• State TI Thinks Resolved
  • Locked Locked
  • Replies 7 replies
  • Answers 3 answers
  • Subscribers 64 subscribers
  • Views 310 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.

BQ76200: FET Driver IC Capability

Bhanu Sandeep Pothana
Prodigy 20 points
Part Number: BQ76200

Tool/software:

We are using BQ76200 FET Driver IC in our Design . Which will turn ON 32 FETs with 16 charge and 16 Discharge FETs. We have kept Three 3.3uF (total of 9.9uF) capacitor in parallel across VDDCP and BAT pins.

And CHG Mosfet has a Total Gate charge of 87nC for each FET and DSG Mosfet has a Total Gate charge of 67nC for each FET. Also has a10E series resistor for all Gate pins.

Whether the BQ76200 is capable to drive the 32 FETS at a time.

Please confirm this design possibility ASAP.

  • 0
    TI__Genius 16205 points

    Hello Bhanu,

    32 FETs in total for CHG and DSG should be possible, however, we have not tested it ourselves.

    I would recommend following Section 6 VDDCP Capacitance Reference Table in the FET Configurations for the bq76200 High-Side N-Channel FET Driver app note to make sure you scale the total FET input capacitance and charge pump capacitance appropriately. I believe with the current values you have shared for them; it may not be enough.

    The 10-ohm series resistor is fine for the gate resistance.

    Best Regards,
    Alexis

  • 0 in reply to Alexis_H
    Prodigy 20 points

    Hello Alexis,

    Thanks for the quick response.

    With the calculation of VDDCP capacitance from Reference table we got the value as 16X470nF=7.5uF we have kept Three parallel 3.3uF which is 9.9uF is this ok to keep or we have to keep 7.5uF only. Please confirm. If it is not enough can you please share the correct value for 32FETs.

    What is the charge value for BQ76200 Gate Driver chip. Whether it is enough to Drive or turn ON 32FETS at a time. In my previous mail I have mentioned the Max gate charge values of the Mosfets which we have used in our design

  • 0 in reply to Bhanu Sandeep Pothana
    TI__Mastermind 42060 points

    Hello Bhanu,

    What MOSFET do you use?

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    Prodigy 20 points

    Hello Luis,

    For Charge : TPH2R408QM,L1Q

    For Discharge: TPH3R70APL1

  • 0 in reply to Bhanu Sandeep Pothana
    TI__Mastermind 42060 points

    Hello Bhanu,

    The capacitance you calculated is much larger than what is needed.

    The input capacitance for these is a max of 6300pF for the DSG FET and 8300pF for the CHG FET.

    For 32 MOSFETs (16 each) this would be 233.6nF, at a ratio of 23.5 (As it is explained in the application note), you would require a Vddcp capacitor of ~5.5uF. This is assuming the maximum input capacitance from the datasheets. If we assume the typical values, the required Vddcp capacitance may be smaller. You can calculate it as I did above.

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    Prodigy 20 points

    Hello Luis,

    Thanks for the calculated Values, I have few other queries.

    1. What effects will it show if I keep Vddcp as 9.9uF?

    2. The Gate Series Resistance I have kept as 10 OHM so the Gate Current Ig=Vgs/Rg=10/10=1A. i.e., Will the Gate current consumption be 1A. Should I need to change the Series resistance. Is my calculation is correct or not? Please suggest.

    3. In this Application note https://www.ti.com/lit/an/slua794/slua794.pdf?ts=1738309768007 the Cf and Cb is written as 10nf but I have kept 100nF in my design. And Rdsg, Rchg values started from 100 Ohms to few KOhms but I have kept 10 Ohms. Do I need to change these values?

    4. Can I know the values of Internal Resistance of BQ76200 references Ri1,Ri2,Ri3,Ri4,Ri5,Ri6 ?

    5. What is the Output Charge of BQ796200 FET Driver IC? 

    Please provide these information.

  • 0 in reply to Bhanu Sandeep Pothana
    TI__Mastermind 42060 points

    Hello Bhanu,

    1. What effects will it show if I keep Vddcp as 9.9uF?
    We have not characterized the device up-to this capacitance. However, it is likely going to slow-down how long the charge-pump takes to initially turn-on or recover from large transients.

    2. The Gate Series Resistance I have kept as 10 OHM so the Gate Current Ig=Vgs/Rg=10/10=1A. i.e., Will the Gate current consumption be 1A. Should I need to change the Series resistance. Is my calculation is correct or not? Please suggest.
    No, this is not accurate. The turn-on of a MOSFET is not linear and our driver cannot provide 1-A of DC current neither. The gate series resistance's main purpose is to help mitigate any parasitic oscillations during the switching a MOSFET. A larger value or Ferrite bead may dampen oscillations better. 

    3. In this Application note https://www.ti.com/lit/an/slua794/slua794.pdf?ts=1738309768007 the Cf and Cb is written as 10nf but I have kept 100nF in my design. And Rdsg, Rchg values started from 100 Ohms to few KOhms but I have kept 10 Ohms. Do I need to change these values?
    I'll recommend following the recommendations from the application note. Change them if they do not match recommendations.

    4. Can I know the values of Internal Resistance of BQ76200 references Ri1,Ri2,Ri3,Ri4,Ri5,Ri6 ?
    These are not explicitly given. But you can look at Table 6.5 Electrical Characteristics - CHARGE /DISCHARGE FET DRIVER of the datasheet to see what the internal resistance of the drivers is when ON/OFF

    5. What is the Output Charge of BQ796200 FET Driver IC? 
    The datasheet has the characterization specifications of the FET drivers. 

    Best Regards,

    Luis Hernandez Salomon