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MAX1947ETA18+-MAX1947ETA18+T-MAX1947ETA30+T-MAX1947ETA33+
Low Input/Output Voltage Step-Up DC-DC Converter with Active-Low RESET
General DescriptionThe 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 RESEToutput flag provides for power-on
reset (POR) and undervoltage detection. The MAX1947
is available in a space-saving 8-pin TDFN package.
ApplicationsMP3 Players, Pagers, and CD Players
PDAs and Organizers
Digital Still Cameras
Cordless Phones
Wireless Mice/Keyboards
Portable Medical Equipment
Other Battery-Powered Systems
FeaturesLow Input (0.7V) and Output (1.8V) Voltage
CapabilityInternal Synchronous RectifierHigh 94% EfficiencyFixed Output Voltages: 1.8V, 2.5V, 3V, and 3.3VUp to 2MHz Switching Allows Small External
Components and Low Output RippleAutomatic Pulse Skipping at Light Loads for
Extended Battery LifeLow 70µA (typ) Operating Supply Current
(Measured at OUT)Low 2µA Logic-Controlled ShutdownTrue Shutdown Fully Discharges Output to GroundUses Only Small Ceramic Capacitors75ms RESETOutput Flag
MAX1947
Low Input/Output Voltage
Step-Up DC-DC Converter with RESETPGNDSHDN
BATT
OUTGND
GND
RESET
TDFN
3mm x 3mmTOP VIEW
MAX1947
A "+" SIGN WILL REPLACE THE FIRST
PIN INDICATOR ON LEAD-FREE PACKAGES.
Pin Configuration
Ordering InformationMAX1947
GND
BATTOUT
PGND
10μF
2.2μF
4.7μH
VOUT
+1.8V, +2.5V,
+3.0V, +3.3V
VIN
+0.7V TO +VOUT
RESET
SHDN
Typical Application Circuit19-3086; Rev 2; 10/06
*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.
+Denotes lead-free package.
EVALUATION KIT
AVAILABLE
PARTTEMP RANGEPIN-PACKAGEPKG
CODEMAX1947ETAxy*-T-40°C to +85°C8 TDFN 3mm x 3mmT833-1
MAX1947ETAxy*+T-40°C to +85°C8 TDFN 3mm x 3mmT833-1
MAX1947
Low Input/Output Voltage
Step-Up DC-DC Converter with RESET
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS(VBATT = 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, SHDNto GND...................................-0.3V to +4.0V
RESETto GND..........................................-0.3V to (VOUT + 0.3V)
PGND to GND.......................................................-0.3V to +0.3V
Switch Current (ILX, IOUT, IPGND) (Note 1).................-1A to +1A
Continuous Power Dissipation (TA = +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
PARAMETERCONDITIONSMINTYPMAXUNITSMinimum Startup VoltageRLOAD = 1kΩ, TA = +25°C0.80.95V
Startup-Voltage Temperature
Coefficient-2.1mV/°C
Maximum Input Operating
Voltage(Note 3)3.6V
Minimum Input Operating Voltage0.7V
MAX1947ETA18, ILOAD = 40mA1.741.81.86
MAX1947ETA25, ILOAD = 32mA2.422.52.58
MAX1947ETA30, ILOAD = 25mA2.93.03.1Output Voltage
MAX1947ETA33, ILOAD = 25mA3.23.33.4
Load RegulationNo load to full load1.2%
MAX1947ETA18160273
MAX1947ETA25130214
MAX1947ETA30100185VBATT = 1V
MAX1947ETA33100169
MAX1947ETA25240380
MAX1947ETA30200361
Full-Load Output Current
VBATT = 1.8V
MAX1947ETA33200329
Supply Current into BATTNo switching24µA
Supply Current into OUTNo switching70110µA
LX Switch Maximum On-Time0.711.3µs
LX Switch Minimum Off-Time0.20.250.3µs
VOUT = 2.5V, 3.0V, 3.3V3.644.6Maximum On-Time to Minimum
Off-Time RatioVOUT = 1.8V3.044.6s/s
Frequency in Startup650kHz
MAX1947
Low Input/Output Voltage
Step-Up DC-DC Converter with RESET
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 Modesection).
ELECTRICAL CHARACTERISTICS (continued)(VBATT = 1.5V, TA = -40°C to +85°C,unless otherwise noted. Typical values are at TA = +25°C.) (Note 2)
PARAMETERCONDITIONSMINTYPMAXUNITSStartup to Normal-Mode Output
Transition Voltage50mV hysteresis, rising edge1.401.621.73V
TA = 0°C to +85°C6008001000NFET Current LimitTA = -40°C to +85°C5808001000mA
TA = 0°C to +85°C1575150PFET Turn-Off CurrentTA = -40°C to +85°C1075150mA
MAX1947ETA180.30.6
MAX1947ETA250.220.44
MAX1947ETA300.170.34
Internal NFET
On-ResistanceILX = 100mA
MAX1947ETA330.150.3
MAX1947ETA180.51.0
MAX1947ETA250.350.7
MAX1947ETA300.280.56
Internal PFET
On-ResistanceILX = 100mA
MAX1947ETA330.250.5
TA = +25°C0.11LX Leakage CurrentSHDN = GND, VOUT = 0V,
VLX = 3.6VTA = +85°C1µA
SHUTDOWN MODEShutdown Supply CurrentSHDN = GND24µA
VIH0.8 x
VBATT
SHDN Input Voltage
VIL0.18 x
VBATT
SHDN = OUT or GND, TA = +25°C1100SHDN Input Bias CurrentSHDN = OUT or GND, TA = +85°C5nA
OUT Discharge Resistance in
ShutdownSHDN = GND5001000Ω
RESET OUTPUT
Reset OUT Voltage Trip LevelVOUT falling, 1% hysteresis879093%
Minimum VOUT for Valid Reset0.9V
Reset Timeout65140235ms
ISINK = 200µA0.3RESET Output VoltageISOURCE = 200µA0.8 x VOUTV
MAX1947
Low Input/Output Voltage
Step-Up DC-DC Converter with RESET
Typical Operating Characteristics(VIN= 1.5V, Circuit of Typical Application Circuit, TA = +25°C, unless otherwise noted.)
MAX1947ETA18
EFFICIENCY vs. LOAD CURRENT
MAX1947toc01
LOAD CURRENT (mA)
EFFICIENCY (%)
100VIN = 1.6V
VIN = 1.25V
VIN = 1V
MAX1947ETA33
EFFICIENCY vs. LOAD CURRENT
MAX1947toc04
LOAD CURRENT (mA)
EFFICIENCY (%)
100VIN = 1.8V
VIN = 1.25VVIN = 1V
VIN = 2.5V
STARTUP VOLTAGE
vs. LOAD CURRENT
MAX1947toc07
STARTUP VOLTAGE (V)
VOUT = 1.8V
VOUT = 2.5V
VOUT = 3.0V
VOUT = 3.3V
MAX1947ETA25
EFFICIENCY vs. LOAD CURRENT
MAX1947toc02
LOAD CURRENT (mA)
EFFICIENCY (%)
100VIN = 1.6V
VIN = 1.25V
VIN = 1V
MAXIMUM OUTPUT CURRENT
vs. INPUT VOLTAGE
MAX1947toc05
INPUT VOLTAGE (V)
MAXIMUM OUTPUT CURRENT (mA)
VOUT = 1.8V
VOUT = 2.5V
VOUT = 3.0V
VOUT = 3.3V
STARTUP VOLTAGE
vs. TEMPERATURE
MAX1947toc08
STARTUP VOLTAGE (V)
RLOAD = 1kΩ
RLOAD = 0Ω
MAX1947ETA30
EFFICIENCY vs. LOAD CURRENT
MAX1947toc03
LOADCURRENT(mA)
EFFICIENCY (%)
100VIN = 1.8V
VIN = 1.25V
VIN = 1V
VIN = 2.5V
NO-LOAD INPUT CURRENT
vs. INPUT VOLTAGE
MAX1947toc06
INPUT VOLTAGE (V)
INPUT CURRENT (
VOUT = 1.8V
VOUT = 2.5V
VOUT = 3.3V
SHUTDOWN THRESHOLD
vs. INPUT VOLTAGE
MAX1947toc09
SHUTDOWN THRESHOLD (V)
MAX1947
Low Input/Output Voltage
Step-Up DC-DC Converter with RESET
Typical Operating Characteristics (continued)(VIN= 1.5V, Circuit of Typical Application Circuit, TA = +25°C, unless otherwise noted.)
OUTPUT VOLTAGE
vs. LOAD CURRENT
MAX1947toc10
LOAD CURRENT (mA)
OUTPUT VOLTAGE (V)
HEAVY-LOAD SWITCHING WAVEFORMSMAX1947toc13
VOUT
(AC-COUPLED)
VLX
VIN
(AC-COUPLED)
50mV/div
50mV/div
2V/div
500mA/div
2μs/div
LINE-TRANSIENT WAVEFORMSMAX1947toc15
VIN
VOUT
(AC-COUPLED)
1.5V
50mV/div
10μs/div
NO-LOAD OUTPUT VOLTAGE
vs. INPUT VOLTAGE
MAX1947toc11
INPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
LIGHT-LOAD SWITCHING WAVEFORMSMAX1947toc14
VOUT
(AC-COUPLED)
VLX
VIN
(AC-COUPLED)
50mV/div
50mV/div
2V/div
500mA/div
2μs/div
LOAD-TRANSIENT WAVEFORMSMAX1947toc16
ILOAD
VOUT
(AC-COUPLED)
200mA/div
50mV/div
10μs/div
OUTPUT VOLTAGE
vs. TEMPERATURE
MAX1947toc12
TEMPERATURE (°C)
OUTPUT VOLTAGE (V)
ILOAD = 40mA
MAX1947
Detailed DescriptionThe MAX1947 compact step-up DC-DC converter starts
up with voltages as low as 0.8V and operates with input
voltages down to 0.7V. An internal synchronous rectifier
reduces cost by eliminating the need for an external
Schottky diode and improves overall efficiency by
reducing losses in the circuit. The efficiency is further
increased with the low 70µA quiescent current and low
on-resistance of the internal n-channel MOSFET power
switch. The MAX1947 uses Maxim’s proprietary True
Shutdown circuitry, which disconnects the output from
the input in shutdown and actively discharges the
output to ground.
Low Input/Output Voltage
Step-Up DC-DC Converter with RESET
Pin Description
PINNAMEFUNCTIONRESET
Active-Low Push-Pull Reset Output. RESET goes high 75ms (min) after the output voltage has
exceeded 90% of its final value. The RESET output is valid for output voltages as low as 0.9V. RESET
is driven low in shutdown.GNDGround. Connect to exposed paddle.GNDGround. Connect to exposed paddle.SHDNShutdown Input. Connect to BATT or logic 1 for normal operation. Connect to GND or logic 0 for a low
quiescent-current shutdown mode.PGNDPower Ground. Connect to exposed paddle.
6LXInductor Connection to the Drains of the Internal n-Channel Switch and p-Channel Synchronous
RectifierOUTRegulator Output. Bypass with 10µF ceramic capacitor to GND for full-load capability. For less than
50% of full load, a 4.7µF capacitor can be used.BATTBatter y C onnecti on. V B A TT i s used for the star tup osci l l ator and to p ow er the chi p w hen V OU T < V B A TT .EPExposed Paddle. Connect to GND and PGND.
POWER-ON RESET WAVEFORMSMAX1947toc17
VIN
VOUT
VRESET
1V/div
1V/div
1V/div
20ms/div
EXITING AND ENTERING
SHUTDOWN WAVEFORMSMAX1947toc18
VOUT
VSHDN
VRESET
1V/div
1V/div
1V/div
20ms/div
Typical Operating Characteristics (continued)(VIN= 1.5V, Circuit of Typical Application Circuit, TA = +25°C, unless otherwise noted.)
