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I'm confused regarding how much current 5LP GPIO pins can drive; any help is appreciated.

Here's where I get confused:

  1. The CY8CKIT-059's "User LED BLUE" is an LTST-C170TBKT from Lite-On Inc.
  2. This LED has a DC Forward Current of 20 mA, according to its data sheet.
  3. On the CY8CKIT-059, this LED is driven by a single pin P2_1 (via a 820 ohm resister), according to the CY8CKIT-059 schematics.
  4. Cypress AN72382, ยง 2.4 states "In general, [PSOC 5LP] GPIO pins can source 4 mA."

My confusion: If the PSOC 5LP GPIO pins can only source 4 mA (unless ganged), then how can pin P2_1 drive enough current to light "User LED BLUE" if that LED has a DC Forward Current of 20 mA?

What am I missing here?

I'm sure it is something really obvious.

Thanks in advance,

-Chris

chris
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1 Answers1

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The key distinction is source vs. sink, the pins can source less current than they can sink. Note: The concepts should be considered in terms of conventional current flow (positive to negative.)

Sourcing current involves connecting the I/O pin to VCCIOx (positive). Sinking current involves connecting the I/O pin to GROUND.

When driving a LED we will typically connect the LED to a positive voltage source, then to the I/O pin through a resistor. When we want the LED to turn on, the pin must sink current to ground. The pins can control more current this way.

enter image description here

(Image from CircuitsToday.com)

Burt_Harris
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