LM5122 slave not helping

K Steenis

Other Parts Discussed in Thread: LM5122

Since my last post I created a double output version of my LM5122 board.

It is a continous flyback design for 18-28VDC in and 24VDC out at 6A.

The master is running but the slave doesn't do anything, it do receive the sync signal from the master.

I also tested with a 100pF between the syncIn/syncOut signal and an extra 18K resistor on the SyncIn signal on the slave.

over 10 years ago

0 EricLee over 10 years ago

TI__Guru 61501 points

I could not find any issue in your schematic.

Please check UVLO, COMP, SS, RES and LO pin status in slave mode.

UVLO, SS, COMP should be greater than 1.2V and RES should be grounded.

Regards,

0 K Steenis over 10 years ago in reply to EricLee

Prodigy 140 points

UVLO is 2V
SS is 4V after startup

COMP:

RES:

SYNCOUT master, SYNCIN slave:

LO:

(looks like he's willing , but just 500mV top)

Maybe the COMP and RES are a bit noise, but the master does work with those values.

Also I already replaced the FET's and LM5122

0 EricLee over 10 years ago in reply to K Steenis

TI__Guru 61501 points

RES should be grounded.

Are you seeing 0V at RES pin on the master side ?

Regards,

0 K Steenis over 10 years ago in reply to EricLee

Prodigy 140 points

No, the signal on the master side is the same. This one is working dough.. Can I force this signal low after startup?

0 EricLee over 10 years ago in reply to K Steenis

TI__Guru 61501 points

You can force the signal low, but first of all, you have to find the reason why it is not grounded.

Maybe, one of your ground connection has a problem.

Regards,

0 K Steenis over 10 years ago in reply to EricLee

Prodigy 140 points

RES was connected to the ground using a capacitor. I don't want/need hiccup mode, so connecting it to the ground disabled this and also made the system working.

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LM5122 slave not helping