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TPS56C215: efficiency 5V vs 12V

Hong Jieun
Prodigy 240 points
Part Number: TPS56C215

Hi, 

I tested TPS56C215 static load ripple and efficiency under Vin=5V and 12V / Vout=0.75V with TPS56C215 EVkit

Vin=5V is more efficient than Vin=12V as datasheet mentioned. 

1) Is there any reason why Vin=5V is more efficient? 

2) And please let me know why Vout ripple is larger (about 2mV) when Vin=12V than Vin=5V? (Iout=10A)

Vin=5V -> △Vout=3.32mV

Vin=12V -> △Vout=5.56mV

3) Is it stable response with this ringing? Could you let me know how much phase margin is with this ringing?

4) Which equipment did you use for test transient response?

I don't have the stability analyzer equipment so I want to test transient response with load step.

But with my equipment, it's slew rate is not set fast enough to see the difference according to the Cff.

  • 0
    TI__Mastermind 24370 points
    Hong Jieun said:

    1) Is there any reason why Vin=5V is more efficient? 

    Yes with lower VIN, the switching losses are lower than the 12V scenario. Also, the conduction losses are slightly lower since the inductor ripple current is smaller with 5V than 12V.

    Hong Jieun said:
    2) And please let me know why Vout ripple is larger (about 2mV) when Vin=12V than Vin=5V? (Iout=10A)

    This is because the inductor ripple current which flows through the output cap that generates the output ripple is smaller with a 5V input than a 12V input.

    Hong Jieun said:

    3) Is it stable response with this ringing? Could you let me know how much phase margin is with this ringing?

    As you can see on Figure 8-7 in datasheet, the phase margin is about 65-70 degrees. 

    Hong Jieun said:

    4) Which equipment did you use for test transient response?

    Yes, we have a board we have built which switches a FET in series with a resistor which can be modulated to change the current step. Sometimes, we also use the  Intel mini slammer product to do this time of transient testing. As long as you follow the table 8-2 recommendations, the design should be stable.

    Thank you,

    Amod

  • 0 in reply to Amod Vaze
    Prodigy 240 points

    Thanks for your reply, 

    1) 

    Amod Vaze said:
    Yes with lower VIN, the switching losses are lower than the 12V scenario. Also, the conduction losses are slightly lower since the inductor ripple current is smaller with 5V than 12V.

    Can I know the specific scenario? And, why the inductor ripple current is smaller with 5V?

  • 0 in reply to Hong Jieun
    TI__Mastermind 24370 points

    You can use WEBENCH power designer to create a design and vary the input voltage to observe the efficiency/power losses and ripple current values.

    Thanks,

    Amod

  • 0 in reply to Amod Vaze
    Prodigy 240 points

    Why the switching losses are lower with 5V than the 12V?

  • 0 in reply to Hong Jieun
    TI__Mastermind 24370 points

    The switching loss is proportional to input voltage. So, lower input voltage will lead to lower switching losses. You can read up application notes on power losses and it should show the equations.

    Thanks,
    Amod