TC820CPL datasheet(21/22 Pages) TELCOM

21 / 22 page

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TELCOM SEMICONDUCTOR, INC.

BP1

BP2

BP3

TC820

3-3/4 A/D CONVERTER WITH

FREQUENCY COUNTER

AND LOGIC PROBE

VDD

VDISP

VDD

VDISP

VDD

VDISP

VDD

VDISP

SEGMENT

LINE

ALL OFF

a SEGMENT

d, g OFF

a, g ON

d OFF

ALL ON

Figure 24. Backplane Waveforms

LCD Source

Although most users will design their own custom LCD,

a standard display for the TC820 (Figure 26), Part No. ST-

1355-M1, is available from:

Crystaloid (USA)

Crystaloid (Europe)

Crystaloid Electronics

Rep France

P.O. Box 628

102, rue des Nouvelles

5282 Hudson Dr.

F92150 Suresnes

Hudson, OH 44238

France

Phone: (216) 655-2429

Phone: 33-1-42 04 29 25

Fax: (216) 655-2176

Fax: 33-1-45 06 46 99

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.

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 connection

for VDISP. Figure 27 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 voltage because VDISP

cannot exceed 0.3V below GND.

Crystal Source

Two sources of the 40 kHz crystal are:

Statek Corp.

SPK Electronics

512 N. Main St.

2F-1, No. 312, Sec. 4,

Orange, CA 92668

Jen Ai Rd

Phone: (714) 639-7810

Taipei, Taiwan R.O.C.

Fax: (714) 997-1256

Phone: (02) 754-2677

Part #: CX-1V-40.0

Fax: 886-2-708-4124

Part#: QRT-38-40.0kHz

Figure 26. Typical TC820 LCD

Figure 25. Typical Display Output Waveforms

HIGH

LOW

OVER

PEAK

BATT

PIN 1

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