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I have selected a TS922 op amp to use in a voltage follower configuration. The specs for the TS922 in summary are:

  • Rail-to-rail input and output
  • Low noise: 9 nV/√Hz
  • Low distortion
  • High output current: 80 mA (able to drive 32 Ω loads)
  • High-speed: 4 MHz, 1 V/μs
  • Operating from 2.7 to 12 V
  • Low input offset voltage: 900 μV max.
  • Latch-up immunity

The voltage follower configuration is

voltage follower

Supply voltage is 5 V.

To test I am using a simple 10k pot arrangement (range v supply to gnd) to apply a voltage to the input (pin 3) with a voltmeter measuring the output on pin 1.

My issue is that the TS922 output latches up to 4.7 V if the input voltage rises above 3.6 V. If the input voltage is less than 3.6 V the TS922 behaves as a voltage follower.

To try to identify why this is happening I have tried:

  • placing a light load (2k resistor) from pin 1 to ground - no effect
  • grounding the inputs to the other dual amp in case there was some interaction - no effect.

Is there something I am missing?? Otherwise I suspect the markings on this device don't match what is inside.

I would ALSO appreciate any advice on other op amps which are close to the TS922. The most important specs are: - single supply 5 V. - rail to rail input/output. - high output current capability > 50 mA.

I know I can search for devices - but I am hoping someone has experience with a device that works well.

Thanks in advance

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  • \$\begingroup\$ This happens no matter which amp you use? You said there are two on the chip. \$\endgroup\$ – DKNguyen Apr 16 at 2:02
  • \$\begingroup\$ Where did you get the part? I've seen parts from brokers do odd things. \$\endgroup\$ – Robert Endl Apr 16 at 2:09
  • \$\begingroup\$ Yes I have tried both amps and have tried the other chips in the batch of 5 I bought. \$\endgroup\$ – IanF Apr 16 at 2:13
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    \$\begingroup\$ The TSS922 were bought on aliexpress from a supplier in Shenzen. Device marking is TS922IN 90B1432 with the ST Microelectronic logo and MAL (I presume Malaysia) \$\endgroup\$ – IanF Apr 16 at 6:20
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    \$\begingroup\$ @IanF most probably the part is counterfeit, AliExpress is well-known for such surprises. \$\endgroup\$ – sx107 Apr 16 at 19:28
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A couple of days ago I tested some opamp in voltage follower configuration. All op-amps were bought from a reputable vendor (TME).

enter image description here

The input signal was coming from the function generator, \$F = 1\textrm{kHz}\$ and the signal amplitude was \$10V\$ peak to peak.

And all Opamp's was also supplied from symmetrical supply \$+/-5V\$.

Hence we can easily examine the allowed input common mode voltage range.

The first one was \$\textrm{LM}358\$ from ST.

enter image description here

As you can clipping accrue for \$Vin > (Vcc-1.4V)\$

And no sign of a famous crossover distortion due to lack of load resistance.

But reducing the input signal amplitude and adding a load resistance reveals the crossover distortion.

enter image description here

The second opamp was \$\textrm{TS922}\$ from ST

enter image description here

As you can see \$Vin = Vout\$ as expected form rail-to-rail input and output opamp.

No sign of "latching-up".

Hence, if your setup is correct I vote for a counterfeit part from China. Not a big surprise either.

Next one was \$\textrm{TL}072\$ from Ti.

enter image description here

As you can see we got a clipping for \$Vin > (Vcc-0.6V)\$ or so. And when the input signal approaches \$V_{EE} - 1.4V\$ phase inversion phenomenon manifests itself.

And finally the \$\textrm{NE}5532\$ from Philips.

enter image description here

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  • \$\begingroup\$ Thanks for the helpful info. Have you tested any of these devices with a single supply? For example the TS922 is optimised for 3 and 5 volts. \$\endgroup\$ – IanF Apr 18 at 0:57
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Place a .1uF ceramic capacitor between Power and Ground and add resistors in series with both inputs to the op amp. The 2KOhm you added to the output would work.

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You bought an electronic IC from a seller in China. Of course it is counterfeit. Here is what Wikipedia says about AliExpress in Google:AliExpress

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    \$\begingroup\$ Really, that's the first result you get for searching "AliExpress"? Sounds like fake news. That said, the source of the parts means there is a non-negligible chance they are counterfeit. I doubt it's 100%. \$\endgroup\$ – immibis Apr 16 at 22:52
  • \$\begingroup\$ I have purchased a wide variety of electronic components via Aliexpress over several years. My experience had actually been good up to this particular part. In this case I contacted Aliexpress and they have refunded with no problem. \$\endgroup\$ – IanF Apr 18 at 0:42
  • \$\begingroup\$ The Wikipedia link above does not give the result as shown. \$\endgroup\$ – IanF Apr 18 at 0:52
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Must be a counterfeit part - there is no other explanation.

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  • \$\begingroup\$ The device is definitely counterfeit. I tested TS922 devices from a reputable supplier and they work as expected in the same test setup - no latch up. Thanks all. \$\endgroup\$ – IanF Apr 20 at 20:59

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