Supply voltage for HT16K33 Breakout

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Coconuts
 
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Supply voltage for HT16K33 Breakout

Post by Coconuts »

Hi. I have an Adafruit 0.56" 4-Digit 7-Segment Display w/I2C Backpack, which I am pretty sure is based on the HT16K33 IC. That is doing just fine when powered by the Raspberry Pi at 3.3 volts. I want to drive some larger 7-segment LED's, for which I have bought the Adafruit HT16K33 breakout. I am all set with UDN2981's and such to handle the large forward voltage of the LED arrays in each segment while the HT16K33 stays at a 3.3 volt supply, but both the data sheet on the HT16K33 chip and the screened text on the breakout state that the HT16K33 needs to be operated at a nominal 5 VDC, with a minimum supply voltage of 4.5 VDC. Does the breakout use a different supply version of the HT16K33 compared to the combo backpack + display? If I do need to run the HT16K33 at 5 VDC, the pull-up's may at 10K be high enough to let the RPi survive, but I would obviously prefer to run the HT16K33 at 3.3 volts and avoid any conflict. Thanks

Kevin

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adafruit_support_rick
 
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Re: Supply voltage for HT16K33 Breakout

Post by adafruit_support_rick »

The display with backpack you have uses the same 4.5-5.5V chip as is used in the breakout.
If it works at 3.3V, then I guess you're OK. If you want to run it at 5V, you'll need a level shifter on the I2C lines to bring them back down to 3.3V

Coconuts
 
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Re: Supply voltage for HT16K33 Breakout

Post by Coconuts »

Thanks, Rick. That will really simplify things. Surprising, but welcome.

Kevin

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adafruit_support_mike
 
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Re: Supply voltage for HT16K33 Breakout

Post by adafruit_support_mike »

The numbers that make it into a datasheet have a safety margin because datasheets are legal documents and parts manufacturers don't like being sued. The usual margin is six standard deviations, meaning you can expect 999,999 parts out of every million to meet the published specs, and the vendor will happily replace the one that doesn't. Sticking to the conservative estimates is important when you're building products in lots of 100,000, but you can be more daring about playing the odds with one-off projects.

Running a chip below the datasheet voltage usually won't damage anything. The most common effect is that the chip won't meet its timing specs.. a logic chip spec'd to run at 85MHz at 5v may only be reliable up to 10MHz at 3.3v. It's up to the circuit designer to find the part's limits for off-spec applications, then decide whether those limits are acceptable.

Fading LEDs allows pretty loose tolerances, and we've found that the HT16K33's works just fine at 3.3v.

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