ROHS AMS4123 Technical data

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Advanced AMS4123
Monolithic 2A BUCK CONVERTER + 1A LDO IN SO-8
Systems

RoHS compliant

FEATURES APPLICATIONS

•••• One Asynchronous Buck Converter + LDO in SO-8 •••• Audio Power Amplifiers

•••• Internally compensated •••• Portable (Notebook) Computers

•••• Built in soft start •••• Point of regulation for high performance electronics

•••• Enable with Zero current shut down •••• Consumer Electronics

•••• 300KHz switching frequency •••• DVD, Blue-ray DVD writers

•••• Hiccup current limit and thermally protected •••• LCD TVs and LCD monitors

•••• Ultra-low dropout LDO (500mV Max.) •••• Distributed Power Systems

•••• Up to 2A output on the Switch and 1A on LDO •••• Battery Chargers

•••• 0.6V reference for low output voltage settings •••• Pre-Regulator for Linear Regulators

GENERAL DESCRIPTION

AMS4123 is a switching regulator capable to deliver up to 2A and one LDO rated for 1A output in a single SO-8 EDP package.
The switching regulator is Internally Compensated internal Soft Start to reduce to minimum external components. The regulator
has hiccup current limit and thermal protection. The Enable pin has built-in power-up sequencing externally programmable. If

2.0V or higher it is applied to EN pin it turns on the Switching Regulator. By increasing the voltage to 2.5V or more it turns on
the LDO section. Since both circuits share one single package the thermal protection turns off both circuits when the die
temperature exceeds approximately 135°C. Both regulators are adjustable using a 0.600V reference for low output voltage
settings. The LDO has options for fixed output voltages from 0.6V to 5V in 100mV steps. The LDO input can be supplied from
the Switching Regulator output increasing the efficiency but can supplied as well from another source that is equal or lower than
the device supply voltage. With a Dropout of 400mV @1A makes AMS4123 the perfect solution for low noise 1.8V from a

2.5V source. The AMS4123 combined with AMS4122 (2A Dual Switching Regulator in SO-8) makes complete solution for
LCD TV power requirements.

ERING INFORMATION

ORD

Package Type

SOI

C EDP

AMS4123S -25°C to 125°C

TYPICAL APPLICATION

TEMP. RANGE

PINCONNECTIONS

8L SOIC
SO Package (S)

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Top View

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PIN DESCRIPTION

Pin Number NAME DESCRIPTION

1 SW This connects the inductor the Internal Switch.

2 BST Bootstrap. This capacitor is needed to drive the power switch above the supply voltage.

3 PVIN Input Power Pin from unregulated power supply.

4 EN Enable. A voltage greater than 2V at this pin enables the switching regulator. By

increasing the voltage on this pin above 2.5V will enable the LDO section.

5 F/B SW Feedback Switch. A resistor network of two resistors is used to set-up the output voltage

connected between Output2 to GND. The node between the two resistors is connected to
Feedback Switch pin.

6 F/B LDO Feedback LDO. A resistor network of two resistors is used to set-up the output voltage

connected between Output1 to GND. The node between the two resistors is connected to
Feedback LDO pin.

7 LDO IN LDO Input pin can be connected from Switch Output pin. LDO IN can be powered up

from another supply that is 2V lower then PVIN.

AMS4123

8 LDO OUT LDO Output pin.

9 GND (PADDLE) Ground paddle to be connected to PCB ground plane. This is also the ground for internal

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voltage reference.

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AMS4123

ABSOLUTE MAXIMUM RATINGS

VIN 4.2V to 23V Junction Temperature +150ºC
F/B -0.3 to +12.0V Storage Temperature -65ºC to +150ºC
EN -0.3V to +20V Lead temperature 260ºC

ELECTRICAL CHARACTERISTICS

Electrical Characteristics at TA= 25 °C and VIN=12V (unless otherwise noted).

RAMETER

PA

Feedback Voltage1 F/B1 (Switching Regulator Feedback Pin) 0.590 0.6 0.610 V

Feedback Voltage2 F/B2 (LDO Feedback Pin) 0.585 0.6 0.615 V
Output Voltage tolerance (LDO) Vo=0.6V to 5V in 100mV increments -1.5 1 1.5 %

Supply Current Switching Section V

Supply Current LDO section V

Supply Current (Shutdown) VEN ≤ 0.4V 90 nA

Thermal Shutdown 145

Current Limit (Switching regulator)

Current Limit (LDO)

Dropout Voltage (LDO) 350 mV

Load Regulation (LDO) 0.5 %

Line Regulation (LDO) 0.1 %

Oscillator Frequency 260 300 340 KHz

Efficiency (Switching regulator) 88 %

Maximum Duty Cycle 99 %

Enable Threshold Switching section 2.0 2.1 V

Enable Hysteresis Switching section 70

Enable Threshold LDO section 2.5 2.55 V

Enable Pull-up Current 0.7

Under Voltage Lockout Voltage Rising

Under Voltage Lockout Hysteresis 400 mV

Total Power dissipation Note (1) 2.5 W

Notes: 1) The total power dissipation for SO-8 EDP package is recommended to 2.5W, rated at 25°C ambient temperatures. The thermal resistance Junction to

Case is 45°C/W. Total power dissipation for both switching regulators should be taken in consideration when calculating the output current for each regulator.

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TEST CONDITIONS

≥ 2.0V; VFB = 1.5V (LDO Off) 1.4 1.9 mA

EN

≥ 2.5V; VFB = 1.5V 400

EN

Vout=5V

LDO Input=5V; LDO Co=2.2µF

Min. Typ. Max.

AMS4123

4.2 A

1.5 A

4.2

Units

µA

°C

mV

µA

V