TC835CBU 查看數據表（PDF） - TelCom Semiconductor Inc => Microchip

零件编号

产品描述 (功能)

生产厂家

TC835CBU

PERSONAL COMPUTER DATA ACQUISITION A/D CONVERTER

TelCom Semiconductor Inc => Microchip 

PERSONAL COMPUTER

DATA ACQUISITION A/D CONVERTER

1

TC835

SW I

+ IN

SW

–

RI

SW

+

RI

REF

IN

SWR

CREF

SWZ

ANALOG

COM

SW

+

RI

SW

–

RI

ANALOG

INPUT BUFFER

+

RINT

–

SWIZ SWZ

CINT

CSZ

–

+

SWZ

INTEGRATOR

COMPARATOR

+

–

TO

DIGITAL

SECTION

SW I

– IN

SW1

SWITCH OPEN

SWITCH CLOSED

Figure 3E. Integrator Output Zero Phase

GENERAL THEORY OF OPERATION

(All Pin Designations Refer to 28-Pin DIP)

Dual-Slope Conversion Principles

The TC835 is a dual-slope, integrating analog-to-digital

converter. An understanding of the dual-slope conversion

technique will aid in following the detailed TC835 opera-

tional theory.

The conventional dual-slope converter measurement

cycle has two distinct phases:

(1) Input signal integration

(2) Reference voltage integration (deintegration)

The input signal being converted is integrated for a fixed

time period. Time is measured by counting clock pulses. An

opposite polarity constant reference voltage is then inte-

grated until the integrator output voltage returns to zero. The

reference integration time is directly proportional to the input

signal.

In a simple dual-slope converter, a complete conversion

requires the integrator output to "ramp-up" and "ramp-

down."

A simple mathematical equation relates the input signal,

reference voltage, and integration time:

∫ 1

tSI VIN(t) dt = VR tRI ,

RC 0

RC

where:

VR = Reference voltage

tSI = Signal integration time (fixed)

tRI = Reference voltage integration time (variable).

For a constant VIN:

[ ] VIN = VR

tRI

t SI

.

TELCOM SEMICONDUCTOR, INC.

The dual-slope converter accuracy is unrelated to the

2 integrating resistor and capacitor values, as long as they are

stable during a measurement cycle. An inherent benefit is

noise immunity. Noise spikes are integrated, or averaged, to

zero during the integration periods. Integrating ADCs are

immune to the large conversion errors that plague succes-

sive approximation converters in high-noise environments.

(See Figure 4.)

3 TC835 Operational Theory

The TC835 incorporates a system zero phase and

integrator output voltage zero phase to the normal two-

phase dual-slope measurement cycle. Reduced system

errors, fewer calibration steps, and a shorter overrange

recovery time result.

The TC835 measurement cycle contains four phases:

(1) System zero

(2) Analog input signal integration

4

(3) Reference voltage integration

(4) Integrator output zero

Internal analog gate status for each phase is shown in

Table 1.

ANALOG

INPUT

SIGNAL

INTEGRATOR

–

+

–COMPARATOR

+

5

REF

VOLTAGE

SWITCH

DRIVER

PHASE

CONTROL

CONTROL

LOGIC

POLARITY CONTROL

CLOCK

6

DISPLAY

COUNTER

VIN Ϸ VFULL SCALE

VIN Ϸ 1/2 VFULL SCALE

FIXED

SIGNAL

INTEGRATE

TIME

VARIABLE

REFERENCE

INTEGRATE

TIME

Figure 4. Basic Dual-Slope Converter

7

8

3-69

Share Link: