LM5010: Driving a Capacitive Load

Danny Andreev

Part Number: LM5010
Other Parts Discussed in Thread: LM5118

Hello,

I am considering using the lm5010 to top off the voltage on a 470uF capacitor bank which will provide a 10A 150us pulse to another application.

I got the AN-1352 LM5010 Evaluation Board and changed R3 to 22k in order for it to put out 52.5V, changed R1 to 470k to change the switching frequency to 920kHz and attached the 470uF load on vout. (Vin is set to 60V).

However, as soon as i attached the load, the output voltage dropped as the chip attempted to charge the capacitor. It would rise to 51.6v and then abruptly stop switching. The voltage would continue to fall until 1.2v until the lm5010 would start switching again.

Any clue how I could get the chip to stay switching?

Best,

-Danny

over 4 years ago

0 Danny Andreev over 4 years ago

Intellectual 310 points

P.S

The blue is the voltage at SW pin and yellow is at Vout

0 Ethan T over 4 years ago in reply to Danny Andreev

TI__Expert 3835 points

Hi Danny,

Please share your schematic design.Did you also change R2 in your feedback network, because I don't think the R3 change is enough for a 52.5 V output.

Regards,

Ethan

0 Danny Andreev over 4 years ago in reply to Ethan T

Intellectual 310 points

I left R2 as 1k and R3 as 20k (mistyped 22k)

Vout=2.5*(r1+r2)/r2

Vout=2.5*(20k+1k)/1k=52.5V

0 Ethan T over 4 years ago in reply to Danny Andreev

TI__Expert 3835 points

Hi Danny,

Is your schematic the same as the EVM with changed feedback resistors? Did you leave C7 and added the capacitive load? I suggest increasing the SS capacitor in case the device is ramping too fast and possibly hitting current limit.

Regards,

Ethan