Datasheet

Circuit description L6229Q
14/28 Doc ID 15209 Rev 3
Figure 10. Output current regulation waveforms
Figure 11 shows the magnitude of the Off Time t
OFF
versus C
OFF
and R
OFF
values. It can be
approximately calculated from the equations:
t
RCFALL
= 0.6 · R
OFF
· C
OFF
t
OFF
= t
RCFALL
+ t
DT
= 0.6 · R
OFF
· C
OFF
+ t
DT
where R
OFF
and C
OFF
are the external component values and t
DT
is the internally generated
Dead Time with:
20 kΩ ≤ R
OFF
≤ 100 kΩ
0.47 nF ≤ C
OFF
≤ 100 nF
t
DT
= 1 µs (typical value)
Therefore:
t
OFF(MIN)
= 6.6 µs
t
OFF(MAX)
= 6 ms
These values allow a sufficient range of t
OFF
to implement the drive circuit for most motors.
The capacitor value chosen for C
OFF
also affects the Rise Time t
RCRISE
of the voltage at the
pin RCOFF. The rise time t
RCRISE
will only be an issue if the capacitor is not completely
charged before the next time the monostable is triggered. Therefore, the on time t
ON
, which
depends by motors and supply parameters, has to be bigger than t
RCRISE
for allowing a
good current regulation by the PWM stage. Furthermore, the on time t
ON
can not be smaller
than the minimum on time t
ON(MIN)
.
OFF
BC
DDA
t
ON
t
OFF
BC
ON
2.5V
0
Slow Decay Slow Decay
1μs t
BLANK
t
RCRISE
t
RCRISE
SYNCHRONOUS RECTIFICATION
1μs t
BLANK
5V
V
RC
V
SENSE
V
REF
I
OUT
V
REF
R
SENSE
D02IN1351
t
OFF
1μs t
DT
1μs t
DT
t
RCFALL
t
RCFALL