EVAL6208N Datasheet, PDF (13/27 Pages) STMicroelectronics – DMOS DRIVER FOR BIPOLAR STEPPER MOTOR

L6208
^tON ^{> t}ON(MIN) ^{= 1.5µ s (typ. value)}


t_ON
>
t_RCRISE
–
t_DT
t_RCRISE = 600 · C_OFF
Figure 13 shows the lower limit for the on time t_ON for having a good PWM current regulation capacity. It has to
be said that t_ON is always bigger than t_ON(MIN) because the device imposes this condition, but it can be smaller
than t_RCRISE - t_DT. In this last case the device continues to work but the off time t_OFF is not more constant.
So, small C_OFF value gives more flexibility for the applications (allows smaller on time and, therefore, higher
switching frequency), but, the smaller is the value for C_OFF, the more influential will be the noises on the circuit
performance.
Figure 12. t_OFF versus C_OFF and R_OFF
1 ^.104
R_off = 100kΩ
1 ^.103
R_off = 47kΩ
R_off = 20kΩ
100
10
1
0.1
1
10
100
Coff [nF]
Figure 13. Area where t_ON can vary maintaining the PWM regulation.
100
10
1.5µs (typ. value)
1
0.1
1
10
100
Coff [nF]
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