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# ISO7761: Absolute max rating IO

Part Number: ISO7761

Hi Team,

Good day! I am posting this to help our customer and find solution for their concern. Kindly help.

I am not sure whether IO denotes just the output current iof one channel or it is the total sum of all channels output?

I made a test connecting all 5 outputs with a 2k2 resitors and observe a Sullpy current of ~14 mA in total.

After approx 30 sec something happens with the chip and supply current. It raises and my current limited voltage supply did reduce the supply voltage and the supply current of the device was reduce by this measure.

If I disconnect one resistor, the time to "abortion" is getting longer.

In chapter 6.8 of your data sheet (Safety limiting values your are giving value much as a multiply of 20 of the value I had adjusted. I assume that values result by a thermal balance of the chip.

a) what happens to chip for a load current of 5 channels each  ~2 mA (2k2 @ 5V) ?

b) is IO = 15 mA (max rating) the total current into the chip which is in respect to the power dissipation, the heat sink and hence the heat transfer to the ambient?

If you like I could send you a picture captured by the oscilloscope of the supply voltage drop when loading the chip with the output current mentioned above.

Best regards,

Jonathan

• Hi Jonathan,

Thanks for reaching out and for sharing questions from customer.

b) is IO = 15 mA (max rating) the total current into the chip which is in respect to the power dissipation, the heat sink and hence the heat transfer to the ambient?

The absolute maximum output current (IO) of 15mA is for each individual channel. The outputs do not have any internal current limits and can source/sink higher currents when forced but we recommend that the worst-case current is limited externally to 15mA either by using resistors or by connecting them to logic inputs which are designed to consume only a few µA of current.
Please note that the absolute maximum ratings are not continuous current ratings, these are to be considered as max ratings for occasional fault conditions.

a) what happens to chip for a load current of 5 channels each  ~2 mA (2k2 @ 5V) ?

The recommended maximum sink/source current for each channel is 4mA at 5V operation. Hence, it is perfectly fine to operate each channel at 2mA when powered by 5V. Please see below snapshot from datasheet indicating max recommended sink/source currents of each individual channel.

I made a test connecting all 5 outputs with a 2k2 resitors and observe a Sullpy current of ~14 mA in total.

After approx 30 sec something happens with the chip and supply current. It raises and my current limited voltage supply did reduce the supply voltage and the supply current of the device was reduce by this measure.

If I disconnect one resistor, the time to "abortion" is getting longer.

I am not sure if I understand the issue completely here.
Did you mean to say that all the outputs had a 2.2kΩ resistor connected to their respective GND? If this is the case then we do not expect this to cause any issues, the device should work just fine.
May I know what is current limit on the supply used to power ISO7761?
If possible, please specify the actual current observed, how much did it increase to and share a connection diagram if my understanding of connection is incorrect.

Regards,
Koteshwar Rao

• Hi Koteshwar,

I am not sure whether IO denotes just the output current iof one channel or it is the total sum of all channels output?

Best regards,

Jonathan

• Hi Jonathan,

Thanks for the follow-up.

Sorry, I briefly answered this question but maybe it wasn't coming out very clearly. As mentioned in the below statement that responded earlier, IO defined in the datasheet is referring to each individual channel. It is the current of only one channel. Thanks.

The absolute maximum output current (IO) of 15mA is for each individual channel.

Regards,
Koteshwar Rao