19-3086; Rev 0; 5/04
KIT
ATION
EVALU
BLE
AVAILA
Low Input/Output Voltage
Step-Up DC-DC Converter with
RESET
General Description
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
The MAX1947 is a compact, high-efficiency, step-up DC-
DC converter that regulates output voltages from 1.8V to
3.3V to power µP/DSP cores, memory, and I/O rails in 1-
and 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 convert-
er is offered in fixed-output voltages of 1.8V, 2.5V, 3.0V,
and 3.3V, requiring no feedback or compensation net-
work. 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
Ordering Information
PART
TEMP RANGE PIN-PACKAGE
MAX1947ETAxy* -40°C to +85°C 8 TDFN 3mm x 3mm
*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.
Typical Application Circuit
V
IN
+0.7V TO +V
OUT
2.2µF
LX
BATT
OUT
10µF
V
OUT
+1.8V, +2.5V,
+3.0V, +3.3V
4.7µH
Pin Configuration
TOP VIEW
RESET
GND
GND
SHDN
1
2
8
7
BATT
OUT
LX
PGND
MAX1947
3
4
6
5
MAX1947
SHDN
PGND
RESET
GND
TDFN
3mm x 3mm
True Shutdown is a trademark of Maxim Integrated Products, Inc.
________________________________________________________________
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.
Low Input/Output Voltage
Step-Up DC-DC Converter with
RESET
MAX1947
ABSOLUTE MAXIMUM RATINGS
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
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.
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
= 1.5V, T
A
= -40°C to +85°C, unless otherwise noted. Typical values are at T
A
= +25°C.) (Note 2)
PARAMETER
Minimum Startup Voltage
Startup-Voltage Temperature
Coefficient
Maximum Input Operating
Voltage
Minimum Input Operating Voltage
MAX1947ETA18, I
LOAD
= 40mA
Output Voltage
MAX1947ETA25, I
LOAD
= 32mA
MAX1947ETA30, I
LOAD
= 25mA
MAX1947ETA33, I
LOAD
= 25mA
Load Regulation
No load to full load
MAX1947ETA18
V
BATT
= 1V
Full-Load Output Current
V
BATT
= 1.8V
Supply Current into BATT
Supply Current into OUT
LX Switch Maximum On-Time
LX Switch Minimum Off-Time
Maximum On-Time to Minimum
Off-Time Ratio
Frequency in Startup
No switching
No switching
0.7
0.2
3.6
MAX1947ETA25
MAX1947ETA30
MAX1947ETA33
MAX1947ETA25
MAX1947ETA30
MAX1947ETA33
160
130
100
100
240
200
200
1.74
2.42
2.9
3.2
(Note 3)
0.7
1.8
2.5
3.0
3.3
1.2
273
214
185
169
380
361
329
2
70
1
0.25
4
650
4
110
1.3
0.3
4.6
kHz
µA
µA
µs
µs
mA
1.86
2.58
3.1
3.4
%
V
CONDITIONS
R
LOAD
= 1kΩ, T
A
= +25°C
MIN
TYP
0.8
-2.1
3.6
MAX
0.95
UNITS
V
mV/°C
V
V
2
_______________________________________________________________________________________
Low Input/Output Voltage
Step-Up DC-DC Converter with
RESET
ELECTRICAL CHARACTERISTICS (continued)
(V
BATT
= 1.5V, T
A
= -40°C to +85°C, unless otherwise noted. Typical values are at T
A
= +25°C.) (Note 2)
PARAMETER
Startup to Normal-Mode Output
Transition Voltage
NFET Current Limit
PFET Turn-Off Current
CONDITIONS
50mV hysteresis, rising edge
T
A
= 0°C to +85°C
T
A
= -40°C to +85°C
T
A
= 0°C to +85°C
T
A
= -40°C to +85°C
MAX1947ETA18
Internal NFET
On-Resistance
I
LX
= 100mA
MAX1947ETA25
MAX1947ETA30
MAX1947ETA33
MAX1947ETA18
Internal PFET
On-Resistance
I
LX
= 100mA
MAX1947ETA25
MAX1947ETA30
MAX1947ETA33
LX Leakage Current
SHUTDOWN MODE
Shutdown Supply Current
SHDN
= GND
V
IH
SHDN
Input Voltage
V
IL
SHDN
Input Bias Current
OUT Discharge Resistance in
Shutdown
RESET
OUTPUT
Reset OUT Voltage Trip Level
Minimum V
OUT
for Valid Reset
Reset Timeout
RESET
Output Voltage
I
SINK
= 200µA
I
SOURCE
= 200µA
0.8 x V
OUT
V
OUT
falling, 1% hysteresis
87
0.9
65
140
235
0.3
90
93
%
V
ms
V
SHDN
= OUT or GND, T
A
= +25°C
SHDN
= OUT or GND, T
A
= +85°C
SHDN
= GND
1
5
500
1000
0.8 x
V
BATT
0.18 x
V
BATT
100
nA
Ω
2
4
µA
SHDN
= GND, V
OUT
= 0V,
V
LX
= 3.6V
T
A
= +25°C
T
A
= +85°C
MIN
1.40
600
580
15
10
TYP
1.62
800
800
75
75
0.3
0.22
0.17
0.15
0.5
0.35
0.28
0.25
0.1
1
MAX
1.73
1000
1000
150
150
0.6
0.44
0.34
0.3
1.0
0.7
0.56
0.5
1
µA
Ω
Ω
UNITS
V
mA
mA
MAX1947
3
V
Note 2:
Limits are 100% production tested at T
A
= +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).
_______________________________________________________________________________________
Low Input/Output Voltage
Step-Up DC-DC Converter with
RESET
MAX1947
Typical Operating Characteristics
(V
IN
= 1.5V, Circuit of Typical Application Circuit, T
A
= +25°C, unless otherwise noted.)
MAX1947ETA18
EFFICIENCY vs. LOAD CURRENT
MAX1947toc01
MAX1947ETA25
EFFICIENCY vs. LOAD CURRENT
MAX1947toc02
MAX1947ETA30
EFFICIENCY vs. LOAD CURRENT
95
90
EFFICIENCY (%)
85
80
75
70
65
60
V
IN
= 1.25V
V
IN
= 1V
V
IN
= 2.5V
V
IN
= 1.8V
MAX1947toc03
100
95
90
EFFICIENCY (%)
85
80
75
70
65
60
0.1
1
10
100
V
IN
= 1.25V
V
IN
= 1.6V
100
95
90
EFFICIENCY (%)
85
80
75
70
65
60
V
IN
= 1.25V
V
IN
= 1V
V
IN
= 1.6V
100
V
IN
= 1V
1000
0.1
1
10
100
1000
0.1
1
10
100
1000
LOAD CURRENT (mA)
LOAD CURRENT (mA)
LOAD CURRENT (mA)
MAX1947ETA33
EFFICIENCY vs. LOAD CURRENT
MAX1947toc04
MAXIMUM OUTPUT CURRENT
vs. INPUT VOLTAGE
MAX1947toc05
NO-LOAD INPUT CURRENT
vs. INPUT VOLTAGE
MAX1947toc06
100
95
90
EFFICIENCY (%)
85
80
75
70
65
60
0.1
1
10
100
V
IN
= 1.25V
V
IN
= 1V
V
IN
= 2.5V
V
IN
= 1.8V
1200
MAXIMUM OUTPUT CURRENT (mA)
1000
800
600
400
200
0
V
OUT
= 1.8V
V
OUT
= 3.0V
V
OUT
= 2.5V
600
500
INPUT CURRENT (µA)
V
OUT
= 3.3V
400
300
V
OUT
= 2.5V
200
100
0
V
OUT
= 1.8V
V
OUT
= 3.3V
1000
0.7
1.2
1.7
2.2
2.7
3.2
3.7
0.7
1.2
1.7
2.2
2.7
3.2
3.7
LOAD CURRENT (mA)
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
STARTUP VOLTAGE
vs. LOAD CURRENT
MAX1947toc07
STARTUP VOLTAGE
vs. TEMPERATURE
MAX1947toc08
SHUTDOWN THRESHOLD
vs. INPUT VOLTAGE
1.8
SHUTDOWN THRESHOLD (V)
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
MAX1947toc09
2.0
1.8
STARTUP VOLTAGE (V)
1.6
1.4
V
OUT
= 3.3V
1.2
1.0
0.8
0.6
0
20
40
60
80
100
120
140
LOAD CURRENT (mA)
V
OUT
= 2.5V
V
OUT
= 3.0V
V
OUT
= 1.8V
1.0
0.9
0.8
STARTUP VOLTAGE (V)
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
-40
-15
10
35
60
R
LOAD
= 0Ω
R
LOAD
= 1kΩ
2.0
85
0.7
1.2
1.7
2.2
2.7
3.2
3.7
TEMPERATURE (°C)
INPUT VOLTAGE (V)
4
_______________________________________________________________________________________
Low Input/Output Voltage
Step-Up DC-DC Converter with
RESET
Typical Operating Characteristics (continued)
(V
IN
= 1.5V, Circuit of Typical Application Circuit, T
A
= +25°C, unless otherwise noted.)
MAX1947
OUTPUT VOLTAGE
vs. LOAD CURRENT
MAX1947toc10
NO-LOAD OUTPUT VOLTAGE
vs. INPUT VOLTAGE
MAX1947toc11
OUTPUT VOLTAGE
vs. TEMPERATURE
MAX1947toc12
1.84
1.84
1.84
1.82
OUTPUT VOLTAGE (V)
1.82
OUTPUT VOLTAGE (V)
1.82
OUTPUT VOLTAGE (V)
1.80
1.80
1.80
1.78
1.78
1.78
1.76
1.76
1.76
I
LOAD
= 40mA
1.74
0
50
100
150
200
250
300
350
LOAD CURRENT (mA)
1.74
0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7
INPUT VOLTAGE (V)
1.74
-40
-15
10
35
60
85
TEMPERATURE (°C)
HEAVY-LOAD SWITCHING WAVEFORMS
MAX1947toc13
LIGHT-LOAD SWITCHING WAVEFORMS
50mV/div
V
OUT
(AC-COUPLED)
V
IN
(AC-COUPLED)
MAX1947toc14
V
OUT
(AC-COUPLED)
V
IN
(AC-COUPLED)
50mV/div
50mV/div
50mV/div
V
LX
2V/div
V
LX
2V/div
I
L
500mA/div
I
L
500mA/div
2µs/div
2µs/div
LINE-TRANSIENT WAVEFORMS
MAX1947toc15
LOAD-TRANSIENT WAVEFORMS
1.5V
1V
I
LOAD
MAX1947toc16
200mA/div
V
IN
V
OUT
(AC-COUPLED)
50mV/div
V
OUT
(AC-COUPLED)
50mV/div
10µs/div
10µs/div
_______________________________________________________________________________________
5
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