Part Number: DRV8702-Q1
I have a DRV8702 running in independent half-bridge mode. When I drive the input IN1/PH the motor connected to half-bridge 1 is working as desired and the motor on half-bridge 2 is off.
When I drive the input IN2/EN the motor connected to half-bridge 2 is working but the motor on half-bridge 1 also makes some noise and the temperature of the DRV increases for about 15°C compared to driving the input IN1/PH. The following measurings show the problem.
Here is my circuit and the measurements:
Circuit for PWM_M2 is exactly the same as above.
Driving IN1/PH / Measuring IN1/PH --> OK
Driving IN1/PH / Measuring IN2/EN --> OK
Driving IN2/EN / Measuring IN1/PH --> NOT OK
Driving IN2/EN / Measuring IN2/EN --> NOT OK
I have the same problem with multiple boards.
Do you have any ideas why this could happen? How can driving IN2/EN cause such a signal at IN1/PH?
Thank you for helping
Hi Robin, Try connecting the MODE pin directly to DVDD with a 0-0hm resistor rather than through a 10 kOhm resistor. The mode pin is designed to sense a Hi-Z state using an internal voltage divider, and sometimes noise can impact the internal node voltage if there is an external impedance. Figure 32 in the datasheet shows the circuitry on the MODE pin.
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In reply to James Lockridge19:
In reply to Robin Maeder:
Thanks again for your response.
1) Remove the load from the FETs so no current flows. Do you still see the ringing on the inputs?
--> Done, no changes
2) Replace your sense resistor with a 0-ohm resistor or a short and recheck if there is ringing.
3) Measure the nets around your FETs with an oscilloscope. There may be some parasitic impedances caused by a difference in routing that causes one output to ring while the other one does not ring.
Blue: Output X5, Green: Source of FET Q10, Yellow: IN1
4) Measure the ground pin on the DRV8702-Q1 and on the low-side FET connected to GL2. Reference your probe to a quieter ground by connecting it directly to the supply ground.
Blue: Source at FET Q10, Yellow: GND at DRV
As you can see the ringing is on every signal I measured including the motor output. But the ringing on the GND pins can be measured also when driving input IN1. But I think the difference between the inputs is as you said the layout.
IN1 drives the bridge on the left, IN2 drives the bridge on the right. Layout is more or less identical. But as you cann see the traces for IN1 and IN2 (highlighted in blue) are routed under the output of bridge 2. I think the ringing of the output signal (blue signal on first pic) couples into the IN1/2 traces and causes the problem.
So I see two possibilities: Prevent the output signal from ringing or improve the layout (will be done for sure for next prototypes).
Do you have an idea how to reduce the ouptut ringing or is this normal?
Thank you for your help.
Thanks again for your help. I changed IDRIVE to the minimum (Pin 5 to GND) just to see the effect.
On the following pic the bottom signal shows the motor output 2 (without load) and the top signal shows IN2.
As you can see the ringing on the output is completely gone. But the peaks on IN2 are still there and pretty slow. And they are definitely at the time when the output is switched on and off.
Here a pic with IN2 on bottom and IN1 on top:
Again the peaks are on both signals when driving IN2.
Is it possible that even with such a slow switching (IDRIVE = 10mA/20mA) the output is distorting both signals that much just becuase the IN1/IN2 traces are layouted underneath the output 2?
I will check this, thank you.
Other question: Why ist the delay between the rising edge on IN2 to the ouptut rising edge about 5us?
The same is from IN2 to GH2 and also when driving the IN2 directly without any resistor in series.
The datasheet specifies a propagation delay of 500ns.
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