TC9400_06 Datasheet, PDF (17/24 Pages) Microchip Technology – Voltage-to-Frequency/Frequency-to-Voltage Converters

TC9400/9401/9402
+5V
14
V_DD
TC9400A
42
TC9401A
See
Figure 7-1:
TC9402A
Threshold
F_IN
"Frequency
Input Level
Detect ₁₁
Shifter"
3msec
Delay
Threshold
Detector
V+
*
F_OUT/2 ₁₀
Output
V+
Common ⁹ _*
*
F_{OUT 8}
*Optional/If
Buffer is Needed
Offset
Adjust
+5V
2 kΩ
-5V
100 kΩ _{2 Zero Adjust}
2.2 kΩ
I_BIAS
V_SS
1
4
10 kΩ
V_REF
7
–
Op
Amp
+
V_REF
(Typically -5V)
V_REF
OUT
5
12 pF
I_{IN 3}
60 pF _Amp
Out 12
C_REF
56 pF
R_INT
1 MΩ
C_INT
1000 pF
V_OUT
GND
6
FIGURE 7-4:
DC – 10 kHz Converter
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
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 7-1. 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.
FIGURE 7-1:
RIPPLE FILTER
V_REF OUT ⁵
TC9400 I_IN ³
AMP OUT 12
47 pF
1M ^{.001 μF}
200
GND
6
.01 μF ^1M
0.1 μF
2–
3+
1M
+5
7
6
4
-5
V_OUT
TL071
FIGURE 7-5:
Ripple Filter
© 2006 Microchip Technology Inc.
DS21483C-page 17