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CS51414G データシート(PDF) 8 Page - ON Semiconductor |
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CS51414G データシート(HTML) 8 Page - ON Semiconductor |
8 / 16 page CS51411, CS51412, CS51413, CS51414 http://onsemi.com 8 VF = diode forward voltage. The anode of the diode can be connected to any DC voltage other than the regulated output voltage. However, the maximum voltage on the BOOST pin shall not exceed 40 V. As shown in Figure 7, the BOOST pin current includes a constant 7.0 mA pre–driver current and base current proportional to switch conducting current. A detailed discussion of this current is conducted in Thermal Consideration section. A 0.1 µF capacitor is usually adequate for maintaining the Boost pin voltage during the on time. Figure 7. The Boost Pin Current Includes 7.0 mA Pre–Driver Current and Base Current when the Switch is Turned On. The Beta Decline of the Power Switch Further Increases the Base Current at High Switching Current 0 0.5 1.0 1.5 Switching Current (A) 0 5 10 15 20 25 30 BIAS Pin (CS51412 and CS51414 Only) The BIAS pin allows a secondary power supply to bias the control circuitry of the IC. The BIAS pin voltage should be between 3.3 V and 6.0 V. If the BIAS pin voltage falls below that range, use a diode to prevent current drain from the BIAS pin. Powering the IC with a voltage lower than the regulator’s input voltage reduces the IC power dissipation and improves energy transfer efficiency. Shutdown The internal power switch will not turn on until the VIN pin rises above the Start Up Voltage. This ensures no switching until adequate supply voltage is provided to the IC. The IC enters a sleep mode when the SHDNB pin is pulled below Shutdown Threshold Voltage. In the sleep mode, the power switch keeps open and the supply current reduces to Shutdown Quiescent Current. This pin has internal pull–up current. So when this pin is not used, leave the SHDNB pin open. Start–Up During power up, the regulator tends to quickly charge up the output capacitors to reach voltage regulation. This gives rise to an excessive in–rush current which can be detrimental to the inductor, IC and catch diode. In V2 control , the compensation capacitor provides Soft Start with no need for extra pin or circuitry. During the power up, the Output Source Current of the error amplifier charges the compensation capacitor which forces VC pin and thus output voltage ramp up gradually. The Soft Start duration can be calculated by TSS + VC CCOMP ISOURCE where: VC = VC pin steady–state voltage, which is approximately equal to error amplifier’s reference voltage. CCOMP = Compensation capacitor connected to the VC pin ISOURCE = Output Source Current of the error amplifier. Using a 0.1 µF CCOMP, the calculation shows a TSS over 5.0 ms which is adequate to avoid any current stresses. Figure 8 shows the gradual rise of the VC, VO and envelope of the VSW during power up. There is no voltage over–shoot after the output voltage reaches the regulation. If the supply voltage rises slower than the VC pin, output voltage may over–shoot. Figure 8. The Power Up Transition of CS5141X Regulator Short Circuit When the VFB pin voltage drops below Foldback Threshold, the regulator reduces the peak current limit by 40% and switching frequency to 1/4 of the nominal frequency. These features are designed to protect the IC and external components during over load or short circuit conditions. In those conditions, peak switching current is clamped to the current limit threshold. The reduced switching frequency significantly increases the ripple current, and thus lowers the DC current. The short circuit can cause the minimum duty cycle to be limited by Minimum Output Pulse Width. The foldback frequency reduces the minimum duty cycle by extending the switching cycle. This protects the IC from overheating, and also limits the power that can be transferred to the output. The current limit foldback effectively reduces the current stress on the |
同様の部品番号 - CS51414G |
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同様の説明 - CS51414G |
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