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RT9174CS Datasheet(PDF) 6 Page - Richtek Technology Corporation |
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RT9174CS Datasheet(HTML) 6 Page - Richtek Technology Corporation |
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6 / 8 page  RT9174 Preliminary www.richtek-ic.com.tw DS9174-00 April 2001 6 Applications Information Capacitors Selection A 0.1 µF minimum capacitor is recommended between VDD and ground to increase stability. The linear controllers use dominant pole compensation integrated into the error amplifier and are sensitive to output capacitor selection. When driving external pass transistor, normally a minimum 470 µF capacitor must be placed at output for stability and good transient response. When using internal pass transistor, just need 10 µF capacitor for stable. Pass Transistor Selection The RT9174 are designed specifically to driver external NPN or NMOSFET pass transistor for up to 5A output current. The driver could deliver more 100mA when driving NPN transistor and sinking for a pull up resistor load when driving a NMOSFET. Typically pass transistor with NPN hfe > 50 at Imax or NMOSFET Rds-on 100m Ω are suitable in most application. Output Voltage Setting The RT9174 develop a 0.8V reference voltage, especially suit for low voltage application. As shown in Fig. 4, the output voltage could be easy set by R1 & R2 resistor. The divided resistor must keep below 1K Ω for quick response and stability. Tri-state Operation A special Tri-state design is empolyed in the RT9174 for AGP 2X/4X power supply. Typical application shown the detail circuit. In AGP 2X SELECT = open, FB1 will be pulled up over 1.3V through R8 to trip the Tri-state threshold. R8 has to meet the following relationship: R8 < 0.75 (V33 - 1.3) ×R2, if 1.5 0.8 R R R 3 2 3 = × + . When in AGP 4X SELECT = GND, VDDQ will work in normal 1.5V setting. Layout Considerations There are two critical layout considerations. One is the divider resistors should be located to RT9174 as possible to avoid inducing any noise. The second is COUT should be put at near the pass transistor to avoid oscillation. RT9174 + 1 µF Fig 4 VDD DRI1 DRI2 DRI3 FB1 FB2 FB3 VDD R1 R2 VIN COUT VOUT As close as to RT9174 |
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