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CSD19534Q5A: Mosfet driver for reducing switching losses and better efficiency

d_zero
Genius 4490 points
Part Number: CSD19534Q5A
Other Parts Discussed in Thread: LM5176, LM5175, , LM5114, UCC27511A, CSD

Dear *,

i want to use CSD19534Q5A as low side output switch in buck-boost converter ( LM5176 CCM or LM5175 DCM).

a)

Do we need a mosfet driver between LM517X LDRV2 pin and the gate of the CSD19534Q5A mosfet ? ( max Fsw of LM517X is 500kHz)

b) 

if the driver is not needed but will lower the switching losses, what is the right way to choose one regarding to driver driving current capability?

c) 

what is the reasonable driver rise and file time (ns) to choose for CSD19534Q5A regarding to drive current , Fsw of the LM517X , Ciss 1000pF, Qg 17nC @ gs=10V and how it is calculated?

d)

how is the output voltage of the driver related to driver power supply ( Vcc) ? Vout= Vcc? So if Vgs needs 10V then set the VCC of driver to 10V?

e) we would like to choose newer driver IC regarding to cost defective solution.

Would you recommend one of the following IC LM5114 or UCC27511A?

Best Regards.

  • 0
    TI__Mastermind 29535 points

    Hi David,

    Thanks for your inquiry. I support the MOSFETs and will have to send your questions to the controller applications team. I checked and both the LM5175 and LM5176 have integrated 2A gate drivers which should be adequate to drive the CSD19534Q5A.

  • 0 in reply to John Wallace1
    TI__Guru 68725 points

    Hi David,

    First, thanks to John for his comments about the FETs, and the LM5175/76 driver.

    Why do you choose an 100V FET while the LM5175/76's max voltage rating is just 60V?  Do you mean your VIN or VOUT is close to 100V?  If so, you will have to employ the external driver, at least for the high side FETs.  You will also need to add a small external circuit additional to the driver to support 100% duty cycle.

    Answers to your other questions:

    c) With any driver and MOSFET, the rise and fall time can be estimated by the following equation:

    Idr_source * tr = Qg_total;  of Idr_sink * tf = Qg_total

    d) The IC's driver voltage is basically VCC, which is about 7.5V, with 8.5V as its abs max rating. So, do not apply >8V to VCC of the LM5175/76.  For external driver, please check the driver datasheet.

    e) Either should work but let me direct the question to our driver group for their advice.

    We wish to review your final schematic for a sanity check. You may send to us TI local sales team, if you don't want to post here. 

    Thanks,

    Youhao Xi, Applications Engineering 

  • 0 in reply to Youhao Xi
    TI__Genius 13445 points

    Hello Youhao,

    I would recommend using UCC27511A as it is one of latest, most optimized IC to drive the 17nC gate charge from CSD MOSFETs. 

    The 4A/8A drive current is largely sufficient to quickly turn-on/off the gate for fast rise at of Idrain. UCC27511A has wider VDD operating range allowing you sufficient margin against transients overvoltage. 

    While you're using this IC, please ensure that operating conditions are within the recommended operating conditions specified in Table 7.3 from the datasheet.

    Regards,

    -Mamadou