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I need to drive 40 leds from a 5V power source. These leds are controlled from a raspberry and I was thinking to use 5 TPIC6B259 but I need a logic level shifting from 3.3 to 5 V for the input of TPIC6B259. I was looking a 3.3V device similar to the TPIC6B259 but I didn't find anything: only addressable latch without power mos (ex 74HC259). Adding 40 power mos is not convenient. Is it possible that the TPIC6B259 is the only addressable latch with power output? Can you please suggest me other solutions? Since the 3.3 power is sourced from raspberry I need a low power addressable latch followed by an open drain mosfet to drive (at 5V) the loads.

Thanks Fabio

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  • \$\begingroup\$ Do you really need 40 individual outputs? Above a few LEDs a matrix is ofte used. More complex is software, but less hardware. For the 3.3 -> 5V issue: check the datsheets, most 5V logic chips will accept a 3.3V input, especially HCT chips. \$\endgroup\$ Feb 27 '16 at 16:13
  • \$\begingroup\$ @WoutervanOoijen - but not the TPIC6B259. \$\endgroup\$ Feb 27 '16 at 17:12
  • \$\begingroup\$ How much current per LED do you need? \$\endgroup\$ Feb 27 '16 at 17:13
  • \$\begingroup\$ Thanks for your comments. Actually I need to drive each led individually because they are in different locations. I need 10-30 mA but, since I'm usign the raspberry, I have few mA at 3.3V and a lot of power at 5V: I could use some 3.3 logic without open-drain but in this case I should use a dc-dc from 5 to 3.3V to provide the needed power. \$\endgroup\$
    – Fabio
    Feb 28 '16 at 12:13
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You can use a simple NPN transistor with a pull-up resistor on each input. The downside is that you need 2 resistor + 1 transistor for each input. If I undestood, you need 3 pins for each IC for addressing (so 5*3) plus 1 input for data and whatever logic signals you may need. That's 16 transistors and 32 resistors. It's possible, but that's a lot of glue circuitry (and there's level shifting ICs on the market to do that).

Another way of doing it would be replacing the addressable latch by a shift register like TPIC6B595. It's high-power just like your latch. The nature of the shift register reduces the number of control signals (and level converters) as you can chain infinite ICs together.

The downside is that information needs to travel in a serial fashion and there's no individual addressing. If you want to light up an LED at the end of the row, you'll need to send the data for every LED on the row.

It will take some time (milisseconds) and you can either let the data flow through the LEDs like a pipe or shut them off until you flush all the data.

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  • \$\begingroup\$ Thanks, this is the way I'm going to use to solve the problem: level shifting ICs. Nice way of doing with shift register. It's very strange that the TPIC6B259 it's the only addrssable latch with open-drain \$\endgroup\$
    – Fabio
    Feb 28 '16 at 12:23

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