3-255

TELCOM SEMICONDUCTOR, INC.

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Component

Value

Nominal Full-Scale Voltage

200mV

2V

0.47

µF

0.1

µF

180 k

Ω

1.8 M

Ω

0.047

µF

0.047

µF

output voltage back to zero during the reference integrate

when V

–

mode voltage exists (V

–

1

µF. Roll-over error will be held to less than 0.5 count. A

Mylar-type dielectric capacitor is adequate.

voltage swing without causing output saturation. Analog

common will normally supply the differential voltage refer-

ence this case, a

±2V full-scale integrator output swing is

0.047

µF value is suggested. For one reading per second,

0.15

µF is recommended. If a different oscillator frequency

maintain the nominal

±2V integrator swing.

Oscillator Components

equation:

.

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,

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

lator frequencies of 200kHz, 100kHz, 66-2/3 kHz, 50kHz,

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

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

Reference Voltage Selection

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

signal be twice the reference voltage.

0.45

RC

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

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

200 mV. This permits the transducer input to be used

directly.

The differential reference can also be used when a

This is common in temperature measuring instrumentation.

A compensating offset voltage can be applied between

analog common and V

–

between V

+

DEVICE PIN FUNCTIONAL DESCRIPTION

Differential Signal Inputs

V

+

–

The TC7136/A is designed with true differential inputs

and accepts input signals within the input stage common-

+1V. Common-mode voltages are removed from the system

when the TC7136A operates from a battery or floating power

Required Full-Scale Voltage*

200 mV

100 mV

2V

1V

roll-over error. A polypropylene capacitor is recommended.

The input buffer amplifier and integrator are designed

with Class A output stages. The output stage idling current

is 6

µA. The integrator and buffer can supply 1 µA drive

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

large that PC board leakage currents induce errors. For a

1.8 M

Ω.

1

(

(

)

)

(4000)

LOW POWER, 3-1/2 DIGIT

ANALOG-TO-DIGITAL CONVERTERS

TC7136

TC7136A