Hi
I made the motor current circuit on page 10 from this h-bridge datasheet (off time control)
http://www.national.com/ds/LM/LMD18200.pdf
A strange thing however is how they made the logic of the h-bridge behaviour which i unfortunately ddin't notice before i build the PCB for the circuit. According to the truth table on page 6, when PWM goes low and the brake is low the motor will be shorted (which is exactly what the brake does but i put that pin low which i find odd).
PWM DIR Brake Active Drivers
H | H | L | Source 1, Sink 2
H | L | L | Sink 1, Source 2
L | X | L | Source 1, Source 2
H | H | H | Source 1, Source 2
H | L | H | Sink 1, Sink 2
L | X | H | NONE
This resulted in strange things when i used the circuit.. If i changed the reference rapidly the motor would stall which is not very preferrable for my purpose.
I noticed that this can be bypassed by inverting the pwm signal and feeding that to the brake pin.. This according to the datasheet must be delayed by 1us.. I need help for the design of that very simple inverter circuit (maybe with some sort of schmitt trigger?)
the help would be much much appreciated!
Thank you!
I made the motor current circuit on page 10 from this h-bridge datasheet (off time control)
http://www.national.com/ds/LM/LMD18200.pdf
A strange thing however is how they made the logic of the h-bridge behaviour which i unfortunately ddin't notice before i build the PCB for the circuit. According to the truth table on page 6, when PWM goes low and the brake is low the motor will be shorted (which is exactly what the brake does but i put that pin low which i find odd).
PWM DIR Brake Active Drivers
H | H | L | Source 1, Sink 2
H | L | L | Sink 1, Source 2
L | X | L | Source 1, Source 2
H | H | H | Source 1, Source 2
H | L | H | Sink 1, Sink 2
L | X | H | NONE
This resulted in strange things when i used the circuit.. If i changed the reference rapidly the motor would stall which is not very preferrable for my purpose.
I noticed that this can be bypassed by inverting the pwm signal and feeding that to the brake pin.. This according to the datasheet must be delayed by 1us.. I need help for the design of that very simple inverter circuit (maybe with some sort of schmitt trigger?)
the help would be much much appreciated! Thank you!
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