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Original question:

BQ25710: MOSFET selection from gate driver

BQ25710: REGN current capability

Kazuto Tatsumi
Intellectual 2820 points
Part Number: BQ25710
Other Parts Discussed in Thread: CSD17551Q3A

Hi Team,

The customer needs to know the gate drive ability of REGN. Could you share V-I curve of REGN?

If the calculation below is appropriate to get the drive current, V_regn at 96mA must be higher than V_th, correct?

I_drv = Qg * [number of MOSFET] *Fsw
         = 30nC * 4 * 800kHz
         = 96mA

(All of FETs are not turn on at the same time, so number of MOSFET should be *2?)

Regards,
Kazuto

  • 0
    TI__Genius 11850 points

    Hi Kazuto,

    The REGN current limit has a typical value of 65 mA when the converter is enabled, as shown in the EC table. We can't share the full V-I curve, but 65 mA is conservative based on our testing. The REGN voltage is still 6 V even with loads slightly higher than 65 mA.

    Regarding your gate drive current calculation, only 2 FETs will be switching at 800 kHz at the same time, so you should multiply by 2 instead of 4. Overall, the REGN current capability should be enough to support the customer’s application with 30 nC FETs, but please make sure the customer validates their design just to be safe. You can use the BQ25710 EVM to assist with evaluation.

    Lastly, what FETs are the customer using? Qg = 30 nC is significantly higher than the Qg of the CSD17551Q3A FETs that are used on the EVM, which have Qg = 6 nC at Vgs = 4.5 V. In our experience, FETs with Qg as high as 30 nC is overkill for efficiency because the switching loss dominates instead of the conduction loss.

    Best regards,

    Angelo

  • 0 in reply to Angelo Zhang87
    TI__Intellectual 2820 points

    Hi Angelo,

    Thanks for your suggestion. I need to confirm about the REGN current limit. 65mA is tested by force VREGN=4V, but you said VREGN can be 6V even with loads slightly higher than 65mA, is that really correct?

    Regards,
    Kazuto

  • 0 in reply to Kazuto Tatsumi
    TI__Genius 11850 points

    Hi Kazuto,

    I have emailed you some more data regarding the REGN current capability. The REGN current limit has a typical value of 65 mA when the converter is enabled, which should be enough to support the customer's application with 30 nC FETs. However, we would still recommend that the customer use lower Qg FETs, such as the CSD17551Q3A FETs that are used on the EVM. This should reduce the switching losses.

    Best regards,

    Angelo

  • 0 in reply to Angelo Zhang87
    TI__Intellectual 2820 points

    Hi Angelo,

    I understood. Thanks for your suggestion!

    Regards,
    Kazuto