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TC500COE Folha de dados(PDF) 10 Page - TelCom Semiconductor, Inc |
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TC500COE Folha de dados(HTML) 10 Page - TelCom Semiconductor, Inc |
10 / 17 page 3-28 TELCOM SEMICONDUCTOR, INC. PRECISION ANALOG FRONT ENDS TC500 TC500A TC510 TC514 APPLICATIONS 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 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 rejec- tion. 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 imme- diately 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). 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 as follows: RINT(in MΩ) = VIN MAX 20 where: VIN MAX = Maximum input voltage (full count voltage) RINT =Integrating Resistor (in MΩ) For loop stability, RINT should be ≥ 50kΩ. 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 1. Larger values for CAZ and CREF may also be used to limit roll-over errors. Table 1. CREF and CAZ Selection Conversions Typical Value of Suggested * Per Second CREF, CAZ ( µF) Part Number >7 0.1 WIMA MK12 .1/63/20 2 to 7 0.22 WIMA MK12 .22/63/20 2 or less 0.47 WIMA MK12 .47/63/20 *WIMA Corp. listing on the last page of this data sheet. Calculate Integrating Capacitor (CINT) The integrating capacitor must be selected to maximize integrator output voltage swing. The integrator output volt- age swing is defined as the absolute value of VDD (or VSS) less 0.9V (i.e., VDD– 0.9V or V SS +0.9V ). Using the 20µA buffer maximum output current, the value of the integrating capacitor is calculated using the following equation. CINT = (in µF) = where: tINT = Integration Period VS = Applied Supply Voltage It is critical that the integrating capacitor has a very low dielectric absorption. Polypropylene capacitors are an ex- ample of one such chemistry. Polyester and Polybicarbonate capacitors may also be used in less critical applications. Table 2 summarizes recommended capacitors for CINT. Table 2. Recommend Capacitor for CINT Value Suggested Part Number* 0.1 WIMA MK12 .1/63/20 0.22 WIMA MK12 .22/63/20 0.33 WIMA MK12 .33/63/20 0.47 WIMA MK12 .47/63/20 *WIMA Corp. listing on the last page of this data sheet. Calculate VREF The reference deintegration voltage is calculated using: VREF (in Volts) = (VS – 0.9) (CINT) (RINT) 2(tINT) (tINT) (20 x 10 –6) (VS – 0.9) |
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