TC9402CPD datasheet(14/20 Pages) MICROCHIP

14 / 20 page

TC9400/9401/9402

DS21483B-page 14

FIGURE 7-4:

DC - 10kHz 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 increas-

ing the value of the integrating capacitor, although this

will reduce the response time of the F/V converter.

Thesawtoothrippleonthe output of anF/V canbe

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.

FIGURE 7-5:

RIPPLE FILTER

TC9400A

TC9401A

TC9402A

+5V

VDD

V+

FOUT/2

FOUT

Output

Common

12pF

CREF

56pF

CINT

1000pF

RINT

Ω

60pF

Amp

Out

VOUT

VSS

IBIAS

10k

Ω

2.2k

Ω

100k

Ω

-5V

+5V

Zero Adjust

(Typically -5V)

VREF

FIN

Threshold

Detector

µsec

Delay

*Optional/If

Buffer is Needed

Offset

Adjust

VREF

OUT

IIN

–

Amp

VREF

See

Figure 7-1:

"Frequency

Input Level

Shifter"

GND

Threshold

Detect

47pF

VOUT

TC9400

VREF OUT

IIN

GND

AMP OUT

.001

µF

–

.01

µF 1M

0.1

µF

-5

TL071

200

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