DRV8705S-Q1EVM: DRV8705S

Hello,

We would need your technical support on a TI product: The gate driver: DRV8705S-Q1.

We encountered a problem of failure of the DRV8705S following a diagnostics validation test ("Test: Short Circuit of SH1 to GND").

*The driver is used to manage two external N-Mosfets (High Side: HS & Low Side: LS): (RDSON=3.3 mΩ) in split HS and LS configuration (with a shunt current resistor of 3mΩ) to control a load of 2Ω resistance.

**Vbattery=13.5V

Ie: In our case, we don’t implement the freewheeling diode in parallel with Load (R=2Ω , L=10uH).

*Diagnosis is performed in “ON STATE” and in “OFF STATE”.

In “ON STATE”: We set VDS_LVL=0.06V

*In “OFF STATE”, we do three consecutive cycles of diagnostics. Each one lasts 4 ms, as follows:

1- Pull-Down_SH1=1           Pull-up_SH1=0

Pull-Down_SH2=1             Pull-up_SH2=0

2- Pull-Down_SH1=0           Pull-up_SH1=1

Pull-Down_SH2=0             Pull-up_SH2=1

3- Pull-Down_SH1=0           Pull-up_SH1=1

Pull-Down_SH2=1             Pull-up_SH2=0

* We launch a cycle with a PWM=100% (Frequency=4Hz) and we apply a short circuit to ground on the signal relied to Pin 21: SH1 of the gate driver.

-Test result:

The gate driver DRV8705S is no more operational following the application of the short circuit.

Investigation of the failure:

*After checking the 2 N-MOSFETS high side and low side and the gate driver, we found a very low impedance between the following pins:

-SH2-SL2: 79Ω

-SH2-GND:45Ω

-SL2-GND:43Ω

->Interpretation: The internal circuit linked to the measurement of the VDS voltage of the LOW SIDE MOSFET of the 2nd half-bridge is faulty.

Questions:

1/-Would you have an explanation for the test result?

2/-Why is it the circuit linked to the Low Side Mosfet that was destroyed and not the one linked to the HIGH-SIDE Mosfet (It's "strange")?

Thank you for answering our questions as soon as possible.

Best regards.