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How much current can the MCP23017 handle?
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Please be positive and constructive with your questions and comments.

How much current can the MCP23017 handle?

by MStylesMS on Mon Aug 14, 2017 11:38 am

My application is that I want to drive 16 LED's (20 mA each) with an MCP23017. As I look at the data sheet I see that each pin can sink up to 25 mA, but the maximum current out of Vss appears to be 150 mA. So, it appears that driving 16 LED's at 20 mA would result in 320 mA.

I can think of several strategies of how to handle this, but before I try to implement those I wanted to confirm that I'm understanding this correctly. I've seen examples on the Internet of driving 16 LED's with nothing but 220 Ohm current limiting resistors which gets the current down to 9 mA (which gets me down to 144 mA), but then I'm concerned about the brightness of the LED's.

Can you confirm if my understanding is correct?

MStylesMS
 
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Re: How much current can the MCP23017 handle?

by adafruit_support_bill on Mon Aug 14, 2017 11:44 am

In any case, current limiting resistors are needed for the leds. Don't rely on the chip maximum current rating for current limiting. That leads to fried chips and/or leds.

There are a few strategies if you want to drive a large number of leds:
1) use current limiting to limit the sum of all led currents to <150mA.
2) limit the number of leds that are on at a given time. (e.g via multiplexing)
3) use transistors on the outputs to switch higher current loads.
4) switch to a led driver chip like the TLC5947 orTLC59711
https://www.adafruit.com/product/1429
https://www.adafruit.com/product/1455

adafruit_support_bill
 
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Please be positive and constructive with your questions and comments.