I/O Expander

[GeoJoe]

This is the least useful response I've ever gotten from Microchip help. Anyway, does anyone know the answer? The question is: Do I need an external RC circuit for the clock generator on MCP23017. Spec sheet doesn't spell it out, but the 23016 did require it. By the way, do not use the 23016. Microchip was helpful enough to recommend that I use the 23017 instead. Little too late though, I have hundreds of boards out in the field failing.

Thanks all!

Area: Analog/Interface Products
Product Group: I/O Expanders
Product: MCP23017 Date Created: 11/30/2010 7:11 AM
Issue: Design Assistance Date Resolved: 12/2/2010 5:01 AM
Description: I am currently redesigning a board to elliminate the use of 23016 and implement the use of 23017. Please confirm that the MCP23017 DOES NOT require the external RC timer components that the 23016 did.
Resolution: Hi,
use the following link for a useful application note:

http://ww1.microchip.com/downloads/en/AppNotes/01043a.pdf

From the following datasheet:

DS21952B

It's not mentioned the need for an external RC circuit but the only way to be sure is to try with a real device in your application.

Regards

(name deleted to protect the...)

[jackjay]

the 23017 does not require q resistor/cap 3k9/33pf for it to run it as its own osc circuit
BUT it does need a pull up resistor on the not reset pin other wise iy just sits there
just watch out for the BANK setting as this moves all the addresses
jack

[Dave]

GeoJoe, I thought about using the Microchip version a few years ago but with all the registers to setup, what a pain... I have been using the PCA8575 16 bit and the PCF8574 8 bit i/o expanders ever since. No registers to setup and they provide 25 ma. per pin to ground. I'll never go back....

Dave Purola,
N8NTA

[jackjay]

found it easy to write to using direct address (paired) but unable to read the ports after a long time gave up
also will sink or source 25MA
the data sheet is better than the 23016 but still leaves a lot out
jack

[Dave]

jackjay ,I supose if you need to source current continously then the 23016 is the way to go. I have never relied on IC's to source current greater than a couple of mill's continously because of the high RDS ON of most P channel fet's. The PCA8575 16 bit and the PCF8574 8 bit i/o expanders DO source 25 mill's but only for a breif period of time to compensate for any loading on the pin. Therefore I usually select a component for it's ability to sink current rather than source it. If you look at the number of drivers IC's that sink current opposed to the number that source it's something like 10 to 1... I have never had a heat related problem in any of my designs in the last 30 years... I guess I'm just OLD SCHOOL....

Dave Purola,
N8NTA