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PDF TC7129 Data sheet ( Hoja de datos )
| Número de pieza | TC7129 | |
| Descripción | 4-1/2 DIGIT ANALOG-TO-DIGITAL CONVERTER WITH ON-CHIP LCD DRIVERS | |
| Fabricantes | TelCom | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de TC7129 (archivo pdf) en la parte inferior de esta página. Total 15 Páginas | ||
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1
TC7129
4-1/2 DIGIT ANALOG-TO-DIGITAL CONVERTER
WITH ON-CHIP LCD DRIVERS
2
FEATURES
GENERAL DESCRIPTION
s Count Resolution ......................................... ±19,999
s Resolution on 200 mV Scale .......................... 10 µV
s True Differential Input and Reference
s Low Power Consumption ................... 500 µA at 9V
s Direct LCD Driver for 4-1/2 Digits, Decimal Points,
Low-Battery Indicator, and Continuity Indicator
s Overrange and Underrange Outputs
s Range Select Input ............................................ 10:1
s High Common-Mode Rejection Ratio ......... 110 dB
s External Phase Compensation Not Required
ORDERING INFORMATION
Part No.
TC7129CKW
TC7129CLW
TC7129CPL
Pin
Layout
Formed
—
Normal
Package
44-Pin PQFP
44-Pin PLCC
40-Pin PDIP
Temperature
Range
0°C to +70°C
0°C to +70°C
0°C to +70°C
TYPICAL OPERATING CIRCUIT
The TC7129 is a 4-1/2 digit analog-to-digital converter
(ADC) that directly drives a multiplexed liquid crystal dis-
play (LCD). Fabricated in high-performance, low-power
CMOS, the TC7129 ADC is designed specifically for high-
resolution, battery-powered digital multimeter applications.
The traditional dual-slope method of A/D conversion has
been enhanced with a successive integration technique to
produce readings accurate to better than 0.005% of full
scale, and resolution down to 10 µV per count.
The TC7129 includes features important to multimeter
applications. It detects and indicates low-battery condition.
A continuity output drives an annunciator on the display, and
can be used with an external driver to sound an audible
alarm. Overrange and underrange outputs and a range-
change input provide the ability to create auto-ranging
instruments. For snapshot readings, the TC7129 includes a
latch-and-hold input to freeze the present reading. This
combination of features makes the TC7129 the ideal
choice for full-featured multimeter and digital measurement
applications.
3
4
5
LOW BATTERY
CONTINUITY
V+
5 pF
20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
TC7129
120 kHz
6
21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
330 kΩ
*
0.1 µF
1 µF
150 kΩ
+ 10 kΩ
9V
+
0.1
µF
20
kΩ
100 kΩ
TC04
0.1 µF
10 pF
V+
–+
VIN
* NOTE: RC network between pins 26 and 28 is not required.
TELCOM SEMICONDUCTOR, INC.
7
8
TC7129-5 10/18/96
3-231
1 page  
4-1/2 DIGIT ANALOG-TO-DIGITAL
CONVERTER WITH ON-CHIP LCD DRIVERS
1
TC7129
PIN DESCRIPTIONS
Pin No.
40-Pin
TC7129CPL
34
35
36
Pin No.
44-Pin
TC7129CKW
32
33
34
Pin No.
44-Pin
TC7129CLW
38
39
40
37 35
41
38 36
42
39 37 43
40 38 44
6,17, 28, 39
12, 23, 34,1
Symbol
REF HI
REF LO
DGND
RANGE
DP2
DP1
OSC2
NC
Function
Positive reference voltage in
Negative reference voltage
Internal ground reference for digital section. See "±5V Power
Supply" paragraph.
3 µA pull-down for 200 mV scale. Pulled HI externally for 2V
scale.
Internal 3 µA pull-down. When HI, decimal point 2 will be on.
Internal 3 µA pull-down. When HI, decimal point 1 will be on.
Output of first clock inverter. Input of second clock inverter.
No Connection
2
3
COMPONENT SELECTION
(All pin designations refer to 40-Pin Dip)
The TC7129 is designed to be the heart of a high-
resolution analog measurement instrument. The only addi-
tional components required are a few passive elements, a
voltage reference, an LCD, and a power source. Most
component values are not critical; substitutes can be chosen
based on the information given below.
The basic circuit for a digital multimeter application is
shown in Figure 1. See "Special Applications" for variations.
Typical values for each component are shown. The sections
below give component selection criteria.
Oscillator (XOSC, CO1, CO2, RO)
The primary criterion for selecting the crystal oscillator
is to chose a frequency that achieves maximum rejection of
line-frequency noise. To do this, the integration phase
should last an integral number of line cycles. The integration
phase of the TC7129 is 10,000 clock cycles on the 200 mV
range and 1000 clock cycles on the 2V range. One clock
cycle is equal to two oscillator cycles. For 60 Hz rejection, the
oscillator frequency should be chosen so that the period of
one line cycle equals the integration time for the 2V range:
1/60 second = 16.7 msec =
1000 clock cycles * 2 osc cycles/clock cycle ,
oscillator frequency
4
The resistor and capacitor values are not critical; those
shown work for most applications. In some situations, the
capacitor values may have to be adjusted to compensate for
parasitic capacitance in the circuit. The capacitors can be
low-cost ceramic devices.
Some applications can use a simple RC network instead
of a crystal oscillator. The RC oscillator has more potential
for jitter, especially in the least significant digit. See "RC
Oscillator."
5
Integrating Resistor (RINT)
The integrating resistor sets the charging current for
the integrating capacitor. Choose a value that provides a
current between 5 µA and 20 µA at 2V, the maximum full-
scale input. The typical value chosen gives a charging
current of 13.3 µA:
6
ICHARGE =
2V 13.3 µA
150 kΩ
Too high a value for RINT increases the sensitivity to
noise pickup and increases errors due to leakage current.
Too low a value degrades the linearity of the integration,
leading to inaccurate readings.
7
giving an oscillator frequency of 120 kHz. A similar calcula-
tion gives an optimum frequency of 100 kHz for 50 Hz
rejection.
8
TELCOM SEMICONDUCTOR, INC.
3-235
5 Page 
4-1/2 DIGIT ANALOG-TO-DIGITAL
CONVERTER WITH ON-CHIP LCD DRIVERS
INTEGRATE
DEINTEGRATE
1
TC7129
2
TIME
OVERSHOOT DUE TO ZERO CROSSING
BETWEEN CLOCK PULSES
INTEGRATOR RESIDUE VOLTAGE
3
ZERO
INTEGRATE
AND LATCH
CLOCK PULSES
OVERSHOOT CAUSED BY
COMPARATOR DELAY OF
1 CLOCK PULSE
Figure 10. Accuracy Errors in Dual-Slope Conversion
4
INT1
INTEGRATE
DE1
DEINTEGRATE REST X10 DE2 REST X10 DE3 ZERO INTEGRATE
5
TC7129
NOTE: Shaded area greatly expanded
in time and amplitude.
6
INTEGRATOR RESIDUAL VOLTAGE
Figure 11. Integrator Waveform
Digital Auto-Zeroing
To eliminate the effect of amplifier offset errors, the
TC7129 uses a digital auto-zeroing technique. After the
input voltage is measured as described above, the mea-
surement is repeated with the inputs shorted internally. The
reading with inputs shorted is a measurement of the internal
errors and is subtracted from the previous reading to obtain
a corrected measurement. Digital auto-zeroing eliminates
the need for an external auto-zeroing capacitor used in other
ADCs.
Inside the TC7129
Figure 12 shows a simplified block diagram of the
TC7129.
7
Integrator Section
The integrator section includes the integrator, compara-
tor, input buffer amplifier, and analog switches used to
change the circuit configuration during the separate mea-
surement phases described earlier.
8
TELCOM SEMICONDUCTOR, INC.
3-241
11 Page | ||
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