DRV8702D-Q1EVM: The Evaluation Kit has a bug in the software related to the Sleep Button and other observations

Robert Cohen

Part Number: DRV8702D-Q1EVM
Other Parts Discussed in Thread: CSD18540Q5B, DRV8702-Q1EVM

The kit worked great once I found that the Sleep Button state was backward. I assumed Enabled was to drive the signal low. After using a DMM I found that the state was backwards. Once this was resolved the kit worked well.

Observations:

I am using a 24 volt motor with a 24 volt power supply. The test configuration was using the motor to lift 50 pounds of weight. I used a clamp current meter to measure the current during the test process. The current meter read 1 amp greater than the EVM software. I saw a high current of 4.9 Amps during the raising of the weight and the holding current to maintain the weight was 3.0 Amps. During the holding time I felt the FETs and was surprised by the heat dissipation. I am concerned that the FET will not be able to hold the weight for an extended period of time (months, years). I reviewed the FET's datasheet and found that they are very robust and should be able to handle my application. Below is the part number of the FET used on the evaluation board.

MOSFET, N-CH, 60 V, 28 A, SON 5x6mm

CSD18540Q5B

Texas Instruments

Question #1:

Has anyone else seen the reverse behavior of the Sleep Button?

Question #2

Was the evaluation board designed with significant heat dissipation to drive high current for 5 Amps?

Thank you

Rob Cohen

Smoke Guard

over 5 years ago

0 Wang5577 over 5 years ago

TI__Guru 56650 points

Rob,

On my bench test, "enable" drives nSLEEP pin high and enables the output. That is why we put "n" in front of "SLEEP". The logic matches the datasheet description.

5A should not be very hot. The FET's Rds_on is only about 1.8mohm. With 100% duty cycle (24V in and 24Vout), the power loss at 5A is about 1.8mohm x 5A x 5A = 45mW. Please measure the input and output current and voltage to verify your test condition when the board is hot.

0 Robert Cohen over 5 years ago in reply to Wang5577

Prodigy 80 points

All,

You are correct. Below are some tests that I ran to determine how much stress I could put on the motor before failure. The bottom line is the TI driver chip and FEts on the evaluation board worked great. I pushed them very had and they got hot but they performed great. I am going to incorporate the driver and FETs into my new design. I will use the design from the Evaluation kit with one minor change; Allow the Mode into to float to get into the appropriate mode. I just completed modifying the evaluation board to work with my Microchip D20 controller and it works great!

I recommend that if you ever revise the evaluation board that you add the ability to the float the MODE input line. I was easy enough to just pull the resistor off but it would be a nice feature.

Observation:

The only strange thing I saw was the current reading in the software was not the same I was reading on my clamp current meter. It was consistently off by 500mA to a 1 Amp.

Question:

Do you have any other recommendations in the design of the Driver and FETs that I should add, other than what is on the evaluation board.?

Thank you,

Rob Cohen

I did some testing with the new motor driver chip and FETs and had some good results.

Test Setup

Two 4.6Amp 24 volt supplies in parallel
The Evaluation kit from TI (DRV8702-Q1EVM) with software in Standard PWM Control
Groschopp Inc Motor PM6025, PN X10457-31, 24 V 3.55 Amps 58 Watts 29:1
Current meter (Clamp Type)
Thermocouple to DMM placed on a FETs
Volt meter to monitor power supply

Test #1

Objective: Using a curtain tube and motor lift 25 pounds and monitor the current and temperature of the chip to ensure that it does not go into thermal runaway.

Starting temperature was 74.6 F

TI SW PWM Value	TI SW Current Value	Clamp Current	Temperature	Motion	Time
56	1	1.2	85.4	Raising weight	1 min
58	1.5	2.3	95.7	Hold	5 min
58	1.5	2.3	98.5	Hold	20 min
58	1.5	2.3	98.0	Hold	30 min
58	1.5	2.4	97.8	Hold	40 min

Conclusion: The current in the software was different than the measured value. The temperature was stable over time. No thermal runaway.

Observation: Motor tube was warm.

Test #2

Objective: Objective: Using a curtain tube and motor lift 50 pounds and monitor the current and temperature of the chip to ensure that it does not go into thermal runaway.

Starting temperature was 74.6 F

TI SW PWM Value	TI SW Current Value	Clamp Current	Temperature	Motion	Time
60	3	5.4	105	Slow	---
70	3	5.2	105	Faster	---
60	2	3.6	105	Hold	5 min
60	2	3.6	106	Hold	10 min
60	2	3.6	107	Hold	15 min
60	2	3.5	107	Hold	20 min
60	2	3.3	107	Hold	30 min

Conclusion: The current in the software was different than the measured value. The temperature was stable over time. No thermal runaway.

Test #3

Objective: Objective: Using a curtain tube and motor lift 75 pounds and monitor the current and temperature of the chip to ensure that it does not go into thermal runaway.

Starting temperature was 74.6 F

TI SW PWM Value	TI SW Current Value	Clamp Current	Temperature	Motion	Time
60	2.8	3.3	95	Raise- Stop	---
65	3.0	4.9	103	Raise- Stop	---
70	5.0	6.3	108	Raise- Stop	---
73	6.0	6.9	115	Stopped	10 min
73	6.0	6.8	130	Stopped	15 min
73	6.0	6.9	128	Stopped	20 min
73	6.0	6.6	124	Stopped	25 min
73	5.6	5.8	126	Stopped	30 min
73	5.6	5.8	129	Stopped	35 min
73	5.6	5.8	129	Stopped	40 min
73	5.0	5.7	124	Stopped	45 min
73	5.6	5.8	130	Stopped	50 min
73	5.0	5.5	126	Stopped	55 min
73	5.6	6.2	130	Stopped	60 min
0	0	0	Dropping	Stuck/Frozen	------

Conclusion: The current in the software was different than the measured value. The temperature was stable over time. No thermal runaway. The motor tube was very warm and at the end of the experiment the motor would not release the load. Extreme heat was on the motor tube.

0 Wang5577 over 5 years ago in reply to Robert Cohen

TI__Guru 56650 points

Rob,

Great to hear your board working. Good feedback on the mode pin. I would write it down for future improvement.

Does the "Starting temperature" mean the ambient temperature?

I do see the GUI shows the current with offset. So, I checked the SO pin output to make sure IC work properly. The SO pin output looks nice which follows the winding current instantly and the gain is listed in the datasheet. I would think the GUI error may come from:
a. the sampling rate may not same as the PWM frequency
b. GUI may not average out the SO pin voltage ripple

0 Robert Cohen over 5 years ago in reply to Wang5577

Prodigy 80 points

Now that the system works I started to research every part in the evaluation board. I researched the FETs and found the values needed to calculate the IDRIVE value. The result of my calculation was off the chart.

The IDRIVE pin is not connected on the Evaluation board. It is currently in the 5-6 position, which is not connected to any resistor values. Therefore, I assume it is set to 150/300mA (SRC/SNK). It does not say anything in the data sheet about leaving it open sets these values.

In the data sheet for the FET the Qgd value is 6.7nC and the tr value (Rise Time) is 9ns

If I do the math…

IDrive= 6.7nC/9ns = .744 or 744mA

This is not even close to what is available! 500mA is the maximum shown on the schematic for the evaluation board.

According to the data sheet for the driver chip Section 9.2.2.2 IDRIVE Configuration, I must have a value set.

Question:
How does the evaluation board work with IDRIVE open? It there a default value set that I am not seeing?

Thank you,
Rob

0 Wang5577 over 5 years ago in reply to Robert Cohen

TI__Guru 56650 points

Rob,

In this case, one of your concern is the board too hot. So, we want to speed up the FET turn-on and turn-off time which requests higher IDRIVE current. Please make sure R(IDRIVE) = 1 kΩ to AVDD (datasheet page 8: spec table). That is the highest DRV8702D IDRIVE we can get.

If we count IDRIVE open as >2Mohm to ground, it is only give about half of the full current capability ((datasheet page 8: spec table). So, please put 1kohm between IDRIVE and AVDD to get full IDRIVE current.

In another e2e post (e2e.ti.com/.../729724), it talks about how to set IDRIVE. Hope it can help you a little bit.

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DRV8702D-Q1EVM: The Evaluation Kit has a bug in the software related to the Sleep Button and other observations