Electronic – NS9750 operating temperatures

arm9temperature

I have a ticketing device with an ARM9 CPU, more specifically a NS9750 module.
In the datasheet, its operating grades/ambient temperatures are listed as follows:

  • 125 MHz: 0 to 70ºC
  • 162 MHz: -40 to +85ºC
  • 200 MHz: 0 to 70ºC

Why is the operating range much wider at 162MHz?
If it were linear, I would guess it has to do with the frequency of the crystal changing according to temperature. But this? No clue.

Also, (this is important) what would happen if I were to run it at 200MHz in sub-zero ambient temperatures (up to -10ºC)? Worst case scenario.

Best Answer

The first thing to mention is that these grades are all manufactured identically, and their performance is measured so that they can be put into one of these three bins. There might only be two real bins, but at this point it's speculation.

The temperature plays a part in the speed as well - the higher the temperature, the lower the maximum clock frequency. At cold temperatures, the chip will run faster. Cold temperature failures are usually hard failures, in the sense that reducing clock frequency won't fix things. "Worst case" depends on your application. Here are a few scenarios that could happen.

  • The PLL could fail, and the chip would not operate.
  • The memory could enter a failure mode (can't write or can't read reliably)
  • Data corruption due to datapath hold-time violations
  • Improper behavior due to hold-time violations
  • Excessive EMI due to uncontrolled transitions in the output busses

There is a distinct possibility that they only qualified the industrial temperature range part because a wider specification means more time and money. In that case, all grades will probably work down to -40C. There may also be more durable packaging with the industrial range part.

If you are using this part for a hobby project, you may be comfortable "risking it". You may also be able to qualify individual parts, but any manufactured device will be a tough sell without the wide temperature range chips.