TC7106CPL datasheet(17/34 Pages) MICROCHIP

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DS21455D-page 17

TC7106/A/TC7107/A

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

measurement 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 20 ppm/°C.

This potential can be used to generate the reference

voltage.

external

voltage

reference

will

unnecessary in most cases because of the 50 ppm/°C

maximum temperature coefficient. See Section 8.5

“Internal Voltage Reference”.

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

internally 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 10 mA 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.

BUF

INT

POL

Segment

Drive

OSC1

OSC3

OSC2

V-

V+

REF+

REF -

Analog

Common

V-

V+

V-

V+

GND

Measured

System

Power

Source

LCD Display

TC7106A

IN -

IN +

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

REF +

24k

REF

Set V

REF

= 1/2 V

FULL SCALE

V+

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