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Op Amp Start up Time

How long does an op amp take to "startup"? I have a very straightforward non-inverting amplifier to amplify an audio signal. It works fine but when enabling power through a switch the audio takes about 0.5 seconds to be heard. I have monitored the power to the op amp as it uses a rail splitter and all the power comes on within 20ms. The op amp is a very low power version(uses < 0.3mA) with 10uF IO coupling.

I have monitored the output of the op amp and it is off when the power is off, when the power comes on it it takes about 0.5 seconds before it jumps to input voltage(with gain of course).

I'm using a TLE2426 and if I add too large of a capacitor for noise reduction then the split rail takes about 1.5 seconds to come on. I removed the capacitor and it comes on in about 20ms. The op amp itself though still takes a while. I imagine this is an issue with low power op amps(takes longer to charge the internal capacitance's?)?

Is there a parameter on the datasheet that specifies how long the op amp takes to "start up" or a way to calculate it from the parameters?

Or is there some other thing possibly going on? I do see that the input also takes a bit of time to ramp up but not as long as the output of the op amp. This maybe due to the scope too as I am using AC coupling. What I do know is that the audio output takes about 0.5 seconds for me to hear it when I power the circuit.

Reply to
bob.jones5400
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Ah, 10uF. Did you check the input? If you have a lot of gain it might take a long time to get the input to where the opamp is in the linear range because then every millivolt counts.

If you have a lot of gain the input needs to be within millivolts or tens of millivolts of target value. That can take a long time if the resistor values are high.

Simple test: Double the value of that 10uF cap. If that doubles the turn-on time you know what causes it :-)

--
Regards, Joerg

http://www.analogconsultants.com/
Reply to
Joerg

Saturated inputs are always a pain on start up. Also damaging in some cases.

Jamie

Reply to
Jamie

It's probably the time required for the 10 uF coupling cap on the input to charge to the split supply level. You might be able to connect a diode from the split supply directly to the input to shorten that time without affecting operation very much, since it will be almost an open circuit when the voltage across it has been reduced to close to zero by the operation of the circuit.

--
John
Reply to
JOF

If a saturated input (without over-stressing parasistic substrate diodes paths) causes an opamp to die upon power up or become damaged, then the IC designer should be dunked into a moat until there is a vow to do better next time :-)

--
Regards, Joerg

http://www.analogconsultants.com/
Reply to
Joerg

I think it's cheaper to replace the chip and patch the problem! :)

Jamie

Reply to
Jamie

Or let a Rottweiler and a Shepherd loose on the team :-)

Did the pain ease up? We've got three big dogs but so far never had a real bad fight happen. Had a Rottie mix until Thanksgiving 2010, when his hind muscles finally gave out at age 13-1/2 and we had to put him to sleep. I still miss him.

--
Regards, Joerg

http://www.analogconsultants.com/
Reply to
Joerg

I'm with Joerg on this: your issue is more likely with the circuit surrounding the op-amp than with the amplifier itself.

Post a schematic somewhere? And maybe tell us _why_ you need it to work faster, and _how short_ a time is acceptable?

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com
Reply to
Tim Wescott

" snipped-for-privacy@gmail.com"

** Reminds me of the slow start up exhibited by most condenser microphones - the kind that use a 60 volt polarising supply. Circuit resistance is about 2Gohms and total capacitance to be charged is about 200pF plus it takes several time constants to settle.

So about 2 seconds in all to get full output level.

..... Phil

Reply to
Phil Allison

We have some one at work that had to do that a couple of days ago, they had a rescue rottie that was up there in age to start with, she had that dog for at least 5 years. The other day she tells me that he is bad and could not get up from the floor, peed on the floor then got scared and try to clean it up because he knew he did wrong.

He was 15 years old. She loved him like one of her own kids. actually that dog got treated better than her husband and he'll confess to that :)

As for my dog, yes, my arm is still a little sore, it is all black and blue. it'll need to go through a healing process but I am sure I'll make it :) I'll just need to watch her teeth a little closer next time she goes for that full size basket ball.

Jamie

Reply to
Jamie

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