We use 3-half bridges to drive three phase motor with the configuration:
Driver TPS51604 + CSD87335Q3D
Problem description (the problem occurs only sometimes):
-
After power switch on the driver low output is LOW (measurement with oscilloscope) although the PWM input is LOW (initial state after power on, SW ).
-
After activating the PWM (50/50) the driver output LOW remains LOW (doesn’t follow the PWM signal).
-
If we measure the driver high output (we don’t know the status before measurement) or the switch node the problem is solved, all the signals are OK. The driver high output
We measured the +5V and PWM input seems to be good. We analyzed the driver logic function (Table 1) but couldn’t find any reason causing the problem.
We assembled other resistor values on low gate (5Ohm) high gate (10Ohm) of the MOSFET but didn’t help.
We assembled other capacitance value as bootstrap (1μF) but also didn’t help.
We assembled a resistor of 100kOhm between SW node and GND which eliminates the problem, as expected because the measurement with the oscilloscope on SW node helps too.
In the previous design we use the Vishay transistors (SI7228DN) and never had such a problem.
The failure only appears sometimes at startup, not during normal operation.
Regards,
Bernd
