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Can the LP3943 source current as well, or only sink it? Answered

The link to the data sheet is here.


All it talks about is sinking current, so my guess is yes.  I really wanted to use two of these to get a huge multiplexed array of LEDs, but one of them would need to be able to source the current, can it with the pins set high?  If not, are there other ICs like this that can do so?

Thanks!

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steveastroukBest Answer (author)2011-08-12

You need sourcing switches and controlled sinking drivers, like the max6977 or the a6275.

For the source switches, you could use PNP transistors
Steve

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mojofilta (author)steveastrouk2011-08-12

I would be able to use the LP3943 and transistors for the source switches, right? Then I could have everything on an I2C bus, address the rows to turn on through one set of LP3943's and the columns to ground through the drains of more LP3943's. I'm pretty sure that the automated PWM dimming of them is disable-able, since that would mess up the muxing.

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steveastrouk (author)mojofilta2011-08-12

Personally, I'd use the chips I suggested, and SPI bus, its a lot faster. PWM dimming can be applied globally then too, by judicious control of the OE pins.


Steve

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mojofilta (author)steveastrouk2011-08-12

Is there a reason the Maxim chips are more expensive?

Just so you know, the A6275 has been retired, the newer version is the A6282. I can chain the data-ins to the data-outs and communicate to each independently by raising the latch enable pin then dropping it at the appropriate times. That sounds good, I didn't realize I2C was slower than SPI, but at up to 30MHz, SPI sounds tough to beat with simple microcontrollers. There also doesn't seem to be a need for much supporting circuitry, which is a plus, although, is there a need for resistors on the data lines, or capacitors on the driver lines, since I'll be running a ton of LEDs (I'm aiming for a 16x32 panel) ?

I'm aiming to control this via an Arduino.

Thanks for all the help!

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seandogue (author)2011-08-11

No. it's designed to sink only. If you can get your hands on them, there's a 1x8 or 1x16 (can't remember) 74HCT... multiplexer that might drive 10-15mA LEDS.

Possibly, this might do the trick too, if they're not all on at the same time

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mojofilta (author)seandogue2011-08-11

Actually, I think that last option could be perfect, assuming what the data sheet refers to as the "analog channels" are the switched ones, because it says those can operate with +/-15 volts, so I could put the Vcc on the "output" side and have the switches set the individual "inputs" high. I apologize for the lack of grammar, its getting late; I may also have a lack of logic, is the above possible?

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mojofilta (author)mojofilta2011-08-12

Actually, I think I was having a lack of logic. It seems doubtful that the IC would work with negative inputs, and I think the listed +/- 15 volt rating is for the supply only. >.< Oh well. This setup would work with transistors to provide the source side of the multiplex though, correct?

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steveastrouk (author)2011-08-12

The A6282 is a fine part too, Allegro Semi do them.

You CAN address each chip individually, but you can also chain right through them all at once. The overhead of SPI is minimal.

There is no need for any pull-ups, capacitors or anything with SPI either.

Steve

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