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CS5151 数据表(PDF) 5 Page - Cherry Semiconductor Corporation |
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CS5151 数据表(HTML) 5 Page - Cherry Semiconductor Corporation |
5 / 14 page 5 Block Diagram Q VID1 VCC1 SS COMP VFB VID0 LGnd VFFB VCC2 VGATE PGnd VID2 VID3 - + 4 BIT DAC COFF Slow Feedback Maximum On-Time Timeout R Q S COFF One Shot PWM COMP SS High Comparator FAULT Latch 2.5V Error Amplifier Fast Feedback - + VCC1 Monitor Comparator - + - + - + - + VFFB Low Comparator PWM Comparator SS Low Comparator R Q S Q R Q S 2µA 5V 60µA Normal Off-Time Timeout Extended Off-Time Timeout Time Out Timer (30µs) Edge Triggered Off-Time Timeout 3.90V 3.85V FAULT FAULT GATE = ON GATE = OFF PWM Latch 1V 0.7V Applications Information V2™ Control Method The V2™ method of control uses a ramp signal that is gen- erated by the ESR of the output capacitors. This ramp is proportional to the AC current through the main inductor and is offset by the value of the DC output voltage. This control scheme inherently compensates for variation in either line or load conditions, since the ramp signal is gen- erated from the output voltage itself. This control scheme differs from traditional techniques such as voltage mode, which generates an artificial ramp, and current mode, which generates a ramp from inductor current. Figure 1: V2™ Control Diagram The V2™ control method is illustrated in Figure 1. The out- put voltage is used to generate both the error signal and the ramp signal. Since the ramp signal is simply the output voltage, it is affected by any change in the output regard- less of the origin of that change. The ramp signal also con- tains the DC portion of the output voltage, which allows the control circuit to drive the main switch to 0% or 100% duty cycle as required. A change in line voltage changes the current ramp in the inductor, affecting the ramp signal, which causes the V2™ control scheme to compensate the duty cycle. Since the change in inductor current modifies the ramp signal, as in current mode control, the V2™ control scheme has the same advantages in line transient response. A change in load current will have an affect on the output voltage, altering the ramp signal. A load step immediately changes the state of the comparator output, which controls the main switch. Load transient response is determined only by the comparator response time and the transition speed of the main switch. The reaction time to an output load step has no relation to the crossover frequency of the error signal loop, as in traditional control methods. The error signal loop can have a low crossover frequency, since transient response is handled by the ramp signal loop. The main purpose of this ‘slow’ feedback loop is to provide DC accuracy. Noise immunity is significantly improved, since the error amplifier bandwidth can be rolled off at a low frequency. Enhanced noise immunity improves remote sens- Reference Voltage C – E + – Ramp Signal Output Voltage Feedback Error Signal VGATE Error Amplifier VFFB COMP VFB PWM Comparator Theory of Operation |
类似零件编号 - CS5151 |
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类似说明 - CS5151 |
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