LM5116: lm5116 60V input 32V output disable/enable problem

Hello Ahmet,

Please can you post your schematic?

Thank You.

kind regards,

David.

Hello David;

Because of privacy rules we can not post the schematic. but i can give the some operating conditions of lm5116 converter.

the input is 60v, output is 32v. load current 3a (the problem occur also at no load) the schematic for Lm5116 has 330khz operating frequency. output inductor is 15uh, the ss has 10nf cap, sense reistor loacate between low side mosfet drain and pgnd which is 12.5mohm (the current sensed from here to lm5116 with 100R 1nF filter). The lm5116 supllied with Vin. allbypass capacitor (Vin, Vcc etc.) located as close as to lm5116. there is resistor volage divider network for UVLO (no cap for this network).
as i said previous mail even if not used there is Vccx 100nf cap to ground. and the conveter enabled with open collector transistor. there is 220k betweebn enable pin and Vin also at enable pin there is 100pf cap to ground.
In datasheet page 15 there is a brief about enable pin as below. So we doubt about the resistor value whisch is 220k but it is suggested 1Meg for high voltage application.

the converter normally operating without problem with no load and full load. But when we disable the converter while operating at no laod (also full load) with open collector enable control. the converter shut down. But we can not enable the converter. We have find out that the high side mosfet also lm5116 damage.

"A 1-MΩ pullup resistor to VIN can be used to interface with an open collector control signal. At low input voltage
the pullup resistor may be reduced to 100 kΩ to speed up the EN transition time. The EN pin can be tied directly
to VIN if this function is not needed. It must not be left floating. If low-power shutdown is not needed, the UVLO
pin should be used as an on/off control"

regards,

Hi,

 

Does the failure occur when you have a supply to VCCx only?  or does a failure occur with and without VCCx supply?

What value SS cap is installed?  Because you have a high vout suggest slowing the SS time down, say Css= 100nF?

How is the layout?  Were the guidelines in the datasheet followed/implemented closely?

 

see attached.

 

Kind regards,

David.1401.lm5116 Flour Plan.pdf

Hi David;

We don't use VCCx normally on board. But we populate a 100nf cap to VCCx supply but VCCx supply not connected to anywhere. I have asked this about. Even if we dont use VCCX, putting a cap to this pin can result a failure?

SS cap is 10nF. We can use a 100nf cap and try it.

The layut guidilines generally apllied to circuit.

Now we have have changed the resistance between enable and Vin 220k to 1MEG. We have better reults. Theere is only one fail for 10 different cards. So can we say high value of this resistor is good?

Also for our circuit. After disable operation then we enabled this enable pin. When enabled there is a rising voltage as expected. but the voltage waveform is like rising function and with a 20khz sinusioidal shepe added to this pin. Is it a normal waveform?

regards,

Hello Ahmet,

If VCCx is not used, connect to Gnd.

Re: Your question about the effects of VCCx. No, I don’t think this is the cause of your failure...

I am not sure that the EN resistor has anything to do with the failures? However, the oscillation you describe on startup does sound like a potential issue.

Is it possible to send the schematic to me directly, via email?

David.Baba@ti.com

Thanks,

David.