Datasheet

L6229Q Circuit description
Doc ID 15209 Rev 3 15/28
t
RCRISE
= 600 · C
OFF
Figure 12 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 11. t
OFF
versus C
OFF
and R
OFF
Figure 12. Area where t
ON
can vary maintaining the PWM regulation
t
ON
t
ON MIN()
> 2.5μs=
t
ON
t
RCRISE
t
DT
–>
⎩⎭
⎨⎬
⎧⎫
(typ. value)
0.1 1 10 100
1
10
100
1
.
10
3
1
.
10
4
Coff [nF]
toff [μs]
R
off
= 100kΩ
R
off
= 47k
Ω
R
off
= 20k
Ω
0.1 1 10 100
1
10
100
Coff [nF]
ton(min) [us]
2.5
μ
s (typ. value)