TC7106A datasheet(16/32 Pages) MICROCHIP

16 / 32 page

TC7106/A/TC7107/A

DS21455C-page 16

FIGURE 8-2:

Common Mode Voltage Removed in Battery Operation with VIN- = Analog Common

The analog common pin serves to set the analog section

reference or common point. The TC7106A is specifically

designed to operate from a battery, or in any measure-

ment system where input signals are not referenced

(float), with respect to the TC7106A power source. The

analog common potential of V+ – 3.0V gives a 6V end of

battery life voltage. The common potential has a 0.001%

voltage coefficient and a 15

Ω output impedance.

With sufficiently high total supply voltage (V+ – V- >

7.0V), analog common is a very stable potential with

excellent temperature stability, typically 20ppm/°C.

This potential can be used to generate the reference

voltage. An external voltage reference will be unneces-

sary in most cases because of the 50ppm/°C maximum

temperature

coefficient.

See

Internal

Voltage

Reference discussion.

8.4

TEST (Pin 37)

The TEST pin potential is 5V less than V+. TEST may

be used as the negative power supply connection for

external CMOS logic. The TEST pin is tied to the inter-

nally generated negative logic supply (Internal Logic

Ground) through a 500

Ω resistor in the TC7106A. The

TEST pin load should be no more than 1mA.

If TEST is pulled to V+ all segments plus the minus sign

will be activated. Do not operate in this mode for more

than

several

minutes

with

the

TC7106A.

With

TEST = V+, the LCD segments are impressed with a

DC voltage which will destroy the LCD.

The TEST pin will sink about 10mA when pulled to V+.

8.5

Internal Voltage Reference

The analog common voltage temperature stability has

been significantly improved (Figure 8-3). The “A”

version of the industry standard circuits allow users to

upgrade old systems and design new systems without

external voltage references. External R and C values

do not need to be changed. Figure 8-4 shows analog

common supplying the necessary voltage reference for

the TC7106A/TC7107A.

FIGURE 8-3:

Analog Common

Temperature Coefficient

FIGURE 8-4:

Internal Voltage Reference

Connection

VBUF

CAZ

VINT

POL

Segment

Drive

OSC1

OSC3

OSC2

V-

V+

VREF+

VREF-

Analog

Common

V-

V+

V-

V+

GND

Measured

System

Power

Source

LCD Display

TC7106A

VIN-

VIN+

Typical

No Maximum Specified

Maximum

Specified

Maximum

Specified

Typical

200

180

160

140

120

100

ICL7136

7106A

ICL7106

Maximum

Limit

V-

Analog

Common

TC7106A

TC7107A

VREF+

24k

VREF-

VREF

Set VREF = 1/2 VFULL SCALE

V+

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