Hi
I am working on a LED array controller based on PAM2863ECR LED driver IC controlled by a microcontroller atmega328p (datasheet: https://datasheet.lcsc.com/szlcsc/1811151536_Diodes-Incorporated-PAM2863ECR_C80312.pdf).

My problem is that the driver IC requires an "[Drive with] PWM signal from open-collector or open-drain transistor, to adjust output current. Adjustment range 1% to 100% of IOUTnom for f < 500Hz" (quote from datasheet). My problem is that i haven't heard anything about "open collector/open drain".
The results of my research so far is that I cant simply connect it to a PWM pin of the microcontroller. The solution I came up with is to place a cheap MOSFET in the date line as shown in the picture.

Is this a suitable solution?



Thank you for your help.
Matthias

 

Yes, provided the MOSFET is a logic-level type (which the 2N7002 is).

 

It depends on the current requirement of the LED and the current sink capacitor of the open collector/open drain output.

Open collector/open drain means that the output pin has no dedicated load attached.
You can connect
+POWER -> LOAD -> OPEN COLLECTOR/OPEN DRAIN PIN

The open collector/open drain pin will sink current into GND.



If the pin is not capable of sinking the desired load current then you resort to an external driver transistor such as 2N7000 as you have shown. In such a case you still need to give the open collector/open drain pin a load (aka pull up resistor).

 

Thank you for your answers.
I assume you mean a pull up resistor to +5V and not to VCC (8.6V-12.4V). Am I right?

 

No. I am referring to the MCU output.
If the MCU is ATmega328 then you do not need pullups.

I will assume that your problem is with regards to PAM2863ECR LED driver chip which I would have to study before I can understand your problem.

 

From the soft start formula (1nF gives 1.5ms) the Vset current is very low so any microcontroller would be able to drive it directly with PWM.

 

Okay so I can connect it directly to the MCU and use the normal PWM signal from it.

 

Okay so I can connect it directly to the MCU and use the normal PWM signal from it.

Probably, but it might be better if the micro can produce open drain PWM. Which micro would you want to use?

 

An ATmega328p-AU with the Arduino ISP.

might be better if the micro can produce open drain PWM

Thats why I was thinking about using the MOSFET.

 

You can't use the built-in PWM with an open drain output on the Arduino so you would need an external MOSFET.

 

So basically in this configuration?
To pull the IC Pin either to ground or to leave it floating right?
I am not sure if I really need the pull down resistor.

 

The resistor serves no useful purpose but otherwise that is the correct circuit.

 

Thank you for your help

 

The pulldown keeps the FET off until the micro has a chance to reconfigure the pin as an output. During reset, all GPIOs are set as inputs so the FET gate would float.