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SC1302FSTRT Datasheet(PDF) 8 Page - Semtech Corporation |
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SC1302FSTRT Datasheet(HTML) 8 Page - Semtech Corporation |
8 / 10 page 8 2008 Semtech Corp. www.semtech.com SC1302A/B/C/D/E/F PRELIMINARY POWER MANAGEMENT Applications Information The SC1302A/B/C/D/E/F is a high speed, high peak current dual MOSFET driver. It is designed to drive power MOSFETs with ultra-low rise/fall time and propagation delays. As the switching frequency of PWM controllers is increased to reduce power converters volume and cost, fast rise and fall times are necessary to minimize switching losses. While discrete solution can achieve reasonable drive capability, implementing delay and other housekeeping functions necessary for safe operation can become cumbersome and costly. The SC1032A/B/C/ D/E/F presents a total solution for the high-speed, high power density applications. Wide input supply range of 4.5V - 16.5V allows use in battery powered applications as well as distributed power systems. Supply Bypass and Layout A 4.7µF to 10µF tantalum bypass capacitor with low ESR (equivalent series resistance) and an additional 0.1µF ceramic capacitor in parallel are recommended as supply bypass to control switching and supply transients. As with any high speed, high current circuit, proper layout is critical in achieving optimum performance of the SC1302A/B/C/D/E/F. Attention should be paid to the proper placement of the driver, the switching MOSFET and the bypass capacitors. The driver should be placed as close as possible to the external MOSFETs to eliminate the possibility of oscillation caused by trace inductance and the MOSFET gate capacitance. A resistor in the range of 10W could be used in series with the gate drive to damp the ringing if the drive output path is not short enough. The bypass capacitors should also be placed closely between Vcc and GND of the driver. A Schottky diode may be used to connect the ground and the output pin to avoid latch- ups in some applications. Drive Capability and Power Dissipation The SC1302A/B/C/D/E/F is able to deliver 1.6A peak current for driving capacitive loads, such as MOSFETs. Fast switching of the MOSFETs significantly reduces switching losses for high frequency applications. Thermal stress is reduced and system reliability is improved. For simplicity, we assume that the gate capacitance of a MOSFET is constant. The power delivered from the power supply can be estimated based on this simplification. The energy needed to charge the capacitor is given by: 2 ON V C 2 1 E ⋅ ⋅ = where C is the load capacitance and V is the output voltage swing of the driver. During turn off, the same amount of energy is dumped to the ground. Therefore, the energy dissipated in one switching cycle is: The power dissipation due to the gate driving actions is given by: 2 GATE V C f P ⋅ ⋅ = where, f is the switching frequency. with V CC= 12V, C = 1nF and f = 200kHz, the power dissipation per output is: () ( ) ( ) mW 29 12 nF 1 kHz 200 P 2 GATE = ⋅ ⋅ = The corresponding supply current is: mA 4 . 2 V 12 mW 29 V P I CC GATE = = = Thermal Information The driver’s junction temperature must be kept within the rated limit at any time. The application system has to effectively remove the heat generated in the driver in order for proper functions and performance. If the junction temperature reaches 150oC, the internal protection circuit will be triggered to shut down the gate driver. The power dissipation of the SC1302A/B/C/D/E/F should be derated according to the following formula: where T A = ambient temperature. 2 TOTAL V C E ⋅ = jA T C 125 n Dissipatio Power A θ − ° < |
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