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TS3405 数据表(PDF) 9 Page - Taiwan Semiconductor Company, Ltd |
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TS3405 数据表(HTML) 9 Page - Taiwan Semiconductor Company, Ltd |
9 / 10 page Application Guidelines (continued) The equations below relate the compensation network’s poles, zeros and gain to the components (R1, R2, R3, C1, C2 and C3) in Fig. 7. Use these guidelines for locating the poles and zeros of the compensation network: 1. Pick Gain (R2/R1) for desired converter bandwidth. 2. Place 1 st zero below filter’s double pole (~75% F LC) 3. Place 2 nd zero at filter’s double pole. 4. Place 1 st pole at the ESR zero. 5. Place 2 nd pole at half the switching frequency 6. Check gain against error amplifier’s open-loop gain. 7. Estimate phase margin – repeat if necessary. Output Capacitor Selection An output capacitor is required to filter the output and supply the load transient current. The filtering requirements are a function of the switching frequency and the ripple current. The load transient requirements are a function of the slew rate (di/dt) and the magnitude of the transient load current. These requirements are generally met with a mix of capacitors and careful layout. Modern components and loads are capable of producing transient load rates above 1A/nS. High frequency capacitors initially supply the transient and slow the current load rate seen by the bulk capacitors. The bulk filter capacitor values are generally determined by the ESR (Effective Series Resistance) and voltage rating requirements rather than actual capacitance requirements. High frequency decoupling capacitors should be placed as close to the power pins of the load as physically possible. Be careful not to add inductance in the circuit board wiring that could cancel the usefulness of these low inductance components. Consult with the manufacturer of the load on specific decoupling requirements. Use only specialized low-ESR capacitors intended for switching-regulator applications for the bulk capacitors. The bulk capacitor’s ESR will determine the output ripple voltage and the initial voltage drop after a high slew-rate transient. An aluminum electrolytic capacitor’s ESR value is related to the case size with lower ESR available in larger case sizes. However, the equivalent Series inductance (ESL) of these capacitors increases with case size and can reduce the usefulness of the capacitor to high slew-rate transient loading. Unfortunately, ESL is not a specified parameter. Work with your capacitor supplier and measure the capacitor’s impedance with frequency to select a suitable component. In most cases, multiple electrolytic capacitors of small case size perform better than a single large case capacitor. Feedback Divider The reference of TS3405 is 0.8V. the output voltage can be set by R1 and R4 as shown in Fig. 4. The equation is following: Vout = 0.8 x (1 + R1 / R4) The R1 should be between 2kΩ to 5kΩ. put the R1, R4 and others compensation component as close to TS3405 as possible. Shutdown Pulling low the COMP pin can shutdown the TS3405 PWM controller. You can use a small single transistor as switch like as JP1 shown in Fig. 4. Compensation Break Frequency Equations As in any high frequency switching converter, layout is very important. Switching current from one power device to another can generate voltage transients across the impedances of the interconnecting bond wires and circuit traces. Using wide, short printed circuit traces should minimize these interconnecting impedances. The critical components should be located as close together as possible, using ground plane construction or single point grounding. To minimize the voltage overshoot, the interconnecting wires indicated by heavy lines should be part of a ground or power plane in a printed circuit board. Locate the TS3405 within 3 inches of the MOSFETs. Q1 and Q2. The circuit traces for the MOSFETs’ gate and source connections from the TS3405 must be sized to handle up to 1A peak current. Provide local Vcc decoupling between Vcc and Gnd pins. Locate the capacitor, CBOOT as close as practical to the Boot and Phase pins. All components used for feedback compensation should be located as close to the IC a practical. TS3405 9-10 2003/12 rev. A |
类似零件编号 - TS3405 |
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类似说明 - TS3405 |
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