decay modes drv8432

Hi Anthony

You can refer to DRV8x datasheets for understanding of decay modes.

For basic, try DRV8825, DRV8818.

For advanced, check DRV8711 datasheet.

Thanks,

Wilson

It is my understanding, in order to achieve slow decay, i need to open the high side gates and close the low side. Can this be done with only control of A amd B? Secondly, how would i get fast decay? PWMing the enable? what do i then do with the A and B signals?

thanks

Hi Anthony

Iet me give an example.

If you want to do fast decay,

during PWM_ON time,

Hold PWM_A = 0, PWM_B = 1 (or PWM_A = 1, PWM_B = 0 according to your current direction),  nRESET_AB = 1.

during PWM_OFF time,

nRESET_AB = 0. HiZ all output for fast decay. So the PWM is feed to nRESET_AB.

if you want to do slow decay, keep nRESET_AB = 1 all the time.

during PWM_ON time,

Hold PWM_A = 0, PWM_B = 1 (or PWM_A = 1, PWM_B = 0 according to your current direction),  nRESET_AB = 1.

during PWM_OFF time,

Hold PWM_A = 0, PWM_B = 0 (or PWM_A = 1, PWM_B = 1 according to high side or low side slow decay). So your PWM is feed to one of the Phase, PWM_A or PWM_B.

Thanks,

Wilson

Motor Appliation Team

Anthony,

There is one more PWM sequence you can follow to get fast decay with DRV8432.

 during PWM_ON time,

 Hold PWM_A = 0, PWM_B = 1 (or PWM_A = 1, PWM_B = 0 according to your current direction),

 During PWM_OFF time

 Complement the PWMs i.e.Hold PWM_A=1, PWM_B=0 (or PWM_A=0, PWM_B=1).

 RESET_AB signal is always high and not required to for above sequence.

 The same logic can be implemented in DRV8432 by selecting mode pins as M3-0, M2-1, M1-1.

 Best Regards

Milan

Thanks for the advice, I'm going to try it out.  I do have question regarding both solutions, are they going to produce the same results?  Is one better than the other?  Also, you both said 'during PWM on time hold PWM_x'.  When you say hold, do you mean hold 1 or PWM, same for OFF time?

I only have PWM pins mapped to A, B, C, D and my resets are tied to standard GPIO pin (using two of these chips, and only have 8 PWM signals). 

Wilson, can you please clarify what you mean by PWM will be fed to the reset? 

thanks

Anthony,

1. The basic difference between two methods comes into picture during PWM off period. In first method, knows an asynchronous decay utilizes RESET to disable all four MOSFETs in bridge,   MOSFET body diodes conducts the current during PWM off period whereas in second method known as synchronous decay, MOSFETs conducts the current. For further details, refer to TI application note at http://www.ti.com/lit/an/slva321/slva321.pdf
2. To clarify your doubt about Hold, In first method PWM is applied to RESET input while PWM_X are kept continuously high or low and in second method PWM are applied to PWM_X inputs as per logic mentioned in the post while RESET input is continuously kept at high logic.

Best Regards

Milan- Motor application Team

Will there be a chip like DRV8825(similar functions and pins) with the power of DRV8432?

Giancarlo, to get above 2.5A with similar functionality to the DRV8825, we have the DRV8711.

Best regards,
RE

Excellent, it drives 2 H-bridge(8 n-mosfet)

Are you tested DRV8711 with a NexFET Power Block like CSD87352Q5D (SON 5x6mm)?
Does NexFET Block need external reverse diode to drive 5-10A stepper motor?

Replacing 4 n-mosfet by 2 NexFET Blocks(1H-bridge) i saw a fancy package.
Lacks vias (dissipation) and capacitor, is a draft.

Giancarlo,

The maximum recommended gate voltage for CSD87352Q5D (8V) is lesser than the gate output voltage of DRV8711 (10V typical) so it is not right fit.

You can definitely give try for power block with 20V gate voltage such as CSD87588N with DRV8711. All the synchronous NEXFETs blocks have inbuilt diode so external diode are not required as long as their reverse recovery characteristics does not significantly impact system efficiency and EMI noise performance.

Best Regards

Milan- Motor Application Team

Hi Milan

 I would like to review  with you FAST Decay   in this answer. without using a RESET_AB or CD

PWM_ON  , we use a DSP   PWM_A = PWMH1 ;PWM_B= PWML1; PWM_C= PWMH2; PWM_D = PWML2.

Let assume we move CW 

PWM_A=1, PWM_B=0; PWM_C=1, PWM_D=0;

In our dsp the PWM is set to complementary  outpout

PWMH1= PWM= PWM_A

PWML1=PWM=PWM_B

PWMH2= PWM= PWM_C

PWML2=PWM=PWM_D

PWM OFF

when H1 and H2 goes low  and L1 and L2 high

the motor does not move short due to a pulse CCW is done

Albert

Sorry I forgot in the previous msg. is any way to have FAST DECAY without using a RESET line 

Albert

 Albert,

Your PWM logic is correct to achieve fast decay. PWMA and PWM B should be complementary and similarly PWMC and PWMD also should be complementary to achieve fast decay.

In fast decay mode, PWM output is bipolar across H-bridge i.e. output toggles between +VM and –VM so at 50% duty cycle of PWM inputs, output voltage across motor is in fact zero. To rotate motor you should apply duty cycle from 50% to 100% for one direction and 50% to 0 for opposite direction.

Best Regards

Milan-Motor Application Team