HI7106 데이터 시트보기 (PDF) - Intersil

부품명

상세내역

제조사

HI7106

3½ Digit, LCD/LED Display, A/D Converter

Intersil 

HI7106

System Timing

Figure 7 shows the clocking arrangement used in the

HI7106. Two basic clocking arrangements can be used:

• Figure 7A. An external oscillator connected to pin 40.

• Figure 7B. An R-C oscillator using all three pins.

The oscillator frequency is divided by four before it clocks the

decade counters. It is then further divided to form the three

convert-cycle phases. These are signal integrate (1000

counts), reference de-integrate (0 to 2000 counts) and

auto-zero (1000 to 3000 counts). For signals less than full

scale, auto-zero gets the unused portion of reference de-inte-

grate. This makes a complete measure cycle of 4,000 counts

(16,000 clock pulses) independent of input voltage. For three

readings/second, an oscillator frequency of 48kHz would be

used.

To achieve maximum rejection of 60Hz pickup, the signal

integrate cycle should be a multiple of 60Hz. Oscillator

frequencies of 240kHz, 120kHz, 80kHz, 60kHz, 48kHz,

40kHz, 331/3kHz, etc. should

tion, Oscillator frequencies of

be selected. For 50Hz rejec-

200kHz, 100kHz, 662/3kHz,

50kHz, 40kHz, etc. would be suitable. Note that 40kHz (2.5

readings/second) will reject both 50Hz and 60Hz (also

400Hz and 440Hz).

INTERNAL TO PART

÷4

CLOCK

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 be selected to give the

maximum voltage swing that ensures tolerance buildup will

not saturate the integrator swing (approximately. 0.3V from

either supply). In the HI7106, when the analog COMMON is

used as a reference, a nominal +2V full- scale integrator

swing is fine. For three readings/second (48kHz clock) nomi-

nal values for ClNT are 0.22µF and 0.10µF, respectively. Of

course, if different oscillator frequencies are used, these val-

ues 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 undetectable

errors at reasonable cost.

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 recov-

ery from overload and is adequate for noise on this scale.

40

39

38

TEST HI7106

FIGURE 7A.

INTERNAL TO PART

÷4

CLOCK

Reference Capacitor

A 0.1µF capacitor gives good results in most applications.

However, where a large common mode voltage exists (i.e.,

the REF LO pin is not at analog COMMON) 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.

Oscillator Components

For all ranges of frequency a 100kΩ resistor is recommended

and the capacitor is selected from the equation:

40

39

38

R

C

RC OSCILLATOR

FIGURE 7B.

FIGURE 7. CLOCK CIRCUITS

Component Value Selection

Integrating Resistor

Both the buffer amplifier and the integrator have a class A

output stage with 100µA of quiescent current. They can

f = 0--R--.--4-C--5-- For 48kHz Clock (3 Readings/sec),

C = 100pF.

Reference Voltage

The analog input required to generate full scale output (2000

counts) is: VlN = 2VREF. Thus, for the 200mV and 2V scale,

VREF should equal 100mV and 1V, respectively. However, in

many applications where the A/D is connected to a

transducer, there will exist a scale factor other than unity

between the input voltage and the digital reading. For

instance, in a weighing system, the designer might like to

have a full scale reading when the voltage from the

transducer is 0.662V. Instead of dividing the input down to

200mV, the designer should use the input voltage directly

7

Share Link: