DRV8353RS-EVM: Test Points

Hello John,

Thanks for your questions.

Is the purpose of Test Points TP1 and TP6 to measure the waveform of Q1? Are TP2 and TP7 to measure the waveform of Q2? If yes, why there were no test points on VM to measure the waveform of Q4/Q5/Q6?

1. TP1, TP2, & TP3 are intended to measure the output to the motor, rather than having to use header J6. You can use a differential measurement across TP1 and TP6 to measure the VDS of Q1 (LS MOSFET), however in practice we are normally looking at these nodes with respect to ground. You can measure from VM to TP1 to capture the VDS of the high-side MOSFET, but we did not put as many test points to make it easy. You can use TP4.

Could the waveform of Q1 directly measured by probing the connector J6 Pin 3 (MOTC) and lower end of R14? If yes, could TP1 and TP6 be eliminated to save the board space?

1. 1. Yes, you can measure the Q1 VDS using the J6 connector (pin 1)  and one terminal of the low-side sense resistor (in this case R14)

TP6, TP7, TP8, and others are not listed in the BOM. Could they be assumed the same as TP1, TP2, etc.

1. These test points are just soldermask openings on the board - so they are not real components soldered on the board.
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The BOM shows TP1, TP2, etc are through-hole test points, which take 4~5 mm in diameter space each in the board. Could they be replaced by SMD test points, which is about 1 mm in diameter? If yes, could the voltage/current waveform of Q1/Q2/Q3 be probed using these SMD test points?

1. Yes, these test points can be replaced by SMD test points to the same effect

Majority of test points were placed next to power stage MOSFETs. I am wondering whether it is necessary to place test points on SOA/SOB/SOC pins, INHA/INLA/INHB/INLB/INHC/INLC pins, SPI pins, and/or nFault pin.

1. These signals are routed to J1 and J2 on the board, and when the launchpad is plugged in you do get easy access to all of these signals. You need to look up which signals are present on which pin of headers J1 and J2.
2. There is no issue adding additional test points on the MCU-DRV signals for easier access

Any advice/suggestions on where to place test points to facilitate the testing of the functionality of the motor drivers board would be greatly appreciated as they are not addressed in the SLVA959A, “Best Practices for Board Layout of Motor Drivers."

1. Test points need to be placed so that the main function of the circuit is preserved. Any additional test points should be added such that you do not need to make the layout worse to accommodate them. Place test points after the entire circuit has been routed,
2. Soldermask openings like TP6 are ideal because they do not interrupt any current path on the board and are easy to place anywhere
   
3. It helps to come up with a list of signals that need to be measured, and ensure there is test point coverage on all of those signals.
   1. VDRAIN, GHx, SHx, GLx, SPx, SNx, and GND  are required to observe the output.
   2. It is sometimes helpful to measure regulators like VCP, VGLS, and DVDD with test points, but it is normally not measured and but easy to solder a wire onto the bypass capacitor to make the measurement if needed.
      
   3. Digital signals to and from from the MCU (i.e. INHx and INLx, SPI) can be routed through a header or test point to facilitate easy measurements
   4. Analog outputs like SOx can have testpoints added but ensure that the capacitance added by these test points and additional routing does not exceed the capability of the amplifier. Using test points directly in line with the path from the DRV to the MCU is ideal.
   5. Placing a resistor in series with the gate drive outputs (GHx, GLx) can be very useful to measure the gate drive current if you have a differential probe. This component should be around 10 ohms.
      

Thanks,

Matt