TC820 datasheet(21/28 Pages) MICROCHIP

21 / 28 page

DS21476B-page 21

TC820

5.11

External Peak Detection

The TC820 will hold the highest A/D conversion or fre-

quency reading indefinitely when the PKHOLD input is

connected to VDD. However, the analog peak input

must be present during the A/D converter's signal inte-

grate period. For slowly changing signals, such as tem-

perature, the peak reading will be properly converted

and held.

If rapidly changing analog signals must be held, an

external peak detector should be added. An inexpensive

circuit can be made from an op amp and a few discrete

components, as shown in Figure 5-12. The droop rate of

the external peak detector should be adjusted so that the

held voltage will not decay below the desired accuracy

level during the converter's 400msec conversion time.

FIGURE 5-12:

EXTERNAL PEAK

DETECTOR

5.12

Liquid Crystal Display (LCD)

The TC820 drives a triplex (multiplexed 3:1) LCD with

three backplanes. The LCD can include decimal points,

polarity sign, and annunciators for over range, peak

hold, high and low logic levels, and low battery.

Table 5-2 shows the assignment of the display seg-

ments to the backplanes and segment drive lines. The

backplane drive frequency is obtained by dividing the

oscillator frequency by 240.

Backplane waveforms are shown in Figure 5-13. These

appear on outputs BP1, BP2, and BP3. They remain the

same, regardless of the segments being driven.

FIGURE 5-13:

BACKPLANE

WAVEFORMS

Other display output lines have waveforms that vary

depending on the displays values. Figure 5-13 shows a

set of waveforms for the a, g, d outputs of one digit for

several combinations of "on" segments.

FIGURE 5-14:

TYPICAL DISPLAY

OUTPUT WAVEFORMS

TABLE 5-2:

LCD BACKPLANE AND

SEGMENT ASSIGNMENTS

*Connect both pins 2 and 16 of LCD to TC820 BP3 of output.

VDD

TC820

VSS

VIN+

PKHOLD

0.01µF

Offset Null

1N4148

+9V

10k

Ω

VIN

TL061

BP1

BP2

BP3

40-Pin

(PDIP)

44-Pin

(PQFP)

LCD Display

Pin Number

BP1

BP2

BP3

140

LOW

241

"—"

HIGH

544

DP3

OVER

DP2

PEAK

DP1

2,16*

—

BP1

—

BATT

LOW

BP2

BP3

VDD

VDISP

VDD

VDISP

VDD

VDISP

VDD

VDISP

Segment

Line

All OFF

a Segment

d, g OFF

a, g ON

d OFF

All ON

TC820 датащи(PDF) 21 Page - Microchip Technology

TC820 датащи(HTML) 21 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

датащи скачать

ссылки URL