點晶科技股½有限公司
SILICON TOUCH TECHNOLOGY INC.
With PDM signal as input, passed through a low pass filter made up by R
A
, R
B
,
and C
IN
, will essentially get the averaged dc value. For the overall 256 steps with
duty ratio 50% and PDM base frequency
f
PDM
=
4.8
MHz
, the effectively PWM
frequency is 18.75 KHz. Therefore, the parameters, R
A
, R
B
, and C
IN
, of LPF
corresponding to the effectively PWM frequency will suggest in the following look
up table.
V
pp
=
2.6
(
V
)
,
f
PDM
=4.8
MHz
,
and
256
steps with
50%
duty
18.75
kHz PWM frequency effectively
R
IM
=1.5
Ω
Max. output
current
I (mA)
100
100
120
120
C
IN
(
μ
F
)
R
A
(
kΩ
)
R
B
(
kΩ
)
0.1
0.01
0.1
0.01
14.7
147
12.3
123
20
200
27.6
276
R
IM
=1.8
Ω
Max. output
current
I (mA)
100
100
120
120
C
IN
(
μ
F
)
R
A
(
kΩ
)
R
B
(
kΩ
)
0.1
0.01
0.1
0.01
12.3
123
10.2
102
27.6
276
50.2
502
SP-MD115-A.005.doc
Version
：
A.005
Page
：
11
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