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TL031CD is misbehaving in voltage follower mode. Any suggestions on schematic design? Is this related to single supply?

Macjan Camilo Fernandes
Prodigy 180 points
Other Parts Discussed in Thread: TL071, TS321, TL031, TLC271, OPA170, TLV2371

Ti,

This below is the schematic design I constructed to work with TL031CD operational amplifier.

The circuit is simple. The analog input is current input 4 to 20mA. Which drops across resistor (5V zener protected) which is given to TL031CD (note: TL071 in schematic) . The output then is given to ADC which can take 0 to 5V. Power to the whole circuit is given +12V as V+ , 0V as V-

The problem I'm facing is that voltage follower works properly only for higher voltages like from 1V to 5V. But voltage below 0V to 0.1V gives me output of 11.6V to 0700mV on the output of operational amplifier. The region between 0.1V to 1V for input, gives constant 0.7V output.

Below given is the graph I plot of Vin vs Vout for this circuit.

Was reading the datasheet and did not find anything. But is this related to Single Supply?

There was one point mentioned in the description saying:

   The TL03x devices are fully specified at ±15 V and ±5 V. For operation in low-voltage and/or single-supply systems, the TI LinCMOS families of     operational amplifiers (TLC prefix) are recommended. When moving from BiFET to CMOS amplifiers, particular attention should be paid to slew rate, bandwidth requirements, and output loading.

Thanks in advance.

  • 0
    TI__Guru*** 146096 points
    Macjan,

    Sorry for the delay, I was suddenly called away.

    The input common mode lower range can be as high as VCC - + 4V. That means the output only needs to be correct for VIN 4V and higher.
    Not all samples will work from 1V and up. The minimum VOUT (VOL) value is limited by the output circuit that is not rail to rail.

    Try TS321 instead.
  • 0 in reply to Ron Michallick
    Prodigy 180 points

    Ron Michallick,

    Thank you for replying ASAP.

    On TL series datasheet they had mentioned to check TLC series for single supply operations.

    Can we use  TLC271ID instead. We have already designed PCB and the package we use is SOIC8.

  • 0 in reply to Macjan Camilo Fernandes
    TI__Guru* 93105 points

    Hello Macjan,

    The TLC271ID is a programmable op amp where the operating current is set by connecting pin 8 the BIAS SELECT to VDD, mid-supply, or GND. The bias connection affects the dc and ac performances of the amplifier. That makes it a bit different than most other op amps. Pin 8 would have to be connected to one of those levels and shouldn't be left floating. Pin 8 of the TL031 is a NC (no internal connection) and probably isn't connected to anything on the printed circuit board. Therefore, the TLC271 isn't an exact drop-in replacement for the TL031.

    The OPA170 might be a good replacement for the TL031. It uses the same package pin arrangement in the 8-pin SOIC. It doesn't have the OFFSET control functions provided by the TL031 pins 1 and 5. However, the OPA170 maximum room temperature is +/-1.8 mV, versus the TL031 with a +/-3.5 mV offset maximum. The OPA170 lower common-mode voltage (VCM) is 0 V, while the upper limit is (V+) - 2 V so that needs to be checked relative to the application. You can find the OPA170 datasheet here:

    Another possibility is the TLV2371. It too doesn't have the offset control pins and its maximum voltage offset is +/- 4.5 mV. Its VCM range is 0 to (V+) - 1.35 V. You can access the datasheet here:

    Regards, Thomas

    PA - Linear Applications Engineering

  • 0 in reply to Thomas Kuehl
    Prodigy 180 points

    Thomas,

    Thank you for the valuable information. I'm going forward with TLV2371.

    Regards, Macjan.