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SC633 Datasheet(PDF) 10 Page - Semtech Corporation |
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SC633 Datasheet(HTML) 10 Page - Semtech Corporation |
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10 / 15 page  SC633 0 General Description The SC633 is a 5.3V output charge pump regulator designed to support up to peak current of 400mA (T A ≤ 55°C, 3.3V ≤ V IN ≤ 4.2V) and 275mA (TA ≤ 85°C, 3.5V ≤ VIN ≤ 5.5V) of continuous current for powering 5.0V devices in portable handheld equipment including Compact Flash and CF+ products. The SC633 has three operating modes — x, .5x, and 2x. The x mode is a linear series regulation mode with a low open-loop output resistance of only 250mW. The x mode functions as a low-noise series linear regulator. The .5x and 2x modes are a low noise, constant frequency, con- stant duty cycle switch mode, using two bucket capacitors. One bucket supports the full output current while the other bucket charges from the input. The two buckets exchange roles in the next phase, supplying continuous output current in both phases and reducing the need for a large output decoupling capacitor. The constant fre- quency, constant duty cycle operation also produces predictable constant frequency harmonics. Thermal Resistance The SC633 package is thermally efficient when the circuit board layout connects the thermal pad through multiple vias to the ground plane. The thermal resistance rating is dependent upon the connection between the thermal pad and the ground plane. A layout that is done correctly should keep the junction temperature below the over- temperature limit while operating the SC633 within the specified electrical conditions. A poor layout may allow the junction temperature to reach the over temperature limit, so it is important to maintain adequate ground plane around the device to maximize heat transfer to the PCB. Temperature Derating The maximum power dissipation of the package can be calculated by the difference between the junction tem- perature of 50 degree and the ambient temperature divided by the thermal impedance 68 °C/W. The higher the ambient temperature, the lower the maximum allow- able power dissipation. At a given V IN condition, the allowable power dissipation will correlates to the specific output current related to the operation efficiency. The following derating curve is obtained based on efficiency at input voltage of 5V and 3.3V. For any input conditions, due to the mode hysteresis, SC633 operation mode might be determined from its previous operation voltage, it could be in X, .5X, or 2X mode. The low efficiency should always be used for worst case consideration. In this case, at V IN =3.3V, SC633 operates in 2X mode. At VIN =5V, SC633 operates either in 2X or .5X mode. In the derating curve below, the DC operating points beneath each curve are in the safe operating temperature range of the MLP package. Maximum Continuous Output Mode Transition As input voltage varies, the SC633 will experience mode transitions. The transition threshold changes with input voltage and load conditions. The mode change hysteresis at several load current conditions are shown in the oper- ating curves on page 6. Mode transition will bring output voltage dip or overshoots. The output voltage deviation in mode transition can be improved by using larger output capacitors if the output voltage going beyond the regulation range. Mode Transition Hysteresis Hysteresis is provided to prevent chatter between charge pump modes for input steps of up to 20mV. Decouple the input to prevent steps greater than 20mV, for Applications Information |
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