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TLV3701-Q1: Negative voltage on +ve input terminal

SATHISH KUMAR KALIAPPAN
Prodigy 80 points
Part Number: TLV3701-Q1
Other Parts Discussed in Thread: TLV3701

Hello,

I am using TLV3701-Q1 as comparator circuit. Please find the circuit attached.

Here the 12V is from battery. So I have to consider reverse battery condition for this design. I have checked the TLV3701 datasheet for the input terminal voltage range capability.

It is stated that  -0.1V to VCC+5V ( datasheet snapshot attached). So I wanted to test it directly.

Test Methode:

-------------------

1. Firstly checked the normal operation: 

Inv terminal - 5.538V (after the divider and diode)

Non Inv terminal - 2.73V

Output - 0V

2. Reverse battery condition: (applied -12V over the 1Mohm resistor) (Expected damage but observed as below)

Inv terminal: - 0.511V (after the divider and diode)

Non Inv terminal - 0.5V

Output - 3.29V

Could anyone explain how it can happen? is there any internal structure (I couldn't find in datasheet).

Thanks in advance.

Thanks,

Sathish

  • 0
    Guru 140200 points

    Hi Satish,

    I would add protection circuitry to make both input voltages always fall within the recommended common mode input voltage range.

    You also might want to read this thread:

    e2e.ti.com/.../800068

    Kai

  • 0
    TI__Mastermind 49896 points

    Hello Sathish,

    As Kai eluded to, if you are pulling the inverting terminal to -0.5V, then you are seeing an output reversal because you are well outside the specified input range.

    The TLV370x has a "beyond the rail" input that allows input voltage up to 5V above Vcc (this is not typical for all devices). So with a 3.3V supply, the "legal" input range is -0.1 to +8.3V. But it does not like negative voltages.

    Try adding a Schottky diode in parallel with the Zener to keep the reverse voltage to around -350mV.

    You can also "split" the divider with a mid-point diode clamp, as shown in section 2.9.2.1 in the following appnote:

     http://www.ti.com/lit/an/snoaa35/snoaa35.pdf