OPA548 and shutdown

[kafka]

I can't force my OPA548 to shutdown mode. Is's working in inverting mode with gain = 6. As a reference it has tl431 +2.5V. It works as a -15V power supply. But I can't shut it down. I even soldered E/S pin to negative rail and there is still voltage on the output. I've tried with several chips... What's wrong?

 

[kafka]

No expirience? No one would help me?

 

[analog_sa]

I am not quite sure why you need the regulated reference. As long as the ref is grounded and e/s logic zero with respect to it the shutdown will work.

 

[pinkmouse]

I, too, am confused. Could you post a schematic?

 

[kafka]

A mistake. It works in noninverting mode. The circut works. I have -15 on the output, but I can't shut it down even then I soldered pin 7 to -20.

 

[analog_sa]

I wonder if the problem is not the single negative supply. From the datasheet it seems that polarity should not make a difference but it's still nice to see what's inside the chip.

Are you measuring the output under load?

 

[kafka]

No I haven't. But I know I can deliver enough current to make the whole system work. Even a 24V relay .

 

[pinkmouse]

Have you tried just using the 3 resistor regulator as shown in the datasheet? Just to see if the chip works with the negative rail.

Have you built a positive rail version that works as it is supposed to?

 

[kafka]

Positive version works excellant. Chip works with negative rail 'cos at the output I have -15V, as I wanted.

 

[pinkmouse]

Hmmm.

Well, If you have two seperate secondaries on your transformer you could just use two +15 versions on dual bridges, that would get you working.

Other than that, drop a line to TI's tech support. When I had a query a couple of years ago they were very helpful.