SPOC+2 Family ISO 7637 immunity/protection

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cirez_proj
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Hi,

we are looking into using SPOC+2 High-Side switch (BTS71220-4ESA) in our product. The switch will be used to drive 4 light bulbs, controlled by 3.3V MCU. The power supply (Vs) is provided directly from the vehicle battery (via 12V wire 3-8m long and local chassis ground 50cm wire).

Does this product provide any ISO 7637 pulse (1, 2a, 2b, 3a, 3b, 4) immunity?

Are there any official Infineon guidelines how to best protect the product to be able to withstand the pulses?

Thank you for your help!

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Anshika_G
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Hi @cirez_proj ,

 2. In daisy chain configuration (ex. 2 drivers) is it possible to share the same Vcc and GND resistors?
It is possible to share the same Vcc and ground resistors.


 3.  You marked a diode as a schottky diode but isn’t that a symbol for a zener? How does a -Ignd current flow if there is a diode? Via Reverse ON circuit?
>>Let me check for this one again


4.“m” means “total number of devices”. Is that total number of SPOC drivers in a module (connected to Vs and module GND, in parallel)?
Yes, it represents the number of devices in a module.

Is the worst case scenario when all outputs are "open load" (like blown light bulbs or disconnected) - in that case n = 0?
>> Yes, n=0 in that situation. 
     n represents the number of load connected to outputs/ no. of channels but without                 channels in open load.

I have attached EMC report of BTS71220-4ESX. Hope it will also help.

Regards,
Anshika

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Anshika_G
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First question asked 50 likes received 250 replies posted

Hi @cirez_proj ,


For transient voltage spikes as described in ISO7637, SPOC+2 is tested with a nominal resistive load connected to the output. These loads partially dissipate the energy of the pulses, reducing the power induced into the IC.

Tests have revealed without these loads, Spoc+2 requires external circuitry to survive these pulses. 

During ISO pulse, a lot of the energy is going through the OUTPUTS of the device.
If an electronic load is connected which has quite a low capacitance such that it does not allow a current flow during the ISO pulse, the energy has to go somewhere else. If there is no other path on the board, there will be a lot of energy flowing through the GND of the device, which could damage the GND structure.
For the safety of GND structure, a TVS diode can be fitted .

I am sharing some relevant documents which might be useful to you  :
1. Test_Scenarios_of_Unintended_Power_Cycles_in_Automotive_Applications 
2. Reverse-Battery-Protection 

Thanks and Regards,
Anshika

Thank you for prompt response!

In our application the unit can be detached from the loads so there could be instances without load – thus we need to protect it from the pulse as you mentioned.

Are there any guidelines from Infineon on how to design such a protective circuit? In the documentation there is bidirectional TVS diode Dz2 (with capacitor Cvs2) present across Vs and chassis ground but without any specs. What should the clamping voltage (in +/-) of such diode be to limit the voltage to safe levels? Larger than vehicle clamping for load dump at 35V for sure.

What is the value of reverse breakdown voltage of an internal GND diode of the module? Is protecting it with a resistor enough?

Best Regards!

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Anshika_G
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First question asked 50 likes received 250 replies posted

Hi @cirez_proj ,

We don't have a exact documentation about guidelines. But I am sharing some articles that I find useful :
1. Why-a-series-resistor-on-VDD-line-is-needed-for-SPOC-2-devices 

2. How-to-size-the-GND-resistor-for-a-SPOC-2-device 
3.   To know which kind of diode are used internally to protect the device against ISO pulse and reverse polarity : 

G_Anshika_1-1661753313045.jpeg

 

 

G_Anshika_0-1661753182787.png

All diodes shown in the figure as zener diodes are behaving like them. For the logic input pins the input structure is show in figure "Input Circuitry"
There are two zener diodes with and resistor in between.
The first diode on the input is the ESD protection. The second diode in combination with the resistor is used for clamping the input pin.

4. Excel tool to calculate the positive voltage Transients (Attached file)

I hope this will help.

Thanks and Regards,
Anshika

Thank you for this comprehensive answer. I will need to study the resources. Some quick questions tho:

1. , 2. In daisy chain configuration (ex. 2 drivers) is it possible to share the same Vcc and GND resistors?

3.  You marked a diode as a schottky diode but isn’t that a symbol for a zener? How does a -Ignd current flow if there is a diode? Via Reverse ON circuit?

4.  “m” means “total number of devices”. Is that total number of SPOC drivers in a module (connected to Vs and module GND, in parallel)? Some simplified schematic would be great to have along the equations.

Is the worst case scenario when all outputs are "open load" (like blown light bulbs or disconnected) - in that case n = 0?

 

Thanks for answering!

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Anshika_G
Moderator
Moderator
Moderator
First question asked 50 likes received 250 replies posted

Hi @cirez_proj ,

 2. In daisy chain configuration (ex. 2 drivers) is it possible to share the same Vcc and GND resistors?
It is possible to share the same Vcc and ground resistors.


 3.  You marked a diode as a schottky diode but isn’t that a symbol for a zener? How does a -Ignd current flow if there is a diode? Via Reverse ON circuit?
>>Let me check for this one again


4.“m” means “total number of devices”. Is that total number of SPOC drivers in a module (connected to Vs and module GND, in parallel)?
Yes, it represents the number of devices in a module.

Is the worst case scenario when all outputs are "open load" (like blown light bulbs or disconnected) - in that case n = 0?
>> Yes, n=0 in that situation. 
     n represents the number of load connected to outputs/ no. of channels but without                 channels in open load.

I have attached EMC report of BTS71220-4ESX. Hope it will also help.

Regards,
Anshika