TC9400/9401/9402
FIGURE 7-4:
DC - 10kHz CONVERTER
+5V
14
V+
V+
V
DD
*
F
/2
OUT
10
9
TC9400A
TC9401A
TC9402A
42
Output
Common
See
*
Figure 7-1:
Threshold
Detect
*
"Frequency
Input Level
Shifter"
F
OUT
8
11
3µsec
Delay
F
IN
*Optional/If
Buffer is Needed
Threshold
Detector
V
REF
OUT
5
C
REF
56pF
12pF
60pF
Offset
Adjust
I
IN
3
R
INT
C
INT
1000pF
+
+5V
100kΩ
2.2kΩ
Amp
Out
1MΩ
–
12
Op
Amp
+
V
OUT
Zero Adjust
2
2kΩ
I
V
V
7
BIAS
SS
4
REF
GND
6
1
10kΩ
V
REF
(Typically -5V)
-5V
FIGURE 7-5:
RIPPLE FILTER
7.4
Output Filtering
The output of the TC9400 has a sawtooth ripple super-
imposed on a DC level. The ripple will be rejected if the
TC9400 output is converted to a digital value by an inte-
grating analog-to-digital converter, such as the TC7107
or TC7109. The ripple can also be reduced by increas-
ing the value of the integrating capacitor, although this
will reduce the response time of the F/V converter.
5
3
V
OUT
REF
47pF
TC9400
I
IN
.001µF
1M
200
12
AMP OUT
The sawtooth ripple on the output of an F/V can be
eliminated without affecting the F/V's response time by
using the circuit in Figure 7-5. The circuit is a capaci-
tance multiplier, where the output coupling capacitor is
multiplied by the AC gain of the Op Amp. A moderately
fast Op Amp, such as the TL071, should be used.
1M
0.1µF
.01µF
GND
+5
6
V
OUT
7
4
2
–
6
TL071
3
+
1M
-5
DS21483B-page 14
2002 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
