DRV8316: Cannot change output slew rate of DRV8316 using SPI

Andrew Chen

Part Number: DRV8316

Hi there,

I have an issue changing the slew rate and dead time of the DRV8316 SPI variant.

When probing the output of the DRV8316 using an oscilloscope, the duty cycle is distorted due to too much dead time being inserted. The dead time seems to be around 2.5us, which matches the dead time for slew rate of 25v/us. However, I have set the slew rate to 200v/us using SPI. Delay compensation is not enabled and I am using 3x PWM.

Here is the code that is used to writes the registers on the DRV8316. The registers should have been written successfully as the device is using 3xPWM correctly.

// format (r=1,w=0),(register 6bit),(even parity),(register data 8bit)
// 0,000011,1,00010011
drv8316communicate(1811, spi_buf);
// 0,000100,0,00011100
drv8316communicate(2076, spi_buf);
// 0,000101,1,00000001
drv8316communicate(2817, spi_buf);
// 0,000110,1,00010001
drv8316communicate(3089, spi_buf);
// 0,000111,0,00000001
drv8316communicate(3585, spi_buf);
// all other registers are left untouched

Trying to write other slew rates to the register results in the same behaviour.

Here is an oscilloscope screenshot showing the input (purple) and driver output (yellow) for 1 channel. Notice the time from the output going below 0v to the time it goes to supply voltage is 2.5us.

In case this is an issue with the preproduction batch of chips, the lot number on the esd bag label is 1159778wdp and the markings on the chips are PDRV 8316X1 TI 148 AH2E G4.

Can someone please provide an explanation of why the dead time is longer than it is meant to be?

Thanks!

over 2 years ago

0 Aaron Barrera over 2 years ago

TI__Mastermind 26046 points

Hi Andrew,

Some basic questions first to clarify the application:

1) Have you tested that SPI writes and reads are working correctly? i.e. if you write a register and read it back, you get back the data you wrote into that register? Ensure clock polarity and clock phase is set correctly in the SPI initialization. We have an E2E FAQ on SPI configuration and use, and we even have an example with SPI using a C2000 MCU: e2e.ti.com/.../faq-spi-configuration-and-use

2) What type of commutation are you using, trapezoidal or sinusoidal control? The current direction can affect dead time measurements due to the DRV8316's state machine to switch the integrated MOSFETs. This app note explains more: https://www.ti.com/lit/pdf/slvaf84

3) Does this happen with the motor unconnected as well, or only when the motor is spinning?

Thanks,
Aaron

0 Andrew Chen over 2 years ago in reply to Aaron Barrera

Prodigy 160 points

Hi Aaron,

SPI writes should be working correctly, as I am able to change the device from 6xPWM (default) to 3xPWM mode. However, I am having some issues with SPI reads not returning expected values. Also after the first few commands, the DRV8316 returns nothing. See oscilloscope screenshots.

nSCS yellow, SCLK purple, SDO cyan, SDI green

First SPI command after power on: unlock registers, expected return value 00010001

Second SPI command: Set 3xPWM and slew rate to 200v/us, expected return value 00011000

Third SPI command: Enable overtemp warning report, expected return value 00000000, from this point onwards SDO always stays low and returns zero for every command.

Then the rest of the commands are sent. No response is received from the driver. The CSA gain register is set to 0.3v/a, which has been tested and is working as expected. This suggests that register writes are succeeding but reads are failing.

After all registers are set, SPI register read back for the slew rate register is attempted, but it returns nothing.

For the commutation type, I am using FOC, but there are some unrelated issues with the brushless motor's sensor, so for these tests a brushed motor has been connected to one of the phases. Current is flowing out of the phase. A 50khz PWM with constant duty cycle is being applied by the microcontroller.

With no load on the output, the issue still occurs. But with no load the dead time reduces slightly to 2.4us.

I hope you can give me some furhter insight into the cause of these issues.

Thanks!

0 Anthony Lodi over 2 years ago in reply to Andrew Chen

Motor drivers

Motor drivers forum

DRV8316: Cannot change output slew rate of DRV8316 using SPI