AN1625 STMicroelectronics, AN1625 Datasheet - Page 13

• Manufacturer Part Number: AN1625
• Description: L6235 THREE PHASE BRUSHLESS DC MOTOR DRIVER
• Manufacturer: STMicroelectronics

Figure 13. Output Current Regulation Waveforms
Figure 14 shows the magnitude of the Off Time t
calculated from the equations:
where R
Therefore:
These values allow a sufficient range of t
The capacitor value chosen for C
Rise Time t
monostable is triggered. Therefore, the On Time t
be bigger than t
can not be smaller than the minimum on time t
R
V
V
SENSE
I
SENSE
OUT
V
REF
2.5V
OFF
V
ON
5V
REF
t
t
20K
0.47nF
t
t
t
0
RC
RCFALL
OFF
DT
OFF(MIN)
OFF(MAX)
OFF
= 1µs (typical value)
= t
RCRISE
SYNCHRONOUS RECTIFICATION
and C
D02IN1351
RCFALL
= 0.6 · R
R
= 6.6µs
RCRISE
C
OFF
= 6ms
OFF
OFF
will only be an issue if the capacitor is not completely charged before the next time the
+ t
100K
OFF
are the external component values and t
for allowing a good current regulation by the PWM stage. Furthermore, the On Time t
100nF
DT
= 0.6 · R
· C
OFF
OFF
OFF
also affects the Rise Time t
· C
OFF
OFF
B
to implement the drive circuit for most motors.
ON(MIN)
+ t
Slow Decay
t
RCFALL
DT
ON
OFF
1 s t
t
1 s t
t
RCRISE
OFF
C
, which depends by motors and supply parameters, has to
.
versus C
BLANK
DT
D
OFF
DT
RCRISE
is the internally generated Dead Time with:
t
ON
and R
A
AN1625 APPLICATION NOTE
of the voltage at the pin RC
OFF
B
values. It can be approximately
Slow Decay
t
RCFALL
1 s t
t
1 s t
t
RCRISE
OFF
C
BLANK
DT
D
OFF
. The
13/39
ON