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TL1454 数据表(PDF) 4 Page - Texas Instruments |
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TL1454 数据表(HTML) 4 Page - Texas Instruments |
4 / 24 page TL1454, TL1454Y DUAL-CHANNEL PULSE-WIDTH-MODULATION (PWM) CONTROL CIRCUIT SLVS086B – APRIL 1995 – REVISED NOVEMBER 1997 4 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 POST OFFICE BOX 1443 • HOUSTON, TEXAS 77251–1443 theory of operation reference voltage A linear regulator operating from VCC generates a 2.5-V supply for the internal circuits and the 1.25-V reference, which can source a maximum of 1 mA for external loads. A small ceramic capacitor (0.047 µF to 0.1 µF) between REF and ground is recommended to minimize noise pickup. error amplifier The error amplifier generates the error signal used by the PWM to adjust the power-switch duty cycle for the desired converter output voltage. The signal is generated by comparing a sample of the output voltage to the voltage reference and amplifying the difference. An external resistive divider connected between the converter output and ground, as shown in Figure 1, is generally required to obtain the output voltage sample. The amplifier output is brought out on COMP to allow the frequency response of the amplifier to be shaped with an external RC network to stabilize the feedback loop of the converter. DC loading on the COMP output is limited to 45 µA (the maximum amplifier source current capability). Figure 1 illustrates the sense-divider network and error-amplifier connections for converters with positive output voltages. The divider network is connected to the noninverting amplifier input because the PWM has a phase inversion; the duty cycle decreases as the error-amplifier output increases. _ + IN – IN + R3 R1 R2 COMP To PWM VO Compensation Network REF Converter Output TL1454 Figure 1. Sense Divider/Error Amplifier Configuration for Converters with Positive Outputs The output voltage is given by: V O + V ref 1 ) R1 R2 where Vref = 1.25 V. The dc source resistance of the error-amplifier inputs should be 10 k Ω or less and approximately matched to minimize output voltage errors caused by the input-bias current. A simple procedure for determining appropriate values for the resistors is to choose a convenient value for R3 (10 k Ω or less) and calculate R1 and R2 using: R 1 + R 3 V O V O –V ref R 2 + R 3 V O V ref |
类似零件编号 - TL1454 |
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类似说明 - TL1454 |
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