TC820CLW データシートの表示（PDF） - Microchip Technology

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TC820CLW

3-3/4 digit A/D converter with frequency counter and logic probe

Microchip Technology 

TC820

3.2.7 10:1 RANGE CHANGE

The analog input full scale range can be changed with

the RANGE/FREQ input. Normally, RANGE/FREQ is

held low by an internal pull-down. Connecting this pin

to VS+ will increase the full scale voltage by a factor

of 10. No external component changes are required.

The RANGE/FREQ input operates by changing the

integrate period. When RANGE/FREQ is connected to

VDD, the signal integration phase of the conversion is

reduced by a factor of 10 (i.e., from 2000 counts to 200

counts).

For the TC820, the 10:1 range change will result in ±4V

full scale. This full scale range will exceed the Common

mode range of the input buffer when operating from a

9V battery. If range changing is required for the TC820,

a higher supply voltage can be provided, or the input

voltage can be divided by 2 externally.

3.3 Frequency Counter

In addition to serving as an analog-to-digital converter,

the TC820 internal counter can also function as a fre-

quency counter (Figure 3-3). In the Counter mode,

pulses at the RANGE/FREQ input will be counted and

displayed.

The frequency counter derives its time-base from the

clock oscillator. The counter time-base is:

EQUATION 3-5:

tCOUNT = FOSC

40,000

Thus, the counter will operate with a 1-second time-

base when a 40kHz oscillator is used. The frequency

counter accuracy is determined by the oscillator accu-

racy. For accurate frequency measurements, a crystal

oscillator is recommended.

The frequency counter will automatically select the

proper range. Auto-range operation extends over four

decades, from 3.999kHz to 3.999MHz. Decimal points

are set automatically in the Frequency mode (Figure 3-4).

The logic switching levels of the RANGE/FREQ input

are CMOS levels. For best counter operation, an exter-

nal buffer is recommended. See the applications sec-

tion for details.

3.4 Logic Probe

The TC820 can also function as a simple logic probe

(Figure 3-5). This mode is selected when the LOGIC

input is high. Two dual purpose pins, which normally

control the decimal points, are used as logic inputs.

Connecting either input to a logic high level will turn on

the corresponding LCD annunciator. When the "low"

annunciator is on, the buzzer will be on. As with the fre-

quency counter input, external level shifters/buffers are

recommended for the logic probe inputs.

FIGURE 3-3:

TC820 COUNTER OPERATION

LCD

Clock

Oscillator

TC820

From Integrator

of A/D Converter

÷2

Comparator

Data Latch, Peak Hold

Register, LCD

Decoder/Drivers

FREQ/

VOLTS

÷20,000

A/D Converter/Frequency

Counter Select

A/D Converter

Frequency Counter

Enable

3-3/4 Digit Counter

Count

Overflow

To Decimal

Point Drivers

Under Range

Control

RANGE/

FREQ

Frequency Input

Programmable

Divider

( ÷1, 10, 100, 1000)

Auto-Range

Control

Over Range

Detect

© 2002 Microchip Technology Inc.

DS21476B-page 11

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