TC7106 データシートの表示（PDF） - TelCom Semiconductor, Inc

部品番号

コンポーネント説明

メーカー

TC7106

3-1/2 DIGIT A/D CONVERTERS

TelCom Semiconductor, Inc 

3-1/2 DIGIT A/D CONVERTERS

1 TC7106

TC7106A

TC7107

TC7107A

Integrating Capacitor – CINT

CINT should be selected to maximize the integrator

output voltage swing without causing output saturation. Due

to the TC7106A/7107A superior temperature coefficient

specification, analog common will normally supply the differ-

ential voltage reference. For this case a ±2V full-scale

integrator output swing is satisfactory. For 3 readings/

second (fOSC = 48kHz) a 0.22µF value is suggested. If a

different oscillator frequency is used, CINT must be changed

in inverse proportion to maintain the nominal ±2 V integrator

swing.

An exact expression for CINT is:

(4000) ( 1 ) ( VFS )

CINT =

fOSC RINT

VINT

Where:

fOSC = Clock frequency at Pin 38

VFS = Full-scale input voltage

RINT = Integrating resistor

VINT = Desired full-scale integrator output swing

CINT must have low dielectric absorption to minimize

rollover error. A polypropylene capacitor is recommended.

Integrating Resistor – RINT

The input buffer amplifier and integrator are designed

with class A output stages. The output stage idling current

is 100µA. The integrator and buffer can supply 20µA drive

currents with negligible linearity errors. RINT is chosen to

remain in the output stage linear drive region but not so large

that printed circuit board leakage currents induce errors. For

a 200mV full-scale, RINT is 47kΩ. 2.0V full-scale requires

470kΩ.

Component

Nominal Full-Scale Voltage

Value

CAZ

RINT

CINT

Note:1.

200.0mV

0.47µF

47kΩ

0.22µF

fOSC = 48kHz (3 readings/sec)

2.000V

0.047µF

470kΩ

0.22µF

Oscillator Components

2 ROSC (Pin 40 to Pin 39) should be 100kΩ. COSC is

selected using the equation:

0.45

fOSC = RC

For fOSC of 48kHz, COSC is 100pF nominally.

Note that fOSC is divided by four to generate the TC7106A

3 internal control clock. The backplane drive signal is derived

by dividing fOSC by 800.

To achieve maximum rejection of 60Hz noise pickup,

the signal-integrate period should be a multiple of 60Hz.

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

48kHz, 40kHz, etc. should be selected. For 50 Hz rejection,

oscillator frequencies of 200kHz, 100kHz, 66 2/3kHz, 50kHz,

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

ings/second) will reject both 50Hz and 60Hz.

4

Reference Voltage Selection

A full-scale reading (2000 counts) requires the input

signal be twice the reference voltage.

Required Full-Scale Voltage*

200.0mV

2.000V

* VFS = 2 VREF

VREF

100.0mV

1.000V

5

In some applications a scale factor other than unity may

exist between a transducer output voltage and the required

digital reading. Assume, for example, a pressure transducer

output is 400mV for 2000 lb/in2. Rather than dividing the

6 input voltage by two the reference voltage should be set to

200mV. This permits the transducer input to be used

directly.

The differential reference can also be used when a

digital zero reading is required when VIN is not equal to zero.

This is common in temperature measuring instrumentation.

A compensating offset voltage can be applied between

analog common and VI–N. The transducer output is con-

7 nected

between

V

+

IN

and

analog

common.

The internal voltage reference potential available at

analog common will normally be used to supply the convert-

er's reference. This potential is stable whenever the supply

potential is greater than approximately 7V. In applications

where an externally-generated reference voltage is desired,

refer to Figure 7.

8

TELCOM SEMICONDUCTOR, INC.

3-193

Share Link: