L6235 查看數據表（PDF） - STMicroelectronics
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L6235 Datasheet PDF : 25 Pages
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L6235
Figure 8. Output Current Regulation Waveforms
IOUT
VREF
RSENSE
tOFF
tON
VSENSE
VREF
0
1µs tBLANK
Slow Decay
tOFF
1µs tBLANK
Slow Decay
VRC
5V
tRCRISE
tRCRISE
2.5V
ON
tRCFALL
1µs tDT
tRCFALL
1µs tDT
SYNCHRONOUS RECTIFICATION
OFF
D02IN1351
B
C
DAB
C
D
Figure 9 shows the magnitude of the Off Time tOFF versus COFF and ROFF values. It can be approximately cal-
culated from the equations:
tRCFALL = 0.6 · ROFF · COFF
tOFF = tRCFALL + tDT = 0.6 · ROFF · COFF + tDT
where ROFF and COFF are the external component values and tDT is the internally generated Dead Time with:
20KΩ ≤ ROFF ≤ 100KΩ
0.47nF ≤ COFF ≤ 100nF
tDT = 1µs (typical value)
Therefore:
tOFF(MIN) = 6.6µs
tOFF(MAX) = 6ms
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 will only be an issue if the capacitor is not completely charged before the next time the
monostable is triggered. Therefore, the On Time tON, which depends by motors and supply parameters, has to
be bigger than tRCRISE for allowing a good current regulation by the PWM stage. Furthermore, the On Time tON
can not be smaller than the minimum on time tON(MIN).
tON > tON(MIN) = 1.5µs (typ. value)
tON
>
tRCRISE
–
tDT
tRCRISE = 600 · COFF
10/25
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