Power Input for Automotive BLDC Applications

[Hilti]

Hello,

I am working on a BLDC motor circuit for the automotive water pump. I have some questions about my power input.

1. In the Littelfuse's application note, it says passed all of the surge voltages which consist of ISO7637-2. Just using this TVS Diode is sufficient to surge these voltages? (Link: Application Note)
2. The power line is 6-18V but all of my components can withstand more voltage (I can change the capacitors). Is it safer to use a TVS which has a greater breakdown voltage?
3. Is this TVS diode also sufficient for ESD protection? It says it is sufficient to protect IEC 61000-4-2 pulses (Link: Datasheet )
4. There is also a PWM input line for motor speed control. Should I use another TVS for this line for ESD?
5. I don't know how to calculate the current that is applied when the pulses occur. Do you have any ideas? Also, I saw a system that connected an RC network between TVS's #1 pin and ground. I believe it is for current limiting. What do you think about that, should I also connect an RC network?
6. Should I connect TVS before or after the filter?
7. Do you think this filter is sufficient or should I use common mode choke or sth else. I am really new at filters

I know my topic is a bit long but I would be so happy if you could help.

Hilti

 

[KlausST]

Hi,

1) it depends on what surge definitions your customer relates. If he relates to ISO7637-2 and your design fulfills the application note requirements (trace width, loop impedance...) then it should be O.K.

2) You need to look for "clamp voltage", not breakdown voltage. Clamp voltage is much higher.

3) Generally ESD and surge is different. Surge usually is for power supply ESD mainly at signal lines. ESD is way less energy thus maybe even your power supply capacitor may be sufficient. But ESD may be faster (in dV/dt as well as decay time) with higher voltage but also higher source impedance.

4) This is the classical ESD case.
Is the TVS
* fast enough and
* low capacitance
* high impedance
* and low clamp voltage enough
... not to modify your PWM signals, but protect the devices?

5) Which path? Which voltage?
A series resistor in my eyes is no good idea. Look for informations why they installed the resistor.

6) If you install it after the filter, then C3 will not be protected and L1 need to widthstand the surge current and voltage....but due to increased loop impedance the protection level will be higher.

7) it depends on the input signals and how sensitive your load is.

I recommend to
* ask the customer for clear definitions
* go through some application note regarding surge and ESD, maybe reference designs.
* look for PCB layout examples. A lot depends on correct current paths
Every related semiconductor manufacturer provides a lot of informations, maybe even videos.

Klaus