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RT9173ACS Datasheet(PDF) 6 Page - Richtek Technology Corporation |
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RT9173ACS Datasheet(HTML) 6 Page - Richtek Technology Corporation |
6 / 10 page RT9173/A www.richtek-ic.com.tw DS9173/A-06 March 2002 6 Applications Information Internal parasitic diode Avoid forward-bias internal parasitic diode, VOUT to VCNTL, and VOUT to VIN, the VOUT should not be forced some voltage respect to ground on this pin while the VCNTL or VIN is disappeared. Consideration while designs the resistance of voltage divider Make sure the sinking current capability of pull-down NMOS if the lower resistance was chosen so that the voltage on REFEN is below 0.2V. In addition to item 1, the capacitor and voltage divider form the low-pass filter. There are two reasons doing this design; one is for output voltage soft-start while another is for noise immunity. How to reduce power dissipation on Notebook PC or the dual channel DDR SDRAM application? In notebook application, using RichTek’s Patent “Distributed Bus Terminator Topology” with choosing RichTek’s product is encouraged. Thermal Consideration RT9173/A regulators have internal thermal limiting circuitry designed to protect the device during overload conditions. For continuous normal load conditions however, the maximum junction temperature rating of 125°C must not be exceeded. Higher continous currents or ambient temperature require additional heatsinking. Heat sinking to the IC package must consider the worst case power dissipation which may occur. It should also be note that with the VCNTL equal to 5V, the point of thermal shutdown will be degraded by approx. 20°C compared to the VCNTL equipped with 3.3V. It is highly recommended that to use the 3.3V rail acted as the VCNTL so as to minimize the thermal concern of the RT9173CS in the SOP-8 package. Layout Consideration The RT9173CS regulator is packaged in plastic SOP- 8 package. This small footprint package is unable to convectively dissipate the heat generated when the regulator is operating at high current levels. In order to control die operating temperatures, the PC board layout should allow for maximum possible copper area at the VCNTL pins of the RT9173CS. The multiple VCNTL pins on the SOP-8 package are internally connected, but lowest thermal resistance will result if these pins are tightly connected on the PC board. This will also aid heat dissipation at high power levels. If the large copper around the IC is unavailable, a buried layer may be used as a heat spreader, Use vias to conduct the heat into the buried or backside of PCB layer. The vias should be small enough to retain solder when the board is wave-soldered. (See Fig.6 shown on next page). Distributed Bus Terminating Topology R0 R2 R3 R4 R5 R6 R7 R8 R9 RN BUS(0) BUS(1) BUS(2) BUS(3) BUS(4) R1 BUS(5) BUS(6) BUS(7) BUS(8) BUS(9) BUS(N+1) RN1 BUS(N) Terminator Resistor RT9173 RT9173 VOUT VOUT REFEN |
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