• State Resolved
  • Locked Locked
  • Replies 1 reply
  • Subscribers 30 subscribers
  • Views 347 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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:

DRV3245Q-Q1: DRV3245Q-Q1

DRV3245Q-Q1: DRV3245Q-Q1 external capacitors selection

Sadek KADRI
Prodigy 35 points
Part Number: DRV3245Q-Q1

Hello,

I have questions about the external bulk capacitors values for PVDD, VCPH, VCP_LSD, AVDD & DVDD.

In your datasheet "SLVSEE4B –NOVEMBER 2017–REVISED OCTOBER 2019" at Table 34, you have recommended some values for external power supplies capacitors.

What happen if we double the recommended value for each supply line, can we expect a Gate Driver reaction if such value is too high like 5 times or 10 times than the recommended (is there no impact, slow start-up time,...)

Same question if we take the half of recommend values or a too low value until 5 or 10 times than the recommended (no impact, ripples...)

Thanks for your answer.

Sadek KADRI

Design Expert at HELLA, Toulouse, France

  • 0
    TI__Mastermind 18981 points

    Hi Sadek,

    Here are some comments below on the proposal items you mentioned: 

    1. PVDD - we recommend >10uF bulk caps placed very close to the DRV IC to prevent the PVDD-level voltage bias from sagging during high current consumption
      1. increasing this should not really have too much problem since the point is to store charge for when it's needed. Excessively high values can slow down your PVDD turn-on time, so device power-on might be delayed slightly 
      2. decreasing this has the opposite effect. If system can't guarantee the PVDD pin can have proper voltage during high-current conditions, then a transient undervoltage spike can trigger under-voltage lockout and then shut off the DRV IC until voltage is restored. your SPI settings will get wiped during this time, I think. 
    2. VCPH - charge pump storage cap. Meant for HS gate-driver voltage to the pre-drivers. 
      1. would not recommend changing this cap value at all. Related are also CPH/CPL 'flying' cap which switches from the charge-pump regulator circuit to transfer charge to the storage cap. 
      2. Too high/low means stability problems for the charge-pump and the charge pump might not maintain the needed voltage to work, directly impacting your gate-driver capability 
    3. VCP_LSD - capacitor for regulator meant to provide LS gate-drive voltage to the pre-drivers
    4. AVDD - capacitor for AVDD (5V) level LDO, I believe. 
    5. DVDD - capacitor for DVDD (3.3V) level LDO, I believe 

    In the case of #3,4,5 for VCP_LSD, AVDD, DVDD: 

    • Because these are LDOs, I believe the caps here serve two functions - one is to act as a sort of output bulk cap to prevent the voltage from changing very rapidly from transients
    • the other might also be to act as a bypass-capacitor to filter out high frequency noise 
    • having too high of a value in any of these cases means that the DRV IC will take longer to power up and clear all the regulator-associated undervoltage fault conditions before gate drive operation can begin
      • having too low of a value means that the cap will not be as effective at maintaining voltage stability
      • if DVDD/AVDD voltage are unstable, this will cause major problems with the DRV device's digital core, current shunt amplifiers, and etc 

    Thanks and Best Regards, 
    Andrew