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PDF FP6321A Data sheet ( Hoja de datos )
| Número de pieza | FP6321A | |
| Descripción | Sunchronous Buck PWM DC-DC Controller | |
| Fabricantes | Fiti | |
| Logotipo |  |
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fitipower integrated technology lnc.
FP6321A
Synchronous Buck PWM
DC-DC Controller
Description
The FP6321A is designed to drive two N-channel
MOSFETs in a synchronous rectified buck topology.
It provides the output adjustment, internal soft-start,
frequency compensation networks, monitoring and
protection functions into a single package.
The IC operating at fixed 300kHz frequency provides
simple, single feedback loop, voltage mode control
with fast transient response. The resulting PWM duty
ratio ranges from 0-100%.
The FP6321A features over current protection. The
output current is monitored by sensing the voltage
drop across the RDS (ON) of the low side MOSFET
which eliminates the need for a current sensing
resistor.
This device is available in SOP-8 package.
Pin Assignment
SO Package (SOP-8)
Features
● Operates from +5V or +12V
● Drives Two Low Cost N-Channel MOSFETs
● Fast Transient Response
● Simple Single-Loop Control Design
( Voltage-Mode PWM Control)
● Internal Soft-Start
● Over-Current Fault Monitor
● Over-Voltage Protection
● Under-Voltage Protection
● SOP-8 Package
● RoHS Compliant
Applications
● Motherboard
● Graphic Card
● Telecomm Equipments
● High Power DC-DC Regulators
● Servers
Ordering Information
FP6321A□□□
TR: Tape / Reel
P: Green
G: Green
Figure 1. Pin Assignment of FP6321A
Package Type
SO: SOP-8
FP6321A-1.1-FEB -2010
1
1 page  
fitipower integrated technology lnc.
Electrical Characteristics
(VCC=12V, TA=25°C, unless otherwise specified)
Parameter
Symbol Conditions
INPUT
VCC Under Voltage Lockout
Quiescent Current
VRISING VCC rising
VFALLING VCC falling
ICC UGATE and LGATE open
ERROR AMPLIFIER
Feedback Voltage
FB Input Bias Current
Open Loop DC Gain (Note2)
VFB
IFB VFB=1V
AO
OSCILLATOR
Frequency
Ramp Amplitude (Note2)
FOSC
△VOSC
VCC=12V
VCC=12V
GATE DRIVERS
Upper Gate Source
Upper Gate Sink
Lower Gate Source
Lower Gate Sink
Dead Time (Note2)
IUGATE
RUGATE
ILGATE
RLGATE
TDT
VBOOT-VPHASE=12V,
VUGATE-VPHASE=6V
VBOOT-VPHASE=12V,
VUGATE-VPHASE=1V
VCC=12V, VLGATE =6V
VCC=12V, VLGATE =1V
PROTECTION
FB Under-Voltage Trip
FB Falling
FB Over-Voltage Trip
OCSET Current Source
Soft-Start Interval (Note2)
IOCSET
Tss
VPHASE=0V
Note2：Guarantee by design.
FP6321A
Min Typ
Max
Unit
3.7 4.1
0.45
6
4.5
15
V
V
mA
0.784
0.8
0.1
85
0.816
V
µA
dB
250 300
350
kHz
1.5 Vp-p
0.6 1
A
48
Ω
0.6 1
A
35
Ω
100 ns
70 75
120
35 40
2 3.5
80
45
%
%
µA
ms
FP6321A-1.1-FEB -2010
5
5 Page 
fitipower integrated technology lnc.
FP6321A
Application Information
Introduction
The FP6321A integrated circuit is a synchronous
PWM controller, it operates over a wide input voltage
range. Being low cost, it is a very popular choice of
PWM controller. This section will describe the
FP6321A application suggestion. The operation and
the design of this application will also be discussed in
detail.
Design Procedures
This section will describe the steps to design
synchronous buck system, and explains how to
construct basic power conversion circuits including
the design of the control chip functions and the basic
loop.
(1) Synchronous buck converter
Since this is a buck output system, the first quantity
to be determined is the duty cycle value. The formula
calculated the PWM duty ratio, apply to the system
which we propose to design:
(2) Inductor Selection
To find the inductor value it is necessary to consider
the inductor ripple current. Choose an inductor which
operated in continuous mode down to 10 percent of
the rated output load:
ΔIL = 2 x 10% x IO
The inductor “L” value for this system is connected to
be:
L≧
(VIN - VDS(sat) – VO) x DMIN
ΔIL x fS
If the core loss is a problem, increasing the
inductance of L will be helpful.
(3) Output Capacitor Selection
a. The output capacitor is required to filter the output
noise and provide regulator loop stability. When
selecting an output capacitor, the important
capacitor parameters are; the 100kHz Equivalent
Series Resistance (ESR), the RMS ripples current
rating, the voltage rating, and capacitance value.
For the output capacitor, the ESR value is the
most important parameter.
The ESR can be calculated from the following
formula.
ESR
=
VRIPPLE
ΔIL
An aluminum electrolytic capacitor's ESR value is
related to the capacitance and its voltage rating.
In most case, higher voltage electrolytic
capacitors have lower ESR values. Most of the
time, capacitors with much higher voltage ratings
may be needed to provide the low ESR values
required for low output ripple voltage.
b. The capacitor voltage rating should be at least 1.5
times greater than the output voltage, and often
much higher voltage ratings are needed to satisfy
the low ESR requirements needed for low output
ripple voltage.
(3) Output N-channel MOSFETs Selection
a. The current ability of the output N-channel
MOSFETs must be at least more than the peak
switching current IPK. The voltage rating VDS of
the N-channel MOSFETs should be at least 1.25
times the maximum input voltage. Choose the
low RDS-ON MOSFETs for reducing the conduction
power loss. Choose the low CISS MOSFETs for
reducing the switching loss. But most of time, the
two factors are trade-off. Consider the system
requirement and define the MOSFETs rating.
b. The MOSFETs must be fast (switch time) and
must be located close to the FP6321A using
short leads and short printed circuit traces. In
case of a large output current, we must layout a
copper to reduce the temperature of these two
MOSFETs.
(4) Input Capacitor Selection
a. The RMS current rating of the input capacitor can
be calculated from the next page formula table.
b. This capacitor should be located close to the IC
using short leads and the volt age rating should
be approximately 1.5 times the maximum input
voltage.
FP6321A-1.1-FEB -2010
11
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet FP6321A.PDF ] | |
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