DRV8305: There is a thermal noise issue in the motor drive

Hi Cherry,

Thank you for the question! I believe one change the customer should make is to use a buck that has an output between 4.4V and 45V (4.3V is a little low, see the attached image). The DRV 8305 has an internal LDO to handle voltages like these. This may be a commutation issue. That said, I'll get back to you with a better answer tomorrow.

Best,

Eli

Hi Eli,

Thank you for the support.

They are using an adjustable regulated power supply of 12v and drv8305 is forced down to 4.3V when it's operating.

Thanks and regards,

Cherry

Hi Cherry,

Thank you for the clarification. The device is specified to operate within the recommended ratings in the datasheet and that recommended operation is between 4.4V and 45V. The current voltage being used is below the recommended operating conditions. It can operate lower (as low as 4.3V) with the LDO but this will not drive the motor or yield good performance. Please let me know if operating at a higher voltage does not solve the issue.

Best,

Eli

Hi Eli,

The 12V adjustable power supply is provided above and the driver board drops to 4.3V during operation, which is not the normal operating range. The motor drive board was originally powered from a 12V (error 1V) battery and converted to 3.3V by an LDO chip. 

The following details are based on the 12v battery powered, six-step control method:

With the motor unconnected, the voltage at which the drive board is operating is shown in the figure below.

It can be seen that the outputs of GHA, GLA, and SHA are good.

When the motor is connected, the drive board stops working for no more than 0.3 s, the outputs of GHA, GLA, and SHA are shown below:

PVDD = 12v, Vcc = 3.3V before the driver board is not working.

However, the failure occurs and stops in less than 0.2 s after the start of operation, and PVDD and Vcc have changed, as shown in the figure below:

The entire drive board does not work and the voltage at PVDD and VCC are as follows: 

Thanks and regards,

Cherry

Hi Cherry, 

Today is a US holiday, so many of our team members are out of office currently, returning later this week - please anticipate a delayed response 

Best Regards, 
Andrew 

Hi Cherry,

Is the fault still listed as PVDD_UV or is it different? Also, what is the customer's slew rate?

Best,

Eli

Hi Eli,

Eli Sorenti-Burns said:

Is the fault still listed as PVDD_UV or is it different?

The DRV8305 register information returned by the driver board is shown below.

Register 16 is represented as b10-b0, for example 0b 100 1000 0001 is represented as 481 and 0b 000 0000 0001 is represented as 1. The drive flow of the driver board operates on the drv8305 as follows: Power up → Initialization → six step control.

It can be seen that PVDD_UVFL and VCPH_UVFL report errors for a short period of time when the fault occurred, after which the entire register information is always 0. 

Eli Sorenti-Burns said:

Also, what is the customer's slew rate?

Mosfet being used is IRFH7085PbF, MOSFET _QGD=36NC is specified in datasheet.

MOSFET _{Slew Rate1} = 36 nC (QGD) / 60 mA (IDRIVEN) = 600 ns

MOSFET _{Slew Rate2} = 36 nC (QGD) / 50 mA (IDRIVEP) = 720ns

Thanks and regards,

Cherry

Hi Eli,

The following figure shows the information about the components surrounding the drv8305 chip in the design driver board schematic. VBat_D = PVDD = 12v, VCC3.3V = Vcc = 3.3V in the figure. C22 and C23 are rated for 50V nominal and should be fully adequate. Is there anything that can be improved? 

Thanks and regards,

Cherry

Hi Eli,

The customer tested with 2.2uf/50V and 4.7uf/50V capacitors, but the problem still persists:

Thanks and regards,

Cherry

Hi Cherry,

I'll align with the team and get back to you on this by Friday.

Best,

Eli

Hi Cherry,

Thank you for your patience. Can the customer give VCPH to GHx and VCP_LSD to GLx resistance measurements? Can they also send over waveforms of the charge pump relative to GND? Have they tried connecting their motor to an EVM and seeing if the issue persists when it is not their board being used? Can they measure AVDD when the issue occurs?

Best,

Eli

Hi Eli,

After the customer has wired the evaluation board of the DRV8305 to the base board of the STM32, the test results are as follows: 

//dead loop

if(g_iMotorPFlag)

{

 g_iMotorPFlag=0;

count1++;

liubukongzhi(count1);

if(count1>=6) count1=0;

}

 //Six-step control method 

void liubukongzhi(int j)

{

    switch(j)

    {

        case 1:

            HAL_GPIO_WritePin(INH_A_GPIO_Port,INH_A_Pin,GPIO_PIN_SET);//A+

            HAL_GPIO_WritePin(INL_A_GPIO_Port,INL_A_Pin,GPIO_PIN_RESET);    

            HAL_GPIO_WritePin(INH_B_GPIO_Port,INH_B_Pin,GPIO_PIN_RESET);

            HAL_GPIO_WritePin(INL_B_GPIO_Port,INL_B_Pin,GPIO_PIN_SET);//B-  

            HAL_GPIO_WritePin(INH_C_GPIO_Port,INH_C_Pin,GPIO_PIN_RESET);

            HAL_GPIO_WritePin(INL_C_GPIO_Port,INL_C_Pin,GPIO_PIN_RESET);

            break;

        case 2:                

            HAL_GPIO_WritePin(INH_A_GPIO_Port,INH_A_Pin,GPIO_PIN_SET);//A+

            HAL_GPIO_WritePin(INL_A_GPIO_Port,INL_A_Pin,GPIO_PIN_RESET);    

            HAL_GPIO_WritePin(INH_B_GPIO_Port,INH_B_Pin,GPIO_PIN_RESET);

            HAL_GPIO_WritePin(INL_B_GPIO_Port,INL_B_Pin,GPIO_PIN_RESET);    

            HAL_GPIO_WritePin(INH_C_GPIO_Port,INH_C_Pin,GPIO_PIN_RESET);

            HAL_GPIO_WritePin(INL_C_GPIO_Port,INL_C_Pin,GPIO_PIN_SET); //C-

            break;

        case 3:                

            HAL_GPIO_WritePin(INH_A_GPIO_Port,INH_A_Pin,GPIO_PIN_RESET);

            HAL_GPIO_WritePin(INL_A_GPIO_Port,INL_A_Pin,GPIO_PIN_RESET);    

            HAL_GPIO_WritePin(INH_B_GPIO_Port,INH_B_Pin,GPIO_PIN_SET);//B+

            HAL_GPIO_WritePin(INL_B_GPIO_Port,INL_B_Pin,GPIO_PIN_RESET);    

            HAL_GPIO_WritePin(INH_C_GPIO_Port,INH_C_Pin,GPIO_PIN_RESET);

            HAL_GPIO_WritePin(INL_C_GPIO_Port,INL_C_Pin,GPIO_PIN_SET);//C-

            break;

        case 4:                

            HAL_GPIO_WritePin(INH_A_GPIO_Port,INH_A_Pin,GPIO_PIN_RESET);

            HAL_GPIO_WritePin(INL_A_GPIO_Port,INL_A_Pin,GPIO_PIN_SET);//A-

            HAL_GPIO_WritePin(INH_B_GPIO_Port,INH_B_Pin,GPIO_PIN_SET);//B+

            HAL_GPIO_WritePin(INL_B_GPIO_Port,INL_B_Pin,GPIO_PIN_RESET);    

            HAL_GPIO_WritePin(INH_C_GPIO_Port,INH_C_Pin,GPIO_PIN_RESET);

            HAL_GPIO_WritePin(INL_C_GPIO_Port,INL_C_Pin,GPIO_PIN_RESET);

            break;

        case 5:                

            HAL_GPIO_WritePin(INH_A_GPIO_Port,INH_A_Pin,GPIO_PIN_RESET);

            HAL_GPIO_WritePin(INL_A_GPIO_Port,INL_A_Pin,GPIO_PIN_SET);//A-

            HAL_GPIO_WritePin(INH_B_GPIO_Port,INH_B_Pin,GPIO_PIN_RESET);

            HAL_GPIO_WritePin(INL_B_GPIO_Port,INL_B_Pin,GPIO_PIN_RESET);    

            HAL_GPIO_WritePin(INH_C_GPIO_Port,INH_C_Pin,GPIO_PIN_SET);//C+

            HAL_GPIO_WritePin(INL_C_GPIO_Port,INL_C_Pin,GPIO_PIN_RESET);

            break;

        case 6:                

            HAL_GPIO_WritePin(INH_A_GPIO_Port,INH_A_Pin,GPIO_PIN_RESET);

            HAL_GPIO_WritePin(INL_A_GPIO_Port,INL_A_Pin,GPIO_PIN_RESET);    

            HAL_GPIO_WritePin(INH_B_GPIO_Port,INH_B_Pin,GPIO_PIN_RESET);

            HAL_GPIO_WritePin(INL_B_GPIO_Port,INL_B_Pin,GPIO_PIN_SET);//B-

            HAL_GPIO_WritePin(INH_C_GPIO_Port,INH_C_Pin,GPIO_PIN_SET);//C+

            HAL_GPIO_WritePin(INL_C_GPIO_Port,INL_C_Pin,GPIO_PIN_RESET);

        break;

    }

}

 

Hi Cherry,

Thank you for the response. I'll align with my team and get back to you by Tuesday. In the meantime, would you be able to ask the customer if they could provide the following?

- Waveforms of the charge pump relative to GND

- More details regarding your power supply. Can the customer switch out their power supply and try a new one and give us waveforms of the performance? This seems to be the main issue as the faults are all PVDD_UV, CP_UV and AVDD_UV errors and the capacitor ratings seem to be good.

Thank you for your patience.

Best,

Eli

Hi Eli,

Eli Sorenti-Burns said:

- More details regarding your power supply.

The power supply is one MD-3010D adjustable power supply and the other is a 12-V battery. 

Customers are currently testing with the DRV8305-EVM evaluation board and using the six-step driving method to drive the DRV8305-EVM evaluation board, the output voltage of the adjustable power setting (i.e. PVDD) is 12V. The adjustable power supply shows that the output voltage drops to 7.3 V and the output current is 9.4 A during the six-step drive method. VVCPH-GND and VPVDD-GND are measured by the oscilloscope to be 12.4 V and 5.27 V, respectively. Battery power stops working for a short period of time after start-up and cannot be measured.

The adjustable power supply works properly when driving the same motor in other motor drive schemes, so they assume it's not a problem with the power supply. 

BTW, the customer is wondering if TI's MCU and motor drive scheme are required to use the DRV8305? Can the DRV8305 be compatible with other external motor drive schemes? Like odrive, simplefoc, stmc, and so on? 

Thanks and regards,

Cherry

Hi Cherry,

Thank you for the reply. I'll align with my team and get back to you on Wednesday.

Best,

Eli