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TS1909CX527 데이터시트(PDF) 3 Page - Taiwan Semiconductor Company, Ltd |
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TS1909CX527 데이터시트(HTML) 3 Page - Taiwan Semiconductor Company, Ltd |
3 / 6 page TS1909 MicroPower VFM Boost DC to Dc Converter 3/3 Version: A10 Detailed Description The TS1909 architecture is built around a VFM CONTROL logic core, switching frequency is set through a built in oscillator. TON time is fixed (Typ. 5uS) while TOFF time is determined by the error amplifier output, a logic signal coming from the comparison made by the Error Amplifier Stage between the signal coming from the output voltage divider network and the internal Band-Gap voltage reference (VREF). TOFF reaches a minimum (Typ. 1.7uS) when heavy load conditions are met (Clock frequency 150KHz). An over current conditions, through the internal power switch, causes a voltage drop VLX=RDSON x ISW and the VLX limiter block forces the internal switch to be off, so narrowing TON time and limiting internal power dissipation. In this case the switching frequency may be higher than the 150KHz set by the internal clock generator. VFM control ensures very low quiescent current and high conversion efficiency even with very light loads. Since the Output Voltage pin is also used as the device Supply Voltage, the versions with higher output voltage present an higher internal supply voltage that results in lower power switch RDSON, slightly greater output power and higher efficiency. Moreover, bootstrapping allows the input voltage to sag to 0.6V (at IOUT=1mA) once the system is started. If the input voltage exceeds the output voltage, the output will follow the input, however, the input or output voltage must not be forced above 5.5V. Application Information Input/Output Capacitor Selection The Output Ripple Voltage, as well as the Efficiency, is strictly related to the behavior of these elements. The output ripple voltage is the product of the peak inductor current and the output capacitor Equivalent Series Resistance (ESR). Best performances are obtained with good high frequency characteristics capacitors and low ESR. The best compromise for the value of the Output Capacitance is 47µF Tantalum Capacitor; Lower values may cause higher Output Ripple Voltage and lower Efficiency without compromising the functionality of the device. An Input Capacitor is required to compensate, if present, the series impedance between the Supply Voltage Source and the Input Voltage of the Application. Inductor Selection A 47µH inductor is recommended for most TS1909 applications. However, the inductance value is not critical, and the TS1909 will work with inductors in the 33µH to 120µH. Diode Selection Schottky diodes with higher current ratings usually have lower forward voltage drop, larger diode capacitance and fast reverse recovery, it is the ideal choices for TS1909 applications. The forward voltage drop of a Schottky diode represents the conduction losses in the system, while the diode capacitance (CT or CD) represents the switching losses. For diode selection, both forward voltage drop and diode capacitance need to be considered. PCB layout guide When laying out the PC board, the following suggestions should be taken to ensure proper operation of the TS1909. These items are also illustrated graphically in below. The power traces, including the GND trace, the SW trace and the VCC trace should be kept short, direct and wide to allow large current flow. Put enough multiply-layer pads when they need to change the trace layer. Do not trace signal line under inductor. |
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