0
\$\begingroup\$

I am a beginner in electronics. I want to use HV5622 serial-to-parallel converter to drive nixie tubes. However, there are two types of datasheets: Recommended condition and absolute maximum ratings. I want to operate the chip with 5VDC like this. However, for recommended operating conditions, the Vdd voltage is shown as 10.8V to 13.2V. What is the benefit of driving the chip to the recommended operating voltage? What are the limitations of driving a chip with a voltage outside the recommended operating voltage (for example, 5V)?

\$\endgroup\$
7
  • 1
    \$\begingroup\$ Absolute maximum is what you must keep to without damaging the device. If you go outside of the recommended operating range it most likely won't work, but won't damage it as long as you stay within the absolute maximum range. \$\endgroup\$
    – DiBosco
    Dec 12, 2017 at 12:03
  • \$\begingroup\$ So if you run the chip at 5vdc, will not the chip performance or switching power decrease? \$\endgroup\$
    – Ho jun
    Dec 12, 2017 at 12:04
  • 2
    \$\begingroup\$ I think it will just not work if you run it at 5V. I think it's saying you should run the chip at 12V and that means you'll have to level shift your micro's outputs from its Vcc up to 12V as per here: soniktech.com/NixieNet/NixieNetSchematic.png \$\endgroup\$
    – DiBosco
    Dec 12, 2017 at 12:16
  • 1
    \$\begingroup\$ I have to say the datasheet is unclear about this level shifting - it does not show any on its example scheamtic, but a few schematics on a Google search do have level shifting from micro to the 5622 \$\endgroup\$
    – DiBosco
    Dec 12, 2017 at 12:18
  • \$\begingroup\$ Datasheet specifies low input as 0 to 2V and high input as (VDD-2V) to VDD, so that makes level shifting from 5V or 3V3 devices mandatory if it's run at recommended supply voltage levels. I'm guessing it needs that supply voltage to ensure sufficient VGS for the output MOSFETs. \$\endgroup\$
    – Finbarr
    Dec 12, 2017 at 12:28

3 Answers 3

1
\$\begingroup\$

Arguing from the example of the CD4000 series logic line, I suggest that full voltage is required for full speed (8 MHz clock rate). Again arguing from other logic series (both the CD4000 and the 74HC) I'd suggest that running at 5 volts rather than 12 will reduce the maximum clock frequency from 8 MHz to something like 3 MHz, but that number MUST be determined by experiment. So you'll need to be careful of your timing.

I would also be concerned that the output transistors may not turn on completely (that is, that their Vgs(th) might be too high), but the article you linked to shows a working project. Nonetheless, you might keep an eye out for overheating and/or low Nixie brightness.

\$\endgroup\$
1
\$\begingroup\$

The maximum values are the limits at which the chip is not immediately destroyed. There is no guarantee that the circuit will work with these values, nor is this recommended.

If you want to use this circuit you'll have to power it with a voltage in the range from +10.8V to +13.2V, typically +12V.

The autor of the article that you've linked made an error while developing the circuit. He explained this himself with the following lines:

The HV5622 datasheet stated that the recommended logic supply voltage should be around 12 V. Uh oh. I was now pretty frustrated, yet disappointed that I didn't see this earlier. But the fact that the cycling worked for a bit gave me hope that a 5 V logic supply would work.

While the autors circuit worked, no one will guarantee that yours will too. This risk is up to you.

There is also the possibility that the lifetime of youre IC will be reduced. For example, because the output transistors are not completely conductive and thus the power dissipation is increased.

\$\endgroup\$
0
\$\begingroup\$

Absolute maximum ratings are what they sound like ! They are a limit you exceed at your peril.

Do try to keep to recommended conditions wherever possible. They aren't actually different datasheets, simply different values for certain parameters. If you exceed the recommended operating conditions by a little bit it's OK but exceeding the abs max ratings is likely to fry your device.

The 'benefits' of exceeding recommended ratings is a bit like overclocking CPUs. The device may work a bit faster and get hotter. Lifetime is likely to be reduced too.

As for Vdd, the abs max is 15V but recommended looks to be 12V. 13.2V (if you think there's an advantage) should be fine.

I/O appears to need translation from 5V logic levels to 12V.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

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