Issue with PG at MPM3510A

DC-DC Power Converters
#1

Hi,

we use a MPM3510A to convert +36V into +5V. We have connected a LED with cathode to the PG signal. We connected +5V via resistor of 270 Ohm to the anode of the LED. We see a short flash when we enable/disable the MPM. But in on state LED stays off. Datasheet only states that it is an open drain signal which may drive up to 4 mA.

Can you explain this behaviour?

We use another MPM3506A with the same circuit. Difference is that we convert from 36V to 30V and have another LED resistor of 2k7 to +30V. But the LED is on when the MPM is on.

Thanks in advance, Sven

#2

Hi Sven,

Welcome to the MPS Technical Forum! Can you please share a schematic of both circuits? What is the p/n and Vf of the LED you are using? High volume customers can also send their questions to mpsnow@monolithicpower.com for specialized support from our FAE team.

#3

Hi,

first image shows the MPM3510 which does not properly control the LED.

mps_issue_1
mps_issue_1834×269 17 KB

Second image shows the MPM3506A -sorry must take another post as i am a new user :(.

LEDs are Kingbright standard LEDs with typical Vf=2.2V at 20 mA.

Regards, Sven

#4

And here is the second image:

mps_issue_2
mps_issue_2936×289 17.7 KB

#5