TC820CPL datasheet(22/28 Pages) MICROCHIP

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TC820

DS21476B-page 22

5.13

LCD Source

Although most users will design their own custom LCD,

a standard display for the TC820 (Figure 5-15), Part No.

ST-1355-M1, is available from the following sources:

Crystaloid (USA)

Crystaloid Electronics

P.O. Box 628

5282 Hudson Drive

Hudson, OH 44238

Phone: 216-655-2429

Crystaloid (Europe)

Rep. France

102, rue des Nouvelles

F92150 Suresnes France

Phone: 33-1-42-04-29-25

Fax: 33-1-45-06-46-99

FIGURE 5-15:

TYPICAL TC820 LCD

5.14

Annunciator Output

The annunciator output is a square wave running

at the backplane frequency (for example, 167Hz when

FOSC = 40kHz). The peak-to-peak amplitude is equal to

(VDD –VDISP). Connecting an annunciator of the LCD

to the annunciator output turns it on; connecting it to its

backplane turns it off.

5.15

LCD Drive Voltage (VDISP)

The peak-to-peak LCD drive voltage is equal to (VDD –

VDISP). In the 40-pin dual in-line package (DIP), VDISP

is internally connected to DGND, providing a typical

LCD drive voltage of 5VP-P.

For applications with a wide temperature range, some

LCDs require that the drive levels vary with temperature

to maintain good viewing angle and display contrast. In

this case, the TC820 44-pin package provides a pin con-

nection for VDISP. Figure 5-16 shows TC820 circuits that

can be adjusted to give a temperature compensation of

about 10mV/°C between VDD and VDISP. The diode

between GND and VDISP should have a low turn on volt-

age because VDISP cannot exceed 0.3V below GND.

5.16

Crystal Source

Two sources of the 40kHz crystal are:

Statek Corp.

512 N. Main St.

Orange, CA 92668

Phone: 714-639-7810

Fax: 714-997-1256

Part #: CX-1V-40.0

SPK Electronics

2F-1, No. 312, Sec, 4, Jen Ai Rd.

Taipei, Taiwan R.O.C.

Phone: (02) 754-2677

Fax: 886-2-708-4124

Part #: QRT-38-40.0kHz

FIGURE 5-16:

TEMPERATURE COMPENSATING CIRCUITS

HIGH

LOW

OVER

PEAK

BATT

PIN 1

V+

VDISP

TC820

DGND

200k

Ω

39k

Ω

75k

Ω

1N4148

V-

V+

VDISP

TC820

DGND

V-

39k

Ω

20k

Ω

2N2222

18k

Ω

Note: Pin numbers shown are for 44-pin flat package.

TL071 1N5817

1N5817

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