Rainbow Electronics MAX1947 User Manual

General Description

The MAX1947 is a compact, high-efficiency, step-up DC­DC converter that regulates output voltages from 1.8V to

3.3V to power µP/DSP cores, memory, and I/O rails in 1­and 2-cell alkaline/NiMH/NiCd battery-powered systems.
It features an internal 800mA switch and synchronous
rectifier to achieve up to 94% efficiency and to eliminate
the need for an external Schottky diode.

High-frequency switching (up to 2MHz) results in low
ripple and small external components, while automatic
pulse skipping at light loads reduces supply current to
just 70µA for extended battery life. Maxim’s proprietary
True Shutdown™ reduces supply current to just 2µA
and fully discharges the output to ground. The convert­er is offered in fixed-output voltages of 1.8V, 2.5V, 3.0V,
and 3.3V, requiring no feedback or compensation net­work. A 75ms RESET output flag provides for power-on
reset (POR) and undervoltage detection. The MAX1947
is available in a space-saving 8-pin TDFN package.

Applications

MP3 Players, Pagers, and CD Players
PDAs and Organizers
Digital Still Cameras
Cordless Phones
Wireless Mice/Keyboards
Portable Medical Equipment
Other Battery-Powered Systems

Features

♦ Low Input (0.7V) and Output (1.8V) Voltage

Capability

♦ Internal Synchronous Rectifier

♦ High 94% Efficiency

♦ Fixed Output Voltages: 1.8V, 2.5V, 3V, and 3.3V

♦ Up to 2MHz Switching Allows Small External

Components and Low Output Ripple

♦ Automatic Pulse Skipping at Light Loads for

Extended Battery Life

♦ Low 70µA (typ) Operating Supply Current

(Measured at OUT)

♦ Low 2µA Logic-Controlled Shutdown

♦ True Shutdown Fully Discharges Output to

Ground

♦ Uses Only Small Ceramic Capacitors
♦ 75ms RESET Output Flag

MAX1947

Low Input/Output Voltage

Step-Up DC-DC Converter with

RESET

________________________________________________________________ Maxim Integrated Products 1

Pin Configuration

Ordering Information

MAX1947

LX

GND

BATT

OUT

PGND

10µF

2.2µF

4.7µH

V

OUT

+1.8V, +2.5V,
+3.0V, +3.3V

V

IN

+0.7V TO +V

OUT

RESET

SHDN

Typical Application Circuit

19-3086; Rev 0; 5/04

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.

*xy represents the output voltage code (e.g., 18 =1.8V).
Standard output voltages include 3.3V (33), 3.0V (30), 2.5V
(25), and 1.8V (18). Contact the factory for other output voltages
in 100mV increments between 1.8V and 3.3V; the minimum
order quantity is 25,000 units.

EVALUATION KIT

AVAILABLE

True Shutdown is a trademark of Maxim Integrated Products, Inc.

PART TEMP RANGE PIN-PACKAGE

MAX1947ETAxy* -40°C to +85°C8 TDFN 3mm x 3mm

TOP VIEW

RESET

1

2

GND

3

4

MAX1947

TDFN

3mm x 3mm

87BATT

OUTGND

LX

6

PGNDSHDN

5

MAX1947

Low Input/Output Voltage
Step-Up DC-DC Converter with

RESET

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(V

BATT

= 1.5V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 2)

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.

Note 1: LX has internal clamp diodes to PGND and OUT. Applications that forward bias these diodes should take care not to exceed the

IC’s package power-dissipation limits.

BATT, OUT, SHDN to GND ...................................-0.3V to +4.0V

RESET to GND..........................................-0.3V to (V

OUT

+ 0.3V)

PGND to GND .......................................................-0.3V to +0.3V

Switch Current (I

LX

, I

OUT

, I

PGND

) (Note 1) .................-1A to +1A

Continuous Power Dissipation (T

A

= +70°C)
8-Pin TDFN (derate 24.4mW/°C

above +70°C)..........................................................1951.2mW

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

Minimum Startup Voltage R
Startup-Voltage Temperature

Coefficient
Maximum Input Operating

Voltage
Minimum Input Operating Voltage 0.7 V

Output Voltage

Load Regulation No load to full load 1.2 %

Full-Load Output Current

Supply Current into BATT No switching 2 4 µA
Supply Current into OUT No switching 70 110 µA
LX Switch Maximum On-Time 0.7 1 1.3 µs
LX Switch Minimum Off-Time 0.2 0.25 0.3 µs

Maximum On-Time to Minimum
Off-Time Ratio

Frequency in Startup 650 kHz

PARAMETER CONDITIONS MIN TYP MAX UNITS

= 1kΩ, TA = +25°C 0.8 0.95 V

LOAD

-2.1 mV/°C

(Note 3) 3.6 V

MAX1947ETA18, I
MAX1947ETA25, I
MAX1947ETA30, I
MAX1947ETA33, I

V

= 1V

BATT

= 1.8V

V

BATT

= 40mA 1.74 1.8 1.86

LOAD

= 32mA 2.42 2.5 2.58

LOAD

= 25mA 2.9 3.0 3.1

LOAD

= 25mA 3.2 3.3 3.4

LOAD

MAX1947ETA18 160 273
MAX1947ETA25 130 214
MAX1947ETA30 100 185
MAX1947ETA33 100 169
MAX1947ETA25 240 380
MAX1947ETA30 200 361
MAX1947ETA33 200 329

3.6 4 4.6

V

mA

MAX1947

Low Input/Output Voltage

Step-Up DC-DC Converter with

RESET

_______________________________________________________________________________________ 3

Note 2: Limits are 100% production tested at TA= +25°C. Limits over the operating temperature range are guaranteed by design.
Note 3: When BATT is greater than the output-voltage set point, the part is in track mode (see the Track Mode section).

ELECTRICAL CHARACTERISTICS (continued)

(V

BATT

= 1.5V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 2)

Startup to Normal-Mode Output
Transition Voltage

NFET Current Limit

PFET Turn-Off Current

Internal NFET
On-Resistance

Internal PFET
On-Resistance

LX Leakage Current

SHUTDOWN MODE

Shutdown Supply Current SHDN = GND 2 4 µA

SHDN Input Voltage

SHDN Input Bias Current

OUT Discharge Resistance in
Shutdown

RESET OUTPUT

Reset OUT Voltage Trip Level V
Minimum V
Reset Timeout 65 140 235 ms

RESET Output Voltage

PARAMETER CONDITIONS MIN TYP MAX UNITS

50mV hysteresis, rising edge 1.40 1.62 1.73 V

TA = 0°C to +85°C 600 800 1000
T

= -40°C to +85°C 580 800 1000

A

TA = 0°C to +85°C 15 75 150
T

= -40°C to +85°C 10 75 150

A

MAX1947ETA18 0.3 0.6

= 100mA

I

LX

I

= 100mA

LX

SHDN = GND, V
V

= 3.6V

LX

V

IH

V

IL

SHDN = OUT or GND, TA = +25°C1100
SHDN = OUT or GND, T

SHDN = GND 500 1000 Ω

falling, 1% hysteresis 87 90 93 %

OUT

for Valid Reset 0.9 V

OUT

I

= 200µA 0.3

SINK

I

= 200µA 0.8 x V

SOURCE

MAX1947ETA25 0.22 0.44
MAX1947ETA30 0.17 0.34
MAX1947ETA33 0.15 0.3
MAX1947ETA18 0.5 1.0
MAX1947ETA25 0.35 0.7
MAX1947ETA30 0.28 0.56
MAX1947ETA33 0.25 0.5

OUT

= 0V,

TA = +25°C 0.1 1
T

= +85°C 1

A

0.8 x

V

BATT

= +85°C5

A

OUT

0.18 x
V

BATT

mA

mA

Ω

Ω

µA

V

nA

V