TSC888 failure modes

bi directional DC Motor Controls?

DC Motors, 4 bidirectional and 3 unidirectional. We use L293 ICs as motor drives.

continuously. (Approximately 80 hours). The sensors always fail in such a way that the output shows 10 times the actual value.

experience in using TSC888 in the motor controllers.

Probably due to over-voltage. We had a similar failure using a TS1100.

John

bi directional DC Motor Controls?

DC Motors, 4 bidirectional and 3 unidirectional. We use L293 ICs as motor drives.

continuously. (Approximately 80 hours). The sensors always fail in such a way that the output shows 10 times the actual value.

experience in using TSC888 in the motor controllers.

We out actually seeing some circuitry, it would be hard to say but I am leaning towards underrated parts or, EMF noise that results in HV is getting back to the sensor circuit via the motors.

But my guess would be that a shunt resistor is opening,

Jamie

Our shunt resistor value is .004 ohms. It is less than a zero ohm substitution part in most cases. The Kelvin connections are now as good as they can get on this second board layout and there have been no failures.

Note that the common-mode specifications are very important here.

Are there any spikes on the line that will exceed the common-mode specs of the chip? My bet is a huge YES!

So, I don't think you have used these parts nor have you studied the specifications in detail.

Hi John,

Thank you so much for your kind interest and comments on this matter.

We have found two things:

1. We have carried out validation measurements to make sure that nothing wo uld exceed the absolute maximum ratings. Only one problem, there is a negat ive going ring 20 us perioud (4V pk-pk) for 60 us when the system is power cycled. It is due to the low quality 12V Switch Mode Power Supply. The rat ing of the IC says the common mode minimum is -0.3V. The negative going pea k of -2V is already exceeding. So we have a preliminary conclusion that thi s could be one of the root causes of IC failure.

1. The ESD spec: of the IC is quite low, HBM 1kV and MM 100V. So it is more sensitive to ESD than other ICs, as we the system is open and the PCB is e xposed to human interactions for this moment in time, it has a high ESD ris k.

Please let me know your opinion also

Regards Aung

es.

Hi Jamie,

Thanks for your kind comment. Actually, there has been no failure in the shunt resistor. After replacing the IC, the current measurement systems works fine. It is basically due to the IC which somehow malfunctioned.

Regards Aung

in bi directional DC Motor Controls?

7 DC Motors, 4 bidirectional and 3 unidirectional. We use L293 ICs as motor drives.

continuously. (Approximately 80 hours). The sensors always fail in such a way that the output shows 10 times the actual value.

experience in using TSC888 in the motor controllers.

IC, the current measurement systems works fine. It is basically due to the IC which somehow malfunctioned.

You need to do a couple of things.

1. You need to provide a clamp diode on the supply line to grab any below ground problems. This is a common issue with flaky supplies and people connecting things backwards. A high current schottkey should work for that. One of my cases, I had to use an active clamp to suppress high currents due to ground faults from other equipment.
2. The current sensor you are using has a diff voltage of 2 volts and if for some reason you get a high current pulse, which does happen for brief moments, you can exceed this. In cases like this, it is more than likely the front end does have diodes internally however, I didn't see if the unit actually has sinking resistors inside? So maybe some extract protection is in order, like R's of your own connecting the inputs to the shunts? Or, two diodes over the shunt to prevent the raise of differential voltage.
3. You may want a big fat suppresser on your DC buss. The drive IC's you are using more than likely have diodes in the bridge to capture the regen energy and the motor could get into a free spin condition there by generating more energy back to the supply. When people are involved it is easy to get a motor load to be free spun out of control! (load swing)

So going back to (1. issue), a high wattage zener of 12 volts is in order or active clamp (dynamic Brake R circuit), like I use..

Jamie