• State TI Thinks Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 2 answers
  • Subscribers 48 subscribers
  • Views 949 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

LMV762Q-Q1: biasing voltage

LMV762Q-Q1: TI gate driver design doubts

Girish K76
Prodigy 90 points
Part Number: LMV762Q-Q1
Other Parts Discussed in Thread: ISO7721, LMV762, LM311

Hai Paul Grohe,

   Thanks for your clarification on the matter. Subjected to this query,please see the attached SiC Mosfet gate driver design of TI.

TI Designs: TIDA-01605 Automotive Dual-Channel, SiC MOSFET Gate Driver Reference Design With Two-Level Turnoff Protection

(Note: The actual web link cannot be copied here)

In the driver design,there is a feature called two-level turn-off given by TI.( See below the screen shot )

The screenshot of the two level turn-off circuitry is shown above where you can see U8A and U8B comparators LMV762 with +Vcc at +5V and -Vcc at -4V..So V+-V- is coming at 9V which is contradictory to the datasheet values

Also in the same design the comparator output is given to digital isolator ISO7721 . In case ,when the output of comparator clamps to -4V,the isolator does not have any provision to address this negative voltage .

The max Vin referred in the datasheet is limited to -0.5 to Vcc+0.5.

Please refer screenshot below.

Kindly look into the TI design refer to Fig.6 shown above.

Highlights: 

Queries on 

*  Negative biasing voltage for LMV762-Q1

*  Negative VIN voltage for ISO7720-Q1

Thanks....

  • 0
    TI__Expert 4555 points
    Girish,

    Currently Paul is Out of Office, so expect a slightly delayed response. I will look into the supply voltage operating conditions as you are right, it seems that the design is violating the recommended operating conditions.

    Regards,
    Jonny
  • 0 in reply to Jonathan Nguyen
    Prodigy 90 points

    Hai Johny,

       Actually one of the inputs for LMV762Q-Q1 comes into a  negative value from our design .

    Since as we discussed if there is no provision for negative Vcc supply for the comparator, the negative input is also restricted to use here.So have we look for another comparator with similar specifications which can abmit negative supply voltage  also???..

    Similarly when we use alternate comparator with negative biasing voltage, the output of the comparator will be clamped to negative voltage , which is given as the input for the ISO7721. 

    And as I already mentioned , ISO7721 wont take negative input . 

    Please clarify this.

    Regards.

  • 0 in reply to Girish K76
    TI__Guru 52116 points
    Hello Girish,

    Yes, there seems to be some issues with this TIDA. The LMV762 is being operated at 9V and the INA input to the ISO7721 is being driven below it's ground. I have submitted an internal notification to the TIDA authors.

    We do not have any comparators that can take a large input voltage below their V- pin. Most are limited to -0.3V or less.

    What is your expected input voltage range?

    It may be possible to level-shift or attenuate the input signal to bring it within the single-supply range?

    We do have some devices, the LM311 and LM319, that can handle the bipolar inputs and have a ground-referenced logic-level output. But they require a pull-up resistor and have a narrow input range (2V from *each* supply rail).
  • 0 in reply to Paul Grohe
    Prodigy 90 points

    Hai Paul,

       Thanks for understanding my design issues.

       According to our design , the reference to the comparator is fixed at -1.2V ( inverting input) . The input to the non inverting terminal is coming at -0.9V and -2.2V at two different conditions .

      Thus the comparator output is toggled accordingly.

      As you said, LM311 is one such option where it is capable to give bipolar input and bipolar Vcc and also have ground-referenced logic level output which may directly be given to ISO7721.

    Thanks for your reply.

    Regards,

    Girish K

      

  • 0 in reply to Girish K76
    TI__Expert 4555 points
    Girish,

    Do you have any more questions regarding this topic? If not, this thread will be closed.

    Regards,
    Jonny