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YB1680 Datasheet(PDF) 8 Page - YOBON TECHNOLOGIES,INC. |
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YB1680 Datasheet(HTML) 8 Page - YOBON TECHNOLOGIES,INC. |
8 / 10 page YB1680 1.5MHz, 600mA Synchronous Step-Down Converter YB1680 Rev.1.0 www.yobon.com.tw 8 turning the main switch off and keeping it off until the fault is no longer present. Idle Mode Operation At very light loads, the YB1680 automatically enters Idle Mode. In the Idle Mode, the inductor current may reach zero or reverse on each pulse. The PWM control loop will automatically skip pulses to maintain output regulation. The bottom MOSFET is turned off by the current reversal comparator, IZERO, and the switch voltage will ring. This is discontinuous mode operation, and is normal behavior for the switching regulator. Dropout Operation When the input voltage decreases toward the value of the output voltage, the YB1680 allows the main switch to remain on for more than one switching cycle and increases the duty cycle until it reaches 100%. The output voltage then is the input voltage minus the voltage drop across the main switch and the inductor. At low input supply voltage, the RDS(ON) of the P-Channel MOSFET increases, and the efficiency of the converter decreases. Caution must be exercised to ensure the heat dissipated not to exceed the maximum junction temperature of the IC. Maximum Load Current The YB1680 will operate with input supply voltage as low as 2.5V, however, the maximum load current decreases at lower input due to large IR drop on the main switch and synchronous rectifier. The slope compensation signal reduces the peak inductor current as a function of the duty cycle to prevent sub-harmonic oscillations at duty cycles greater than 50%. Conversely the current limit increases as the duty cycle decreases. Application Information Setting the Output Voltage Figure 1 above shows the basic application circuit with YB1680 adjustable output version. The external resistor sets the output voltage according to the following equation: R1=300KΩ for all outputs; R2=300KΩ for VOUT=1.2V, R2=200KΩ for VOUT=1.5V, R2=150KΩ for VOUT=1.5V, and R=95.3KΩ for VOUT=2.5V. Inductor Selection For most designs, the YB1680 operates with inductors of 1μH to 4.7μH. Low inductance values are physically smaller but require faster switching, which results in some efficiency loss. The inductor value can be derived from the following equation: Where ΔIL is inductor Ripple Current. Large value inductors lower ripple current and small value inductors result in high ripple currents. Choose inductor ripple current |
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