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TC500 Scheda tecnica(PDF) 11 Page - Microchip Technology |
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TC500 Scheda tecnica(HTML) 11 Page - Microchip Technology |
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11 / 28 page  © 2002 Microchip Technology Inc. DS21428B-page 11 TC500/A/510/514 6.0 TYPICAL APPLICATIONS 6.1 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 6.2 Select Integration Time Integration time must be picked as a multiple of the period of the line frequency. For example, TINT times of 33msec, 66msec and 132msec maximize 60Hz line rejection. 6.3 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 initi- ated immediately following INT and terminated when an integrator output zero-crossing is detected. In gen- eral, the maximum number of counts chosen for DINT is twice thatofINT (with VREF chosen at VIN(MAX) /2). 6.4 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 currentof20 µA. The value of RINT is therefore directly calculated in the following equation: EQUATION 6-1: 6.5 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 capac- itors for CREF and CAZ are shown in Table 6-1. Larger values for CAZ and CREF mayalsobe usedtolimit rollover errors. TABLE 6-1: CREF AND CAZ SELECTION 6.6 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)less0.9V (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 6-2: It is critical that the integrating capacitor has a very low dielectric absorption. Polypropylene capacitors are an example of one such dielectic. Polyester and Polybicar- bonate capacitors may also be used in less critical applications. Table 6-2 summarizes recommended capacitors for CINT. TABLE 6-2: RECOMMENDED CAPACITOR FOR CINT 6.7 Calculate VREF The reference deintegration voltage is calculated using the following equation: EQUATION 6-3: VIN(MAX) 20 RINT(in MΩ)= Where: VIN(MAX) = Maximum input voltage (full count voltage) RINT = Integrating Resistor (in MΩ) For loop stability, RINT should be ≥ 50kΩ. Conversions Per Second Typical Value of 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 Note: Manufactured by Evox-Rifa, Inc. Value Suggested Part Number* 0.1 SMR5 104K50J01L4 0.22 SMR5 224K50J02L4 0.33 SMR5 334K50J03L4 0.47 SMR5 474K50J04L4 Note: Manufactured by Evox-Rifa, Inc. CINT = (VS -0.9) (TINT)(20 x 10 -6) µF Where: TINT = Integration Period VS =IVDDIorIVSSI, whichever is less (TC500/A VS =IVDDI (TC510, TC514) (VS –0.9) (CINT)(RINT) VREF = 2(RINT) V |
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