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PDF AS5430 Fiche technique - A1semi

Numéro de référence AS5430
Description 3A 400KHz Synchronous Rectified Step-Down Converter
Fabricant A1semi 
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AS5430 Datasheet, Description
A1
A1semi
Electronics Ltd
AS54303A 400KHz Synchronous Rectified
Step-Down Converter
„ GENERAL DESCRIPTION
The AS5430 is a monolithic synchronous buck regulator.
The device integrates 100mMOSFETS that
provide 3A continuous load current over a wide
operating input voltage of 4.75V to 23V. Current
mode control provides fast transient response
and cycle-by-cycle current limit.
An adjustable soft-start prevents inrush current at
turn-on. In shutdown mode, the supply current
drops below 1uA. The device provides a very
compact system solution with minimal reliance on
external components.
„ FEATURES
‹ 3A Output Current
‹ Integrated 100mPower MOSFETS
‹ Wide 4.75~23V Input Voltage Range
‹ Programmable Soft-start
‹ Up to 95% Efficiency
‹ Stable with Low ESR Ceramic Output Capacitors
‹ Output Adjustable From 0.925V to 20V
‹ Cycle-by-Cycle Over Current Protection
‹ Input Under Voltage Lockout
‹ Fixed 400KHz Frequency
„ APPLICATION
‹ Distribute Power Supply
‹ Networking Systems
‹ Notebook or Mini-book
‹ LCD TV/LCD Monitor
„ ORDER INFORMATION
Order Number
AS5430D/TR-LF
Package
SOP8(Exposed Pad)
„ BLOCK DIAGRAM
Packing
Tape&Reel, MPQ=2500
Remark
Lead-Free
AS5430Ver1.0
1 http://www.a1semi.com
AS5430 Fiche technique
A1
A1semi
Electronics Ltd
3A 400KHz Synchronous Rectified
AS5430Step-Down Converter
„ ABSOLUTE MAXIMUM RATING(Note1)
Input Voltage, VIN--------------------------------- -0.3V to 26V
Switch Voltage, VSW-------------------------- -1V to VIN+0.3V
Bootstrap Voltage,VBS-------------VSW-0.3V to VSW+6V
Enable/UVLO Voltage,VEN----------------------- -0.3V to 6V
Comp Voltage,Vcomp-------------------------------- -0.3V to 6V
Feedback Voltage, VFB---------------------------- -0.3V to 6V
Storage Temperature Range, TS---------- -55to 150
Lead Temperature------------------------------------- 260
Junction Temperature, TJ---------------------------- 150
OPERATION RATING(Note2)
Input Voltage, VIN-------------------------- 4.75V to 23V
Output Voltage, VSW---------------------- 0.925V to 20V
Operation Temperature------------------ -20to +85
THERMAL RESISTANCE(Note3)
SOIC8, θJA--------------------------------------- 50/W
SOIC8, θJC--------------------------------------- 10/W
„ ELECTRICAL CHARACTERISTICS(VIN=12V,TA=+25,unless otherwise noted)
Parameter
Test Conditions Min Typ Max
Shutdown Supply Current
Supply Current
Feedback Voltage
Feedback Overvoltage Threshold
VEN0.3V
VEN2.6V,VFB=1.0V
4.75VVIN23V
0.3 3.0
1.3 1.5
900 925 950
1.1
Error Amplifier Voltage
480
Error Amplifier Transconductance
ΔIC=±10uA
800
High-side Switch-On Resistance
100
Low-side Switch-On Resistance
100
High-side Switch Leakage
Upper Switch Current Limit
VEN=0V,VSW=0V
1 10
4.0 6.0
Lower Switch Current Limit
0.9
COMP to Current Sense
Transconductance
5.2
Oscillator Frequency
350 400 450
Short Circuit Frequency
Maximum Duty Cycle
Minimum On Time
VFB=0V
VFB=0.8V
150
90
120
EN Shutdown Threshold Voltage
EN Shutdown Threshold Voltage
Hysterisis
VEN Rising
1.1 1.5 2.0
200
EN Lockout Threshold Voltage
2.2 2.5 2.7
Units
uA
mA
mV
V
V/V
uA /V
m
m
uA
A
A
A/V
KHz
KHz
%
nS
V
mV
V
AS5430Ver1.0
3 http://www.a1semi.com

3 Page

AS5430 pdf
A1
A1semi
Electronics Ltd
3A 400KHz Synchronous Rectified
AS5430Step-Down Converter
OPTIONAL SCHOTTKY DIODE
During the transition between high-side switch and
low-side switch, the body diode of the low-side
power MOSFET conducts the inductor current.
The forward voltage of this body diode is high. An
optional schottky diode may be paralleled between
the SW pin and GND pin to improve overall
efficiency. Table2 lists example schottky diodes
and their manufacturers.
Table2—Diode Selection Guide
Part#
Voltage/Current
Rating
Vendor
B130
30V,1A
Diodes
SK130
30V,1A
Diodes
MBRS130
30V,1A
International
Rectifier
INPUT CAPACITOR
The input current to the step-down converter is
discontinuous, therefore a capacitor is required to
supply the AC current to the step-down converter
while maintaining the DC input voltage. Use low
ESR capacitors for the best performance. Ceramic
capacitors are preferred,but tantalum or low-ESR
electrolytic capacitors may also suffice. Choose
X5R or X7R dielectrics when using ceramic
capacitors. Since the input capacitor absorbs the
input switching current it requires an adequate
ripple current rating. The RMS current in the input
capacitor can be estimated by:
The worst-case condition occurs at
Vin=2VOUT,where ICIN=ILOAD/2. For
simplification ,choose the input capacitor whose
RMS current rating greater than half of the
maximum load current. The input capacitor can be
electrolytic,tantalum or ceramic. When using
electrolytic or tantalum or capacitors,a small, high
quality ceramic capacitor, i.e. 0.1uF, should be
placed as close to the IC as possible. When using
ceramic capacitors,make sure that they have
enough capacitance to provide sufficient charge to
prevent excessive voltage ripple at input. The input
Voltage ripple for low ESR capacitors can be
estimated by:
Where C1 is the input capacitance value.
OUTPUT CAPACITOR
The output capacitor is required to maintain the DC
output voltage. Ceramic, tantalum, or low ESR
electrolytic capacitors are recommended. Low ESR
capacitors are preferred to keep the output voltage
ripple low. The output voltage ripple can be
estimated by:
Where C2 is the output capacitance value and
RESR is the equivalent series resistance(ESR)
value of the output capacitor. In the case of
ceramic capacitors, the impedance at the switching
frequency is dominated by the capacitance. The
output voltage ripple is mainly caused by the
capacitance. For simplification, the output voltage
ripple can be estimated by:
In the case of tantalum or electrolytic capacitors,
the ESR dominates the impedance at the switch-
ing frequency. For simplification, the outout ripple
can be approximated to:
The characteristics of the output capacitor also
affect the stability of the regulation system. The
AS5430 optimized for a wide range of capacitance
and ESR values.
COMPENSATION COMPONENTS
AS5430 employs current mode control for easy
compensation and fast transient response. The
system stability and transient response are
controlled through the COMP pin. COMP pin is the
output of the internal transconductance error ampl-
ifier. A series capacitor-resistor combination sets a
pole-zero combination to control the characteristics
of the control system.
AS5430Ver1.0
6 http://www.a1semi.com

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