OPA2365: Opamp output going to rail voltage

Allan Panaligan

Part Number: OPA2365

I am using a OPA2365AID opamp in a voltage follower configuration. It is being powered from a 3.3V supply ( +3.3VH_ISO). The input to the opamp is coming from an ADG706BRUZ-REEL7 MUX which is being powered from a 5V supply ( +5VC_ISO). The purpose of the MUX is to monitor the voltage supplies on the Board. One of the voltages being monitored (SNS_3V3C) on channel S2 happens to be the voltage supply of the Opamp but it is stepped down to 2.65V via a resistor divider. The issue which I am seeing is that the output of the opamp is railed to 3.3 V only for signal SNS_3V3C yet the voltage out of the MUX and into the Opamp are 2.65V.

over 2 years ago

0 kai klaas69 over 2 years ago

Guru 140200 points

Hi Allan,

looks like the OPAmp is damaged. Has it received an insane voltage at the output?

Kai

0 Sam Burnett over 2 years ago

TI__Expert 3620 points

Hi Allan,

It is strange that the amplifier is working for the other channels. Is it possible to capture a scope trace of the 3.3V rail, the amplifier input, and the amplifier output when it rails out as the Mux switches to the S2 channel?

Best,
Sam

0 Allan Panaligan over 2 years ago in reply to Sam Burnett

Prodigy 10 points

here is the scope pic CH1: 3.3V supply U27-3, CH2: +Vin U27-3 & CH3 Vout U27-1

0 Sam Burnett over 2 years ago in reply to Allan Panaligan

TI__Expert 3620 points

Hi Allan,

Thanks for the measurement. Looks like it briefly has the right output before latching up, strange. Where does the Voltage SNS 9 signal end up? Also have you tried replacing the part just in case it was damaged as Kai suggests?

Best,

Sam

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OPA2365: Opamp output going to rail voltage