• State
  • Locked Locked
  • Replies 2 replies
  • Subscribers 63 subscribers
  • Views 839 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LM25010 low load problems

Bogumil Pacan
Prodigy 120 points
Other Parts Discussed in Thread: LM25010

Hi

We are facing a new problem in our units, which are for few years on market, few thousands of them sold. Device operates as 24-to-3V3 buck converter. During startup of unit the load is very small (only ARM uController). It seems voltage is ok, but switching frequency is low (I'm not sure, but we see that DCDC is skipping some pulses because of weak load). After that we do inits of other devices on board (SDRAM, ethernet PHY, etc.). After that we did not see any pulses skipped.

The problem is visible on most of new boards batch (no changes in hardware project). During inits of other devices, output voltage from DCDC drops below 2V9, which cause a system-wide reset. What we found is replacing diode in DCDC circuit into faster one help in 100% of cases (we always used ES2D, reverse recovery time trr = 20 - 35ns, depending on manufacturer of diode). Funny thing that we replace ES2D into ES2D from other manufacturer. We can't measure trr in circuit as per datasheet, but low power measurements shows that these bad diodes turn off about 20ns later than good ones. We are not sure is it a bad series of diodes or we have a wrong project (doesn't work in worse case of trr).

My question is how to estimate a safe trr for DCDC converter and how to choose diode?

Any tips for future would be helpful, because we are still using this converter in our other products.

  • 0
    TI__Genius 11490 points

    Hi Bogumil,

    Thank you for choosing TI part. We typically use a schokkty diode for this part.

    Can you share the schematic?

    Regards,

    Vijay

  • 0 in reply to Vijay86929
    Prodigy 120 points

    Hi Vijay

    Thank's for Your answer. This is my schematic.

    We use Schottky (B160-13-F) with the same controller LM25010 in other unit with no problems. When I look into datasheets of these diodes, Schottky has larger total capacitance (Ct) 110pF vs 25pF in ES2D. Reverse recovery time is not even mentioned in datasheet of Schottky, but my small signal measurements show it's a little bit faster than ES2D (a good one). So it seems that trr is a critical parameter in our application.

    Do You know how to calculate max. trr for the application? You suggest to use Schottky diodes, is it sure they will be always fast enough (no trr in datasheet)?