LPC1769 issue with NXP PCF8574P

[fernandoresquín]

Dear All:

Please can you help me with this?

I´m trying to add 16 additional digital outputs to LCP1769FBD100, using two PCF8574P. For test purposes, I´m using a single PCF

for now. The problem is the PCF doesn´t send the ACK. The curious thing is I´ve tried with 4 different units and one of them worked perfectly

and the rest don´t. 

I know it´s not an address issue. The PCF units are all identical and was tested in the same circuit. For your knowledge, my pullup resistors are

2K2.

There is any known issue of incompatibility between these two ICs that can depend of dispersion of the chips or I should assume they sold me three

damaged PCFs?

Thank you.

Best Regards.

[Hui_Ma]

Hi

I checked the PCF8574P and LPC1769 errata record, there without related record.

How about the PCF8574P chips' VDD voltage? Is it same with LPC1769 board VDD voltage?

Could you try to change using the 10K pull up resistor instead with 2.2K value?

Wish it helps.

Have a great day,
Ma Hui
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[fernandoresquín · Accepted solution]

Dear Hui Ma:

Thanks for answering. I really appretiate that.

Finally I ´ve solved the issue. I have three of my four PCF8574P that are responding

like they were PCF8574AP, so there were really an addresss problem, but I was not

my mistake. I think these chips are defective or were marked erroneously at the factory.

Best Regards.