OPA548 and shutdown

kafka · 2nd September 2004, 06:48 PM

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 · 5th September 2004, 09:39 AM

No expirience? No one would help me?

analog_sa · 5th September 2004, 10:29 AM

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 · 5th September 2004, 10:37 AM

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

kafka · 5th September 2004, 12:08 PM

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 · 5th September 2004, 02:56 PM

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 · 5th September 2004, 04:16 PM

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

.

pinkmouse · 5th September 2004, 05:07 PM

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 · 5th September 2004, 05:17 PM

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

pinkmouse · 5th September 2004, 05:26 PM

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.

2nd September 2004, 06:48 PM	#1
kafka diyAudio Member Join Date: Jun 2004 Location: Lublin	OPA548 and shutdown 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?

5th September 2004, 10:37 AM	#4
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	I, too, am confused. Could you post a schematic? __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

5th September 2004, 05:07 PM	#8
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	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? __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

5th September 2004, 05:26 PM	#10
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	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. __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

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5th September 2004, 09:39 AM	#2
kafka diyAudio Member Join Date: Jun 2004 Location: Lublin	No expirience? No one would help me?

5th September 2004, 10:29 AM	#3
analog_sa diyAudio Member Join Date: Aug 2002 Location: Sofia	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.

5th September 2004, 02:56 PM	#6
analog_sa diyAudio Member Join Date: Aug 2002 Location: Sofia	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?

5th September 2004, 04:16 PM	#7
kafka diyAudio Member Join Date: Jun 2004 Location: Lublin	No I haven't. But I know I can deliver enough current to make the whole system work. Even a 24V relay .

5th September 2004, 05:17 PM	#9
kafka diyAudio Member Join Date: Jun 2004 Location: Lublin	Positive version works excellant. Chip works with negative rail 'cos at the output I have -15V, as I wanted.

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