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General Description

The MAX1730 regulated step-down charge pump gen-

erates up to 50mA at fixed output voltages of 1.8V or

1.9V from an input voltage in the 2.7V to 5.5V range.

Specifically designed to provide high-efficiency logic

supplies in applications that demand a compact

design, the MAX1730 employs fractional conversion

techniques to provide efficiency exceeding that of a lin-

ear regulator.

The MAX1730 operates at up to 2MHz, permitting the

use of small 0.22µF flying capacitors while maintaining

low 75µA quiescent supply current. Proprietary soft-

start circuitry prevents excessive current from being

drawn from the supply during startup, making the

MAX1730 compatible with higher impedance sources

such as alkaline and lithium-ion cells.

The MAX1730 is available in a space-saving 10-pin

µMAX package that is only 1.09mm high and occupies

one-half the area of an 8-pin SO.

Applications

Low-Voltage Logic Supplies

Wireless Handsets

PDAs

PC Cards

Hand-Held Instruments

Features

♦ > 85% Peak Efficiency

♦ 50mA Guaranteed Output Current

♦ Dual-Mode 1.8V or 1.9V Output

♦ ±3% Output Voltage Accuracy

♦ Up to 2MHz Operating Frequency

♦ Small 0.22µF Capacitors

♦ No Inductor Required

♦ 2.7V to 5.5V Input Voltage Range

♦ Output Disconnects from Input in Shutdown Mode

♦ Small 10-Pin µMAX Package (1.09mm max height)

MAX1730

50mA Regulated Step-Down Charge Pump

for 1.8V or 1.9V Logic

________________________________________________________________ Maxim Integrated Products 1

OUT

C2P

C2NC1N

C1P

SHDN

MAX1730

µMAX

TOP VIEW

PGNDGND

0.22µF

MAX1730

OUT

C2P

C2N

PGND

0.22µF

4.7µF

1µF

GND

C1P

C1N

OUTPUT

1.8V OR 1.9V, UP TO 50mA

INPUT

2.7V TO 5.5V

SHDN

Typical Operating Circuit

19-1618; Rev 0; 4/00

PART

MAX1730EUB -40°C to +85°C

TEMP. RANGE PIN-PACKAGE

10 µMAX

Pin Configuration

Ordering Information

For free samples and the latest literature, visit www.maxim-ic.com or phone 1-800-998-8800.

For small orders, phone 1-800-835-8769.

Summary of content (8 pages)

PAGE 1
9-1618; Rev 0; 4/00 50mA Regulated Step-Down Charge Pump for 1.8V or 1.9V Logic Features The MAX1730 regulated step-down charge pump generates up to 50mA at fixed output voltages of 1.8V or 1.9V from an input voltage in the 2.7V to 5.5V range. Specifically designed to provide high-efficiency logic supplies in applications that demand a compact design, the MAX1730 employs fractional conversion techniques to provide efficiency exceeding that of a linear regulator.
PAGE 2
MAX1730 50mA Regulated Step-Down Charge Pump for 1.8V or 1.9V Logic ABSOLUTE MAXIMUM RATINGS IN, OUT, SHDN, FB to GND .....................................-0.3V to +6V C1P, C1N, C2P, C2N to GND ......................-0.3V to (VIN + 0.3V) GND to PGND.....................................................................±0.3V Output Short-Circuit Duration ........................................Indefinite Continuous Power Dissipation (TA = +70°C) 10-Pin µMAX (derate 5.6mW/°C above +70°C) ...........
PAGE 3
50mA Regulated Step-Down Charge Pump for 1.8V or 1.9V Logic MAX1730 ELECTRICAL CHARACTERISTICS (VIN = +3.6V, FB = GND, SHDN = IN, TA = -40°C to +85°C, unless otherwise noted.) (Note 1) PARAMETER Input Voltage Range SYMBOL MIN MAX UNITS 2.7 5.5 V 2.3 2.6 V FB = GND 1.746 1.854 FB = IN 1.843 1.957 VIN Input Undervoltage Lockout Output Voltage CONDITIONS Falling edge (100mV hysteresis) VOUT VIN = 2.7V to 5.5V, IOUT = 0 to 50mA Output Leakage Current OUT forced to 1.8V, VIN = 1.8V to 5.
PAGE 4
Typical Operating Characteristics (VIN = +3.6V, FB = GND, SHDN = IN, CIN = 1µF, C1 = C2 = 0.22µF, COUT = 4.7µF, TA = +25°C, unless otherwise noted.) EFFICIENCY vs. INPUT VOLTAGE 60 VIN = 2.7V 50 90 EFFICIENCY (%) 70 VIN = 5.0V 40 85 80 75 70 85 80 75 70 65 65 60 60 10 55 55 0 50 10 100 1000 50 2.5 3.0 3.5 4.0 4.5 OUTPUT CURRENT (mA) INPUT VOLTAGE (V) INPUT CURRENT vs. INPUT VOLTAGE OUTPUT VOLTAGE vs. OUTPUT CURRENT 50 40 30 20 VIN = 5.0V 1.
PAGE 5
0mA Regulated Step-Down Charge Pump for 1.8V or 1.9V Logic LINE-TRANSIENT RESPONSE STARTUP AND SHUTDOWN RESPONSE LOAD-TRANSIENT RESPONSE MAX1730 TOC07 MAX1730 TOC09 MAX1730 TOC08 4V RL = 72Ω 50mA IOUT 5mA VIN VO 1V/div 3V IIN 50mA/div VOUT AC-COUPLED 20mV/div VOUT AC-COUPLED 50mV/div VSHDN 5V/div 10µs/div 100µs/div 10µs/div Pin Description PIN NAME FUNCTION 1 FB Feedback Input. Connect FB to GND for a 1.8V output. Connect FB to IN for a 1.9V output. Do not leave FB unconnected.
PAGE 6
50mA Regulated Step-Down Charge Pump for 1.8V or 1.9V Logic MAX1730 Functional Diagram OUT FB FB CONTROL C1P DRIVERS C1N VREF + OSCILLATOR MAX1730 SWITCH ARRAY C2P CONTROL LOGIC C2N SHUTDOWN PGND SHDN GND Detailed Description The MAX1730 step-down charge pump automatically switches between charge pump configurations (Figures 1, 2, and 3) and utilizes pulse-skipping pulse-frequency modulation (PFM) to provide a regulated output voltage with high efficiency.
PAGE 7
50mA Regulated Step-Down Charge Pump for 1.8V or 1.9V Logic MAX1730 VIN VOUT = VIN CIN COUT C1 C2 NOTE: SWITCH STATES SET FOR STAGE 1. ALL SWITCHES REVERSE STATE FOR STAGE 2. Figure 1. 1:1 Capacitor Configuration VIN VIN CIN CIN C1 C2 C2 C1 VOUT = 2 VIN 3 COUT NOTE: SWITCH STATES SET FOR STAGE 1. ALL SWITCHES REVERSE STATE FOR STAGE 2. Figure 2. 3:2 Capacitor Configuration To maximize efficiency, the MAX1730 automatically switches between charge-pump configurations (Figures 1, 2, and 3).
PAGE 8
Shutdown Layout Considerations The MAX1730 features an active-low shutdown pin (SHDN) to decrease supply current to below 5µA. When in shutdown, the output disconnects from the input and OUT goes to high impedance. The MAX1730’s high-frequency operation demands careful layout. All components should be placed as close to the IC as possible, with priority going to CIN, C1, and C2. Traces should be kept short, wide, and as straight as possible.