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TLV2172: Reverse Current Conditions

Jejomar Ildefonso
Genius 9550 points
Part Number: TLV2172


Hi Team,

Our customer is using TLV2172 to drive a piezo sound element. It works during normal conditions but when the piezo element suffers mechanical shocks, it generates electrical surge to the amplifier. What would be the recommended reverse current and voltage conditions that the amplifier can withstand?

They were able to measure ±1.6V and up to ±5mA during no supply conditions. In cases of (V+)-(V-)=15V, surge voltage can't be measured at 10mV/div range,  but surge current was +-16mA peak.

Are these conditions allowable?

Thanks in advance!


Kind Regards,

Jejomar

  • 0
    Guru 140200 points

    Hi Jejomar,

    I would add a protection circuit using diode clamps. Can you show a schematic?

    Kai

  • 0
    TI__Genius 15410 points

    Hi Jejomar,

    Having 16mA injected into the input violates the absolute maximum rating of the device and may cause damage to the device. Please see Section 7.1 of the datasheet. As Kai mentioned it would be best to use some protection to direct this current away from the device. Also take a look at Section 8.3.3 and Figure 26 in the datasheet. Section 8.3.3 discusses Electrical Overstress of the device and shows the internal ESD diodes and 2.5kohm internal resistor.

    Thank you,

    Tim Claycomb 

  • 0 in reply to Tim Claycomb
    TI__Genius 9550 points

    Hi Tim,

    Thank you for the helpful response. We've shared your answer to our customer and they've asked additional confirmation.

    In case of 0V supply voltage(chip was not working), injection current is just 5mA, less than 10mA. It doesn't damage TLV2172. Is this correct?
    In case of 15V supply voltage (chip was working), your answer was exceeded 10mA and not allowed.

    But the query is that the current 16mA doesn't flow through ESD protection diode in TLV2172. It comes through internal OPAMP output FETs under normal operation. It seems TLV2172 is working as normal operation. It just controlled the output voltage to cancel the surge current. Figure 5 of the datasheet shows Output current and it seems output current more than 20mA is not prohibited. Is this current still not allowable?

    If you could help us identify the maximum limitation for output (injection and withdraw) current, would really appreciate it as well. Thanks!


    Kind Regards,

    Jejomar

  • 0 in reply to Jejomar Ildefonso
    TI__Genius 15410 points

    Hi Jejomar,

    That is correct, if only 5mA is injected there should not be damage to the device. However, it would be a good idea to add some protection to ensure >10mA does not get injected. The only reason I recommend this is to allow for variation of output current from the sensor when experiencing a mechanical shock.

    For the powered 15V condition, the op amp can sink >16mA of current into the output. This assumes that the piezo sensor output voltage does not exceed the power supplies of the op amp to forward bias the internal ESD diodes.

    For limits on sinking/sourcing output current I recommend taking a look at the output voltage vs output current curves shown in the datasheet. This is Figure 5 in the TLV2172 datasheet. These graphs are only valid when the device is powered. 

    Thank you,

    Tim Claycomb