Part Number: PCA9557
In my circuit I detect current flowing into the P0 pin when I connect it to a pullup. There is a diode drop across P0 and VCC. This is not shown on the diagram.
When this part is powered by 3.3V and the P0 input is used as 5V tolerant inputs, is it normal for current to flow into the pin? If so does this mean the pin can't go higher than VCC + 0.7V and that I must limit the current to 20uA to cmply with the absolute maximum I[IOK] of -20uA.
Hi Charles,
The device supports 5V tolerant I/O's when powered up. This is supported by the VIH spec:
Where the VIH spec can be up to 5.5V max regardless of supply voltage.
Is there any other device on P0 that is not 5V tolerant?
Regards,
Tyler
Here is the circuit:
It pulls P0 up to 3.96V, a diode drop over 3.3V. I replaced the part with NXP's version of the part, and P0 goes to 5V. With NXP part 500nA flows through R8, R19, Q1's reversed-biased B-C junction. I don't detect any branch current flowing into P0. With the TI part, however, it appears like there's a typical 0.7V protection diode from P0 to VCC.
