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LM2635M Datasheet(PDF) 1 Page - National Semiconductor (TI) |
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LM2635M Datasheet(HTML) 1 Page - National Semiconductor (TI) |
1 / 13 page LM2635 5-Bit Programmable Synchronous Buck Regulator Controller General Description The LM2635 is a high speed controller designed specifically for use in synchronous DC/DC buck converters for the Pentium™ II or Deschutes microprocessor. A 5-bit DAC ac- cepts the VID code directly from the CPU and adjusts the output voltage from 1.8V to 3.5V. It provides the power good, over-voltage protection, and output enable features as re- quired by Intel VRM specifications. Current limiting is achieved by monitoring the voltage drop across the r DS_ON of the high side MOSFET, which eliminates an expensive current sense resistor. The LM2635 employs a fixed-frequency voltage mode PWM architecture. To provide a faster response to a large and fast load transient, two ultra-fast comparators are built in to moni- tor the output voltage and override the primary control loop when necessary. The PWM frequency is adjustable from 50 kHz to 1 MHz through an external resistor. The wide range of PWM frequency gives the power supply designer the flexibil- ity to make trade-offs between load transient response per- formance, MOSFET cost and the overall efficiency. The adaptive non-overlapping MOSFET gate drivers help avoid any potential shoot-through problem while maintaining high efficiency. BiCMOS gate drivers with rail-to-rail swing ensure that no spurious turn-on occur. When only 5V is available, a bootstrap structure can be employed to accommodate an NMOS high side switch. The precision reference trimmed to 2% over temperature is available externally for use by other regulators. Dynamic positioning of load voltage, which helps cut the number of output capacitors, can also be imple- mented easily. Features n 1.8V to 3.5V 5-bit programmable output voltage n Synchronous rectification n Power Good flag and output enable n Over-voltage protection n Initial Output Accuracy: 2% over temperature n Current limit without external sense resistor n Adaptive non-overlapping MOSFET gate drives n Adjustable switching frequency: 50 kHz to 1 MHz n Dynamic output voltage positioning n 1.256V reference voltage available externally n Plastic SO-20 package Applications n Motherboard power supply/VRM for Cyrix Gxm, Cyrix Gxi, Cyrix MII, Pentium II, Deschutes, Pentium Pro, 6x86 and K6 processors n 5V to 1.8V–3.5V high current power supplies Typical Application Pentium™ is a trademark of Intel Corporation. DS100119-1 FIGURE 1. 5V to 1.8V–3.5V, 14A Power Supply May 2000 © 2000 National Semiconductor Corporation DS100119 www.national.com |
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