TC820CPL datasheet(11/22 Pages) TELCOM

11 / 22 page

3-159

TELCOM SEMICONDUCTOR, INC.

If the logic probe is active while FREQ/VOLTS is high

(counter mode), the frequency counter will continue to

operate. The display will read "OL" but the decimal points will

be visible. If the logic probe input is also connected to the

RANGE/FREQ input, bringing the LOGIC input low will

immediately display the frequency at the logic probe input.

Analog Pin Functional Description

Differential Signal Inputs (V

IN), (V

–

IN)

The TC820 is designed with true differential inputs, and

accepts input signals within the input stage common-mode

voltage (VCM) range. The typical range is VDD –1V to VSS

+1.5V. Common-mode voltages are removed from the sys-

tem when the TC820 operates from a battery or floating

power source (isolated from measured system) and VSS is

connected to analog common. (See Figure 8.)

TC820

3-3/4 A/D CONVERTER WITH

FREQUENCY COUNTER

AND LOGIC PROBE

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

when a 40 kHz oscillator is used. The frequency counter

accuracy is determined by the oscillator accuracy. 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 3.999 kHz to 3.999 MHz. Decimal points are

set automatically in the frequency mode (Figure 5).

The logic switching levels of the RANGE/FREQ input

are CMOS levels. For best counter operation, an external

buffer is recommended. See the applications section for

details.

Logic Probe

The TC820 can also function as a simple logic probe

(Figure 6). 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 frequency counter input, external level

shifters/buffers are recommended for the logic probe inputs.

When the logic probe function is selected while FREQ/

VOLTS is low (A/D mode), the ADC will remain in the auto-

zero mode. The LCD will read "OL" and all decimal points will

be off (Figure 7).

DATA LATCH, PEAK

HOLD REGISTER,

LCD DECODER/DRIVERS

OVERRANGE

DETECT

UNDERRANGE

DETECT

AUTO-RANGE

CONTROL

PROGRAMMABLE

DIVIDER

(

÷1, 10, 100, 1000)

CLOCK

OSCILLATOR

TO DECIMAL

POINT DRIVERS

FREQUENCY

INPUT

RANGE/

FREQ

÷20,000

FROM INTEGRATOR

OF A/D CONVERTER

COMPARATOR

LCD

3-3/4 DIGIT COUNTER

ENABLE

COUNT

OVERFLOW

A/D CONVERTER

FREQUENCY COUNTER

A/D CONVERTER/FREQUENCY

COUNTER SELECT

TC820

÷2

FREQ/

VOLTS

Figure 4. TC820 Counter Operation

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