TC820CPL datasheet(12/22 Pages) TELCOM

12 / 22 page

3-160

TELCOM SEMICONDUCTOR, INC.

3-3/4 A/D CONVERTER WITH

FREQUENCY COUNTER

AND LOGIC PROBE

TC820

In systems where common-mode voltages exist, the

86dB common-mode rejection ratio minimizes error. Com-

mon-mode voltages do, however, affect the integrator out-

put level. A worst-case condition exists if a large, positive

VCM exists in conjunction with a full-scale, negative differen-

tial signal. The negative signal drives the integrator output

positive along with VCM (Figure 9). For such applications, the

integrator output swing can be reduced below the recom-

mended 2V full-scale swing. The integrator output will swing

within 0.3V of VDD or VDD without increased linearity error.

Reference (VDD, VSS)

The TC820 reference, like the analog signal input, has

true differential inputs. In addition, the reference voltage can

be generated anywhere within the power supply voltage of

the converter. The differential reference inputs permit

ratiometric measurements and simplify interfacing with sen-

sors, such as load cells and temperature sensors.

DP3

DP2

DP1

0Hz – 3999Hz

4kHz – 39.99kHz

40kHz – 399.9kHz

400kHz

≥

DP3

DP2

DP1

NONE

DECIMAL POINT

fIN

Figure 5. TC820 Auto-Range Decimal Point Selection

vs Frequency Counter Input

HIGH

LOW

LCD

DRIVERS

DISABLE A/D CONVERTER

BUZZER

DP0/LO

DP1/HI

LOGIC

CMOS

LOGIC

LEVELS

EXTERNAL

LOGIC LEVEL

DETECTION

AND PULSE

STRETCHING

VDD

TC820

LOGIC

PROBE

INPUT

LCD

Figure 6. Logic Probe Simplified Schematic

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