600 mA, 6 MHz, Synchronous

Step-Down DC-to-DC Converter

ADP2121

Rev. B

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FEATURES

Peak efficiency: 92%

Operating frequency: 6 MHz

Typical quiescent current in auto mode: 36 µA

Fixed output voltage: 1.8 V, 1.82 V, 1.85 V, 1.875 V, 2.3 V

Maximum guaranteed load current: 600 mA atV

Input voltage: 2.3 V to 5.5 V

Typical shutdown supply current: 0.3 µA

Automatic power-saving mode

Compatible with tiny multilayer inductors

Internal synchronous rectifier

Internal compensation

Internal soft start

Output to ground short-circuit protection

Cycle-by-cycle current-limit protection

Enable/shutdown logic input

Undervoltage lockout

Thermal shutdown protection

APPLICATIONS

Mobile phones

Digital cameras

Digital audio

Portable equipment

GENERAL DESCRIPTION

The ADP2121 is a high frequency, low quiescent current

step-down dc-to-dc converter optimized for portable applications

in which board area and battery life are critical constraints. The

6 MHz operating frequency enables the use of tiny ceramic induc-

tors and capacitors. Additionally, the synchronous rectification

improves efficiency and results in fewer external components.

At high load currents, the device uses a voltage regulating pulse-

width modulation (PWM) mode that maintains a constant

frequency with excellent stability and transient response. In forced

PWM mode, the converter continues operating in PWM for light

loads. At light load conditions in auto mode, the ADP2121 can

automatically enter a power-saving mode that uses pulse-frequency

modulation (PFM) to reduce the effective switching frequency and

ensure the longest battery life in portable applications. During logic

controlled shutdown (EN ≤ 0.4 V), the input is disconnected

from the output and draws less than 0.3 μA current (typical)

from the source.

TYPICAL APPLICATION CIRCUIT

VIN

GND

MODE

EN

FB

SW

2.2µF

4.7µF

ADP2121

L

0.47µH

ON

OFF

PWM

AUTO

B2

C1

A2

C2

A1

B1

OUTPUT VOLTAGE

1.8V, 1.82V, 1.85V, 1.875V, 2.3V

INPUT VOLTAGE*

2.3V TO 5.5V

*FOR OUTPUT VOLTAGE = 2.3 V, INPUT VOLTAGE = 2.9 V TO 5.5V.

Figure 1.

TYPICAL PERFORMANCE

55

0.1

1

10

100

1000

65

75

85

95

LOAD CURRENT (mA)

AUTO MODE

Figure 2. Efficiency vs. Load Current for Each Voltage Option

The ADP2121 has an input voltage range of 2.3 V to 5.5 V (2.9 V

polymer cell, 3-cell alkaline or Ni-MH cell, and other standard

power sources. The converter can source up to 600 mA and is

internally compensated to minimize external components. Other

key features, such as cycle-by-cycle peak current limit, soft start,

undervoltage lockout (UVLO), output-to-ground short-circuit

protection, and thermal shutdown, protect the internal and

external circuit components.

Table 1. Output Voltage Options

Input Voltage

Range (V)

Typical Start-Up

Time (μs)

Fixed Output

Voltage (V)

2.3 to 5.5

75

1.8, 1.85, 1.875

2.3 to 5.5

275

1.82

2.9 to 5.5

100

2.3