TC9401 datasheet(17/24 Pages) MICROCHIP

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DS21483C-page 17

TC9400/9401/9402

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

FIGURE 7-5:

Ripple Filter

TC9400A

TC9401A

TC9402A

+5V

VDD

V+

FOUT/2

FOUT

Output

Common

12 pF

CREF

56 pF

CINT

1000 pF

RINT

1 M

60 pF Amp

Out

VOUT

VSS

IBIAS

10 k

2.2 k

100 k

2 k

-5V

+5V

Zero Adjust

(Typically -5V)

VREF

FIN

Threshold

Detector

3msec

Delay

*Optional/If

Buffer is Needed

Offset

Adjust

VREF

OUT

IIN

–

Amp

VREF

See

Figure 7-1:

"Frequency

Input Level

Shifter"

GND

Threshold

Detect

47 pF

VOUT

TC9400

VREF OUT

IIN

GND

AMP OUT

.001

μF

–

.01

μF 1M

0.1

μF

-5

TL071

200

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