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TC500ACPE View Datasheet(PDF) - Microchip Technology

Part NameTC500ACPE Microchip
Microchip Technology Microchip
DescriptionPrecision Analog Front Ends with Dual Slope ADC


TC500ACPE Datasheet PDF : 38 Pages
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7.0 TYPICAL APPLICATIONS
7.1 Component Value Selection
The procedure outlined below allows the user to arrive
at values for the following TC5XX design variables:
1. Integration Phase Timing.
2. Integrator Timing Components (RINT, CINT).
3. Auto-zero and Reference Capacitors.
4. Voltage Reference.
7.2 Select Integration Time
Integration time must be picked as a multiple of the
period of the line frequency. For example, TINT times of
33 ms, 66 ms and 132 ms maximize 60 Hz line
rejection.
7.3 DINT and IZ Phase Timing
The duration of the DINT phase is a function of the
amount of voltage stored on the integrator during TINT
and the value of VREF. The DINT phase must be initiated
immediately following INT and terminated when an
integrator output zero-crossing is detected. In general,
the maximum number of counts chosen for DINT is twice
that of INT (with VREF chosen at VIN(MAX) /2).
7.4 Calculate Integrating Resistor
(RINT)
The desired full-scale input voltage and amplifier output
current capability determine the value of RINT. The
buffer and integrator amplifiers each have a full-scale
current of 20 μA.
The value of RINT is, therefore, directly calculated in the
following equation:
EQUATION 7-1:
Where:
RINT(in MΩ)
=
-V---I--N----(--M----A---X---)
20
VIN(MAX) = Maximum input voltage (full count
voltage)
RINT = Integrating Resistor (in M)
For loop stability, RINT should be 50 k
7.5 Select Reference (CREF) and Auto-
zero (CAZ) Capacitors
CREF and CAZ must be low leakage capacitors (such as
polypropylene). The slower the conversion rate, the
larger the value CREF must be. Recommended
capacitors for CREF and CAZ are shown in Table 7-1.
Larger values for CAZ and CREF may also be used to
limit rollover errors.
© 2008 Microchip Technology Inc.
TC500/A/510/514
TABLE 7-1: CREF AND CAZ SELECTION
Conversions Typical Value of
Per Second
CREF, CAZ (μF)
Suggested* Part
Number
>7
0.1
SMR5 104K50J01L4
2 to 7
0.22
SMR5 224K50J02L4
2 or less
0.47
SMR5 474K50J04L4
* Manufactured by Evox Rifa, Inc.
7.6 Calculate Integrating Capacitor
(CINT)
The integrating capacitor must be selected to maximize
integrator output voltage swing. The integrator output
voltage swing is defined as the absolute value of VDD
(or VSS) less 0.9V (i.e., IVDD - 0.9VI or IVSS + 0.9VI).
Using the 20 μA buffer maximum output current, the
value of the integrating capacitor is calculated using the
following equation.
EQUATION 7-2:
CINT
=
(---T---I--N----T---)--(---2---0----×-----1---0------6---)
(VS 0.9)
Where:
TINT = Integration Period
VS = IVDDI or IVSSI, whichever is less
(TC500/A)
VS = IVDDI (TC510, TC514)
It is critical that the integrating capacitor has a very low
dielectric absorption. Polypropylene capacitors are an
example of one such dialectic. Polyester and poly-
bicarbonate capacitors may also be used in less critical
applications. Table 7-2 summarizes recommended
capacitors for CINT.
TABLE 7-2:
RECOMMENDED CAPACITOR
FOR CINT
Value
Suggested
Part Number*
0.1
SMR5 104K50J01L4
0.22
SMR5 224K50J02L4
0.33
SMR5 334K50J03L4
0.47
SMR5 474K50J04L4
* Manufactured by Evox Rifa, Inc.
7.7 Calculate VREF
The reference de-integration voltage is calculated
using the following equation:
EQUATION 7-3:
VREF
=
(---V----S--------0---.--9---)--(---C----I--N----T---)--(--R----I--N----T---)
2(TINT)
V
DS21428E-page 15
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General Description:
TheTC500/A/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 with the exception that 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/TC514)
• 4 Input, Differential Analog MUX (TC514)
• Automatic Input Voltage Polarity Detection
• Low Power Dissipation:
   - (TC500/TC500A): 10 mW
   - (TC510/TC514): 18 mW
• Wide Analog Input Range:
   - ±4.2V (TC500A/TC510)
• Directly Accepts Bipolar and Differential Input Signals

Applications:
• Precision Analog Signal Processor
• Precision Sensor Interface
• High Accuracy DC Measurements

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