Suggested SPI I/O Expander

Hi Anson,

It looks like there are several shift register devices listed here:

www.ti.com/.../products.html

I'm not an expert on these, so I will try to loop in someone from that product team to give their recommendation.

You mentioned that I2C-based expanders may be a little slow - do you know how fast you will need to toggle the outputs?

There is also the possibility of implementing this in an MCU. For more information on that, you may want to reference this application note:

www.ti.com/.../slaa807.pdf

Regards,
Max

Thanks Max. I've looked at the product line before and I've had a difficult time finding one that meets all of the requirements especially the resetting of the latch output option. I failed to mention that I will need to have 10+ of these chips on board so an MCU might not be the best option, plus it's a bit overkill for our application and that would be extra software we'd have to write. We would control these expanders via multiple SPI ports from an FPGA, but we're limited on the amount of pins we can use from it. 

Basically, we need to control ~60+ pins with a little amount of pins as possible via SPI. I'm not exactly sure how fast we would need to control all of them but some of them would be in the single digit microseconds. 

I may have found one but I can't seem to find the actual product in stock.

http://www.ti.com/lit/ds/symlink/sn74hc594.pdf

Hello,
The SN54HC595 is rated for -55 to 125C operation and is an 8-bit serial-in parallel-out shift register.

There's also an SN74HC595B that's rated from -55 to 125C.

Would one of these work for your application?

Thanks for the suggestion, but we've already looked at those options. The issue with those is that they don't have a CLR pin for the latch. 

Our main concern is the state of the output pins upon power up. If it powered up with the outputs in a low-state, then that would be perfect. The datasheets seem to suggest it powers up in an unknown state. 

Perhaps I'm approaching this the wrong way. The main issue we're trying to address is controlling multiple outputs with very few inputs. My first thoughts were to use a shift register with latched outputs but perhaps there are other means to solve this issue.

What about starting the device in high-impedance mode with pull-down resistors on the outputs to guarantee a low-state at startup, then clock data through once the system is up and enable the outputs?