Other Parts Discussed in Thread: ISO7721,
Hi,
Due to the current market situation I wanted to replace the ISO7421D with an ISO7721.
For power reduction during sleep mode, the Vcc is turned of via a µC-Pin (ATMEGA168-PA) but the input pin of the ISO remains in high state. Replacing the ISO7421 with the ISO7721 resulted in a much higher current consumption during sleep mode and the main reason is clamping diode from the input (Anode) to VDD (Kathode). While Vcc is in this case shorted to GND via µC, current is flowing throw this clamping diode.
But this additional clamping diode is not available in the ISO7421D, see pictures below:
And this is the input of the ISO7721:
As you can see, replacing the ISO7421D with the ISO7721 is not possible, it would result in software changes which is not an option.
But as I noticed in the "Absolute Maximum Ratings", the ISO7421D is still used outside the specification. The logic level is 5V and results in a voltage which is at least 4.5V higher when Vcc is 0V, but there hasn't been an issue for several years now. From an electrical perspective the design is save at this point, a small current of 5µA is flowing throw the 1MOhm resistor to Vcc, if the input is high and Vcc low.
Some measurements also gave some certainty that this shouldn't be an issu at all.
Yellow: Vcc-Voltage
Green: Input-Pin
Orange: Vcc-Current
My questions is now: Is the design of the ISO7421D still robust enough to last for a lifetime (10 years) and in case of a "yes" why is it so (silicon design etc.) ?
kind regards
Tobias