19-1735; Rev 0; 7/01

1.5µA I

Q

, Step-Up DC-DC Converters in Thin SOT23-5

Pagers

Remote Controls

Remote Wireless

Transmitters

Personal

Medical Devices

Digital Still Cameras

General Description

The MAX1722/MAX1723/MAX1724 compact, high-efficiency, step-up DC-DC converters are available in tiny, 5pin thin SOT23 packages. They feature an extremely low

1.5µA quiescent supply current to ensure the highest possible light-load efficiency. Optimized for operation from one to two alkaline or nickel-metal-hydride (NiMH) cells, or a single Li+ cell, these devices are ideal for applications where extremely low quiescent current and ultra-small size are critical.

Built-in synchronous rectification significantly improves efficiency and reduces size and cost by eliminating the need for an external Schottky diode. All three devices feature a 0.5

Ω N-channel power switch. The MAX1722/

MAX1724 also feature proprietary noise-reduction circuitry, which suppresses electromagnetic interference (EMI) caused by the inductor in many step-up applications. The family offers different combinations of fixed or adjustable outputs, shutdown, and EMI reduction (see Selector

Guide).

Applications

Single-Cell Battery-

Powered Devices

Low-Power Hand-Held

Instruments

MP3 Players

Personal Digital

Assistants (PDA)

Typical Operating Circuit

Features

♦ Up to 90% Efficiency

♦ No External Diode or FETs Needed

♦ 1.5µA Quiescent Supply Current

♦ 0.1µA Logic-Controlled Shutdown

♦ ±1% Output Voltage Accuracy

♦ Fixed Output Voltage (MAX1724) or Adjustable

Output Voltage (MAX1722/MAX1723)

♦ Up to 150mA Output Current

♦ 0.8V to 5.5V Input Voltage Range

♦ 0.91V Guaranteed Startup (MAX1722/MAX1724)

♦ Internal EMI Suppression (MAX1722/MAX1724)

♦ Thin SOT23-5 Package (1.1mm max Height)

Ordering Information

PART

MAX1722EZK-T

MAX1723EZK-T

MAX1724EZK27-T

MAX1724EZK30-T

MAX1724EZK33-T

MAX1724EZK50-T

PART

MAX1722EZK

MAX1723EZK

MAX1724EZK27

MAX1724EZK30

MAX1724EZK33

MAX1724EZK50

TEMP. RANGE

-40°C to +85°C

-40°C to +85°C

-40°C to +85°C

-40°C to +85°C

-40°C to +85°C

-40°C to +85°C

PIN-

PACKAGE

5 SOT23

5 SOT23

5 SOT23

5 SOT23

5 SOT23

5 SOT23

TOP

MARK

ADQF

ADQG

ADQH

ADQI

ADQJ

ADQK

Selector Guide

OUTPUT (V)

Adjustable

Adjustable

Fixed 2.7

Fixed 3.0

Fixed 3.3

Fixed 5.0

SHDN

No

Yes

Yes

Yes

Yes

Yes

LX

DAMPING

Yes

No

Yes

Yes

Yes

Yes

Pin Configurations

10

µH

TOP VIEW

IN

0.8V TO 5.5V

BATT LX

BATT 1 5 LX

ON

OFF

MAX1724

OUT

SHDN

GND

OUT

3.3V AT

UP TO 150mA

GND 2

MAX1722

FB 3 4 OUT

THIN SOT23-5

Pin Configurations are continued at end of data sheet.

________________________________________________________________ Maxim Integrated Products 1

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at

1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

1.5µA I

Q

, Step-Up DC-DC Converters in Thin SOT23-5

ABSOLUTE MAXIMUM RATINGS

OUT, SHDN, BATT, LX to GND ................................-0.3V to +6V

FB to GND ................................................-0.3V to (V

OUT

+ 0.3V)

OUT, LX Current.......................................................................1A

Continuous Power Dissipation (T

A

= +70°C)

5-Pin Thin SOT23 (derate 7.1mW/°C above +70°C) ...571mW

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

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

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

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

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

(V

BATT

= 1.2V, V

OUT

= 3.3V (MAX1722/MAX1723), V

OUT

= V

OUT(NOM)

(MAX1724), SHDN = OUT, R

L

=

∞, T

A

unless otherwise noted. Typical values are at T

A

= +25°C.) (Note 1)

= 0°C to +85°C,

PARAMETER

Minimum Input Voltage

Operating Input Voltage

Minimum Startup Input Voltage

Output Voltage

Output Voltage Range

Feedback Voltage

Feedback Bias Current

N-Channel On-Resistance

P-Channel On-Resistance

N-Channel Switch Current Limit

Switch Maximum On-Time

Synchronous Rectifier Zero-

Crossing Current

Quiescent Current into OUT

Shutdown Current into OUT

Quiescent Current into BATT

SYMBOL

V

IN

V

OUT

V

OUT

V

FB

I

FB

R

DS(ON)

R

DS(ON)

I

LIM t

ON

CONDITIONS

MAX1722/MAX1724

T

A

= +25°C

MAX1722/MAX1724

MAX1723 (Note 2)

T

R

A

L

= +25°C,

= 3k

Ω

MAX1724EZK27

MAX1724EZK30

MAX1724EZK33

MAX1724EZK50

MAX1722/MAX1724

MAX1723 (Note 2)

T

A

= +25°C

T

A

= 0°C to +85°C

T

A

= +25°C

T

A

= 0°C to +85°C

T

A

= +25°C

T

A

= 0°C to +85°C

T

A

= +25°C

T

A

= 0°C to +85°C

MAX1722/MAX1723

MAX1722/MAX1723

MAX1722/MAX1723

T

A

= +25°C

T

A

= 0°C to +85°C

T

A

= +25°C

T

A

= +85°C

V

OUT forced to 3.3V

V

OUT forced to 3.3V

V

OUT forced to 3.3V

V

OUT forced to 3.3V

(Notes 3, 4)

MAX1723/MAX1724

(Notes 3, 4)

MAX1722/MAX1724

(Note 4)

T

A

= +25°C

T

A

= +85°C

T

A

= +25°C

T

A

= +85°C

MIN

400

3.5

TYP

0.8

0.91

1.2

0.83

0.87

2.7

2.673

2.633

2.970

2.925

3.267

3.218

4.950

4.875

3.0

3.3

5.0

2

1.223

1.235

1.210

1.5

2.2

0.5

1.0

500

5

5 20

1.5

0.01

0.1

0.001

0.01

MAX UNITS

V

5.5

5.5

V

0.91

1.2

2.727

2.767

3.030

3.075

3.333

3.383

5.050

5.125

5.5

1.247

1.260

20

V

V

V

V nA

1.0

2.0

600

6.5

35

3.6

0.5

0.5

Ω

Ω mA

µs mA

µA

µA

µA

2 _______________________________________________________________________________________

1.5µA I

Q

, Step-Up DC-DC Converters in Thin SOT23-5

ELECTRICAL CHARACTERISTICS (continued)

(V

BATT

= 1.2V, V

OUT

= 3.3V (MAX1722/MAX1723), V

OUT

= V

OUT(NOM)

(MAX1724), SHDN = OUT, R

L

=

∞, T

A

unless otherwise noted. Typical values are at T

A

= +25°C.) (Note 1)

= 0°C to +85°C,

PARAMETER

Shutdown Current into BATT

SHDN Voltage Threshold

SHDN Input Bias Current

SYMBOL

V

IL

V

IH

CONDITIONS

MAX1724 (Note 4)

T

A

= +25°C

T

A

= +85°C

MAX1723/MAX1724

MAX1723/MAX1724

MAX1723/MAX1724,

V

SHDN

= 5.5V

T

A

= +25°C

T

A

= +85°C

MIN

75

TYP

0.001

0.01

400

500

2

7

MAX

UNITS

0.5

µA

800

100 mV nA

ELECTRICAL CHARACTERISTICS

(V

BATT

= 1.2V, V

OUT

= 3.3V (MAX1722/MAX1723), V

OUT

= V

OUT(NOM)

(MAX1724), SHDN = OUT, R

L

=

∞, T

A

unless otherwise noted.) (Note 1)

= -40°C to +85°C,

PARAMETER TYP

O utp ut V ol tag e

O utp ut V ol tag e Rang e

Feedback Voltage

N-Channel On-Resistance

P-Channel On-Resistance

N-Channel Switch Current Limit

Switch Maximum On-Time

Synchronous Rectifier Zero-

Crossing Current

Quiescent Current into OUT

SYMBOL

V

V

OUT

OUT

V

FB

R

DS(ON)

R

DS(ON)

I

LIM t

ON

CONDITIONS

MAX1724EZK27

MAX1724EZK30

MAX1724EZK33

MAX1724EZK50

MAX1722/MAX1723

MAX1722/MAX1723

V

OUT

forced to 3.3V

V

OUT

forced to 3.3V

V

OUT

forced to 3.3V

V

OUT

forced to 3.3V

MIN

2.633

2.925

3.218

4.875

2

1.200

400

3.5

5

MAX UNITS

2.767

3.075

3.383

V

5.125

5.5

1.270

1.0

2.0

620

6.5

V

V

Ω

Ω mA

µs

35

3.6

mA

µA

SHDN Voltage Threshold

V

IL

V

IH

(Notes 3,4)

MAX1723/MAX1724

MAX1723/MAX1724

75

800 mV

Note 1: Limits are 100% production tested at T

A

= +25°C. Limits over the operating temperature range are guaranteed by design.

Note 2: Guaranteed with the addition of a Schottky MBR0520L external diode between LX and OUT when using the MAX1723 with only one cell, and assumes a 0.3V voltage drop across the Schottky diode (see Figure 3).

Note 3: Supply current is measured with an ammeter between the output and OUT pin. This current correlates directly with actual battery supply current, but is reduced in value according to the step-up ratio and efficiency.

Note 4: V

OUT forced to the following conditions to inhibit switching: V

OUT

= 1.05

✕

V

OUT(NOM)

(MAX1724), V

OUT

= 3.465V

(MAX1722/MAX1723).

_______________________________________________________________________________________ 3

1.5µA I

Q

, Step-Up DC-DC Converters in Thin SOT23-5

Typical Operating Characteristics

(Figure 3 (MAX1723), Figure 7 (MAX1722), Figure 8 (MAX1724), V

BATT

= V

IN

= 1.5V, L = 10µH, C

IN

= 10µF, C

OUT

= 10µF, T

A

= +25°C, unless otherwise noted.)

EFFICIENCY vs. LOAD CURRENT

(V

OUT

= 5.0V)

EFFICIENCY vs. LOAD CURRENT

(V

OUT

= 3.3V)

EFFICIENCY vs. LOAD CURRENT

(V

OUT

= 2.5V)

100 100 100

V

IN

= 3.3V

V

IN

= 4.0V

V

IN

= 2.0V

V

IN

= 2.5V

90

90

V

IN

= 2.0V

90

V

IN

= 2.0V

80

80

80

V

IN

= 1.5V

70

70

70

60

V

IN

= 1.0V

V

IN

= 1.5V

L = DO1606

50

0.01

0.1

1 10

LOAD CURRENT (mA)

100

MAXIMUM OUTPUT CURRENT vs. INPUT VOLTAGE

1000

200

V

OUT

= 2.5V

160

120

80

40

0

0

V

OUT

= 5.0V

V

OUT

= 3.3V

1 2 3

INPUT VOLTAGE (V)

4 5

60

V

IN

= 1.5V

V

IN

= 1.0V

L = DO1606

50

0.01

0.1

1 10

LOAD CURRENT (mA)

STARTUP VOLTAGE vs. LOAD CURRENT

100

2.4

2.2

1.4

1.2

1.0

2.0

1.8

1.6

0.8

0.6

0.01

RESISTIVE LOAD

V

OUT

= 5.0V

0.1

1

LOAD CURRENT (mA)

10

1000

100

60

V

IN

= 1.0V

L = DO1606

50

0.01

0.1

1 10

LOAD CURRENT (mA)

100

QUIESCENT CURRENT INTO OUT vs. OUTPUT VOLTAGE

1000

2.0

1.8

1.6

1.4

1.2

1.0

NO LOAD

0.8

0.6

0.4

0.2

0

1.0

1.5

2.0 2.5 3.0

3.5 4.0 4.5 5.0 5.5

OUTPUT VOLTAGE (V)

1.2

1.0

0.8

0.6

0.4

0.2

0

-40

STARTUP VOLTAGE vs.

TEMPERATURE

NO LOAD

-15 10 35

TEMPERATURE (

°C)

60 85

SWITCHING WAVEFORMS

1

µs/div

I

OUT

= 50mA, V

OUT

= 5.0V, V

IN

= 3.3V

I

LX

500mA/div

V

OUT

50mV/div

V

LX

2V/div

4 _______________________________________________________________________________________

1.5µA I

Q

, Step-Up DC-DC Converters in Thin SOT23-5

Typical Operating Characteristics (continued)

(Figure 3 (MAX1723), Figure 7 (MAX1722), Figure 8 (MAX1724), V

BATT

= V

IN

= 1.5V, L = 10µH, C

IN

= 10µF, C

OUT

= 10µF, T

A

= +25°C, unless otherwise noted.)

LOAD-TRANSIENT RESPONSE

SHUTDOWN RESPONSE

3.3V

5V

V

OUT

2V/div

A

50mA

0

2V

B V

SHDN

1V/div

0

0

A: V

OUT

, 50mV/div

B: I

OUT

, 20mA/div

200

µs/div

1ms/div

V

IN

= 3.3V, V

OUT

= 5.0V, R

OUT

= 100

Ω

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

-40

SHUTDOWN INPUT THRESHOLD vs. TEMPERATURE

FALLING EDGE

RISING EDGE

-15 10 35

TEMPERATURE (

°C)

60 85

Pin Description

PIN

MAX1722 MAX1723

1

—

2

—

1

2

MAX1724

1

3

2

3

4

5

3

4

5

—

4

5

NAME

BATT

SHDN

GND

FB

OUT

LX

FUNCTION

Battery Input and Damping Switch Connection

Shutdown Input. Drive high for normal operation. Drive low for shutdown.

Ground

Feedback Input to Set Output Voltage. Use a resistor-divider network to adjust the output voltage. See Setting the Output Voltage section.

Power Output. OUT also provides bootstrap power to the IC.

Internal N-channel MOSFET Switch Drain and P-Channel Synchronous

Rectifier Drain

_______________________________________________________________________________________

5

1.5µA I

Q

, Step-Up DC-DC Converters in Thin SOT23-5

OUT

MAX1723

STARTUP

CIRCUITRY

ZERO-

CROSSING

DETECTOR

P

SHDN

FB

CONTROL

LOGIC

DRIVER

LX

ERROR

COMPARATOR

1.235V REFERENCE

N

CURRENT

LIMIT

GND

Figure 1. MAX1723 Simplified Functional Diagram

Detailed Description

The MAX1722/MAX1723/MAX1724 compact, high-efficiency, step-up DC-DC converters are guaranteed to start up with voltages as low as 0.91V and operate with an input voltage down to 0.8V. Consuming only 1.5µA of quiescent current, these devices include a built-in synchronous rectifier that reduces cost by eliminating the need for an external diode and improves overall efficiency by minimizing losses in the circuit (see Synchronous

Rectification section). The MAX1722/MAX1724 feature a clamp circuit that reduces EMI due to inductor ringing.

The MAX1723/MAX1724 feature an active-low shutdown that reduces quiescent supply current to 0.1µA. The

MAX1722/MAX1723 have an adjustable output voltage, while the MAX1724 is available with four fixed-output voltage options (see Selector Guide). Figure 1 is the

MAX1723 simplified functional diagram and Figure 2 is the MAX1724 simplified functional diagram.

PFM Control Scheme

A forced discontinuous, current-limited, pulse-frequencymodulation (PFM) control scheme is a key feature of the

MAX1722/MAX1723/MAX1724. This scheme provides ultra-low quiescent current and high efficiency over a wide output current range. There is no oscillator; the inductor current is limited by the 0.5A N-channel current limit or by the 5µs switch maximum on-time.

Following each on cycle, the inductor current must ramp to zero before another cycle may start. When the error comparator senses that the output has fallen below the regulation threshold, another cycle begins.

Synchronous Rectification

The internal synchronous rectifier eliminates the need for an external Schottky diode, thus reducing cost and board space. While the inductor discharges, the Pchannel MOSFET turns on and shunts the MOSFET body diode. As a result, the rectifier voltage drop is significantly reduced, improving efficiency without the addition of external components.

Low-Voltage Startup Circuit

The MAX1722/MAX1723/MAX1724 contain a low-voltage startup circuit to control DC-DC operation until the output voltage exceeds 1.5V (typ). The minimum start-

6 _______________________________________________________________________________________

BATT

R

2

SHDN

R

1

1.5µA I

Q

, Step-Up DC-DC Converters in Thin SOT23-5

DAMPING

SWITCH

OUT

MAX1724

STARTUP

CIRCUITRY

ZERO-

CROSSING

DETECTOR

P

CONTROL

LOGIC

DRIVER

LX

ERROR

COMPARATOR

N

1.235V REFERENCE

CURRENT

LIMIT

GND

Figure 2. MAX1724 Simplified Functional Diagram

1.2V

TO V

OUT

10

µF

SHDN

10

µ

H

LX

OUT

GND

MAX1723

FB

R2

2.37M

Ω

R1

1.24M

Ω

D1

V

OUT

= 3.6V

10

µF

Figure 3. MAX1723 Single-Cell Operation

up voltage is a function of load current (see Typical

Operating Characteristics). This circuit is powered from the BATT pin for the MAX1722/MAX1724, guaranteeing startup at input voltages as low as 0.91V. The MAX1723 lacks a BATT pin; therefore, this circuit is powered through the OUT pin. Adding a Schottky diode in parallel with the P-channel synchronous rectifier allows for startup voltages as low as 1.2V for the MAX1723

(Figure 3). The external Schottky diode is not needed for input voltages greater than 1.8V. Once started, the output maintains the load as the battery voltage decreases below the startup voltage.

Shutdown (MAX1723/MAX1724)

The MAX1723/MAX1724 enter shutdown when the

SHDN pin is driven low. During shutdown, the body diode of the P-channel MOSFET allows current to flow from the battery to the output. V

OUT falls to approximately V

IN

- 0.6V and LX remains high impedance.

Shutdown can be pulled as high as 6V, regardless of the voltage at BATT or OUT. For normal operation, connect SHDN to the input.

_______________________________________________________________________________________ 7

1.5µA I

Q

, Step-Up DC-DC Converters in Thin SOT23-5

V

OUT

V

IN

OUT

MAX1722

MAX1724

PDRV

TIMING

CIRCUIT

DAMP

P

BATT

DAMPING

SWITCH

LX

NDRV

N

GND

Figure 4. Simplified Diagram of Damping Switch

1V/div 1V/div

1

µs/div

Figure 5. LX Ringing Without Damping Switch (MAX1723)

BATT/Damping Switch

(MAX1722/MAX1724)

The MAX1722/MAX1724 include an internal damping switch (Figure 4) to minimize ringing at LX and reduce

EMI. When the energy in the inductor is insufficient to supply current to the output, the capacitance and inductance at LX form a resonant circuit that causes ringing. The damping switch supplies a path to quickly dissipate this energy, suppressing the ringing at LX.

This does not reduce the output ripple, but does reduce EMI with minimal impact on efficiency. Figures

5 and 6 show the LX node voltage waveform without and with the damping switch, respectively.

1

µs/div

Figure 6. LX Ringing With Damping Switch (MAX1722/MAX1724)

Design Procedure

Setting the Output Voltage

(MAX1722/MAX1723)

The output voltage can be adjusted from 2V to 5.5V

using external resistors R1 and R2 (Figure 7). Since FB leakage is 20nA (max), select feedback resistor R1 in the 100k

Ω to 1MΩ range. Calculate R2 as follows:

R 2

=

R 1





V

OUT

V

FB

−

1



 where V

FB

= 1.235V.

8 _______________________________________________________________________________________

INPUT

0.8V TO V

OUT

10

µF

BATT

10

µH

1.5µA I

Q

, Step-Up DC-DC Converters in Thin SOT23-5

MAX1722

LX

OUT

R2

OUTPUT

2V TO 5.5V

10

µF

For maximum output current, choose the inductor value so that the controller reaches the current-limit before the maximum on-time is triggered:

L

<

V t

)

I

LIM where the maximum on-time is typically 5µs, and the current limit (I

LIM

) is typically 500mA (see Electrical

Characteristics table).

FB

GND

R1

For larger inductor values, determine the peak inductor current (I

PEAK) by:

I

PEAK

=

V t

)

L

Figure 7. Adjustable Output Circuit

Inductor Selection

The control scheme of the MAX1722/MAX1723/

MAX1724 permits flexibility in choosing an inductor. A

10µH inductor value performs well in most applications.

Smaller inductance values typically offer smaller physical size for a given series resistance, allowing the smallest overall circuit dimensions. Circuits using larger inductance values may start up at lower battery voltages, provide higher efficiency, and exhibit less ripple, but they may reduce the maximum output current. This occurs when the inductance is sufficiently large to prevent the maximum current limit (I

LIM

) from being reached before the maximum on-time (t

ON(MAX)

) expires.

Table 1. Suggested Inductors and

Suppliers

MANUFACTURER

Coilcraft

Murata

Sumida

INDUCTOR

DO1608 Series

DO1606 Series

LQH4C Series

PHONE

WEBSITE

847-639-2361 www.coilcraft.com

770-436-1300 www.murata.com

CDRH4D18 Series

CR32 Series

CMD4D06 Series

847-545-6700 www.sumida.com

Sumitomo/

Daidoo Electronics

Toko

CXLD140 Series

3DF Type

D412F Type

+81 (06) 6355-5733 www.daidoo.co.jp

847-297-0070 www.toko.com

INPUT

0.8V TO V

OUT

C1

10

µF

ON

OFF

10

µH

BATT

MAX1724

LX

OUT

SHDN

GND

OUTPUT

V

OUT (NOM)

C2

10

µF

Figure 8. MAX1724 Standard Application Circuit

The inductor’s incremental saturation current rating should be greater than the peak switching current. However, it is generally acceptable to bias the inductor into saturation by as much as 20%, although this will slightly reduce efficiency. Table 1 lists suggested inductors and suppliers.

Maximum Output Current

The maximum output current depends on the peak inductor current, the input voltage, the output voltage, and the overall efficiency (

η):

I

OUT MAX )

=

1

2

I

PEAK





V

BATT

V

OUT





η

_______________________________________________________________________________________ 9

1.5µA I

Q

, Step-Up DC-DC Converters in Thin SOT23-5

Table 2. Suggested Surface-Mount Capacitors and Manufacturers (C1 and C2)

MANUFACTURER

AVX

Kemet

Sanyo

Taiyo Yuden

TDK

Vishay Sprague

CAPACITOR

VALUE

1

µF to 10µF

10

µF to 330µF

1

µF to 22µF

10

µF to 330µF

68

µF to 330µF

33

µF to 330µF

33

µF to 330µF

1

µF to 10µF

10

µF to 330µF

DESCRIPTION

X7R Ceramic

TAJ Tantalum Series

TPS Tantalum Series

X5R/X7R Ceramic

T494 Tantalum Series

T520 Tantalum Series

TPC Polymer Series

X5R/X7R Ceramic

X7R Ceramic

594D Tantalum Series

595D Tantalum Series

PHONE

WEBSITE

843-448-9411 www.avxcorp.com

864-963-6300 www.kemet.com

408-749-9714 www.secc.co.jp

800-368-2496 www.t-yuden.org

847-803-6100 www.tdk.com

203-452-5664 www.vishay.com

For most applications, the peak inductor current equals the current limit. However, for applications using large inductor values or low input voltages, the maximum ontime limits the peak inductor current (see Inductor

Selection section).

Capacitor Selection

Choose input and output capacitors to supply the input and output peak currents with acceptable voltage ripple. The input filter capacitor (C

IN

) reduces peak currents drawn from the battery and improves efficiency.

Low equivalent series resistance (ESR) capacitors are recommended. Ceramic capacitors have the lowest

ESR, but low ESR tantalum or polymer capacitors offer a good balance between cost and performance.

Output voltage ripple has two components: variations in the charge stored in the output capacitor with each

LX pulse, and the voltage drop across the capacitor’s

ESR caused by the current into and out of the capacitor:

V

RIPPLE

V

=

V

( )

( )

≈

I

+

R

V

( )

( )

V ( )

≈

1

2







(

V

OUT

-

L

V

BATT

)

C

OUT







(

I

PEAK

2

I

OUT

2

) where I

PEAK is the peak inductor current (see Inductor

Selection section). For ceramic capacitors, the output voltage ripple is typically dominated by V

RIPPLE(C)

. For example, a 10µF ceramic capacitor and a 10µH inductor typically provide 75mV of output ripple when stepping up from 3.3V to 5V at 50mA. Low input-to-output voltage differences (i.e. two cells to 3.3V) require higher output capacitor values.

Capacitance and ESR variation of temperature should be considered for best performance in applications with wide operating temperature ranges. Table 2 lists suggested capacitors and suppliers.

PC Board Layout Considerations

Careful PC board layout is important for minimizing ground bounce and noise. Keep the IC’s GND pin and the ground leads of the input and output capacitors less than 0.2in (5mm) apart using a ground plane. In addition, keep all connections to FB

(MAX1722/MAX1723 only) and LX as short as possible.

TRANSISTOR COUNT: 863

Chip Information

10 ______________________________________________________________________________________

1.5µA I

Q

, Step-Up DC-DC Converters in Thin SOT23-5

Pin Configurations (continued)

TOP VIEW

SHDN 1

GND

2

MAX1723

5 LX

FB 3

THIN SOT23-5

4 OUT

BATT 1

GND

2

MAX1724

5 LX

SHDN

3

THIN SOT23-5

4 OUT

Package Information

______________________________________________________________________________________ 11

1.5µA I

Q

, Step-Up DC-DC Converters in Thin SOT23-5

Package Information (continued)

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

12 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600

© 2001 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.