• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Subscribers 29 subscribers
  • Views 353 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.

DRV8889-Q1: Relationship between SLEW_RATE/Blanking_Time and output slew rate

Yoshiki Ochi
Expert 7555 points
Part Number: DRV8889-Q1

Hello team,

This is Ochi. I have a question for a relationship between SLEW_RATE/Blanking_Time and output slew rate tSR.

Does SR in p.6 mean SLER_RATE in Table8?

As shown in 6.5 (Electrical characteristics, p.6), tSR are 10, 35, 50, and 105V/us if SR=00b, 01b, 10b, and 11b respectively. Also, I saw a relationship table between SLEW_RATE and Blanking_Time in Table8 (Blanking time). Could you tell me these relationship?

Best regards,

Ochi.

  • 0
    TI__Guru** 114905 points

    Hi Ochi-san,

    Please note the latest datasheet online SLVSEE9 -- April 2019 shows tSR on page 7.

    Does SR in p.6 mean SLER_RATE in Table8?

    Yes, SR means Slew Rate in Table 8, and SLEW_RATE[1:0] in Register 0x03 of Tables 13 and 20.

    As shown in 6.5 (Electrical characteristics, p.6), tSR are 10, 35, 50, and 105V/us if SR=00b, 01b, 10b, and 11b respectively. Also, I saw a relationship table between SLEW_RATE and Blanking_Time in Table8 (Blanking time). Could you tell me these relationship?

    The blanking time is adjusted based on the slew rate. This allows the output to fully switch at maximum voltage prior checking for an overcurrent condition.

  • 0 in reply to Rick Duncan
    TI__Expert 7555 points

    Hello Rick,

    thank you for your reply.

    Could you tell some trade-offs to decrease blanking-time (or increase slew rate)?

    I guess ripple of motor voltage and motor current increase in this case. Is it correct and are there any other trade-offs?

    Best regards,

    Ochi

  • 0 in reply to Yoshiki Ochi
    TI__Guru** 114905 points

    Hi Ochi-san,

    Increasing the slew rate can lead to:

    slower PWM switching frequencies
    more heat due to FET turn on being slower -- this can be a tradeoff because the higher switching frequencies may create more switching losses
    more current ripple
    minimized radiated emissions

  • 0 in reply to Rick Duncan
    TI__Expert 7555 points

    Hello Rick,

    thank you for supporting.

    Could you tell me the trade-off among slew rate and other parameters again? 

    I thought increasing slew rate can lead to faster PWM switching frequency. Also, I thought more current ripple leads to more radiated emissions.

    Best regards,

    Ochi

  • 0 in reply to Yoshiki Ochi
    TI__Guru** 114905 points

    Hi Ochi-san,

    Sorry for the confusion.

    I meant to say decreasing (changing from 105V/us to 10V/us) in the prior response.

    To restate the prior response,

    Decreasing the slew rate can lead to:(changing from 105V/us to 10V/us)

    slower PWM switching frequencies
    more heat due to FET turn on being slower -- this can be a tradeoff because the higher switching frequencies may create more switching losses
    more current ripple
    minimized radiated emissions

    Increasing the slew rate can lead to: (changing from 10V/us to 105V/us)

    faster PWM switching frequencies
    less heat due to FET turn on being slower -- this can be a tradeoff because the higher switching frequencies may create more switching losses
    less current ripple
    more radiated emissions

    Please note these are general statements. This could change based on system voltage, inductance, and decay mode selections.