Hi, since the RST pin has a 100k pulldown, can I connect a 1M resistor between that and my 40V VMOT to give it the approx 4V pullup voltage it needs?
I’ll connect RST to SLP and put a small filter cap on them to GND.
VMOT will have a 100uF 63V cap across it.
I want to do this as I don’t have enough wires in my current wiring to run a separate logic supply.
Thanks!
Hello.
The driver also pulls the SLEEP pin down through an internal 1MΩ pull-down resistor, which will be in parallel with the 100k pull-down on RESET, but the digital inputs only need 2.2V to read as logic high, so using a 1M pull-up should be fine. However, please note that this could be a bit risky if there is too much noise or voltage spikes on the motor supply line, so a separate logic supply connection is probably still preferable.
Brandon
Brilliant, thanks Brandon.
Yes I’d forgotten to factor in the 1Meg pulldown on the SLEEP pin.
If the 1Meg resistor to VMOT doesn’t work I’ll try 820K, that should give close to 10:1 division with the 2 pulldown resistors.
I’m looking to use a 100nF cap from those 2 pins to Gnd to help with spikes/noise, which hopefully should only be small after the 1Meg resistor… do you think this is an appropriate value?
Or should I go further and make a low pass RC filter on the feed to the pins?
I guess I’ll give it a go and see what happens!
Adding capacitance to the supply voltage line should help reduce noise, but it’s still possible to see some voltage spikes, especially while controlling a motor. 100nF seems like a reasonable starting point. ideally, if you have access to a scope, you could use it to look at the supply voltage and add more if necessary.
Brandon
