Short version: would driving the Pico's pin (set to output PWM) in this diagram damage the pin?
I'm planning on using a Pico to drive the PWM pin of a Mean Well NLDD-700H LED driver (datasheet). The datasheet is a little light on details, but it says you can drive it from 100-1000Hz, 0V-0.8V is off, and 2.5V-5V is on. They also say you can leave the PWM pin open to turn the LEDs on at full power. That implies some sort of internal pull-up to get the pin above 2.5V.
I hooked up the NLDD-700H to 48V and measured the PWM pin with my multimeter. With the pin open, it measured 4.7V. With a 10kOhm resistor from the PWM pin to ground, I measured 0.5V to ground; with a 4.7kOhm resistor instead, I measured 0.25V to ground. So, it looks like there's a roughly 100kOhm pull up to ~5V inside the LED driver.
I am planning on adding my own pull-down connecting a resistor, as shown at the top of my post. (This will make sure the LEDs are off if the Pico has to restart or gets disconnected.) As a result, I'm effectively creating a voltage divider and my Pico shouldn't ever see the full 4.7V, but I'm not sure what will happen when I try to drive the pin high. Will it just go to 3.3V and stay there, or will the weak pull-up inside the LED driver cause the actual pin voltage to go higher (or feed back to the Pico's voltage source) and damage the Pico? Would the choice of 10k or 4.7k resistor affect the possibility of damage?
I hooked up the NLDD-700H to 48V and measured the PWM pin with my multimeter. With the pin open, it measured 4.7V. With a 10kOhm resistor from the PWM pin to ground, I measured 0.5V to ground; with a 4.7kOhm resistor instead, I measured 0.25V to ground. So, it looks like there's a roughly 100kOhm pull up to ~5V inside the LED driver.
I am planning on adding my own pull-down connecting a resistor, as shown at the top of my post. (This will make sure the LEDs are off if the Pico has to restart or gets disconnected.) As a result, I'm effectively creating a voltage divider and my Pico shouldn't ever see the full 4.7V, but I'm not sure what will happen when I try to drive the pin high. Will it just go to 3.3V and stay there, or will the weak pull-up inside the LED driver cause the actual pin voltage to go higher (or feed back to the Pico's voltage source) and damage the Pico? Would the choice of 10k or 4.7k resistor affect the possibility of damage?
Statistics: Posted by kickstart — Fri Mar 15, 2024 3:06 pm — Replies 1 — Views 64