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UC2577TD-ADJ датащи(PDF) 4 Page - Texas Instruments |
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UC2577TD-ADJ датащи(HTML) 4 Page - Texas Instruments |
4 / 14 page The Block Diagram shows a step-up switching regulator utilizing the UC2577. The regulator produces an output voltage higher than the input voltage. The UC2577 turns its switch on and off at a fixed frequency of 52kHz, thus storing energy in the inductor (L). When the NPN switch is on, the inductor current is charged at a rate of VIN/L. When the switch is off, the voltage at the SWITCH termi- nal of the inductor rises above VIN, discharging the stored current through the output diode (D) into the out- put capacitor (COUT) at a rate of (VOUT - VIN)/L. The en- ergy stored in the inductor is thus transferred to the output. The output voltage is controlled by the amount of energy transferred, which is controlled by modulating the peak inductor current. This modulation is accomplished by feeding a portion of the output voltage to an error ampli- fier which amplifies the difference between the feedback voltage and an internal 1.23V precision reference volt- age. The output of the error amplifier is then compared to a voltage proportional to the switch current, or the induc- tor current, during the switch on time. A comparator ter- minates the switch on time when the two voltages are equal and thus controls the peak switch current to main- tain a constant output voltage. Figure 2 shows voltage and current waveforms for the circuit. Formulas for calcu- lation are shown in Figure 3. STEP-UP REGULATOR DESIGN PROCEDURE Refer to the Block Diagram Given: VINmin = Minimum input supply voltage VOUT = Regulated output voltage UC2577-ADJ Step-up (Boost) Regulator Duty Cycle D VOUT + VF − VIN VOUT + VF − VSAT ≈ VOUT − VIN VOUT Avg. Inductor Current IIND(AVG) ILOAD 1 − D Inductor Current Ripple ∆IIND VIN − VSAT L • D 52,000 Peak Inductor Current IIND(PK) ILOAD 1 −D + ∆IIND 2 Peak Switch Current ISW(PK) ILOAD 1 −D + ∆IIND 2 Switch Voltage when Off VSW(OFF) VOUT + VF Diode Reverse Voltage VR VOUT - VSAT Avg. Diode Current ID(AVG) ILOAD Peak Diode Current ID(PK) ILOAD 1 −D + ∆IIND 2 . Power Dissipation PD 0.25 Ω ILOAD 1 −D 2 D + ILOAD • D • VIN 50 (1−D) VF = Forward Biased Diode Voltage, ILOAD = Output Load Figure 2. Step-up Regulator Waveforms First, determine if the UC2577 can provide these values of VOUT and ILOADmax when operating with the minimum value of VIN. The upper limits for VOUT and ILOADmax are given by the following equations. VOUT ≤ 60V and VOUT ≤ 10 • VINmin ILOADmax ≤ 2.1A • VINmin VOUT These limits must be greater than or equal to the values specified in this application. 1. Output Voltage Section Resistors R1 and R2 are used to select the desired out- put voltage. These resistors form a voltage divider and present a portion of the output voltage to the error ampli- fier which compares it to an internal 1.23V reference. Se- lect R1 and R2 such that: R1 R2 = VOUT 1.23V − 1 Figure 3. Step-up Regulator Formulas APPLICATIONS INFORMATION 4 |
Аналогичный номер детали - UC2577TD-ADJ |
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Аналогичное описание - UC2577TD-ADJ |
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