MAX1921EUT15+T - Maxim Integrated

General Description

The MAX1920/MAX1921 step-down converters deliver

over 400mA to outputs as low as 1.25V. These converters

use a unique proprietary current-limited control scheme

that achieves over 90% efficiency. These devices maintain

extremely low quiescent supply current (50μA), and their

high 1.2MHz (max) operating frequency permits small,

low-cost external components. This combination makes

the MAX1920/MAX1921 excellent high-efficiency alterna-

tives to linear regulators in space-constrained applications.

Internal synchronous rectification greatly improves effi-

ciency and eliminates the external Schottky diode required

in conventional step-down converters. Both devices also

include internal digital soft-start to limit input current upon

startup and reduce input capacitor requirements.

The MAX1920 provides an adjustable output voltage

(1.25V to 4V). The MAX1921 provides factory-preset

output voltages (see the Selector Guide). Both are

available in space-saving 6-pin SOT23 packages. The

MAX1920 is also available in a 6-pin TDFN package.

Applications

●Next-Generation Wireless Handsets

● PDAs, Palmtops, and Handy-Terminals

●Battery-Powered Equipment

● CDMA Power Amplier Supply

Features

●400mA Guaranteed Output Current

●Internal Synchronous Rectifier for > 90% Efficiency

●Tiny 6-Pin SOT23 Package

● Available in 6-Pin TDFN Package (MAX1920)

●Up to 1.2MHz Switching Frequency for Small

External Components

● 50μA Quiescent Supply Current

● 0.1μA Logic-Controlled Shutdown

●2V to 5.5V Input Range

● Fixed 1.5V, 1.8V, 2.5V, 3V, and 3.3V Output

Voltages (MAX1921)

● Adjustable Output Voltage (MAX1920)

●±1.5% Initial Accuracy

● Soft-Start Limits Startup Current

19-2296; Rev 3; 8/05

Note: The MAX1921 offers five preset output voltage options.

See the Selector Guide, and then insert the proper designator

into the blanks above to complete the part number.

+Denotes a lead-free package.

Ordering Information

MAX1921

AGND

SHDN

PGND

OUT

OFF

4.75kΩ4.7µF

4.7µH

5600pF

OUTPUT

1.5V UP TO 400mA

INPUT

2V TO 5.5V

CIN

AGND

OUT (FB)SHDN

1 6 LX

5 PGND

PGND

MAX1920

MAX1921 MAX1920

SOT23-6

TOP VIEW

3 4

( ) ARE FOR MAX1920 ONLY

A "+" SIGN WILL REPLACE THE FIRST PIN INDICATOR ON LEAD-FREE PACKAGES.

SHDN

1 2 3

6 5 4

TDFN

•

Typical Operating Circuit Pin Conguration

PART TEMP RANGE PIN-PACKAGE

MAX1920EUT-T -40°C to +85°C 6 SOT23-6

MAX1920EUT+T -40°C to +85°C 6 SOT23-6

MAX1920ETT-T -40°C to +85°C 6 TDFN

MAX1920ETT+T -40°C to +85°C 6 TDFN

MAX1921EUT_ _-T -40°C to +85°C 6 SOT23-6

MAX1921EUT_ _+T -40°C to +85°C 6 SOT23-6

MAX1920/MAX1921 Low-Voltage, 400mA Step-Down

DC-DC Converters in SOT23

IN, FB, SHDN to AGND ...........................................-0.3V to +6V

OUT to AGND, LX to PGND.........................-0.3V to (IN + 0.3V)

AGND to PGND ....................................................-0.3V to +0.3V

OUT Short Circuit to GND ..................................................... 10s

Continuous Power Dissipation (TA = +70°C)

6-Pin SOT23-6 (derate 8.7mW/°C above +70°C) .......695mW

6-Pin TDFN (derate 18.2mW/°C above +70°C) .....1454.5mW

Operating Temperature Range ........................... -40°C to +85°C

Junction Temperature ...................................................... +150°C

Storage Temperature ........................................ -65°C to +150°C

Lead Temperature (soldering, 10s) .................................+300°C

(VIN = 3.6V, SHDN = IN, TA = 0°C to +85°C. Typical parameters are at TA = +25°C, unless otherwise noted.) (Note 1)

Absolute Maximum Ratings

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these

or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect

device reliability.

Electrical Characteristics

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Input Voltage Range V

I(LX) < 400mA 2.5 5.5

I(LX) < 200mA

(MAX1921EUT15, MAX1921EUT18) 2.0 2.5

Startup Voltage 2.0 V

UVLO Threshold UVLO V

rising 1.85 1.95 V

falling 1.50 1.65

UVLO Hysteresis 200 mV

Quiescent Supply Current I

No switching, no load 50 70 µA

Quiescent Supply Current Dropout I

SHDN = IN, OUT/FB = 0 220 300 µA

Shutdown Supply Current I

SHDN

SHDN = GND 0.1 4.0 µA

Output Voltage Accuracy

(MAX1921)

OUT

= 0, T

= +25°C -1.5 +1.5

OUT

= 0 to 400mA, T

= -40°C to +85°C -3 +3

OUT

= 0 to 200mA, T

= -40°C to +85°C -3 +3

OUT BIAS Current I

OUT

SHDN = 0 1 µA

OUT at regulation voltage 816

Output Voltage Range

(MAX1920) Figure 4, IN = 4.5V 1.25 4.00 V

FB Feedback Threshold

(MAX1920) V

= +25°C 1.231 1.25 1.269

V1.220 1.25 1.280

= -40°C to +85°C 1.210 1.280

FB Feedback Hysteresis

(MAX1920) V

HYS

5 mV

FB Bias Current (MAX1920) I

FB = 1.5V 0.01 0.20 µA

Load Regulation I

OUT

= 0 to 400mA 0.005 %/mA

Line Regulation V

= 2.5V to 5.5V 0.2 %/V

SHDN Input Voltage High V

1.6 V

SHDN Input Voltage Low V

0.4 V

SHDN Leakage Current I

SHDN

SHDN = GND or IN 0.001 1.000 µA

High-Side Current Limit I

LIMP

525 730 950 mA

MAX1920/MAX1921 Low-Voltage, 400mA Step-Down

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(VIN = 3.6V, SHDN = IN, TA = 0°C to +85°C. Typical parameters are at TA = +25°C, unless otherwise noted.) (Note 1)

Note 1: All devices are 100% production tested at TA = +25°C. Limits over the operating temperature range are guaranteed by

design.

(CIN = 2.2μF ceramic, Circuit of Figure 1, components of Table 1, unless otherwise noted.)

Electrical Characteristics (continued)

Typical Operating Characteristics

3.201

3.234

3.267

3.300

3.333

3.366

3.399

0 10050 150 200 250 300 350 400

OUTPUT VOLTAGE ACCURACY vs. LOAD

(VOUT = 3.3V)

MAX1920 toc04

LOAD (mA)

OUTPUT VOLTAGE

VIN = 3.6V

VIN = 5V

VIN = 4.2V

100

0.1 1 10 100 1000

EFFICIENCY vs. LOAD CURRENT

(VOUT = 3.3V)

MAX1920 toc01

LOAD CURRENT (mA)

EFFICIENCY (%)

VIN = 3.6V

VIN = 4.2V

VIN = 5V

1.455

1.470

1.485

1.500

1.515

1.530

1.545

0 10050 150 200 250 300 350 400

OUTPUT VOLTAGE ACCURACY vs. LOAD

(VOUT = 1.5V)

MAX1920 toc06

LOAD (mA)

OUTPUT VOLTAGE

VIN = 5V

VIN = 3.3V

VIN = 2.5V

100

0.1 1 10 100 1000

EFFICIENCY vs. LOAD CURRENT

(VOUT = 1.5V)

MAX1920 toc03

LOAD CURRENT (mA)

EFFICIENCY (%)

90 VIN = 2.5V

VIN = 3.3V

VIN = 5V

100

0.1 1 10 100 1000

EFFICIENCY vs. LOAD CURRENT

(VOUT = 2.5V)

MAX1920 toc02

LOAD CURRENT (mA)

EFFICIENCY (%)

VIN = 2.7V

VIN = 3.3V VIN = 5V

2.425

2.450

2.475

2.500

2.525

2.550

2.575

0 10050 150 200 250 300 350 400

OUTPUT VOLTAGE ACCURACY vs. LOAD

(VOUT = 2.5V)

MAX1920 toc05

LOAD (mA)

OUTPUT VOLTAGE

VIN = 3V

VIN = 5V

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Low-Side Current Limit I

LIMN

350 550 800 mA

High-Side On-Resistance R

ONHS

= -40mA, V

= 3V 0.6 1.1 Ω

Rectier On-Resistance R

ONSR

= 40mA, V

= 3V 0.5 0.9 Ω

Rectier Off-Current Threshold I

LXOFF

60 mA

LX Leakage Current I

LXLEAK

IN = SHDN = 5.5V, LX = 0 to IN 0.1 5.0 µA

LX Reverse Leakage Current I

LXLKR

IN unconnected, V

= 5.5V, SHDN = GND 0.1 5.0 µA

Minimum On-Time t

ON(MIN)

0.28 0.4 0.5 µs

Minimum Off-Time t

OFF(MIN)

0.28 0.4 0.5 µs

MAX1920/MAX1921 Low-Voltage, 400mA Step-Down

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(CIN = 2.2μF ceramic, Circuit of Figure 1, components of Table 1, unless otherwise noted.)

Typical Operating Characteristics (continued)

MEDIUM-LOAD

LINE-TRANSIENT RESPONSE

MAX1920 toc13

VIN

AC-COUPLED

200mV/div

VOUT

AC-COUPLED

5mV/div

4µs/div

VIN = 3.8V to 4.2V,

VOUT = 1.5V, ILOAD = 250mA

LIGHT-LOAD SWITCHING WAVEFORM

MAX1920 toc10

VOUT

AC-COUPLED

5mV/div

VLX

2V/div

1µs/div

VIN = 3.3V, VOUT = 1.5V,

ILOAD = 40mA

10,000

0.1 1 100 1000

SWITCHING FREQUENCY vs. LOAD

(VOUT = 1.8V)

100

1000

MAX1920 toc07

LOAD (mA)

SWITCHING FREQUENCY (kHz)

VIN = 3.3

LOAD-TRANSIENT RESPONSE

MAX1920 toc15

VOUT

AC-COUPLED

100mV/div

ILOAD

200mA/div

40µs/div

VIN = 3.3V, VOUT = 1.5V,

ILOAD = 20mA TO 320mA

SOFT-START AND SHUTDOWN RESPONSE

MAX1920 toc12

VOUT

1V/div

IIN

100mA/div

VSHDN

5V/div

200µs/div

VIN = 3.3V, VOUT = 1.5V,

RLOAD = 6Ω

NO LOAD SUPPLY CURRENT

vs. SUPPLY VOLTAGE

MAX1920 toc09

SUPPLY VOLTAGE (V)

NO-LOAD SUPPLY CURRENT (µA)

5.04.54.03.53.02.52.0

100

1000

10,000

1.5 5.5

VOUT = 3.3V

VOUT = 2.5V

VOUT = 1.5V

MEDIUM-LOAD SWITCHING WAVEFORM

MAX1920 toc11

VOUT

AC-COUPLED

5mV/div

VLX

2V/div

1µs/div

VIN = 3.3V, VOUT = 1.5V,

ILOAD = 250mA

10,000

0.1 1 100 1000

SWITCHING FREQUENCY vs. LOAD

(VOUT = 1.5V)

100

1000

MAX1920 toc08

LOAD (mA)

SWITCHING FREQUENCY (kHz)

VIN = 3.3

LIGHT-LOAD

LINE-TRANSIENT RESPONSE

MAX1920 toc14

VIN

AC-COUPLED

200mV/div

VOUT

AC-COUPLED

5mV/div

4µs/div

VIN = 3.8V to 4.2V,

VOUT = 1.5V, ILOAD = 20mA

MAX1920/MAX1921 Low-Voltage, 400mA Step-Down

DC-DC Converters in SOT23

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Detailed Description

The MAX1920/MAX1921 step-down DC-DC converters

deliver over 400mA to outputs as low as 1.25V. They use

a unique proprietary current-limited control scheme that

maintains extremely low quiescent supply current (50μA),

and their high 1.2MHz (max) operating frequency permits

small, low-cost external components.

Control Scheme

The MAX1920/MAX1921 use a proprietary, current-limited

control scheme to ensure high-efficiency, fast transient

response, and physically small external components. This

control scheme is simple: when the output voltage is out of

regulation, the error comparator begins a switching cycle

by turning on the high-side switch. This switch remains

on until the minimum on-time of 400ns expires and the

output voltage regulates or the current-limit threshold is

exceeded. Once off, the high-side switch remains off until

the minimum off-time of 400ns expires and the output

voltage falls out of regulation. During this period, the low-

side synchronous rectifier turns on and remains on until

either the high-side switch turns on again or the inductor

current approaches zero. The internal synchronous recti-

fier eliminates the need for an external Schottky diode.

This control scheme allows the MAX1920/MAX1921 to

provide excellent performance throughout the entire load-

current range. When delivering light loads, the high-side

switch turns off after the minimum on-time to reduce

peak inductor current, resulting in increased efficiency

and reduced output voltage ripple. When delivering medi-

um and higher output currents, the MAX1920/MAX1921

extend either the on-time or the off-time, as necessary to

maintain regulation, resulting in nearly constant frequency

operation with high-efficiency and low-output voltage ripple.

Shutdown Mode

Connecting SHDN to GND places the MAX1920/

MAX1921 in shutdown mode and reduces supply cur-

rent to 0.1μA. In shutdown, the control circuitry, internal

switching MOSFET, and synchronous rectifier turn off and

LX becomes high impedance. Connect SHDN to IN for

normal operation.

Soft-Start

The MAX1920/MAX1921 have internal soft-start circuitry

that limits current draw at startup, reducing transients on

the input source. Soft-start is particularly useful for higher

impedance input sources, such as Li+ and alkaline cells.

Soft-start is implemented by starting with the current limit

at 25% of its full current value and gradually increas-

ing it in 25% steps until the full current limit is reached.

See Soft-Start and Shutdown Response in the Typical

Operating Characteristics.

*MAX1920 only.

Figure 1. Typical Output Application Circuit (MAX1921)

Pin Description

PIN NAME FUNCTION

SOT TDFN*

1 2 IN

Supply voltage input for MAX1921EUT15 and MAX1921EUT18 is 2V to 5.5V. Supply voltage

input for MAX1920 and other voltage versions of MAX1921 is 2.5V to 5.5V. Bypass IN to GND

with a 2.2µF ceramic capacitor as close as possible to IN.

2 6 AGND Analog Ground. Connect to PGND.

3 1 SHDN Active-Low Shutdown Input. Connect SHDN to IN for normal operation. In shutdown, LX

becomes high-impedance and quiescent current drops to 0.1µA.

4 — OUT MAX1921 Voltage Sense Input. OUT is connected to an internal voltage-divider.

4 5 FB MAX1920 Voltage Feedback Input. FB regulates to 1.25V nominal. Connect FB to an external

resistive voltage-divider between the output voltage and GND.

5 3 PGND Power Ground. Connect to AGND.

6 4 LX Inductor Connection

MAX1921

AGND

SHDN

PGND

OUT

OFF

R1 COUT

CFF

OUTPUT

UP TO 400mA

INPUT

2V TO 5.5V

CIN

MAX1920/MAX1921 Low-Voltage, 400mA Step-Down

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Design Procedure

The MAX1920/MAX1921 are optimized for small external

components and fast transient response. There are sev-

eral application circuits (Figures 1 through 4) to allow the

choice between ceramic or tantalum output capacitor and

internally or externally set output voltages. The use of a

small ceramic output capacitor is preferred for higher reli-

ability, improved voltage-positioning transient response,

reduced output ripple, and the smaller size and greater

availability of ceramic versus tantalum capacitors.

Voltage Positioning

Figures 1 and 2 are the application circuits that utilize

small ceramic output capacitors. For stability, the circuit

obtains feedback from the LX node through R1, while

load transients are fed-forward through CFF. Because

there is no D.C. feedback from the output, the output

voltage exhibits load regulation that is equal to the output

load current multiplied by the inductor’s series resistance.

This small amount of load regulation is similar to voltage

positioning as used by high-powered microprocessor sup-

plies intended for personal computers. For the MAX1920/

MAX1921, voltage positioning eliminates or greatly reduc-

es undershoot and overshoot during load transients (see

the Typical Operating Characteristics), which effectively

halves the peak-to-peak output voltage excursions com-

pared to traditional step-down converters.

For convenience, Table 1 lists the recommended external

component values for use with the MAX1921 application

circuit of Figure 1 with various input and output voltages.

Induction Selection

In order to calculate the smallest inductor, several calcula-

tions are needed. First, calculate the maximum duty cycle

of the application as:

OUT

DutyCycle(MAX) 100%

V (MIN)

= ×

Second, calculate the critical voltage across the inductor as:

if DutyCycle(MAX) < 50%,

then VCRITICAL = (VIN(MIN) - VOUT),

else VCRITICAL = VOUT

Last, calculate the minimum inductor value as:

L(MIN) = 2.5 ×10-6 × VCRITICAL

Select the next standard value larger than L(MIN). The

L(MIN) calculation already includes a margin for inductance

tolerance. Although values much larger than L(MIN) work,

transient performance, efficiency, and inductor size suffer.

A 550mA rated inductor is enough to prevent saturation

for output currents up to 400mA. Saturation occurs when

the inductor’s magnetic flux density reaches the maximum

level the core can support and inductance falls. Choose a

low DC-resistance inductor to improve efficiency. Tables 2

and 3 list some suggested inductors and suppliers.

Table 1. MAX1921 Suggested

Components for Figure 1

Table 2. Suggested Inductors

OUTPUT

INPUT SOURCE

5V 3.3V, 1 Li+,

3 x AA 2.5V, 2 x AA

3.3V

3.0V

L = 10µH, COUT = 10µF,

R1 = 8.25kΩ, CFF = 3300pF N/A

2.5V L = 6.8µH, COUT = 6.8µF,

R1 = 5.62kΩ, CFF = 4700pF

1.8V

1.5V

L = 10µH,

COUT = 10µF,

R1 = 8.25kΩ,

CFF = 3300pF

L = 4.7µH, COUT = 4.7µF,

R1 = 4.75kΩ, CFF = 5600pF

PART

NUMBER

(μH)

(ohms max)

Isat

(A) SIZE

Coilcraft

LPO1704

4.7 0.200 1.10

6.6 x 5.5 x 1.0

= 36.3mm3

6.8 0.320 0.90

10 0.410 0.80

Sumida

CDRH3D16

4.7 0.080 0.90 3.8 x 3.8 x 1.8

= 26.0mm3

6.8 0.095 0.73

10 0.160 0.55

Sumida

CDRH2D18

4.7 0.081 0.63 3.2 x 3.2 x 2.0

= 20.5mm3

6.8 0.108 0.57

Toko

D312F

4.7 0.38 0.74 3.6 x 3.6 x 1.2

= 15.6mm3

10 0.79 0.50

Toko

D412F

4.7 0.230 0.84 4.6 x 4.6 x 1.2

= 25.4mm3

10 0.490 0.55

Toko

D52LC

4.7 0.087 1.14

5.0 x 5.0 x 2.0

= 50.0mm3

6.8 0.105 0.95

10 0.150 0.76

MAX1920/MAX1921 Low-Voltage, 400mA Step-Down

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Capacitor Selection

For nearly all applications, the input capacitor, CIN,

may be as small as 2.2μF ceramic with X5R or X7R

dielectric. The input capacitor filters peak currents and

noise at the voltage source and, therefore, must meet the

input ripple requirements and voltage rating. Calculate the

maximum RMS input current as:

OUT IN OUT

IN OUT IN

V (V V )

I (RMS) I (MAX ) V

−

= ×

The output capacitor, COUT, may be either ceramic or

tantalum depending upon the chosen application circuit

(see Figures 1 through 4). Table 3 lists some suggested

capacitor suppliers.

Ceramic Output Capacitor

For ceramic COUT, use the application circuit of Figure 1

or Figure 2. Calculate the minimum capacitor value as:

COUT(MIN) = 2.5 x 10-6 × VCRITICAL

Select the next standard value larger than COUT(MIN).

The COUT(MIN) calculation already includes a margin for

capacitor tolerance. Values much larger than COUT(MIN)

always improve transient performance and stability, but

capacitor size and cost increase.

Tantalum Output Capacitor

For tantalum COUT, use the application circuit of Figure

3 or Figure 4. With tantalum COUT, the equivalent series

resistance (ESR) of COUT must be large enough for sta-

bility. Generally, 25mV of ESR-ripple at the feedback node

is sufficient. The simplified calculation is:

ESRCOUT(MIN) = 8.0 x 10-2 × VOUT

Because tantalum capacitors rarely specify minimum

ESR, choose a capacitor with typical ESR that is about

twice as much as ESRCOUT(MIN). Although ESRs great-

er than this work, output ripple becomes larger.

For tantalum COUT, calculate the minimum output

capacitance as:

OUT

OUT COUT CRITICAL

L I (MAX)

C (MIN) 1.25 ESR (MIN) V

= × ×

The 1.25 multiplier is for capacitor tolerance. Select any

standard value larger than COUT(MIN).

Feedback and Compensation

The MAX1921 has factory preset output voltages of 1.5V,

1.8V, 2.5V, 3V, and 3.3V, while the MAX1920 is externally

adjusted by connecting FB to a resistive voltage-divider.

When using a ceramic output capacitor, the feedback

network must include a compensation feed-forward

capacitor, CFF.

Figure 2. Typical Application Circuit (MAX1920) Figure 3. MAX1921 Application Circuit Using Tantalum Output

Capacitor

MAX1920

AGND

SHDN

PGND

OFF

R1 COUT

CFF

OUTPUT

UP TO 400mA

INPUT

2V TO 5.5V

CIN

MAX1921

AGND

SHDN

PGND

OUT

OFF

COUT

LOUTPUT

UP TO 400mA

INPUT

2V TO 5.5V

CIN

MAX1920/MAX1921 Low-Voltage, 400mA Step-Down

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MAX1921 Using Ceramic COUT

When using the application circuit of Figure 1, the induc-

tor’s series resistance causes a small amount of load

regulation, as desired for a voltage-positioning load tran-

sient response. Choose R1 such that VOUT is high at no

load by about half of this load regulation. The simplified

calculation is:

R1 = 5 x 104 x RL(MAX)

where RL(MAX) is the maximum series resistance of the

inductor. Select a standard resistor value that is within

20% of this calculation.

Next, calculate CFF for 25mV ripple at the internal feed-

back node. The simplified calculation is:

CFF = 2.5 × 10-5/R1

where R1 is the standard resistor value that is used.

Select a standard capacitor value that is within 20% of

the calculated CFF.

MAX1920 Using Ceramic COUT

When using the application circuit of Figure 2, the induc-

tor’s series resistance causes a small amount of load reg-

ulation, as desired for a voltage-positioning load transient

response. Choose R1 and R2 such that VOUT is high at

no load by about half of this load regulation:

OUT L OUT

REF

V R I ( MAX ) / 2

R1 R 2 1

+×



=×−





where R2 is chosen in the 50kΩ to 500kΩ range, VREF

= 1.25V and RL is the typical series resistance of the

inductor. Use 1% or better resistors.

Next, calculate the equivalent resistance at the FB node as:

R 1 R 2

Req R1|| R 2 R 1 R 2

= = +

Then, calculate CFF for 25mV ripple at FB. The simplified

calculation is:

CFF = 2.5 × 10-5/Req

Select a standard capacitor value that is within 20% of the

calculated CFF.

MAX1920 Using Tantalum COUT

When using the application circuit of Figure 4, choose R1

and R2 such as to obtain the desired VOUT:

OUT

REF

R1 R 2 1



=×−





where R2 is chosen to be less than 50kΩ and VREF =

1.25V. Use 1% or better resistors.

Layout Considerations

High switching frequencies make PC board layout a very

important part of design. Good design minimizes exces-

sive EMI on the feedback paths and voltage gradients in

the ground plane, both of which can result in instability or

regulation errors. Connect the inductor, input filter capacitor,

and output filter capacitor as close to the device as possible,

and keep their traces short, direct, and wide. Connect their

ground pins at a single common node in a star ground con-

figuration. The external voltage-feedback network should

be very close to the FB pin, within 0.2in (5mm). Keep

noisy traces, such as the LX trace, away from the voltage-

feedback network; also keep them separate, using grounded

copper. The MAX1920/MAX1921 evaluation kit data sheet

includes a proper PC board layout and routing scheme.

Table 3. Component Suppliers

Figure 4. MAX1920 Application Circuit Using Tantalum Output

Capacitor

SUPPLIER PHONE WEBSITE

Coilcraft 847-639-6400 www.coilcraft.com

Kemet 408-986-0424 www.kemet.com

Murata 814-237-1431 www.murata.com

Sumida USA 847-956-0666 www.sumida.com

Japan 81-3-3607-5111

Taiyo

Yuden

USA 408-573-4150 www.T-Yuden.com

Japan 81-3-3833-5441 www.yuden.co.jp

Toko USA 847-297-0070 www.tokoam.com

Japan 81-3-3727-1161 www.toko.co.jp

MAX1920

AGND

SHDN

PGND

OFF

COUT

LOUTPUT

UP TO 400mA

INPUT

2V TO 5.5V

CIN

MAX1920/MAX1921 Low-Voltage, 400mA Step-Down

DC-DC Converters in SOT23

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│

Selector Guide

PART VOUT (V) TOP MARK

MAX1920EUT Adjustable ABCO

MAX1920ETT Adjustable ADR

MAX1921EUT33 3.3 ABCJ

MAX1921EUT30 3.0 ABCK

MAX1921EUT25 2.5 ABCL

MAX1921EUT18 1.8 ABCM

MAX1921EUT15 1.5 ABCN

Chip Information

TRANSISTOR COUNT: 1467

Package Information

For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”,

“#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing

pertains to the package regardless of RoHS status.

-(52/'/((

MAX1920/MAX1921 Low-Voltage, 400mA Step-Down

DC-DC Converters in SOT23

www.maximintegrated.com Maxim Integrated

│

Package Information (continued)

For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”,

“#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing

pertains to the package regardless of RoHS status.

-(52/'/((

MAX1920/MAX1921 Low-Voltage, 400mA Step-Down

DC-DC Converters in SOT23

www.maximintegrated.com Maxim Integrated

│

Package Information (continued)

For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”,

“#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing

pertains to the package regardless of RoHS status.

MAX1920/MAX1921 Low-Voltage, 400mA Step-Down

DC-DC Converters in SOT23

www.maximintegrated.com Maxim Integrated

│

Package Information (continued)

For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”,

“#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing

pertains to the package regardless of RoHS status.

Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses

are implied. Maxim Integrated reserves the right to change the circuitry and specications without notice at any time. The parametric values (min and max limits)

shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.

Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.

MAX1920/MAX1921 Low-Voltage, 400mA Step-Down

DC-DC Converters in SOT23

│

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.