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LTC1871 Datasheet(PDF) 8 Page - Linear Technology |
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LTC1871 Datasheet(HTML) 8 Page - Linear Technology |
8 / 36 page LTC1871 8 1871fe BLOCK DIAGRAM + 1.230V 85mV OV 50k EA UV TO START-UP CONTROL BURST COMPARATOR S R Q LOGIC PWM LATCH CURRENT COMPARATOR 0.30V 1.230V 5.2V 2.00V 1.230V SLOPE 1.230V ILOOP FB ITH gm 3 MODE/SYNC 5 FREQ 4 2 INTVCC 8 LDO V-TO-I OSC V-TO-I SLOPE COMPENSATION BIAS AND START-UP CONTROL VIN BIAS VREF IOSC RLOOP – + – + C1 SENSE 10 GND 1871 BD 6 GATE INTVCC GND 7 VIN 1.248V 9 RUN C2 1 0.6V Main Control Loop The LTC1871 is a constant frequency, current mode con- troller for DC/DC boost, SEPIC and flyback converter ap- plications. The LTC1871 is distinguished from conventional current mode controllers because the current control loop can be closed by sensing the voltage drop across the power MOSFET switch instead of across a discrete sense resistor, as shown in Figure 2. This sensing technique improves efficiency, increases power density, and reduces the cost of the overall solution. For circuit operation, please refer to the Block Diagram of the IC and Figure 1. In normal operation, the power MOSFET is turned on when the oscillator sets the PWM latch and is turned off when the current comparator C1 resets the latch. The divided-down output voltage is compared to an internal 1.230V reference by the error amplifier EA, which outputs an error signal at the ITH pin. The voltage on the ITH pin sets the current comparator C1 input threshold. When the load current increases, a fall in the FB voltage relative to the reference voltage causes the ITH pin to rise, which causes the current comparator C1 to trip at a higher peak inductor current value. The average inductor current will therefore rise until it equals the load current, thereby maintaining output regulation. OPERATION |
Similar Part No. - LTC1871_15 |
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Similar Description - LTC1871_15 |
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