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TVS diode overvoltage protection

Rajinder1268

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Hi all,
I am using a BTT6030-2ERA high side power switch in a automotive application. This wil be powered from a car battery. The load current will be around 0.5A to 2A.
I have read the application note and they recommend a TVS diode as overvoltage protection. I have selected the SMC3K24CAHM3 as a potential option.
Can I connect this across my Vsupply and GND of my circuit? Do I need to add a current limiting resistor?
The clamping voltage is 38.9V, however I am a bit confused, does the device start to clamp at 77.1A (peak surge current from datasheet?).
Can anyone assist?
 

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The TVS position is suggested in the datasheet application circuit. BOM specifies a "58 V zener diode". Problem with your selected SMC3K24CA is that it surely protects the power switch, but probably doesn't comply with overvoltage tests according to ISO 7637-1.
The clamping voltage is 38.9V, however I am a bit confused, does the device start to clamp at 77.1A (peak surge current from datasheet?).
No. The specification is marking a point in the basically monotonous I/V characteristic. The peak surge current value results from applying the signal of an industry standard surge test generator. Consider that ISO 7637-1 assumes different overvoltage waveforms.
--- Updated ---

There are TVS diodes with dedicated automotive load dump specification, e.g. Vishay SM8S series.
 
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Rajinder1268

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The TVS position is suggested in the datasheet application circuit. BOM specifies a "58 V zener diode". Problem with your selected SMC3K24CA is that it surely protects the power switch, but probably doesn't comply with overvoltage tests according to ISO 7637-1.

No. The specification is marking a point in the basically monotonous I/V characteristic. The peak surge current value results from applying the signal of an industry standard surge test generator. Consider that ISO 7637-1 assumes different overvoltage waveforms.
Is there anything else I could do to protect the power switch? I have read about the different surge voltages i.e. ISO 7637-1. What else could you recommend so I can meet these standards?
 

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I believe, BTT6030 and similar smart switches are already protected against autmotive load dump if you observe the datasheet suggestions, e.g. using Rgnd. The TVS diode has the purpose of clamping higher voltage surges. I would use something like SM8S40CA.
 

Rajinder1268

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I believe, BTT6030 and similar smart switches are already protected against autmotive load dump if you observe the datasheet suggestions, e.g. using Rgnd. The TVS diode has the purpose of clamping higher voltage surges. I would use something like SM8S40CA.
I will have a look at this.
 

james.qiu

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Hi all,
I am using a BTT6030-2ERA high side power switch in a automotive application. This wil be powered from a car battery. The load current will be around 0.5A to 2A.
I have read the application note and they recommend a TVS diode as overvoltage protection. I have selected the SMC3K24CAHM3 as a potential option.
Can I connect this across my Vsupply and GND of my circuit? Do I need to add a current limiting resistor?
The clamping voltage is 38.9V, however I am a bit confused, does the device start to clamp at 77.1A (peak surge current from datasheet?).
Can anyone assist?
you should first check the whole circuit from system of view, check the every component's maximum allowed voltage which connect to V battery ,
from ISO 7637-2 ,you need check which voltage level is valid for your project ,it always depened on customer's requriement.

for TVS diode , you need check the load dump test spec, generally in 12V system , 600W tvs is enough, but for some japan customer they require high level.
e.g if load dump voltage is 35V 400ms with 0.5ohm resistor. SMC3K24CAHM3 clamping voltage is too high than 35V, it is not a good choice.
if load dump voltage is 56V 400ms with 0.5ohm resistor. SMC3K24CAHM3 clamping voltage is 38.9V, then you can calculate the clamping current. if you add a resistor, it is hard to survived under test.
 

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