[OT] 7-segment LED driver SAA1064 with +12V supply

kender · Joined: 09 Aug 2004 Posts: 768 Location: Silicon Valley

Folks,

I’d like to power a 7-segment display with a +12V supply and control it with SAA1064. My I2C bus runs off +5V. Have read the datasheet. Typical supply voltage +5V, max +15V. I didn’t find any contraindication for using +12V power supply.

Have anyone tried this? Could anyone confirm?

Cheers,
- Nick
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PCM programmer · Joined: 06 Sep 2003 Posts: 21708

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kender · Joined: 09 Aug 2004 Posts: 768 Location: Silicon Valley

I'd like to report my findings.

Made the circuit powered off +12V. It's similar to the one in the PDF linked by PCM (obviously). It has 3x 7-seg characters with decimal points and SAA1064 in 24-SOIC package.

Wrote a driver. This and this was helpful.

It works.
Caveat. DIP version of SAA1064 can dissipate 1000mW (from Absolute Max Ratings). SOIC version can dissipate only 500mW (it doesn't have special provisions for heat sinking such as a thermal pad). Tips for analyzing power dissipation on pp.14-15 of the datasheet*. I've played with numbers. It turns out that +12V supply pretty much forces you to use the DIP package**. Another (obvious) option is to regulate the the supply voltage down to +5V. Additional burden would be 300-400mA; it's doable with a buck or a well heat sunk linear regulator.

* Notice that the example there has a slight error between 12e-3 and mW. The answer 148.5mW agrees, though.

** The schematic linked by PCM implies SAA1064 in DIP, because a lot of other components there are throughole.
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