ICL7106CM44_Intersil_elenota.pl.pdf

Low Cost Digital Panel Meter Designs and

Complete Instructions for LCD and LED Kits

Application Note

AN023

Introduction

The ICL7106 and ICL7107 are the ﬁrst ICs to contain all the

active circuitry for a 3 1 / 2 digit panel meter on a single chip.

The ICL7106 is designed to interface with a liquid crystal

display (LCD) while the ICL7107 is intended for light-emitting

diode (LED) displays. In addition to a precision dual slope

converter, both circuits contain BCD to seven segment

decoders, display drivers, a clock and a reference. To build a

high performance panel meter (with auto zero and auto

polarity features) it is only necessary to add display, 4

resistors, 4 capacitors, and an input ﬁlter if required (Figures

1 and 2).

The ICL7136 is an ultra low power version of the ICL7106.

Except for the passive component values as shown in Figure

3 and Table 1, all references in this document to the ICL7106

also apply to the ICL7136.

TP5

TP1TP2

R 1

TP3

C 3

C 5

R 2

C 1

C 2

R 3

DISPLAY

C 4

C 1 = 0.1

C 2 = 0.47 µ

C 4 = 100pF

C 5 = 0.01 µ

R 1 = 24k

ICL7106

Ω

R 3 = 100k Ω

R 4 = 1k

TRIMPOT

R 5 = 1M

DISPLAY

FIGURE 1. LCD DIGITAL PANEL METER USING ICL7106

+5V

-5V

R 6

TO DECIMAL

POINT

TP5

TP1TP2

R 1

TP3

C 3

C 5

R 2

C 1

C 2

R 3

DISPLAY

C 4

C 1 = 0.1

C 2 = 0.47 µ

C 4 = 100pF

C 5 = 0.01 µ

R 1 = 24k

ICL7107

Ω

R 3 = 100k Ω

R 4 = 1k

TRIMPOT

R 5 = 1M

R 6 = 150

DISPLAY

FIGURE 2. LED DIGITAL PANEL METER USING ICL7107

C 3 = 0.22

R 2 = 47k

C 3 = 0.22

R 2 = 47k

Application Note 023

TP5

V+

AB4

POL

OSC 1

OSC 2

OSC 3

TEST

REF HI

REF LO

C REF

COMMON

IN HI

IN LO

A-Z

BUFF

INT

V -

R 3

180k Ω

C 4

50pF

TP1

R 4

TP2

R 1

10k

220k

C 1

TP3

R 5

DISPLAY

C 5

0.01 µ

1M Ω

C 2

0.01

R 2

180k Ω

C 3

0.047 µ

TP4

DISPLAY

FIGURE 3. LCD DIGITAL PANEL METER USING ICL7136

The Evaluation Kits

After purchasing a sample of the ICL7106 or the ICL7107,

the majority of users will want to build a simple voltmeter.

The parts can then be evaluated against the data sheet

speciﬁcations, and tried out in the intended application.

However, locating and purchasing even the small number of

additional components required, then wiring a breadboard,

can often cause delays of days or sometimes weeks. To

avoid this problem and facilitate evaluation of these unique

circuits, Intersil offers a kit which contains all the necessary

components to build a 3 1 / 2 digit panel meter. With the help of

this kit, an engineer or technician can have the system “up

and running” in about half an hour.

dramatically. Aside from the display, all the components can

easily be placed in less than 4 square inches of board

space.

Molex™ pins are used to provide a low cost IC socket; one

circuit board can thus be used to evaluate several ICs.

(Strips of 20 pins should be soldered onto the PC boards;

the top of the strip holding the pins together can then be

broken off by bending it back and forth using needle-nose

pliers.) Solder terminals are provided for the ﬁve test points,

and for the

5V input on the ICL7107 kit.

Full Scale Reading - 200mV or 2.000V?

The component values supplied with the kit are those

speciﬁed in the schematics of Figure 1 or Figure 2. They

have been optimized for 200mV full scale reading. The

complete absence of last digit jitter on this range illustrates

the exceptional noise performance of the ICL7106 and

ICL7107. In fact, the noise level (not exceeded 95% of time)

is about 15

Two kits are offered, ICL7106EV/KIT and ICL7107EV/KIT.

Both contain the appropriate IC, a circuit board, a display

(LCD for ICL7106EV/KIT, LEDs for ICL7107EV/KIT), passive

components, and miscellaneous hardware.

Assembly Instructions

The circuit board layouts and assembly drawings for both

kits are given in Figures 10, 11. The boards are single-sided

to minimize cost and simplify assembly. Jumpers are used to

allow maximum ﬂexibility. For example, provision has been

made for connecting an external clock (Test Point #5).

Provision has also been made for separating REF Lo from

COMMON when using an external reference zener. In a

production instrument, the board area could be reduced

V, a factor of 10 less than some competitive one

chip panel meters.

To modify the sensitivity for 2.000V full scale, the integrator

time constant and the reference should be changed by

substituting the component values given in Table 1. The

auto-zero capacitor (C 2 ) should also be changed. These

additional components are not supplied in the kits. In

addition, the decimal point jumper should be changed so the

display reads 2.000.

Molex® is a registered trademark of Molex Incorporated.

0.1 µ

Application Note 023

TABLE 1. COMPONENT VALUES FOR FULL SCALE OPTIONS

Before soldering the display onto the circuit board, make

sure that it is inserted correctly. Many LCD packages do not

have pin #1 marked, but the segments of an unenergized

display can be seen by viewing with reﬂected light.

COMPONENT

200.0mV

FULL SCALE

2.000V

FULL SCALE

C 2 (Mylar ™ )

0.47 µ F

0.047 µ F

R 1

24k Ω

1.5k Ω

(Note)

V+

R 2

47k Ω

470k Ω

V+

0.1 µ

0.022 µ F

220k Ω

150k Ω

ICL7106

DECIMAL

POINT

SELECT

TO LCD

DECIMAL

POINTS

180k Ω

1.8M Ω

SEGMENTS

CONTROL

(V+/GND)

10k Ω

100k Ω

NOTE: Changing R 1 to 1.5k Ω will reduce the battery life of the ICL7106

kit. As an alternative, the potentiometer can be changed to 25k Ω

TEST

CD4030

GND

Liquid Crystal Display (ICL7106)

Liquid crystal displays are generally driven by applying a

symmetrical square wave to the Back Plane (BP). To turn on

a segment, a waveform 180 o out of phase with BP (but of

equal amplitude) is applied to that segment. Note that

excessive DC voltages (>50mV) will permanently damage

the display if applied for more than a few minutes. The

ICL7106 generates the segment drive waveform internally,

but the user should generate the decimal point front plane

drive by inverting the BP (pin 21) output (Note 1). In

applications where the decimal point remains ﬁxed, a simple

MOS inverter can be used (Figure 4). For instruments where

the decimal point must be shifted, a quad exclusive OR gate

is recommended (Figure 5). Note that in both instances,

TEST (pin 37, TP1) is used as V- for the inverters. This pin is

capable of sinking about 1mA, and is approximately 5V

below V+. The BP output (pin 21) oscillates between V+ and

TEST.

FIGURE 5. EXCLUSIVE ‘OR’ GATE FOR DECIMAL POINT DRIVE

Light Emitting Diode Display (ICL7107)

The ICL7107 pulldown FETs will sink about 8mA per

segment. Using standard common anode 0.3in or 0.43in red

LEDs, this drive level produces a bright display suitable for

almost any indoor application. However, additional brightness

can be achieved through the use of Hewlett Packard high-

efficiency LEDs. Note that the display contrast can be

increased substantially by using a red filter. Reference [4]

discusses filter techniques and lists manufacturers of suitable

materials.

resistor. The

circuit boards supplied with the kit will accommodate either

HP 0.3in displays or the popular MAN 3700 types. The

difference between the two is that the HP has the decimal

point cathode on pin 6, whereas the MAN 3700 uses pin 9.

Due to the limited space on the circuit board, not all decimal

points are brought to jumper pads; it may be necessary to

wire directly from the 150

NOTE:

1. In some displays, a satisfactory decimal point can be achieved by

tying the decimal front plan to COMMON (pin 32). This pin is

internally regulated at about 2.8V below V+. Prolonged use of

this technique, however, may permanently burn-in the decimal,

because COMMON is not exactly midway between BP high and

BP lo.

resistor to the display. For

multiple range instruments, a 7400 series CMOS quad gate

or buffer should be used. The majority of them are capable

of sinking about 8mA.

V+

Capacitors

The integration capacitor should be a low dielectric-loss

type. Long term stability and temperature coefﬁcient are

unimportant since the dual slope technique cancels the

effect of these variations. Polypropylene capacitors have

been found to work well; they have low dielectric loss

characteristics and are inexpensive. However, that is not to

say that they are the only suitable types. Mylar capacitors

are satisfactory for C 1 (reference) and C 2 (auto-zero).

For a more detailed discussion of recommended capacitor

types, see page three of Reference [2].

IT1750

TO LCD

DECIMAL

POINT

ICL7106

TEST

TO LCD

BACKPLANE

FIGURE 4. SIMPLE INVERTER FOR FIXED DECIMAL POINT

Mylar is a trademark of E. I. Du Pont De Nemours and Company.

A ﬁxed decimal point can be turned on by tying the

appropriate cathode to ground through a 150

Application Note 023

The Clock

A simple RC oscillator is used in the kit. It runs at about

48kHz and is divided by 4 prior to being used as the system

clock (Figure 6). The internal clock period is thus 83.3 µ

The Reference

For 200.0mV full scale, the voltage applied between REF Hi

and REF Lo should be set at 100.0mV. For 2.000V full scale,

set the reference voltage at 1.000V. The reference inputs are

ﬂoating, and the only restriction on the applied voltage is that

it should lie in the range V- to V+.

and the signal integration period (1000 clock pulses) is

83.3ms. This gives a measurement frequency of 3 readings

per second since each conversion sequence requires 4000

clock pulses. Setting the clock oscillator at precisely 48kHz

will result in optimum line frequency (60Hz) noise rejection,

since the integration period is an integral number of line

frequency period. [2] Countries with 50Hz line frequencies

should set the clock at 50kHz.

The voltage between V+ and COMMON is internally

regulated at about 2.8V. This reference is adequate for many

applications and is used in the evaluation kits. It has a typical

temperature coefﬁcient of 100ppm/ o C.

The limitations of the on-chip reference should also be

recognized, however. With the ICL7107, the internal heating

which results from the LED drivers can cause some

degradation in performance. Due to its high thermal

resistance, plastic parts are poorer in this respect than

ceramic. The user is cautioned against extrapolating from

the performance of the kit, which is supplied with a ceramic

ICL7107, to a system using the plastic part. The combination

of reference TC, internal chip dissipation, and package

thermal resistance can increase noise near fullscale from

25 µ V to 80 µ V P-P .

The linearity in going from a high dissipation count such as

1000 (19 segments on) to a low dissipation count such as

1111 (8 segments on) can also suffer by a count or more.

Devices with a positive TC reference may require several

counts to pull out of an overload condition. This is because

overload is a low dissipation mode, with the three least

signiﬁcant digits blanked. Similarly, units with a negative TC

may cycle between overload and a nonoverload count as the

die alternately heats and cools. These problems are of

course eliminated if an external reference is used.

ICL7106/ICL7107

100k Ω

100pF

SYSTEM CLOCK

FIGURE 6. ICL7106/ICL7107 INTERNAL OSCILLATOR CLOCK

An external clock can also be used. In the ICL7106, the

internal logic is referenced to TEST. External clock

waveforms should therefore swing between TEST and V+

(Figure 7A). In the ICL7107, the internal logic is referenced

to GND so any generator whose output swings from ground

to +5V will work well (Figure 7B).

OSC1

The ICL7106, with its negligible dissipation, suffers from

none of these problems. In either case, an external

reference can easily be added as shown in Figures 8A or 8B.

TEST

ICL7106

FIGURE 7A. ICL7106

OSC1

ICL7107

FIGURE 7B. ICL7107

FIGURE 7. EXTERNAL CLOCK OPTIONS

Application Note 023

V+

CD4009

V+

REF HI

V+

OSC 1

6.8V

ZENER

REF LO

IN914

OSC 2

I Z

ICL7106

OSC 3

0.047

ICL7107

GND

IN914

V-

FIGURE 8A.

V- = 3.3V

V+

FIGURE 9. GENERATING NEGATIVE SUPPLY FROM +5V

V+

Input Filters

One of the attractive features of the ICL7106 and ICL7107 is

the extremely low input leakage current, typically 1pA at

25 o C. This minimizes the errors caused by high impedance

passive ﬁlters on the input. For example, the simple RC

(1M Ω /0.01 µ F) combination used in the evaluation kits

introduces a negligible 1

ICL7106

ICL7107

REF HI

ICL8069

1.2V

REFERENCE

REF LO

COMMON

V error.

FIGURE 8B.

Preliminary Tests

Auto Zero

With power on and the inputs shorted, the display should

read zero. The negative sign should be displayed about 50%

of the time, an indication of the effectiveness of the auto-zero

system used in the ICL7106 and ICL7107. Note that some

competitive circuits ﬂash negative on every alternate

conversion for inputs near zero. While this may look good to

the uninitiated, it is not a true auto zero system!

FIGURE 8. USING AN EXTERNAL REFERENCE

Power Supplies

The ICL7106 kit is intended to be operated from a 9V dry

cell. INPUT Lo is shorted to COMMON, causing V+ to sit

2.8V positive with respect to INPUT Lo, and V- 6.2V negative

with respect to INPUT Lo.

The ICL7107 kit should be operated from ±

5V. Noisy

Over-Range

Inputs greater than full scale will cause suppression of the

three least significant digits; i.e., only 1 or -1 will be displayed.

F capacitors to

ground at the point where the supplies enter the board.

INPUT Lo has an effective common mode range with

respect to GND of a couple of volts.

Polarity

The absence of a polarity signal indicates a positive reading.

A negative reading is indicated by a negative sign.

The precise value is determined by the point at which the

integrator output ramps within ~0.3V of one or other of the

supply rails. This is governed by the integrator time constant,

the magnitude and polarity of the input, the common mode

voltage, and the clock frequency: for further details, consult

the data sheet. Where the voltage being measured is

ﬂoating with respect to the supplies, INPUT Lo should be

tied to some voltage within the common mode range such as

GROUND or COMMON. If a -5V supply is unavailable,

suitable negative rail can be generated locally using the

circuit shown in Figure 9.

Further evaluation should be performed with the help of a

precision DC voltage calibrator such as Fluke Model 343A.

Alternatively a high quality 4 1 / 2 digit DVM can be used,

provided its performance has been measured against that of

a reliable standard.

DPM Components: Sources of Supply

It has already been shown that the ICL7106 and ICL7107

require an absolute minimum of additional components. The

only critical ones are the display and the integration capacitor.

The following list of possible suppliers is intended to be of

assistance in putting a converter design into production. It

should not be interpreted as a comprehensive list of

suppliers, nor does it constitute an endorsement by Intersil.

supplies should be bypassed with 6.8

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