TC9402EJD【PDF 16/28 页】IC V-FREQ/FREQ-V CONV 14CDIP

TC9400/9401/9402

DS21483D-page 16

?2007 Microchip Technology Inc.

FIGURE 6-4: DC 10kHz 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/Vs response time by

using the circuit in Figure6-1. 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+

F

OUT

/2

F

OUT

Output

Common

10

9

8

5

3

12

12pF

C

REF

56pF

C

INT

1000pF

R

INT

1M?/DIV>

60pF

Amp

Out

V

OUT

V

SS

I

BIAS

1

4

10k?/DIV>

2.2k?/DIV>

100k?/DIV>

2k?/DIV>

-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

47pF

V

OUT

TC9400

12

3

5

V

REF

OUT

I

IN

GND

AMP OUT

6

.001礔

+

1

3

2

.01礔

1M?nbsp 0.1礔

+5

7

6

4

-5

TL071

200?/DIV>

M?/DIV>

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