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TPS63070: output ripple becomes larger when Vin is close to Vout

Given Ding
Genius 10155 points
Part Number: TPS63070

Hi Team, 

Here are several questions on TPS63070. 

1. Vout=3.52V, L=1uH, Cout=80uf ( derating is 50%). 

When Vin is ~3.52V, output ripple becomes much larger than the condition that Vin is smaller or larger.  Is it normal? To my understanding, maybe it changes between buck and boost, so the ripple is larger. 

2.  To decrease ripple, increase L to 2.2uH.  

When Vin is 3.7V, output ripple becomes much larger.  what's the reason for this that Vin-Vout changes with inductor? 

3.  In datasheet, it mentioned when inductor is increased, you need to increase Cout. And it is related with RHPZ of boost and need more Cout to decrease the cross over frequency, could you please kindly provide more details? 

Thanks. 

BRs

Given 

  • 0
    TI__Mastermind 21565 points

    Hi Given:

    What's the load condition? For your questions 1# and 2#, I need more details information, including:

    1. is the Vout same for two question?

    2. what's the load condtion?

    3. please share the waveform including Vin, L1,L2, Vout with me. 

    The ripple could be caused by switching ripple, loop unstable, power save mode. That's why I need such info. 

    For question 3. It;s related to boost right plane zero. If you are interested about that, I recommend you to read some paper from IEEE. Or you can contact me with Email, I'll send you some documents about it.

  • 0
    TI__Mastermind 40080 points

    Hi Given,

    This is a normal behavior for TPS63070. When Vin close to Vout, the ripple will gets very high because of the several cycle buck several cycle boost operation. The ripple can be as high as 80mV according to the EVM.

    What is the Vin/Vo and Io at the customer side? What is the target output ripple?