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UC1854A датащи(PDF) 4 Page - Texas Instruments |
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UC1854A датащи(HTML) 4 Page - Texas Instruments |
4 / 7 page PARAMETER TEST CONDITIONS MIN TYP MAX UNITS GATE DRIVER Output High Voltage IOUT = –200mA, VCC = 15V 12 12.8 V Output Low Voltage IOUT = 200mA 1 2.2 V IOUT = 10mA 300 500 mV Output Low (UVLO) IOUT = 50mA, VCC = 0V 0.9 1.5 V Output Rise / Fall Time CLOAD = 1nF, (Note 1) 35 ns Output Peak Current CLOAD = 10nF, (Note 1) 1.0 A UC1854A/B UC2854A/B UC3854A/B Note 1: Guaranteed by design, not 100% tested in production. Note 2: Gain constant (K) = IAC × (Va − 1.5V) VRMS 2 × IMO ELECTRICAL CHARACTERISTICS (cont.) Unless otherwise stated, VCC=18V, RT=8.2k, CT=1.5nF, PKLMT=1V, VRMS=1.5V, IAC=100 µA, ISENSE=0V, CA Out=3.5V, VA Out=5V, VSENSE=3V, –55 oC<TA<125oC for the UC1854A/B, –40 oC<TA<85oC for the UC2854A/B, and 0oC<TA<70oC for the UC3854A/B, and TA=TJ. The UC1854A/B products were designed as pin compatible upgrades to the industry standard UC1854 active Power Factor correction circuits. The circuit enhancements allow the user to eliminate in most cases several external components currently required to successfully apply the UC1854. In addition, linearity improvements to the Multiply, Square, and Divide circuitry optimizes overall system performance. Detailed descriptions of the circuit enhancements are provided below. For in-depth design applications reference data refer to Unitrode application notes U-134 and DN-44. MULTIPLY / SQUARE AND DIVIDE The UC1854A/B Multiplier design maintains the same gain constant (K = −1), as the UC1854. The relationship between the inputs and output current is given as: IMO = IAC(VAO - 1.5V) / K •VRMS2 This is nearly the same as the UC1854, but circuit differences have improved the performance and application. The first difference is with the IAC input. The UC1854A/B regulates this pin voltage to a nominal 500mV over the full operating temperature range, rather than the 6.0V used on the UC1854. This low offset voltage eliminates the need for a line zero crossing compensating resistor to VREF from IAC that UC1854 designs require. The maximum current at high line into IAC should be limited to 250 µA for best performance. Therefore, if VAC (max) = 270V, then RAC = 270(1.414) / 250 µA = 1.53MΩ. The VRMS pin linear operating range is improved with the UC1854A/B as well. The input range for VRMS extends from 0 to 5.5V. Since the UC1854A squaring circuit employs an analog multiplier, rather than a linear approximation, accuracy is improved, and discontinuities are eliminated. The external divider network connected to VRMS should produce 1.5V at low line (85VAC). This will put 4.77V on VRMS at high line (27VAC) which is well within its operating range. The Voltage Amplifier output forms the third input to the Multiplier and is internally clamped to 6.0V. This eliminates an external zenerclamp often used in UC1854 designs. The offset voltage at this input to the Multiplier has been raised on the UC1854A/B to 1.5V. The Multiplier output pin, which is also common to the Current Amplifier non-inverting input, has a −0.3V to 5.0V output range,compared to the −0.3 to 2.5V range of the UC1854. This improvement allows the UC1854A/B to be used in applications where the current sense signal amplitude is very large. VOLTAGE AMPLIFIER The UC1854A/B Voltage Amplifier design is essentially similar to the UC1854 with two exceptions. The first is with the internal connection. The lower voltage reduces the amount of charge on the compensation capacitor, which provides improved recovery from large signal events, such as line dropouts, or power interruption. It also minimizes the DC current flowing through the feedback. The output of the Voltage amplifier is also changed. In addition to a 6.0V temperature compensated clamp, the output short circuit current has been lowered to 2mA typical, and an active pull down has replaced the passive pulldown of the UC1854. CURRENT AMPLIFIER The Current Amplifier for an average current PFC controller needs a low offset voltage in order to minimize AC line current distortion. With this in mind, the UC1854A/B Current Amplifier has improved the input offset voltage from ±4mV to 0 to −3mV. The negative FUNCTIONAL DESCRIPTION 4 |
Аналогичный номер детали - UC1854A |
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Аналогичное описание - UC1854A |
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