Step-Down DC-to-DC Controller

ADP1821

Rev. B

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FEATURES

Wide power-input voltage range: 1 V to 24 V

Chip supply voltage range: 3 V to 5.5 V

Wide output voltage range: 0.6 V to 85% of input voltage

1% accuracy, 0.6 V reference voltage

All N-channel MOSFET design for low cost

Fixed-frequency operation 300 kHz, 600 kHz, or

synchronized operation up to 1.2 MHz

No current sense resistor required

Power-good output

Programmable soft start with reverse current protection

Soft start, thermal overload, current-limit protection

Undervoltage lockout

10 μA shutdown supply current

Small, 16-lead QSOP

APPLICATIONS

Telecom and networking systems

Set-top boxes

Printers

Servers

Medical imaging systems

Microprocessor and DSP core power supplies

Mobile communication base stations

GENERAL DESCRIPTION

The ADP1821 is a versatile and inexpensive, synchronous, pulse

width-modulated (PWM), voltage-mode, step-down controller.

It drives an all N-channel power stage to regulate an output voltage

as low as 0.6 V. The ADP1821 can be configured to provide

output voltages from 0.6 V to 85% of the input voltage and is

sized to handle large MOSFETs for point-of-load regulators.

The ADP1821 is well suited for a wide range of high power

applications, such as DSP and processor core power in telecom,

medical imaging, high performance servers, and industrial

applications. It operates from a 3.0 V to 5.5 V supply with a

power input voltage ranging from 1.0 V to 24 V.

The ADP1821 operates at a pin-selectable, fixed switching

frequency of either 300 kHz or 600 kHz, minimizing external

component size and cost. For noise-sensitive applications, it

can be synchronized to an external clock to achieve switching

frequencies between 300 kHz and 1.2 MHz. The ADP1821

includes soft start protection to limit the inrush current from

the input supply during startup, reverse current protection

during soft start for precharged outputs, as well as a unique

adjustable lossless current-limit scheme utilizing external

MOSFET sensing.

The ADP1821 operates over the –40°C to +85°C temperature

range and is available in a 16-lead QSOP.

GND

PVCC

ADP1821

SHDN

VCC

BST

DH

SW

CSL

DL

PGND

FB

FREQ

SYNC

PWGD

COMP

SS

1µF

1µF

10Ω

2kΩ

300Ω

1kΩ

100kΩ

BIAS INPUT

5V

M1

M2

M3

L1 = 1µH

OUTPUT

1.8V, 20A

POWER INPUT

2.5V TO 20V

D1

AGND

100nF

4.7kΩ

6.8nF

1.5nF

0.47µF

+

2.2µF

25V

+

2.2µF

25V

×2

10µF

6.3V

×2

+

820µF

2.5V

×2

10nF

L1: COILTRONICS, HC7-1R0

M1: IRLR7807Z

M2, M3: IRFR3709Z

D1: VISHAY BAT54

3.3kΩ

Figure 1. Typical Operating Circuit

97

87

0

16

LOAD CURRENT (A)

96

95

94

93

92

91

90

89

88

2

4

6

8

10

12

14

1.8V OUTPUT

3.3V OUTPUT

FREQUENCY = 300kHz

Figure 2. Efficiency vs. Load Current, 5 V Input