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OPA170: Single supply, negative voltage input, invert OPAMP

user5163865
Genius 3850 points
Part Number: OPA170
Other Parts Discussed in Thread: LM7705, TLV9001

Hi,

The customer configured the inverted OPAMP (Gain = -1) under the conditions of 5V Single supply, negative voltage input = -2.5V to 0V.

If I design it, I will use dual power supplies, but if the inverting AMP has a negative input as in the customer's design, is it okay to use a single power supply because the output is a positive voltage?

Also, if the input voltage can be less than -0.5V, it will exceed the absolute maximum rating. Is this okay if the input current is within 10mA?
The absolute maximum rating of the input current is 10mA.
I think this is the rated current of the ESD diode.

Best regards,

Hiroshi

  • 0
    Guru 140200 points

    Hi Hiroshi,

    as the common mode input voltage range of OPA170 goes 0.1V below the negative supply rail (0V), even over the full temperature range, this circuit seems to work with an input voltage of -2.5V.

    But as the output of OPA170 cannot fully go down to 0V, the circuit cannot handle an input voltage of 0V. From this point of view a negative supply voltage would be helpful. But as you do not need much negative supply voltage, you could take the LM7705 to provide a supply voltage of -0.232V Relaxed

    Kai

  • 0
    TI__Guru**** 159451 points

    Hello Hiroshi-san,

    Try TLV9001 for lower cost and a part optimized for 5V supply.

    For OPA170 or TLV9001 and 5V power on, both inputs will be 0V, so the amp op does not have any negative voltages at its pins. If RSSI input precedes the 5V supply on op amp then there will be negative voltage on the input. The absolute maximum current is 10mA. The application is less than 250uA.

    On V+ power up, op map will go high to make inputs zero. Both op amps state, "no-phase reversal". 

    For 0V input, the lowest output voltage depends on the sink current demand of the ADC load. With no sink current expect about 2mV

  • 0 in reply to Ron Michallick
    Genius 3850 points

    Hi Ron-san,

    Thank you for your response.

    Best regards,

    Hiroshi.