L6208Q View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'L6208Q' PDF : 34 Pages View PDF
Circuit description
L6208Q
These values allow a sufficient range of tOFF to implement the drive circuit for most motors.
The capacitor value chosen for COFF also affects the rise time tRCRISE of the voltage at the
pin RCOFF. The rise time tRCRISE is only an issue if the capacitor is not completely charged
before the next time the monostable is triggered. Therefore, the ON time tON, which
depends on motors and supply parameters, must be bigger than tRCRISE to allow a good
current regulation by the PWM stage. Furthermore, the ON time tON can not be smaller than
the minimum ON time tON(MIN).
Equation 4
tON tONMIN
tON tRCRISE – tDT
= 1,5styp
tRCRISE = 600 COFF
Figure 15 shows the lower limit for the ON time tON for having a good PWM current
regulation capacity. It should be mentioned that tON is always bigger than tON(MIN) because
the device imposes this condition, but it can be smaller than tRCRISE - tDT. In this last case
the device continues to work but the OFF time tOFF is not more constant.
Therefore, a small COFF value gives more flexibility to the applications (allows smaller ON
time and, therefore, higher switching frequency), but, the smaller the value for COFF, the
more influential the noises on the circuit performance.
Figure 14. tOFF vs. COFF and ROFF
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DocID018710 Rev 3
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