M7206

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

8 of 8

www.unisonic.com.tw

QW-R502-Q37.A



Detailed Description(Cont.)

TEST

The TEST pin serves two functions. Within IC it is coupled to the internally generated digital supply through an

NMOS. 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. The second function is a “lamp test”.

When TEST is pulled high(to V+)all segment will be turned on and output should be “1888”.

Component Value Selection

Integrating Resistor

Both the buffer amplifier and the integrator have an output stage with 100μA of quiescent current. They can supply

4μA of drive current with negligible nonlinearity. The integrating resistor should be large enough to remain in this

very linear region over the input voltage range, but small enough that undue leakage requirements are not placed on

the PC board. For 2V full scale, 470kΩ is near optimum and similarly a 47kΩ for a 200mV scale.

Integrating Capacitor

The integrating capacitor should give the maximum voltage swing that ensures tolerance buildup will not saturate

the integrator swing (approximately. 0.3V from either supply). When the analog COMMON is used as a reference, a

nominal +2V full-scale integrator swing is fine. For three readings /second (48 kHz clock) nominal values for ClNT

are 0.22μF and 0.10μF, respectively. Of course, if different oscillator frequencies are used, these values should be

changed in inverse proportion to maintain the same output swing.

An additional requirement of the integrating capacitor is that it must have a low dielectric absorption to prevent

roll-over errors. While other types of capacitors are adequate for this application, polypropylene capacitors give the

best choice.

Auto-Zero Capacitor

The size of the auto-zero capacitor has some influence on the noise of the system. For 200mV full scale where

noise is very important, a 0.47μF capacitor is recommended. On the 2V scale, a 0.047μF capacitor increases the

speed of recovery from overload and is adequate for noise on this scale.

Oscillator Components

For all ranges of frequency a 100kΩ resistor is recommended and the capacitor is selected from the equation:

f0.45 /RC



For 48kHz clock(3 Reading/sec),

C=100pF.

Reference Capacitor

A 0.1μF capacitor gives good results in most applications. However, where a large common mode voltage exists

and a 200mV scale is used, a larger value is required to prevent roll-over error. Generally 1μF will hold the roll-over

error to 0.5 count in this instance.

Reference Voltage

The analog input required to generate full scale output (2000 counts) is:

IN

REF

V2V



. Thus, for the 200mV and 2V

scale,

REF

V

should equal 100mV and 1V, respectively. However, in some applications the full-scale input voltage may

be other than 200mV or 2V, but 600mV. For example, the reference voltage should be set to 300mV and the input

signal can be used directly without being divided.

The differential reference can be used during the measurement of resistor by the ratio metric method and when a

and the voltage of being measured is connected between COM and IN HI.

UTC assumes no responsibility for equipment failures that result from using products at values that

exceed, even momentarily, rated values (such as maximum ratings, operating condition ranges, or

other parameters) listed in products specifications of any and all UTC products described or contained

herein. UTC products are not designed for use in life support appliances, devices or systems where

malfunction of these products can be reasonably expected to result in personal injury. Reproduction in

whole or in part is prohibited without the prior written consent of the copyright owner. The information

presented in this document does not form part of any quotation or contract, is believed to be accurate

and reliable and may be changed without notice.