MPM3822C max output capacitance, Toff limitation

DC-DC Power Converters
1

Hi,

I am looking to replace the Enpirion DC-DC modules and we identified MPM3822C as a candidate. We have some questions about the part

  1. the datasheet states the maximum output capacitance is 100uF. We have additional bulk and decoupling near the load more than 100uF, and it is filtered from the enpirion module with ferrite bead (since enpirion had similar Cout value in datasheet but they also state can have additional bulk decoupling as long as it is separated from the Vsense pin on the module - is the same true for the MPM3822C outs pin?

  2. I don’t understand the results for the Vin/Vout ratio when i use the DC DC Designer Online tool. WHen I try 5Vin, 3.3V output I get error in the tool “Vout is too large due to the minimum off time limitation under this switching frequency!”
    However, when I try calculate this it seems like it should work. The datasheet says minimum off time Tmin_off is 230ns and the switching freq is 1150kHz, so the maximum duty cycle is 0.7355, with 5V in the maximum output for this duty cycle would be 0.7355*5V= 3.68V which is > 3.3V, so unless I make a mistake or not considering something it seems like it should work?

2

Hi c.dai,

Welcome to the MPS Forum!
We will contact you directly from MPS Now and provide guidance regarding your questions.

3

Hi Sunandhitha,

I have the exact same questions as c.dai, trying to achieve 3.3V output from a USB power (as low as 4.5V). and also dealing with high capacitive load, is it possible to have access to the answer you provided to c.dai?

Thanks in advance,
Kind regards,
Xavier

4

Hi Xavier,

You could possibly have output capacitance greater than 100uF. But our concern is that if Cout is too large, this might cause the soft start to fail due to overcurrent.
We would recommend getting the evaluation board EVM3822C and trying this out for your specifications.

About the DCDC designer tool issue, the error mentioned above should not be shown in the tool anymore.