mbed LPC1768 with optocoupler for 5 V output

Question

I am generating a PWM at 20kHz to drive a motor. The signal goes into a motor controller which range is from 0 to 5 volts.

Since the PWM output is 3.2 volts I need to amplify it. For that I am using this optocoupler:

This is the electronic circuit I am using:

The optocouplers are inverted, pin 1 is down-right. The capacitors are 0.1uf as specified in the datasheet and the resistors are 330 ohms.

The optocoupler output is not working, it gives me less than one volt.

I already try supplying the optocouplers Vcc with an external power source, but the result is the same.

^{simulate this circuit – Schematic created using CircuitLab}

Answer 1

Look at figure 13 in the datasheet. There is a load resistor between Vcc and the output pin. This is an open collector output, so you can use it to sink current from the motor, but only if you connect the positive of the motor to Vcc externally.