Indication LED driver IC

[alank2]

Probably only need to drive the LED at 4-5mA, but want to drive a bunch of them, perhaps 50 or so.  No shift registers as each one is an independent signal.  You could use logic buffers and resistors, but my question is, are there any better LED driver IC's for this type of job that have a high impedance input and can constant current drive LED's without a resistor that have X channels?  What do you recommend?

[ajb]

You could check the LED driver catalogs at TI, NXP, etc, but I don't think there's really any demand for such parts in high channel counts and low currents.  Mostly when you want to drive a bunch of LEDs you want to use as few pins as possible, hence I2C/SPI interfaces.  There are single-channel current source ICs, but those aren't going to save you any money or board space.  Is a set of regular octal buffers (assuming you really need high impedance inputs) and some resistor packs not a simple/cheap enough solution?

[james_s]

Can they be multiplexed or Charliplexed?

[alank2]

No, they are all individual signals.  It sounds like the best way is a buffer and resistors.

[Benta]

74HC4066 plus a resistor per LED. Or ULN2003 plus resistors. I don't think you can do it simpler or cheaper.

[5upercircuits]

Might be a little unconventional solution, but you could also try using I2C I/O expanders. They've got multiple channels that would allow you to save some I/O space on the uCT. Some of them can handle driving LEDs quite well.

However, they might not really be what you're looking for and are also not always cheap.

[Benta]

Might be a little unconventional solution, but you could also try using I2C I/O expanders.

What's difficult to understand about "all individual signals"?   

[David Chamberlain]

Line drivers?

http://www.ti.com/lit/ds/symlink/sn74lvth16543.pdf

[westfw]

For 4-5mA, there are a bunch of standard logic drivers that should work fine.   The BEAM Robotics folks recommend 74ACxx series drivers as generally delivering higher currents.  You need resistors, though.  (China has bunch of LED driver chips, but I don't know of anything offhand with individual IO.)

Heh.  For a "legacy microprocessor front panel", I've considered using a microcontroller that has parallel inputs and drives the LEDs multiplexed.  So a cheap 40pin uC (~32 IO) could easily do 24 inputs/LEDs.  (I mean, you only have to update the LEDs at human-compatible speeds, right?)  A "minor SW change" could output in Hex/Octal/OLED instead...