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SC488 Datasheet(PDF) 1 Page - Semtech Corporation |
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SC488 Datasheet(HTML) 1 Page - Semtech Corporation |
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1 / 24 page  www.semtech.com 1 POWER MANAGEMENT SC488 Complete DDR1/2/3 Memory Power Supply September 28, 2006 Description Features The SC488 is a combination switching regulator and lin- ear source/sink regulator intended for DDR1/2 memory systems. The purpose of the switching regulator is to gen- erate the supply voltage, VDDQ, for the memory system. It is a pseudo-fixed frequency constant on-time controller designed for high efficiency, superior DC accuracy, and fast transient response. The purpose of the linear source/sink regulator is to generate the memory termination voltage, VTT, with the ability to source and sink 2.8A peak cur- rents. For the VDDQ regulator, the switching frequency is constant until a step in load or line voltage occurs at which time the pulse density, i.e., frequency, will increase or decrease to counter the transient change in output or input voltage. After the transient, the frequency will return to steady-state operation. At lighter loads, the selectable Power-Save Mode enables the PWM converter to reduce its switching frequency and improve efficiency. The integrated gate drivers feature adaptive shoot-through protection and soft- switching. Additional features include cycle-by-cycle current limiting, digital soft-start, over-voltage and under-voltage protection and a power good flag. For the VTT regulator, the output voltage tracks REF, which is ½ VDDQ to provide an accurate termination voltage. The VTT output is generated from a 1.2V to VDDQ input by a linear source/sink regulator which is designed for high DC accuracy, fast transient response, and low external component count. All three outputs (VDDQ, VTT and REF) are actively discharged when VDDQ is disabled, reducing external component count and cost. The SC488 is avail- able in a 24-pin MLPQ (4x4 mm) package. Constant On-Time Controller for Fast Dynamic Response on VDDQ DDR1/DDR2/DDR3 Compatible VDDQ = Fixed 1.8V or 2.5V, or Adjustable From 1.5V to 3.0V 1.5% Internal Reference (2.5% System Accuracy) Resistor Programmable On-Time for VDDQ VCCA/VDDP Range = 4.5V to 5.5V VIN Range = 2.5V to 25V VDDQ DC Current Sense Using Low-Side R DS(ON) Sensing External R SENSE in Series with Low-Side FET Cycle-by-Cycle Current Limit for VDDQ Digital Soft-Start for VDDQ Analog Soft-Start for VTT/REF Smart Over-Voltage VDDQ Protection Combined EN and PSAVE Pin for VDDQ Over-Voltage/Under-Voltage Fault Protection Power Good Output Separate VCCA and VDDP Supplies VTT/REF Range = 0.75V – 1.5V VTT Source/Sink 2.8A Peak Internal Resistor Divider for VTT/REF VTT is High Impedance in S3 VDDQ, VTT, REF are Actively Discharged in S4/S5 24 Lead MLPQ (4x4 mm) Lead-Free Package Product Is Fully WEEE and RoHS Compliant Notebook Computers CPU I/O Supplies Handheld Terminals and PDAs LCD Monitors Network Power Supplies Applications Typical Application Circuit REF R7 10R C10 1uF VTT C8 0.1uF Q1 Q2 D1 C3 2x10uF VBAT R1 1Meg L1 + C6 VDDQ VTT_EN R6 10R C9 1uF VBAT C7 1nF C1 1uF EN/PSV C4 10uF PGND2 1 VTTS 2 VSSA 3 TON 4 REF 5 VCCA 6 PGND1 18 PGND1 17 ILIM 16 VDDP 15 VDDP 14 PGD 13 PAD U1 SC488 R4 VDDQ 5V VTTSNS PAD C2 0.1uF 5V PGOOD RILIM C11 1uF C5 10uF VDDQ VDDQ |
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