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GRM31CR60J476M Datasheet(PDF) 11 Page - Richtek Technology Corporation |
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GRM31CR60J476M Datasheet(HTML) 11 Page - Richtek Technology Corporation |
11 / 14 page RT8286 11 DS8286-02 June 2012 www.richtek.com © Copyright 2012 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. Table 2. Suggested Inductors for Typical Application Circuit Component Supplier Series Dimensions (mm) TDK VLF10045 10 x 9.7 x 4.5 TDK SLF12565 12.5 x 12.5 x 6.5 TAIYO YUDEN NR8040 8 x 8 x 4 Input and Output Capacitors Selection The input capacitance, CIN, is needed to filter the trapezoidal current at the source of the high side MOSFET. To prevent large ripple current, a low ESR input capacitor sized for the maximum RMS current should be used. The RMS current is given by : This formula has a maximum at VIN = 2VOUT, where IRMS = IOUT / 2. This simple worst case condition is commonly used for design because even significant deviations do not offer much relief. Choose a capacitor rated at a higher temperature than required. Several capacitors may also be paralleled to meet size or height requirements in the design. For the input capacitor, one 22 μF low ESR ceramic capacitors are recommended. For the recommended capacitor, please refer to Table 3 for more detail. OUT IN RMS OUT(MAX) IN OUT V V I = I 1 VV − Table 3. Suggested Capacitors for CIN and COUT Location Component Supplier Part No. Capacitance ( μF) Case Size CIN MURATA GRM32ER71C226M 22 1210 CIN TDK C3225X5R1C226M 22 1210 COUT MURATA GRM31CR60J476M 47 1206 COUT TDK C3225X5R0J476M 47 1210 COUT MURATA GRM32ER71C226M 22 1210 COUT TDK C3225X5R1C226M 22 1210 The selection of COUT is determined by the required ESR to minimize voltage ripple. Moreover, the amount of bulk capacitance is also a key for COUT selection to ensure that the control loop is stable. Loop stability can be checked by viewing the load transient response. The output ripple, ΔVOUT, is determined by : Higher values, lower cost ceramic capacitors are now becoming available in smaller case sizes. Their high ripple current, high voltage rating and low ESR make them ideal for switching regulator applications. However, care must be taken when these capacitors are used at input and output. When a ceramic capacitor is used at the input OUT L OUT 1 VI ESR 8fC ⎡⎤ Δ≤ Δ + ⎢⎥ ⎣⎦ and the power is supplied by a wall adapter through long wires, a load step at the output can induce ringing at the input, VIN. At best, this ringing can couple to the output and be mistaken as loop instability. At worst, a sudden inrush of current through the long wires can potentially cause a voltage spike at VIN large enough to damage the part. Thermal Shutdown Thermal shutdown is implemented to prevent the chip from operating at excessively high temperatures. When the junction temperature is higher than 150 °C, the whole chip is shutdown. The chip is automatically re-enable when the junction temperature cools down by approximately 30 degrees. |
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