2
\$\begingroup\$

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.

\$\endgroup\$
7
  • \$\begingroup\$ Looks like an error in the datasheet to me. \$\endgroup\$ – stevenvh Apr 13 '11 at 12:26
  • \$\begingroup\$ It looks like there are 3 different speed grades for this chip. 0 to $70^oC$ is typically dubbed "commercial grade" and $-40^oC$ to $+85^oC$ as "industrial grade". \$\endgroup\$ – MikeJ-UK Apr 13 '11 at 12:38
  • \$\begingroup\$ @stevenvh Why? The speeds are mentioned throughout the datasheet, and surely you wouldn't accidentally qualify a part for a different temperature range accidentally? \$\endgroup\$ – W5VO Apr 13 '11 at 14:29
  • \$\begingroup\$ @W5VO - It makes sense that, when you can allow higher temperatures, you can go to higher frequencies as well. In that sense you would expect frequency to go monotonous with temperature. \$\endgroup\$ – stevenvh Apr 13 '11 at 14:39
  • \$\begingroup\$ @stevenvh I disagree. Increasing temperature decreases maximum speed, no matter what chip you're talking about. \$\endgroup\$ – W5VO Apr 13 '11 at 17:07
1
\$\begingroup\$

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.

\$\endgroup\$
3
  • 1
    \$\begingroup\$ @V5VO is correct, but I'd like to add a little. When talking about the minimum temp, like -40C in this case, it is assumed to be "Non-Condensing". Meaning, the temp hasn't dropped below the dew point and water starts condensing on the PCB's. Water condensing is bad. \$\endgroup\$ – user3624 Apr 13 '11 at 14:41
  • \$\begingroup\$ This kind of answers the second part of my question. "Risking it" is not an option here, we're talking about thousands of devices already running in an industrial environment... I was just wondering why the manufacturer chose to clock them @ 162MHz, and if we could give them a performance boost by clocking them higher. \$\endgroup\$ – Vincent Van Den Berghe Apr 14 '11 at 12:46
  • \$\begingroup\$ Honestly, this is something that the manufacturer decides. There's a good chance that they will work at a higher frequency at room temperature, but the manufacturer will not guarantee it over the full temperature range. \$\endgroup\$ – W5VO Apr 14 '11 at 15:52

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.