value of enable threshold in next power? can you change enable divider resister of next power to have enough margin for dip voltage?

    best regards,

    Edwin.

  • Dear Edwin,



    In Actual board Scenario the voltage drop is below 5% which generates pgood signal to shut down the next regulator(TPS54821RHLR).

    SoC has a tight tolerance requirement of only +-30mv. So, we need is in keeping the dip very low.

    We need a solution to minimize the voltage dip as much as possible, please suggest with the solution.


    Best Regards,
    Shashi.
  • Hello Shashi,

    I understand your meaning.

    please change R177 to 10kohm or 15kohm to increase bandwidth. load transient performance will be better.

    can you test the bode plot? it's better to know the phase margin and cross frequency.

    best regards,

    Edwin.