UTC7106

CMOS IC

8

QW-R502-018,B

only 10μA of source current, so COMMON may easily be tied to a more negative voltage thus overriding the internal

reference.

Iz

6.8V

ZENER

V-

V+

V

REF HI

REF LO

UTC 7106

COMMON

REF LO

REF HI

UTC 7106

V

20kΩ

6.8kΩ

ICL8069

V+

1.2V

REFERENCE

FIGURE 2B.

FIGURE 2A.

FIGURE 2. USING AN EXTERNAL REFERENCE

TEST

The TEST pin serves two function. On the UTC 7106 it is coupled to the internally generated digital supply through

a 500Ω resistor. Thus it can be used as the negative supply for externally generated segment drivers such as

decimal points or any other presentation the user may want to include on the LCD display. Figures 3 and 4 show

such an application. No more than a 1mA load should be applied.

The second function is a “lamp test”. When TEST is pulled high (to V+) all segments will be turned on and the

display should read ”1888”. The TEST pin will sink about 15mA under these conditions.

CAUTION: In the lamp test mode, the segments have a constant DC voltage (no square-wave) . This may burn the

LCD display if maintained for extended periods.

V+

TO LCD

BACKPLANE

1MΩ

TO LCE

DECIMAL

POINT

21

37

TEST

BP

UTC 7106

FIGURE 3. SIMPLE INVERTER FOR

FIXED DECIMAL POINT

V+

TEST

UTC 7106

BP

DECIMAL

POINT

SELECT

TO LCD

DECIMAL

POINTS

CD4030

GND

V+

FIGURE 4. EXCLUSIVE "OR" GATE FOR

DECIMAL POINT DRIVE

DIGITAL SECTION

Figure 5 show the digital section for the UTC 7106, respectively. In the UTC 7106, an internal digital ground is

generated from a 6V Zener diode and a large P-Channel source follower. This supply is made stiff to absorb the

relative large capacitive currents when the back plane(BP) voltage is switchied. The BP frequency is the clock

frequency divided by 800. For three readings/sec, this is a 60Hz square wave with a nominal amplitude of 5V. The