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TC500COE View Datasheet(PDF) - TelCom Semiconductor Inc => Microchip

Part NameTC500COE TelCom-Semiconductor
TelCom Semiconductor Inc => Microchip TelCom-Semiconductor
DescriptionPRECISION ANALOG FRONT ENDS
TC500COE Datasheet PDF : 17 Pages
1 2 3 4 5 6 7 8 9 10 Next Last
PRECISION ANALOG FRONT ENDS
1 TC500
TC500A
TC510
TC514
1
RINT CINT
tINT
0
VIN (t) dt =
VREF tDEINT
RINT CINT
where:
VREF = Reference Voltage
tINT = Signal Integration time (fixed)
tDEINT = Reference Voltage Integration time (variable)
For a constant VIN:
VIN = VREF
tDEINT
tINT
The dual-slope converter accuracy is unrelated to the
integrating resistor and capacitor values as long as they are
stable during a measurement cycle.
An inherent benefit is noise immunity. Input noise spikes
are integrated (averaged to zero) during the integration
periods. Integrating ADCs are immune to the large conver-
sion errors that plague successive approximation convert-
ers in high-noise environments.
Integrating converters provide inherent noise rejection
with at least a 20dB/decade attenuation rate. Interference
signals with frequencies at integral multiples of the integra-
tion period are, theoretically, completely removed since the
average value of a sine wave of frequency (1/t) averaged
over a period (t) is zero.
Integrating converters often establish the integration
period to reject 50/60Hz line frequency interference signals.
The ability to reject such signals is shown by a normal mode
rejection plot (Figure 4). Normal mode rejection is limited in
practice to 50 to 65dB, since the line frequency can deviate
by a few tenths of a percent (Figure 3).
80
70
t = 0.1 sec
60
50
40
30
NORMAL
MODE = 20 LOG
REJECTION
SIN 60 π t (1 ± D1E00V)
60t (1 ± D1E00V)
DEV = DEVIATION FROM 60 Hz
t = INTEGRATION PERIOD
20
0.01
0.1
1.0
LINE FREQUENCY DEVIATION FROM 60 Hz (%)
Figure 3. Line Frequency Deviation
TELCOM SEMICONDUCTOR, INC.
30
T = MEASUREMENT
PERIOD
2
20
10
0
0.1/T
1/T
INPUT FREQUENCY
10/T
Figure 4.. Integrating Converter Normal Mode Rejection
3
4 TC500/500A/510/514 CONVERTER OPERATION
The TC500/500A/510/514 incorporates an Auto zero
and Integrator phase in addition to the input signal Integrate
and reference Deintegrate phases. The addition of these
phases reduce system errors and calibration steps, and
shorten overrange recovery time. A typical measurement
cycle uses all four phases in the following order:
(1) Auto zero
(2) Input signal integration
5
(3) Reference deintegration
(4) Integrator output zero
The internal analog switch status for each of these
phases is summarized in Table 1. This table is referenced
6 to the Functional Block Diagram on the first page of this data
sheet.
Auto-Zero Phase (AZ)
During this phase, errors due to buffer, integrator and
comparator offset voltages are nulled out by charging CAZ
(auto-zero capacitor) with a compensating error voltage.
7 The external input signal is disconnected from the
internal circuitry by opening the two SWI switches. The
internal input points connect to analog common. The refer-
ence capacitor is charged to the reference voltage potential
through SWR. A feedback loop, closed around the integrator
and comparator, charges the CAZ capacitor with a voltage to
compensate for buffer amplifier, integrator and comparator
offset voltages.
8
3-25
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GENERAL DESCRIPTION
The TC500/500A/510/514 family are precision analog front ends that implement dual slope A/D converters having a maximum resolution of 17 bits plus sign. As a minimum, each device contains the integrator, zero crossing comparator and processor interface logic. The TC500 is the base (16 bit max) device and requires both positive and negative power supplies. The TC500A is identical to the TC500, except it has improved linearity allowing it to operate to a maximum resolution of 17 bits. The TC510 adds an on board negative power supply converter for single supply operation. The TC514 adds both a negative power supply converter and a 4 input differential analog multiplexer.

FEATURES
■ Precision (up to 17 Bits) A/D Converter "Front End"
■ 3-Pin Control Interface to Microprocessor
■ Flexible: User Can Trade-Off Conversion Speed for Resolution
■ Single Supply Operation (TC510/514)
■ 4 Input, Differential Analog MUX (TC514)
■ Automatic Input Voltage Polarity Detection
■ Low Power Dissipation ........... TC500/500A: 10mW
                                          TC510/514: 18mW
■ Wide Analog Input Range ....... ±4.2V (TC500A/510)
■ Directly Accepts Bipolar and Differential Input Signals

 

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