DRV8873: DRV8873

Thank you for your helpness.

First of all, I will try to check the thermal condition wth the EVM kit.

It has arrived at my office this evening.

thank you ..

Hi, Wang Li

The EVM Kit (DRV8873H-Q1EVM) has been in my lab.

It is working well.

This time, I have some questions for the current sensing function of the driver chip.

According to the data sheet as blow as,

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8.2.1.3 Sense Resistor
For optimal performance, the sense resistor must have the following features:
• Surface-mount device
• Low inductance
• Placed closely to the motor driver device
Use Equation 10 to calculate the power dissipation (PD) of the sense resistor.
PD = (I(RMS) / k)2 × R(SENSE) (10)
In this example, for the RMS motor current is 2.5 A, the sense resistor of 1.5 kΩ dissipates approximately 7.5
mW of power. The power quickly increases with higher current levels. Resistors typically have a rated power
within some ambient temperature range, along with a derated power curve for high ambient temperatures. When
a PCB is shared with other components that generate heat, the system designer should add margin. Measuring
the actual sense resistor temperature in a final system is best.

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at the Equation, PD = (I(RMS) / k)2 × R(SENSE)

I think that the voltage at the Rsense resistor is about 3.3V, at 2.5A load current, R is 1.5K.

if it is right, I could prob the voltage with scope.

But there is no voltage out on the condition with my EVM kit.

The pin number is 10 and 12 each other. the names are IPROPI1 and IPROPI2.

The voltage is tested by multimeter.

I don't know why the voltage is not out from the chipset.

can you give me any tip for it?

KW,

Can you measure the winding current and IPROPIx signal in a same scope? I would think the IPROPIx voltage low may caused by low winding current or a narrow current pulse.

Wang,

What does the winding and narrow pulse mean?

Does the narrow pulse mean pwm pulse? PWM frequency is 12KHz. about 80usec period.

I don't know what the winding' mean is. The load is a coil of solnenoid type.

Refer to my test bed capture.

1. current wave capture

2. test bed block

KW,

1. IPROPIx reflects the high side FET current.

2. What SR setting do you have? From your test waveform, the solenoid winding current goes up sharply (maybe only few us). If SR setting is too low, IPROPIx may miss that current info.

3. How do you drive the current going up sharply and going down slowly? If the solenoid winding current in falling period doesn't go through the high FET. IPROPIx doesn't have output.

Hi, Wang,

After I changed SR to NC state(High Impedance), the sensing wave was out.

Refer to captuer wave.

But it seems to be difficult for me to use the sensing signal for my unit.

because the signal is pulse wave, to use it, it must be synchronized to PWM pulse.

if we make it to flat by using low pass filter, it is possible to use it for my unit.

So I have to use other sensing function, for example, a effective hall sensor(ACS724).

Anyway, thank you again for your helpness.

good luck..