PDF FAN6520B Data sheet ( Hoja de datos )

Número de pieza	FAN6520B
Descripción	Single Synchronous Buck PWM Controller
Fabricantes	Fairchild Semiconductor
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No Preview Available ! February 2006 FAN6520B Single Synchronous Buck PWM Controller www.DataSheet4U.com Features ■ Accepts 1.5V to 5V for VIN ■ Output Range 0.8V to VIN – 0.8V Internal Reference – ±1.5% Over Line Voltage and Temperature ■ Drives N-Channel MOSFETs ■ Simple Single-Loop Control Design – Voltage-Mode PWM Control ■ Fast Transient Response – High-Bandwidth Error Ampliﬁer – Full 0% to 100% Duty Cycle ■ Small Converter Size – 300kHz Fixed Frequency Oscillator – Internal Soft-Start – 8-Lead SOIC Applications ■ Power Supplies for PC Subsystems and Peripherals ■ MCH, GTL, and AGP Supplies ■ Cable Modems, Set Top Boxes, and DSL Modems ■ DSP, Memory ■ Low-Voltage Distributed Power Supplies ■ ACPI Power Control ■ 5V Input DC-DC Regulator Description The FAN6520B makes simple work out of implementing a complete control and protection scheme for a DC-DC stepdown converter. Designed to drive N-channel MOSFETs in a synchro- nous buck topology, the FAN6520B integrates the con- trol, output adjustment, and monitoring functions into a single 8-lead package. The FAN6520B is easy to use, employs a single feed- back loop, and voltage-mode control with fast transient response. The output voltage can be precisely regulated to as low as 0.8V, with a maximum tolerance of ±1.5% over temperature and line voltage variations. A ﬁxed fre- quency oscillator reduces design complexity, while bal- ancing typical application cost. The error ampliﬁer features a 15MHz gain-bandwidth product and an 8V/µs slew rate which enables high converter bandwidth for fast transient performance. The resulting PWM duty cycles range from 0% to 100%. The FAN6520B is rated for operation from 0° to +70°C with the FAN6520BI rated from –40° to +85°C. Ordering Information Part Number FAN6520BM FAN6520BMX FAN6520BIM FAN6520BIMX Temperature Range 0°C to 70°C 0°C to 70°C –40°C to 85°C –40°C to 85°C Package SOIC-8 SOIC-8 SOIC-8 SOIC-8 Packing Rails Tape and Reel Rails Tape and Reel ©2006 Fairchild Semiconductor Corporation FAN6520B Rev. 1.0.3 1 www.fairchildsemi.com 1 page Electrical Speciﬁcations VCC = 5V, and TA = 25°C using circuit in Figure 1 unless otherwise noted. The • denotes speciﬁcations which apply over the full operating temperature range. Parameter Supply Current VCC Current Power-On Reset Rising VCC POR Threshold VCC POR Threshold Hysteresis Oscillator Frequency Ramp Amplitude Reference Reference Voltage Error Ampliﬁer DC Gain Gain – Bandwidth Product Slew Rate Gate Drivers HDRV pull-up resistance HDRV pull-down resistance LDRV pull-up resistance LDRV pull-down resistance Disable Disable Threshold Symbol Conditions IVCC POR HDRV, LDRV open FOSC ∆VOSC VREF FAN6520B FAN6520BI TA = 0 to 70°C FAN6520BI GBW S/R Note 2 Note 2 Note 2 RHUP RHDN RLUP RLDN VDISABLE Note 3 Min. Typ. Max. Units • 1.5 2.4 3.8 mA • 4.00 4.22 4.45 170 V mV • 250 300 340 kHz • 230 300 340 kHz • 1.5 Vp-p • 788 800 812 mV • 780 800 820 mV 88 dB 15 MHz 8 V/µs 2.5 Ω 2.0 Ω 2.5 Ω 1.0 Ω 400 800 mV Notes: 1. All limits at operating temperature extremes are guaranteed by design, characterization and statistical quality control. 2. Specifications guaranteed by design/characterization (not production tested). 3. To ensure shutdown, COMP/SD pin should be held below 400mV while sinking 6mA of current. FAN6520B Rev. 1.0.3 5 www.fairchildsemi.com 5 Page ts ≈ -Q-----G----(--S---W-----) IDRIVER ≈ -----------------Q-----G----(--S----W----)-----------------   -R----D----R-V---I-CV----E-C--R----–-+---V--R--S--G--P--A----T---E-- (16) Most MOSFET vendors specify QGD and QGS. QG(SW) can be determined as: QG(SW) = QGD + QGS – QTH where QTH is the gate charge required to get the MOS- FET to its threshold (VTH). For the high-side MOSFET, VDS = VIN, which can be as high as 20V in a typical por- table application. Care should also be taken to include the delivery of the MOSFET’s gate power (PGATE) in cal- culating the power dissipation required for the FAN6520B: PGATE = QG × VCC × FSW (17) where QG is the total gate charge to reach VCC. Low-Side Losses Q2, however, switches on or off with its parallel shottky diode conducting, therefore VDS ≈ 0.5V. Since PSW is proportional to VDS, Q2’s switching losses are negligible and we can select Q2 based on RDS(ON) only. Conduction losses for Q2 are given by: PCOND = (1-D) × IOUT2 × RDS(ON) (18) where RDS(ON) is the RDS(ON) of the MOSFET at the highest operating junction temperature and D = -V--V--O---I-UN---T-- is the minimum duty cycle for the converter. Since DMIN < 20% for portable computers, (1-D) ≈ 1 produces a conservative result, further simplifying the calculation. The maximum power dissipation (PD(MAX) ) is a function of the maximum allowable die temperature of the low- side MOSFET, the θJ-A, and the maximum allowable ambient temperature rise: PD(MAX) = T----J---(--M----A----X-θ--)--J-–--–---T-A---A---(--M----A----X---) (19) θJ-A, depends primarily on the amount of PCB area that can be devoted to heat sinking (see Fairchild app note AN-1029 for SO-8 MOSFET thermal information). FAN6520B Rev. 1.0.3 11 www.fairchildsemi.com 11 Page

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