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LMP8601: LMP860x Common mode versus supply voltage

Carlos Silva85
Expert 4915 points
Part Number: LMP8601
Other Parts Discussed in Thread: LMP8603

Hi Colleagues,

Hope all is well over there, where sun always shines :-)

I have a customer evaluating the LMP8603 and was wondering if we have data to plot the common mode voltage versus supply voltage.

The information in the datasheet is as shown below:

  • 3.3V Supply                                        -4 to +27V
  • 5V supply                                            -22 to +60V

For this particular application the customer is trying to perform current measurement on a +/-15V supply, with Vs = 4.7V.

According to the parameters above, the negative common mode rises sharply with the supply, so I'm unsure

  • At what supply voltage is the -15V threshold guaranteed
  • Will there be any damage caused to the device, for example, if the supply rail fails, while the common mode remains at -15V

Much appreciated for the support and wish you all a happy Halloween!

  • 0
    TI__Mastermind 26660 points
    Hey Carlos,

    We appreciate the support. Anyway, I think the wording in the Absolute Maximum Ratings Table might be a little vague, but it could be that the absolute max input common mode voltage range is -22V to +60V for any power supply. The input common mode voltage range listed for the 3.3V supply is reduced because this is the optimal range to produce 80-dB CMRR over temperature and the rest of the electrical characteristic spec. Thus -4V to +27V is listed as simply a testing condition for the 3.3V specs, not as an absolute max for the device when powered with a 3.3V supply.

    I'll look more into this though for confirmation.

    Peter
  • 0 in reply to Peter Iliya
    TI__Expert 4915 points

    Great Peter. I look forward to your confirmation.

  • 0 in reply to Carlos Silva85
    TI__Mastermind 26660 points

    Hey Carlos,

    After taking with the team I can say this part can accept common-mode voltages from -22 to +60V (for either power supply) so there is no limitation to the input common mode voltage range based on the power supplied to the part. The device still needs to be operating in the recommended power supply range, but that is all.

    Additionally, this "Continuous input voltage (-INA and +IN)" absolute max spec applies to differential signals as well as common mode, which is somewhat unique compared to our other current shunt monitors because this means you could apply 60V one pin and -22V on the other input pin and the part will not be damaged.

    Best,

    Peter Iliya

  • 0 in reply to Peter Iliya
    TI__Expert 4915 points
    Thank you Peter.

    So, to clarify, the LMP860x can accept a continuous input voltage (-INA and +IN) ranging from -22 to +60V without damage to the part, however, the electrical test condition at 3.3V was limited to -4 to 27V and therefore these are the values shown in the datasheet.

    Is my understanding correct?
  • 0 in reply to Carlos Silva85
    TI__Mastermind 26660 points
    Yes exactly. The -4V to 27V input Vcm range is shown in datasheet for the 3.3V Electrical Characterstics table because this was the range chosen to test and derive the specifications for the device when supplied with 3.3V at the power rail. This testing condition is only that, a testing condition. It is not absolute spec. The Abs Max Vcm range for all valid power supplies is listed in the Abs Max table 6.1.