I'm trying to breadboard something to show a colleague, and my LMD18200 is being recalcitrant. The circuit is so simple it's practically a reference ckt:
Pin 1 - 22n ceramic to pin 2 Pin 2 - Goes to motor (output 1) Pin 3 - Direction input Pin 4 - Brake input, tied low (not braking) Pin 5 - PWM input, tied to +5V Pin 6 - +24V input Pin 7 - GND Pin 8 - Not used (current sense output). Pin 9 - Not used (thermal flag output) Pin 10 - Output 2 Pin 11 - 22n ceramic to pin 10.
Additionally, I have a 220uF 63V bypass cap between pins 6 and 7.
When I set pin 3 @ +5V, output 1 shows a slightly asymmetric 24V square wave with a period of about 15.2ms, but the motor is at least running in the right direction. Very suspicious that this noise is so close to AC line frequency.
When I have pin 3 LOW, I see an odd noise waveform on both outputs, and the chip starts to draw about 450mA on the 24V line. (The motor only draws 60mA).
The 22n caps should nominally be 10nF, but I didn't have any lying around so I subbed in the closest value I have. But these don't seem to be critical anyway, because I still see exactly the same symptom when I remove those caps.
What am I doing wrong? I googled and found a few sample circuits on the web, e.g. and except for some sugar in those circuits that isn't in mine, I'm doing exactly the same things in exactly the same ways.
Very frustrating, because I've used this chip many times before and it was always very simple.