BS50015-1TAD SSmart Hi-Side Power Switch tripping issue.

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Here is the data sheet for the Infineon BS50015-1TAD Smart High Side Switch -

I have a prototype 3-channel switch system using this device as the power switches for three circuits normally switched by a three-ganged manual switch
I'm having problem where the switches will turn off if the load changes. The only way to reset is to remove Vin and re-apply.

Vin is at VS potential - common control signal is fed through three independent 4k7 resistors to each of the Vin terminals of each device; there is also a 0.15uF capacitor between pin 2 & pin 1 (ground); I have a local 15V TSV connected between the Vs input terminal and ground on each device.

I have eliminated my control circuit, by applying battery voltage directly to the inputs via the 4k7's; Vs is Constant supply from battery;

What happens is that the switches turn on when Vin is applied;

Initial load conditions at turn-on are
There is a given load on circuit one of about 10A;
there is a smaller load on circuit 2 of about 1A
There is open load at this stage on circuit 3 (this circuit feeds ancillaries that have series manual switches or relays i.e. brake light switch, horn switch, turn signal switch)

What I had found was initially was during engine starting the engine would start and immediately shut down the ignition circuit (and in the process shut off one or more of the other switches also). This would not happen EVERY time but quite often.
What I found is that Vin was still active 'hi' and had not changed state.
Although it did not appear to control circuit problem I bypassed it anyway, giving the inputs a direct manual switch to Vs.

With my manual switch operating Vin, I then found that, without even attempting a 'start' I could get the power switches to trip just by turning the headlight load on/off/on or changing it from high beam to low beam to high again in cycles; or on circuit 2, simply turning that circuit's "kill" interrupt switch on or off
And when I thought further about it, the condition whereby they were tripping during engine start procedure actually also mimics this situation - this is actually a motorcycle and to maximize current capability for starter, it turns off the headlights while starter is running.
i.e. what was happening was, at turn on, all circuits enable as expected; press start button (headlight current goes off and starter runs) - engine starts, release start button, headlights come back on and circuit trips (sometimes all three circuits)
I have actually been able to make one of the other channels trip just by using the turn signals (where clearly it is applying and disconnecting the load)

Now - none of these currents are anywhere near max limits

Here is the bizarre part - the high current headlight circuit itself might not be turning off (when operating the lighting on/off or switching high to low) but one of the other channels (which actuates the relays that then switch the output power to the actual load)

To clarify that configuration - circuit 1 feeds current via relay switched contacts on the output of the smart switch to the headlights; circuit 2 feeds power from output of that smart switch, via manual switch to the relay coil of the relay which is the aforementioned interrupt for the first circuit load.
So when operating the switch on output of circuit 2 to turn those relays coils on or off, THAT is the circuit that trips, NOT the high current circuit itself (note that sometimes the high current circuit 1 might also/alternatively be the one that trips)

it does not appear to be a current overload that is causing the trip
Vs is not being disconnected, nor does it fall below the Vs (ext) or Vs (uv) thresholds
There are however changing conditions from load to no load (open load if you will)
There are small inductive loads (automotive relays - but using diode suppressed relays)
Vs has 15V TSV locally at each device

I also attempted to give a small fixed load (1k0) on each output so there was at least some current out of each device (ie so they are never completely open load) - this made no difference

Any suggestions as to what is causing the problem of the devices tripping off would be most appreciated - and how I can eliminate this!

One thought I am having is that I did not employ a Vs Snubber circuit and starting to think that it is transient on the Vs side that is causing the issue
- for example, in the diagram below, the common VS connection to circuits 2 & 3, both will trip off together, even though the other circuit has no load changing condition.
Is that possibly the issue? i.e. Would omitting this cause this issue (or conversely, if I employ it, will it resolve it? Or do I have something else going on.
The application guide suggests a 3.9 ohm/4.7uF series snubber between VS and Ground (locally) - I did not include this, space was becoming tight on layout and didn't think it would be necessary, especially with the TSV
Maybe I underestimated it!
I also see in the application guide, the alternative snubber arrangement of a small capacitor of 100nF between Vs and ground pin, coupled with small resistor (4 ohms) between ground pin and actual ground.
Which of these would be best?

But any other suggestions would also be most appreciated

Here is simplified scheme

1 Reply
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decosse wrote:
... One thought I am having is that I did not employ a Vs Snubber circuit and starting to think that it is transient on the Vs side that is causing the issue

I have confirmed that the problem is definitely being caused by the lack of the snubber - even with non-ideal values a quick test improved the situation no-end!
I completely underestimated the impact of the Vs contribution