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# DRV8802-Q1: how to set R(ISENx), Abs max of ISENSEx pin

Dear all,

I read following post, but I could not understand. Could you help me?

Finally, I could understand this device will not be broken over 8V in short current with small peak.

And you mentioned that 2.1V is the worst case because of ESD cell...

Could you teach me following three things?

■QUESTION 1,

Must not the voltage at ISENx pin be over 2.1V?

■QUESTION 2,

If the answer of Q1 is 'No', should we select the resistor value less than 420mΩ?

*calculation...I(OCP)_max = 5A, ISENX_max = 2.1V ====> resistor_max = 2.1 / 5 = 0.42.

■QUESTION 3,

When the voltage of ISENx is over 2.1V and break down leakage current occur,

will the damaged section be ESD cell only?

Best regards,

• Hi Yamamoto-san,

Takao Yamamoto said:

■QUESTION 1,

Must not the voltage at ISENx pin be over 2.1V?

The ISENx pin must not be over +0.8V according to the datasheet absolute maximum. There is no reason for the Isense to be greater than .66V because the internal amplifier is maxed out.

Takao Yamamoto said:

■QUESTION 2,

If the answer of Q1 is 'No', should we select the resistor value less than 420mΩ?

*calculation...I(OCP)_max = 5A, ISENX_max = 2.1V ====> resistor_max = 2.1 / 5 = 0.42.

The OCP circuit operates independently of the sense resistor. The OCP circuit will activate when 1.8 to 5A flows through the FETs for approximately 3us.

If using the current regulation feature, the sense resistor should be set based on the equation in the datasheet. The chopping current should be set to 1.6A or less.

Takao Yamamoto said:

■QUESTION 3,

When the voltage of ISENx is over 2.1V and break down leakage current occur,

will the damaged section be ESD cell only?

As mentioned above, 2.1V violates the absolute maximum for the pin.

• Dear Rick,

I would like to know additionally.

You said that OCP and Current Regulation is different.

Is this because xISEN pin is clamped to GND with something internally?

5A is OK for xISEN pin connected to some value resistor because the voltage of xISEN will not be over 0.8V by something clamped?

Best regards,

• Hi Yamamoto-san,

Takao Yamamoto said:

You said that OCP and Current Regulation is different.

Is this because xISEN pin is clamped to GND with something internally?

The OCP and current regulation circuits are designed to perform different functions. OCP is designed to prevent too much current flowing through the FETs. Current regulation is designed to automatically regulate the current to a desired level. An example of using the current regulation is during motor startup or stall. If the stall current is not need to start the motor, the current limit during startup can be set to a lower value. This can reduce the power during starting, increasing battery life and potentially reducing the size of the bulk capacitors.

The OCP circuit limits the current through the FETs. The OCP circuit is described in section 7.3.7.1 of the datasheet and shown in Figure 5 on page 9 of the datasheet. The OCP circuit is shown at the top of each pair of high side FETs and the bottom of each pair of low side FETs. This OCP circuit limits the current to between 1.8 and 5A. This OCP circuit is listed under Protection Circuits in the Electrical Characteristics.

The Current Regulation circuit is shown in Figure 5 of the datasheet also. The current regulation circuit consists of the DAC, comparator, and amplifier providing signals into the PWM logic. The signal is based on the voltage across the sense resistor. The current regulation specifications are listed under Current Control in the Electrical Characteristics.

Takao Yamamoto said:

5A is OK for ISENx pin connected to some value resistor because the voltage of xISEN will not be over 0.8V by something clamped?

There are two constraints for the device. One is the voltage on ISENs, which must be less than the absolute maximum of 0.8V. The second is the maximum current through each output should be less than 1.8A. The device can tolerate slightly more for brief periods of time (<3us) but the OCP circuit can assert if the current is higher than 1.8A for more than ~3us.

So 5A is not OK because of the OCP circuit.

• Dear Rick,

Thank you for your kindness support!

Best regards,