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PDF FAN6520A Data sheet ( Hoja de datos )
| Número de pieza | FAN6520A | |
| Descripción | Single Synchronous Buck PWM Controller | |
| Fabricantes | Fairchild Semiconductor | |
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FAN6520A
Single Synchronous Buck PWM Controller
October 2006
www.DataSheet4U.com
Features
■ 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
■ Lossless, Programmable, Over-Current Protection
– Uses Upper MOSFET’s RDS(ON)
■ 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
Description
The FAN6520A simplifies implementing a complete con-
trol and protection scheme for a DC-DC stepdown con-
verter. Designed to drive N-channel MOSFETs in a
synchro-nous buck topology, the FAN6520A integrates
the control, output adjustment, monitoring, and protec-
tion functions into a single 8-lead package.
The FAN6520A employs a single feedback loop and volt-
age-mode control with fast transient response. The out-
put 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-frequency oscillator
reduces design complexity, while balancing typical appli-
cation cost. The error amplifier features a 15MHz gain-
bandwidth product and an 8V/µs slew rate, which
enables high converter bandwidth for fast transient per-
formance. The resulting PWM duty cycles range from
0% to 100%.
The IC monitors the drop across the upper MOSFET and
inhibits PWM operation appropriately to protect against
over-current conditions. This approach simplifies the
implementation and improves efficiency by eliminating
the need for a current sense resistor.
The FAN6520A is rated for operation from 0° to +70°C,
with the FAN6520AI rated from –40° to +85°C.
Ordering Information
Part Number
FAN6520AM
FAN6520AMX
FAN6520AIM
FAN6520AIMX
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
© 2005 Fairchild Semiconductor Corporation
FAN6520A Rev. 1.0.5
www.fairchildsemi.com
1 page  
Electrical Specifications
VCC = 5V and TA = 25°C, using the circuit shown in Figure 1 unless otherwise noted. The • denotes specifications that
apply over the full operating temperature range.
Symbol Parameter
Supply Current
IVCC VCC Current
Power-On Reset
POR Rising VCC POR Threshold
VCC POR Threshold Hysteresis
Oscillator
FOSC Frequency
ΔVOSC Ramp Amplitude
Reference
VREF Reference Voltage
Error Amplifier
DC Gain
GBWP Gain – Bandwidth Product
S/R Slew Rate
Gate Drivers
RHUP HDRV Pulll-Up Resistance
RHDN HDRV Pull-Down Resistance
RLUP LDRV Pull-Up Resistance
RLDN LDRV Pull-Down Resistance
Protection/Disable
IOCSET OCSET Current Source
VDISABLE Disable Threshold
Conditions
Min. Typ. Max. Units
HDRV, LDRV open • 1.5 2.4 3.8 mA
• 4.00 4.22 4.45
170
V
mV
FAN6520A
FAN6520AI
• 250 300 340 kHz
• 230 300 340 kHz
• 1.5
Vp-p
TA = 0 to 70°C
FAN6520AI
• 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
FAN6520A
FAN6520AI
• 17 20 22 μA
• 14 20 24 μA
800 mV
Notes:
1. All limits at operating temperature extremes are guaranteed by design, characterization, and statistical quality
control.
2. AC specifications guaranteed by design/characterization (not production tested).
© 2005 Fairchild Semiconductor Corporation
FAN6520A Rev. 1.0.5
5
www.fairchildsemi.com
5 Page 
High-Side Losses
Figure 10 shows a MOSFET’s switching interval, with the
upper graph being the voltage and current on the drain-
to-source and the lower graph detailing VGS vs. time with
a constant current charging the gate. The x-axis, there-
fore, is also representative of gate charge (QG). CISS =
CGD + CGS and it controls t1, t2, and t4 timing. CGD
receives the current from the gate driver during t3 (as
VDS is falling). The gate charge (QG) parameters on the
lower graph are either specified or can be derived from
the MOSFET’s datasheet.
Assuming switching losses are about the same for both
the rising edge and falling edge, Q1’s switching losses
occur during the shaded time when the MOSFET has
voltage across it and current through it.
These losses are given by:
PUPPER = PSW + PCOND
PSW
=
⎛
⎝
-V----D----S------×-----I--L-
2
×
2
×
ts⎠⎞
FSW
(24)
(25)
PCOND
=
⎛
⎜
⎝
V----V-O---I--UN----T---⎠⎟⎞
×
IOU
2
T
×
RDS(ON
)
(26)
where PUPPER is the upper MOSFET’s total losses, PSW
and PCOND are the switching and conduction losses for a
given MOSFET, RDS(ON) is at the maximum junction tem-
perature (TJ), and tS is the switching period (rise or fall
time) and is t2+t3 (Figure 10).
The driver’s impedance and CISS determine t2, while t3’s
period is controlled by the driver’s impedance and QGD.
Since most of tS occurs when VGS = VSP, use a constant
current assumption for the driver to simplify the calcula-
tion of tS:
ts
≈
-Q-----G-----(---S----W------)-
IDRIVER
≈
--------------------Q-----G-----(--S----W------)--------------------
⎛
⎜
⎝
-R----D-----R----VI--V---C--E-C---R--–----+-V----SR----P-G-----A----T----E-- ⎠⎟⎞
(27)
VDS
C ISS
C GD
C ISS
ID
VSP
VTH
VGS
QGS
QGD
QG(SW)
t1 t2
t3
4.5V
t4 t5
Figure 10. Switching Losses and QG
5V
RD
HDRV
SW
CGD
RGATE
G
CGS
VIN
Figure 11. Drive Equivalent Circuit
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 reach the MOSFET
threshold (VTH). For the high-side MOSFET, VDS = VIN,
which can be as high as 20V in a typical portable appli-
cation. Care should be taken to include the delivery of
the MOSFET’s gate power (PGATE) in calculating the
power dissipation required:
PGATE = QG × VCC × FSW
where QG is the total gate charge to reach VCC.
(28)
©2005 Fairchild Semiconductor Corporation
FAN6520A Rev. 1.0.5
11
www.fairchildsemi.com
11 Page | ||
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