AMS4123 Datasheet, PDF (1/18 Pages) Advanced Monolithic Systems Ltd – 3A 20V Step-Down Converter plus 1A LDO

General Description
The AMS4123 combines a 3A Step-Down converter
with a 1A LDO in a single SO-8 exposed paddle
package. Both the LDO and Step-Down converter
are low ESR, ceramic capacitor output, stable. The
Step-Down converter is internally compensated with
internal soft-start to minimize the number of external
components. An Enable pin provides built-in
externally programmable power-up sequencing. The
Step-Down converter enable threshold is 2.0V and
the LDO enable threshold is 2.5V. It also has hiccup
current limit and thermal protection. Thermal
protection shuts down both the Step-Down converter
and LDO when the die temperature exceeds 135°C.
Both regulators are adjustable using a 0.6V
reference for low output voltage settings. The LDO
has options for fixed output voltages from 0.6V to 5V
in 100mV steps. The LDO external input can be
powered from the Step-Down converter output, for
improved efficiency, or from any voltage source that
is less than or equal to the device supply voltage
(Vin). With a dropout voltage of less than 350mV at
1A, the AMS4123 LDO makes the perfect solution
for a low noise 1.8V power source developed from
2.5V Step-Down converter output. The AMS4123 is
a complete solution for LCD TV power requirements
when combined with the AMS4122 (2A Dual
Switching Regulator in SO-8).
AMS4123
3A 20V Step-Down Converter + 1A LDO
Features
• Step-Down Converter + LDO in SO-8EP
• Internally Compensated
• Up to 95% Efficiency
• Low ESR Ceramic Output Capacitor Stable
• Soft Start
• Under-Voltage Lockout
• Dual Threshold Enable
• 300 kHz Switching Frequency
• Hiccup Current Limit
• Over-Temperature Shutdown
• Ultra-Low Dropout LDO 350mV @ 1A
• Up to 3A Step-Down Output Current
• Up to 1A LDO Output Current
• Excellent Light Load Efficiency
Applications
• Audio Power Amplifiers
• Portable (Notebook) Computers
• Point of Regulation for High Performance
Electronics
• Consumer Electronics
• DVD, Blue-ray DVD writers
• LCD TVs and LCD monitors
• Distributed Power Systems
• Battery Chargers
• Pre-Regulator for Linear Regulation
Typical Application
Vin 4.5V to 20V
U1
3 _Vin
AMS4123
SW
2.5V
7 _LDOin
BST
C1
10uF
1.8V at 1A
8 _{LDOout FB SW}
C3
2.2uF
R1
20.0k
6 _{FB LDO}
EN
R2
10.0k
Enable
C5
220nF
1
2
5
4
R3
10.0k
L1
10uH
2.5V at 2A
SW out
C2
D1
22uF
B340LB
C9
100uF
R4
31.6k
C8
4.7nF
R1 and R4 Voltage Options
1.8V 20.0k
2.5V 31.6k
3.3V 45.3k
5.0V 73.2k
3/5/2010
www.advanced-monolithic.com
1
Phone [phone]
Fax [phone]