DRV8714-Q1: Duty cycle limitation

Hello Scarlett,

The min duty cycle is constrained by the rise and fall times. propagation delay and dead time requirements. The min length pulse would be on the order of t_r+ t_pd + t_dead + t_f.. For the DRV8873 if SR was connected to ground and VM was 12 V, then it would be:

 (12 [V] / 53.2 [V/us])*2 + 1.5 [us] + 0.5 [us] = 2.45 us

The CSA accuracy will be impacted when the duty cycle gets low and the current being sense also gets low. The readings will be less accurate due to the input offset voltage on the CSA having a bigger impact on lower voltage across R_shunt from the lower current.

You can try to use the same approach described in the other linked e2e, where if they wanted 100% duty cycle, then they switched to DC/continuous instead of PWM.

Best, 

Keerthi 

Hi, expert

What is the maximum frequency that DRV8714 can achieve to the duty cycle of 5% or 95%? Does it still depend on the selection of external MOS? Or other reasons?

Best, 

hanbin

Hello Hanbin,

The maximum frequency is determined as follows:

The minimum on time as described above is 

t_min = dead time + rise time + fall time

For external FETs the

rise time/fall time = Qgd/ Idrive

Then the maximum frequency for 5% duty cycle is 

f_max = 1/ (t_min/0.05)

Best,

Keerthi 

Hi, expert

Thank you for your reply.

I would also like to know the current monitoring accuracy of DRV8714?

Hi Hanbin,

Refer to this e2e, which talks about a very similar device and page 18 of the datasheet

https://e2e.ti.com/support/motor-drivers-group/motor-drivers/f/motor-drivers-forum/1228923/drv8718-q1-about-pwm-control-and-csa-gain?tisearch=e2e-sitesearch&keymatch=DRV8718-Q1

Best,

Keerthi 

Hi, expert

The link refers to is amp's slew rate (V/us).

However,  I want to know is the accuracy of current monitoring，exp

Best, 

hanbin