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Número de pieza | FAN6520B | |
Descripción | Single Synchronous Buck PWM Controller | |
Fabricantes | Fairchild Semiconductor | |
Logotipo | ||
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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 |
Páginas | Total 14 Páginas | |
PDF Descargar | [ Datasheet FAN6520B.PDF ] |
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