LM2635MX

Product Summary

The LM2635MX 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 accepts the VID code directly from the CPU and adjusts the output voltage from 1.8V to 3.5V. The LM2635MX provides the power good, over-voltage protection, and output enable features as required by Intel VRM specifications. Current limiting is achieved by monitoring the voltage drop across the rDS_ON of the high side MOSFET, which eliminates an expensive current sense resistor. The LM2635MX 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 monitor 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 flexibility to make trade-offs between load transient response performance, 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 implemented easily.

Parametrics

LM2635MX absolute maximum ratings: (1)VCC: 7V; (2)BOOTV: 15V; (3)Junction Temperature: 150℃; (4)DC Power Dissipation: 1.42W; (5)Storage Temperature: -65℃ to +150℃; (6)Soldering Time, Temperature Wave (4 seconds): 260℃; (7)Infrared (10 seconds): 240; (8)Vapor Phase (75 seconds): 219℃; (9)ESD Susceptibility (Note 3) 2 kV.

Features

LM2635MX features: (1)1.8V to 3.5V 5-bit programmable output voltage; (2)Synchronous rectification; (3)Power Good flag and output enable; (4)Over-voltage protection; (5)Initial Output Accuracy: 2% over temperature; (6)Current limit without external sense resistor; (7)Adaptive non-overlapping MOSFET gate drives; (8)Adjustable switching frequency: 50 kHz to 1 MHz; (9)Dynamic output voltage positioning; (10)1.256V reference voltage available externally; (11)Plastic SO-20 package.

Diagrams