Datasheet

TC9400/9401/9402
DS21483D-page 16 © 2007 Microchip Technology Inc.
FIGURE 6-4: DC – 10 kHz Converter.
6.4 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
integrating Analog-to-Digital Converter, such as the
TC7107. The ripple can also be reduced by increasing
the value of the integrating capacitor, although this will
reduce the response time of the F/V converter.
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 6-1. The circuit is a
capacitance 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.
FIGURE 6-5: Ripple Filter.
TC9400A
TC9401A
TC9402A
+5V
14
V
DD
V+
V+
F
OUT
/2
F
OUT
Output
Common
10
9
8
5
3
12
12 pF
C
REF
56 pF
C
INT
1000 pF
R
INT
1MΩ
60 pF
Amp
Out
V
OUT
V
SS
I
BIAS
14
10 kΩ
2.2 kΩ
100 kΩ
2kΩ
-5V
+5V
Zero Adjust
2
7
(Typically -5V)
V
REF
F
IN
11
Threshold
Detector
3ms
Delay
*
*
*
*Optional If
Buffer is Needed
Offset
Adjust
V
REF
OUT
I
IN
42
–
+
Op
Amp
+
V
REF
See
Figure 7-1:
Frequency
Input Level
Shifter
6
GND
Threshold
Detect
1
47 pF
V
OUT
TC9400
12
3
5
V
REF
OUT
I
IN
GND
AMP OUT
6
.001 µF
+
–
1
3
2
.01 µF
1MΩ
0.1 µF
+5
7
6
4
-5
TL071
200Ω
MΩ
MΩ