Viper 26LD loosing regulation

vitor1 · ‎2016-07-02

Posted on July 02, 2016 at 12:44

Hi,

I have used eDesign to implement viper on my application. My specs are input voltage 70Vdc to 160Vdc / output 15Vdc (5.1W). For some reason, the viper 26LD is loosing regulation (when connecting to a load) - the output voltage decreases as the load increases. Furthermore, I heard buzz coming out of it. After replacing the component a few times, the buzz stopped but I still didn't get the right output voltage.

You may find attached the schematics!

Thanks in advance for your support.

#retification #viper-26ld

Patrizia BELLITTO · ‎2016-07-04

Posted on July 04, 2016 at 09:00

Hallo,

thanks for your reporting. I'm forwarding your post to the application engineer responsible for VIPerx6 devices, he'll answer you as soon as possible.

Best regards,

Patrizia Bellitto

eDesignSuite developer team

vitor1 · ‎2016-07-04

Posted on July 04, 2016 at 12:17

Hi Patrizia,

I have done a current measurements today and I have noticed that my circuitry is working ok (15V output voltage) only when my load is drawing 0 to 85mA. With a current consumption over 85mA, the circuitry looses regulation (the output voltage oscillates between 0 and 2V). It would be nice if the Viper's engineer could find out the circuitry miss functioning.

Thanks,

Patrizia BELLITTO · ‎2016-07-06

Posted on July 06, 2016 at 09:24

Hello,

sorry but our application engineer has some problems in his account and was not able to answer you directly.

I'm copying his reply here:

Hello,

The design should be ok for such output power. Itâ€™s not clear to me what does the buzz consists of, and what do you mean by â€œreplacing the component a few times, the buzz stoppedâ€�, could you please specify?

Furthermore, we would like to see some oscilloscope shots of inductor current and output voltage, both with IOUT < 85mA and with IOUT > 85mA.

Could you please let us have three shots for each of the two above conditions, with following time scales: 10usec, 20msec and 200msec respectively?

thanks

vitor1 · ‎2016-07-07

Posted on July 07, 2016 at 10:43

Hi

As I have everything soldered on a PCB, I couldn't get the shots for the inductor current.You may find attached the output voltage shots (at 70V and 160V).

I have noticed that at 70V the circuitry is stable (and the load can draw 0 to 340mA). On the other hand, at 160V there are some current range which it looses regulation. It is more or less like:

- 0 to 80mA: ok

- 80 to 170mA: NOT ok

-190mA to 260: ok

PS: Relating to the buzz, I am not sure if this would be the correct word to described but it sounds like a mosquito would be inside of the IC.

Kind regards,

________________

Attachments :

PRINT_OSC_Viper26LD.zip : https://st--c.eu10.content.force.com/sfc/dist/version/download/?oid=00Db0000000YtG6&ids=0680X000006HzD6&d=%2Fa%2F0X0000000bIS%2FftufELUg3fyZE7j8XlPYrpP6gfTIYaUZvhslEKO13tE&asPdf=false

Patrizia BELLITTO · ‎2016-07-08

Posted on July 08, 2016 at 15:05

Hello sir,

can the buzz be heard only during the â€œfaultâ€� conditions (as in figure ~280mA_200ms (1)_160V-input.jpg), or also during â€œstandardâ€� condition (as in the 70V figures)?

â€œAfter replacing the component a few times, the buzz stoppedâ€� means that if you replace the VIPer the issue disappears?

Since you are experiencing a malfunctioning in a limited input/output range, it could be related to stability and be solved by playing on the compensation network (C12, R13).

Could you please share the exact part number of L1 and C15?

Try also removing R14.

In any case, it would be very useful to have a look at the inductor current shape.

vitor1 · ‎2016-07-08

Posted on July 08, 2016 at 17:10

Hi,

--> I have already removed the R14. All the shots were taken without it.

--> I can hear the buzz at any voltage and current, but it happens more often when loosing regulation. At first I thought that a defective IC would be the reason for the buzz. However, it is also happening on the new soldered one.

--> Is the a formula to calculate the compensation?

--> Please find here the used

http://www.mouser.ch/ProductDetail/Coilcraft/RFS1317-474KL/?qs=/ha2pyFaduhF%252bOy/s5ZmDuz7c72id950T9FTwN51v/6KFlMTL8mcDQ%3d%3d

(L1) and

http://www.newark.com/united-chemi-con/emzj250ada680mf61g/cap-alu-elec-68uf-25v-rad-can/dp/68Y4758

(C15).

Regards,

Patrizia BELLITTO · ‎2016-07-13

Posted on July 13, 2016 at 14:08

Hi,

you could try to use an output capacitor with an higher current rating and check the compensation formula as described in this application note:

http://www.st.com/content/ccc/resource/technical/document/application_note/e6/81/42/cf/74/28/4f/78/DM00127577.pdf/files/DM00127577.pdf/jcr:content/translations/en.DM00127577.pdf

Even details about the layout of your board could be useful.

Best regards,

Patrizia Bellitto

vitor1 · ‎2016-09-14

Posted on September 14, 2016 at 11:44

Could you check may board layout? Please find the print attached.

________________

Attachments :

Board_layout.pdf : https://st--c.eu10.content.force.com/sfc/dist/version/download/?oid=00Db0000000YtG6&ids=0680X000006HyzV&d=%2Fa%2F0X0000000bIT%2FZwMzzyN9SM_kF9w2Jsxj.r6IEK_Ro.rWqnpMTQzbeVs&asPdf=false

Patrizia BELLITTO · ‎2016-09-14

Posted on September 14, 2016 at 16:35

Also the schematic could be useful...