AN908 Datasheet | STMicroelectronics

DESCRIPTION The actual generation of Pentium Pro® microprocessors, requires a power supply with a programmable output voltage that decreases with the increasing of the processor internal clock. At the same time higher output currents are required and superior load transient performance has to be supplied due to very high d I/dt requests. The VRM (Voltage Regulator Module) proposed (Fig 1) is a step down converter based on the L4990A, very fast current mode controller. A plete system solution is given and described. A connector with a standard VRM pinout is used, with 4 bit for Voltage Identify system, Power Good, Enable and constant limiting current functions are available. Output Over Voltage Protection is also available. ELECTRICAL SPECIFICATION Input Characteristics Symbol Vi di/dt Vbias Parameter Input Voltage Slew Rate Bias Voltage Load Transient I12 = 45m A 11.4 12 Test Condition Min. 4.75 Typ. 5 Max. 5.25 0.04 14 Unit V A/µs V Output Characteristics Symbol Parameter Output Voltage range Vonom Io Nominal Output Voltage Output Current Peak Current Regulation Pulse by pulse mode Including variation due to: - Io = min-max - Vo imitial set point accuracy - Line regulation - Output ripple and noise - Load transient d Io/dt = 30A/µs - Temperature Vo = min-max; Io = min-max Vo = min-max Short circuit condition 70 85 1.18 ⋅ VO 12 300 A k Hz 0.4 13 ±5 Test Condition By 4 bits VID Min. 2.1 2.9 12.5 Typ. Max. 3.5 Unit V V A A % η Efficiency Output Over Voltage Protection Foldback Current % fsw Switching frequency July 1999 1/9 Data Sheet 4 U . 2/9 Data Sheet 4 U . R2 5V ±5% Vi L3 L2 50T D2 D1 STPS 20L25CT R3 10K VCC 8 10 OUT R6 510 9 14 15 VC DIS DC_LIM Q1 STP80N03 L1 2.6µH Vo=2.1V-3.5V Io=0.3A-12.5A C5-8 330µF-6.3V SANYO-OSCON C18 C1-4 330µF-25V LXF-NCC R8 4.7 .. 12V C13 47µF C20 220n F SYNC VREF AN908 APPLICATION NOTE L4990A IC1 13 6 7 P SS VFB C11 150p F R5 27K R9 1K(0.1%) R27 C12 220p F R7 3.3 RR1 11 5 PGND ISEN R1 6.8K VREF Figure 1....