| 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? |
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| kafka |
| No expirience? No one would help me? |
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| 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. |
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| pinkmouse |
| I, too, am confused. Could you post a schematic? |
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| 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. |
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| 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? |
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| kafka |
| No I haven't. But I know I can deliver enough current to make the whole system work. Even a 24V relay :xeye: . |
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| 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? |
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| kafka |
| Positive version works excellant. Chip works with negative rail 'cos at the output I have -15V, as I wanted. |
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| 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. |
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