TC7106 데이터 시트보기 (PDF) - TelCom Semiconductor Inc => Microchip
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TC7106 Datasheet PDF : 19 Pages
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TC7106
TC7106A
TC7107
TC7107A
3-1/2 DIGIT A/D CONVERTERS
Decimal Point and Annunciator Drive
The TEST pin is connected to the internally-generated
digital logic supply ground through a 500 Ω resistor. The
TEST pin may be used as the negative supply for external
CMOS gate segment drivers. LCD display annunciators for
decimal points, low battery indication, or function indication
may be added without adding an additional supply. No more
than 1mA should be supplied by the TEST pin: its potential
is approximately 5V below V+.
V+
TC7106A
BP 21
TEST 37
V+
4049
GND
TO LCD
DECIMAL
POINT
TO LCD
BACK-
PLANE
V+ BP
TC7106A
DECIMAL
POINT
SELECT
V+
TO LCD
DECIMAL
POINTS
TEST
4030
GND
Ratiometric Resistance Measurements
The true differential input and differential reference
make ratiometric reading possible. Typically in a ratiometric
operation, an unknown resistance is measured with respect
to a known standard resistance. No accurately defined
reference voltage is needed.
The unknown resistance is put in series with a known
standard and a current passed through the pair. The voltage
developed across the unknown is applied to the input and
the voltage across the known resistor is applied to the
reference input. If the unknown equals the standard, the
display will read 1000. The displayed reading can be deter-
mined from the following expression:
R Unknown
Displayed Reading =
x 1000
R Standard
The display will overrange for R Unknown ≥ 2 x R
standard.
RSTANDARD
RUNKNOWN
VR+EF V+
VR–EF
VI+N
TC7106A
VI–N
ANALOG
COMMON
LCD DISPLAY
Figure 17. Low Parts Count Ratiometric Resistance
Measurement
Figure 16. Decimal Point Drive Using TEST as Logic Ground
3-198
TELCOM SEMICONDUCTOR, INC.
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