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19-3086; Rev 0; 5/04
KIT ATION EVALU ABLE AVAIL
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 70A (typ) Operating Supply Current (Measured at OUT) Low 2A 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 DCDC converter that regulates output voltages from 1.8V to 3.3V to power P/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 70A for extended battery life. Maxim's proprietary True ShutdownTM reduces supply current to just 2A 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
Ordering Information
PART TEMP RANGE PIN-PACKAGE MAX1947ETAxy* -40C to +85C 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
VIN +0.7V TO +VOUT 2.2F LX BATT OUT 10F VOUT +1.8V, +2.5V, +3.0V, +3.3V 4.7H
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 (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 = +70C) 8-Pin TDFN (derate 24.4mW/C above +70C)..........................................................1951.2mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C
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
(VBATT = 1.5V, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 2)
PARAMETER Minimum Startup Voltage Startup-Voltage Temperature Coefficient Maximum Input Operating Voltage Minimum Input Operating Voltage MAX1947ETA18, ILOAD = 40mA Output Voltage MAX1947ETA25, ILOAD = 32mA MAX1947ETA30, ILOAD = 25mA MAX1947ETA33, ILOAD = 25mA Load Regulation No load to full load MAX1947ETA18 VBATT = 1V Full-Load Output Current VBATT = 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 A A s s mA 1.86 2.58 3.1 3.4 % V CONDITIONS RLOAD = 1k, TA = +25C MIN TYP 0.8 -2.1 3.6 MAX 0.95 UNITS V mV/C V V
2
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Low Input/Output Voltage Step-Up DC-DC Converter with RESET
ELECTRICAL CHARACTERISTICS (continued)
(VBATT = 1.5V, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 2)
PARAMETER Startup to Normal-Mode Output Transition Voltage NFET Current Limit PFET Turn-Off Current CONDITIONS 50mV hysteresis, rising edge TA = 0C to +85C TA = -40C to +85C TA = 0C to +85C TA = -40C to +85C MAX1947ETA18 Internal NFET On-Resistance ILX = 100mA MAX1947ETA25 MAX1947ETA30 MAX1947ETA33 MAX1947ETA18 Internal PFET On-Resistance ILX = 100mA MAX1947ETA25 MAX1947ETA30 MAX1947ETA33 LX Leakage Current SHUTDOWN MODE Shutdown Supply Current SHDN = GND VIH SHDN Input Voltage VIL SHDN Input Bias Current OUT Discharge Resistance in Shutdown RESET OUTPUT Reset OUT Voltage Trip Level Minimum VOUT for Valid Reset Reset Timeout RESET Output Voltage ISINK = 200A ISOURCE = 200A 0.8 x VOUT VOUT falling, 1% hysteresis 87 0.9 65 140 235 0.3 90 93 % V ms V SHDN = OUT or GND, TA = +25C SHDN = OUT or GND, TA = +85C SHDN = GND 1 5 500 1000 0.8 x VBATT 0.18 x VBATT 100 nA 2 4 A SHDN = GND, VOUT = 0V, VLX = 3.6V TA = +25C TA = +85C 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 A UNITS V mA mA
MAX1947
3
V
Note 2: Limits are 100% production tested at TA = +25C. 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).
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Low Input/Output Voltage Step-Up DC-DC Converter with RESET MAX1947
Typical Operating Characteristics
(VIN = 1.5V, Circuit of Typical Application Circuit, TA = +25C, 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 VIN = 1.25V VIN = 1V VIN = 2.5V VIN = 1.8V
MAX1947toc03
100 95 90 EFFICIENCY (%) 85 80 75 70 65 60 0.1 1 10 100 VIN = 1.25V VIN = 1.6V
100 95 90 EFFICIENCY (%) 85 80 75 70 65 60 VIN = 1.25V VIN = 1V VIN = 1.6V
100
VIN = 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 VIN = 1.25V VIN = 1V VIN = 2.5V VIN = 1.8V
1200 MAXIMUM OUTPUT CURRENT (mA) 1000 800 600 400 200 0 VOUT = 1.8V VOUT = 3.0V VOUT = 2.5V
600 500 INPUT CURRENT (A) VOUT = 3.3V 400 300 VOUT = 2.5V 200 100 0 VOUT = 1.8V
VOUT = 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 VOUT = 3.3V 1.2 1.0 0.8 0.6 0 20 40 60 80 100 120 140 LOAD CURRENT (mA) VOUT = 2.5V VOUT = 3.0V VOUT = 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 RLOAD = 0 RLOAD = 1k
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)
(VIN = 1.5V, Circuit of Typical Application Circuit, TA = +25C, 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 ILOAD = 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 VOUT (AC-COUPLED) VIN (AC-COUPLED)
MAX1947toc14
VOUT (AC-COUPLED) VIN (AC-COUPLED)
50mV/div
50mV/div
50mV/div
VLX
2V/div
VLX
2V/div
IL
500mA/div
IL
500mA/div
2s/div
2s/div
LINE-TRANSIENT WAVEFORMS
MAX1947toc15
LOAD-TRANSIENT WAVEFORMS
1.5V 1V ILOAD
MAX1947toc16
200mA/div
VIN
VOUT (AC-COUPLED)
50mV/div
VOUT (AC-COUPLED)
50mV/div
10s/div
10s/div
_______________________________________________________________________________________
5
Low Input/Output Voltage Step-Up DC-DC Converter with RESET MAX1947
Typical Operating Characteristics (continued)
(VIN = 1.5V, Circuit of Typical Application Circuit, TA = +25C, unless otherwise noted.)
EXITING AND ENTERING SHUTDOWN WAVEFORMS
MAX1947toc17 MAX1947toc18
POWER-ON RESET WAVEFORMS
VIN
1V/div
VOUT
1V/div
VRESET
1V/div
VRESET
1V/div
VOUT 20ms/div
1V/div
VSHDN 20ms/div
1V/div
Pin Description
PIN NAME FUNCTION 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. Ground. Connect to exposed paddle. Ground. Connect to exposed paddle. Shutdown Input. Connect to BATT or logic 1 for normal operation. Connect to GND or logic 0 for a low quiescent-current shutdown mode. Power Ground. Connect to exposed paddle. Inductor Connection to the Drains of the Internal N-Channel Switch and P-Channel Synchronous Rectifier Regulator Output. Bypass with 10F ceramic capacitor to GND for full-load capability. For less than 50% of full load, a 4.7F capacitor can be used. Battery Connection. VBATT is used for the startup oscillator and to power the chip when VOUT < VBATT. Exposed Paddle. Connect to GND and PGND.
1 2 3 4 5 6 7 8 --
RESET GND GND SHDN PGND LX OUT BATT EP
Detailed Description
The 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
6
increased with the low 70A 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
Functional Diagram
MAX1947
BATT
75ms TIMER STARTUP OSCILLATOR 0.9 x REF
RESET
OUT
SHDN
SHUTDOWN CIRCUITRY
ERROR AMPLIFIER
REF
tON MAX TIMER tOFF MIN TIMER
P*
CONTROL LOGIC AND GATE DRIVERS
ZERO-CROSSING AMPLIFIER
LX
N
REF 1.25V REFERENCE (REF) CURRENT-LIMIT AMPLIFIER PGND
MAX1947
GND *BODY DIODE CONTROL
Control Scheme
The MAX1947 is a bootstrapped design. Upon turn-on, a startup oscillator brings the output voltage high enough to allow the main DC-DC circuitry to run. Once the output voltage reaches 1.62V (typ) the main DC-DC circuitry turns on and boosts the output voltage to the final regulation point. The unique minimum off-time, current-limited control scheme is the key to the MAX1947's low operating current and high efficiency over a wide load range. The architecture combines the high output power and efficiency of a pulse-width modulation (PWM) device with the ultra-low quiescent current of a traditional pulseskipping controller. The switching frequency can be as high as 2MHz and depends upon the load current and input voltage. The MAX1947 is designed to operate using low-ESR ceramic capacitors, so output voltage ripple due to ESR is very small (approximately 10mVP-P).
VBATT > VOUT, VOUT > VOUT regulation point, and the minimum off-time expires. During track mode, the synchronous rectifier is turned on 100% of the time and the output voltage tracks the battery voltage. Track mode is exited by VOUT falling below the VOUT regulation point.
Synchronous Rectification
The internal synchronous rectifier eliminates the need for an external Schottky diode, reducing cost and board space. During the cycle off-time, the p-channel MOSFET turns on and shunts the MOSFET body diode. As a result, the synchronous rectifier significantly improves efficiency without the addition of an external component. Conversion efficiency can be as high as 94%.
RESET
The MAX1947 features an active-low push-pull RESET output for use with a microcontroller (C). It signals the C when the MAX1947 output voltage is within operating limits. During startup, RESET is held low. When the RESET threshold (90% of the output regulation voltage) is reached, a 75ms (min) timer begins counting. RESET is switched high once the timer expires.
Track Mode
The MAX1947 enters track mode when BATT is greater than the output-voltage regulation point. Track mode can only be entered under the following conditions:
_______________________________________________________________________________________
7
Low Input/Output Voltage Step-Up DC-DC Converter with RESET MAX1947
Table 1. Suggested Component Values
APPLICATION 1-Cell Input, Output < 2.7V 1-Cell Input, Output > 2.7V 2-Cell Input LOAD 50% full load >50% full load 50% full load >50% full load 50% full load >50% full load INPUT CAPACITOR (F) 2.2 2.2 2.2 2.2 2.2 2.2 OUTPUT CAPACITOR (F) 4.7 10 4.7 10 4.7 10 INDUCTOR (H) 3.3 3.3 4.7 4.7 6.8 6.8
Table 2. Suggested Component Manufacturers
MANUFACTURER Sumida Taiyo Yuden PART Inductor Output capacitors Input capacitors TDK Output capacitors Input capacitors PART NUMBER CDRH3D16 series 4.7F JMK212BJ475MG, 10F JMK212BJ106MG 2.2F LMK107BJ225MA 4.7F C2012X5R0J475K, 10F C2012X5R0J106K 2.2F C1608X5R03225M 888-835-6646 www.TDK.com PHONE 81-3-3667-3381 408-573-4150 WEBSITE www.sumida.com www.t-yuden.com
Shutdown
The MAX1947 enters shutdown mode when SHDN is driven low. During shutdown, the synchronous rectifier disconnects the output from the input, eliminating the DC conduction path that normally exists with traditional boost converters in shutdown mode. The output is actively discharged to ground through an internal 500 resistor. The quiescent current is reduced to 2A while in shutdown mode. Drive SHDN high for normal operation. The output reaches regulation approximately 650s after SHDN goes high.
Applications Information
Inductor Selection
An inductor value of 4.7H performs well in most applications. The MAX1947 also works with inductors in the
2.2H to 6.8H range. Smaller inductance values typically offer a smaller physical size for a given series resistance, allowing the smallest overall circuit dimensions but with lower output-current capability. Circuits using larger inductance values exhibit higher outputcurrent capability, but are larger for the same series resistance and current rating. The inductor's incremental saturation current rating should be greater than the peak switch-current limit. However, it is generally acceptable to bias the inductor into saturation by as much as 20%, although this slightly reduces efficiency (see the Electrical Characteristics for the MAX1947 NFET current limit). Table 1 lists the suggested components for several typical applications. Also, the inductor's DC resistance significantly affects efficiency.
8
_______________________________________________________________________________________
Low Input/Output Voltage Step-Up DC-DC Converter with RESET
Calculate the maximum output current (IOUTMAX) using inductor ripple current (IRIPPLE) and duty cycle (D) as follows:
Capacitor Selection
The MAX1947 is specifically designed for using small, inexpensive, low-ESR ceramic capacitors. X5R and X7R dielectrics are recommended when operating over wide temperature ranges. Bypass the output of the MAX1947 with 10F when using maximum load currents. When using less than half the maximum load current capability, the output capacitor can be reduced to 4.7F. Bypass the input with a 2.2F or larger ceramic capacitor. Table 1 lists the suggested values for the input and output capacitors for typical applications.
MAX1947
IRIPPLE =
VOUT + ILIM x (RDS(ON)PFET + RL ) - VBATT L / t OFF + (RDS(ON)PFET + RL ) 2
IRIPPLE )x VOUT + (ILIM - 2 (RDS(ON)PFET + RL ) - VBATT D= IRIPPLE VOUT + (ILIM - )x 2 (RDS(ON)PFET - RDS(ON)NFET + RL ) I IOUTMAX = (ILIM - RIPPLE ) x (1- D) 2
PC Board Layout and Grounding
Careful printed circuit-board layout is important for minimizing ground bounce and noise. Keep the IC's GND pins and the ground leads of the input and output filter capacitors very close together. Connect GND and PGND directly to the exposed paddle. In addition, keep all connections to the OUT and LX pins as short as possible. To maximize output power and efficiency and minimize output ripple voltage, use short, wide traces from the input and output. A sample layout is available in the MAX1947 evaluation kit.

Chip Information
Here, ILIM is the NFET current limit (800mA typ), tOFF is the LX switch's off-time (0.25s typ), and R L is the series resistance of the inductor. TRANSISTOR COUNT: 5156 PROCESS: BiCMOS
_______________________________________________________________________________________
9
Low Input/Output Voltage Step-Up DC-DC Converter with RESET MAX1947
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to www.maxim-ic.com/packages.)
6, 8, &10L, DFN THIN.EPS
C L
D
N
PIN 1 INDEX AREA
E
DETAIL A
E2
C L
L A e e
L
PACKAGE OUTLINE, 6, 8, 10 & 14L, TDFN, EXPOSED PAD, 3x3x0.80 mm
NUMBER OF LEADS SHOWN ARE FOR REFERENCE ONLY
21-0137
F
1
2
COMMON DIMENSIONS SYMBOL A D E A1 L k A2 MIN. 0.70 2.90 2.90 0.00 MAX. 0.80 3.10 3.10 0.05
0.40 0.20 0.25 MIN. 0.20 REF.
PACKAGE VARIATIONS PKG. CODE T633-1 T833-1 T1033-1 T1433-1 T1433-2 N 6 8 10 14 14 D2 1.500.10 1.500.10 1.500.10 1.700.10 1.700.10 E2 2.300.10 2.300.10 2.300.10 2.300.10 2.300.10 e 0.95 BSC 0.65 BSC 0.50 BSC 0.40 BSC 0.40 BSC JEDEC SPEC MO229 / WEEA MO229 / WEEC MO229 / WEED-3 ------b 0.400.05 0.300.05 0.250.05 0.200.03 0.200.03 [(N/2)-1] x e 1.90 REF 1.95 REF 2.00 REF 2.40 REF 2.40 REF
PACKAGE OUTLINE, 6, 8, 10 & 14L, TDFN, EXPOSED PAD, 3x3x0.80 mm
21-0137
F
2
2
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.
10 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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