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TELCOM SEMICONDUCTOR, INC.

Figure 2. Basic Dual-Slope Converter

PHASE

CONTROL

COMPARATOR

INTEGRATOR

CINT

ANALOG

INPUT

(VIN)

SWITCH DRIVER

REF

VOLTAGE

CONTROL

LOGIC

POLARITY

CONTROL

S1

I/O

TIMER

COUNTER

ROM

RAM

MICROCOMPUTER

AB

CMPTR OUT

VSUPPLY

±

TINT

TC510

VINT

VIN

VFULL SCALE

VIN

1/2 VFULL SCALE

TDEINT

–

+

RINT

VINT

–

+

PIN DESCRIPTION (Cont.)

Pin No

Pin No

Pin No

(TC500/A)

(TC510)

(TC514)

Symbol

Description

10

Negative analog input pin. MUX channel 4

20

A0

Multiplexer input channel select input LSB. (See A1).

19

A1

Multiplexer input channel select input MSB.

00 = Channel 1

Phase control input pins: A1, A0 =

01 = Channel 2

10 = Channel 3

11 = Channel 4

GENERAL THEORY OF OPERATION

Dual-Slope Conversion Principles (Figure 2)

Actual data conversion is accomplished in two phases:

input signal Integration and reference voltage Deintegration.

The integrator output is initialized to 0V prior to the start

of Integration. During Integration, analog switch S1 con-

integrator output to depart 0V at a rate determined by the

During Deintegration, S1 connects a reference voltage

At the same time, an external precision timer is started. The

Deintegration phase is maintained until the comparator

output changes state, indicating the integrator has returned

to its starting point of 0V. When this occurs, the precision

measured by the precision timer, is directly proportional to

the magnitude of the applied input voltage.

A simple mathematical equation relates the Input

Signal, Reference Voltage and Integration time:

PRECISION ANALOG FRONT ENDS

TC500

TC500A

TC510

TC514