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19-1360; Rev 0; 7/98
KIT ATION EVALU E AILABL AV
High-Efficiency, Low-Supply-Current, Compact, Step-Up DC-DC Converters
General Description ____________________________Features
o 94% Efficient at 200mA Output Current o 16A Quiescent Supply Current o Internal Synchronous Rectifier (no external diode) o 0.1A Logic-Controlled Shutdown o LBI/LBO Low-Battery Detector o Selectable Current Limit for Reduced Ripple o Low-Noise, Anti-Ringing Feature (MAX1676) o 8-Pin and 10-Pin MAX Packages o Preassembled Evaluation Kit (MAX1676EVKIT)
MAX1674/MAX1675/MAX1676
The MAX1674/MAX1675/MAX1676 compact, high-efficiency, step-up DC-DC converters fit in small MAX packages. They feature a built-in synchronous rectifier, which improves efficiency and reduces size and cost by eliminating the need for an external Schottky diode. Quiescent supply current is only 16A. The input voltage ranges from 0.7V to VOUT, where VOUT can be set from 2V to 5.5V. Start-up is guaranteed from 1.1V inputs. The MAX1674/MAX1675/ MAX1676 have a preset, pin-selectable output for 5V or 3.3V. The outputs can also be adjusted to other voltages using two external resistors. All three devices have a 0.3 N-channel MOSFET power switch. The MAX1674 has a 1A current limit. The MAX1675 has a 0.5A current limit, which permits the use of a smaller inductor. The MAX1676 comes in a 10-pin MAX package and features an adjustable current limit and circuitry to reduce inductor ringing.
_______________Ordering Information
PART MAX1674EUA MAX1675EUA MAX1676EUB TEMP. RANGE -40C to +85C -40C to +85C -40C to +85C PIN-PACKAGE 8 MAX 8 MAX 10 MAX
________________________Applications
Pagers Wireless Phones Medical Devices Hand-Held Computers PDAs RF Tags 1 to 3-Cell Hand-Held Devices
Pin Configurations
TOP VIEW
Typical Operating Circuit
FB 1 INPUT 0.7V TO VOUT LBI LBO 2 3 8 OUT LX GND SHDN
MAX1674 MAX1675
7 6 5
REF 4 ON OFF SHDN LX OUTPUT 3.3V, 5V, OR ADJ (2V TO 5.5V) UP TO 300mA
MAX
MAX1674 OUT MAX1675
FB 1 LBI 2 LOW-BATTERY DETECT IN LBI REF 0.1F FB LBO GND LOW-BATTERY DETECT OUT LBO 3 CLSEL 4 REF 5
10 OUT 9 LX GND BATT SHDN
MAX1676
8 7 6
MAX ________________________________________________________________ Maxim Integrated Products 1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800. For small orders, phone 408-737-7600 ext. 3468.
High-Efficiency, Low-Supply-Current, Compact, Step-Up DC-DC Converters MAX1674/MAX1675/MAX1676
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (OUT to GND) ..............................-0.3V to +6.0V Switch Voltage (LX to GND) .....................-0.3V to (VOUT + 0.3V) Battery Voltage (BATT to GND).............................-0.3V to +6.0V SHDN, LBO to GND ..............................................-0.3V to +6.0V LBI, REF, FB, CLSEL to GND ...................-0.3V to (VOUT + 0.3V) Switch Current (LX) ...............................................-1.5A to +1.5A Output Current (OUT) ...........................................-1.5A to +1.5A Continuous Power Dissipation (TA = +70C) 8-Pin MAX (derate 4.1mW/C above +70C) .............330mW 10-Pin MAX (derate 5.6mW/C above +70C) ...........444mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +165C Lead Temperature (soldering, 10sec) .............................+300C
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 = 2V, FB = OUT (VOUT = 3.3V), RL = , TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER Minimum Input Voltage Operating Voltage Start-Up Voltage Start-Up Voltage Tempco Output Voltage Output Voltage Range FB = OUT (VOUT = 3.3V) Steady-State Output Current (Note 2) IOUT FB = GND (VOUT = 5V) Reference Voltage Reference Voltage Tempco Reference Voltage Load Regulation Reference Voltage Line Regulation FB, LBI Input Threshold Internal NFET, PFET On-Resistance LX Switch Current Limit (NFET) LX Leakage Current RDS(ON) ILIM ILEAK ILX = 100mA MAX1674, MAX1676 (CLSEL = OUT) MAX1675, MAX1676 (CLSEL = GND) VLX = 0, 5.5V; VOUT = 5.5V 0.80 0.4 VREF TEMPCO VREF_LOAD VREF_LINE IREF = 0 to 100A VOUT = 2V to 5.5V 1.274 IREF = 0 MAX1674, MAX1676 (CLSEL = OUT) MAX1675, MAX1676 (CLSEL = GND) MAX1674, MAX1676 (CLSEL = OUT) MAX1675, MAX1676 (CLSEL = GND) VOUT FB = OUT FB = GND 3.17 4.80 2 300 150 180 90 1.274 420 220 mA 285 130 1.30 0.024 3 0.08 1.30 0.3 1 0.5 0.05 15 2.5 1.326 0.6 1.20 0.65 1 1.326 V mV/C mV mV/V V A A VIN TA = +25C TA = +25C, RL = 3k (Note 1) 1.1 0.9 -2 3.30 5 3.43 5.20 5.5 SYMBOL CONDITIONS MIN TYP 0.7 5.5 1.1 MAX UNITS V V V mV/C V V
2
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High-Efficiency, Low-Supply-Current, Compact, Step-Up DC-DC Converters
ELECTRICAL CHARACTERISTICS (continued)
(VBATT = 2V, FB = OUT (VOUT = 3.3V), RL = , TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER Operating Current into OUT (Note 3) Shutdown Current into OUT Efficiency LX Switch On-Time LX Switch Off-Time FB Input Current LBI Input Current CLSEL Input Current SHDN Input Current LBO Low Output Voltage LBO Off Leakage Current Damping Switch Resistance SHDN Input Voltage CLSEL Input Voltage VIL VIH VIL VIH 0.8VOUT 0.8VOUT 0.2VOUT I LBO tON tOFF IFB ILBI ICLSEL I SHDN SYMBOL CONDITIONS VFB = 1.4V, VOUT = 3.3V SHDN = GND VOUT = 3.3V, ILOAD = 200mA VOUT = 2V, ILOAD = 1mA VFB = 1V, VOUT = 3.3V VFB = 1V, VOUT = 3.3V VFB = 1.4V VLBI = 1.4V MAX1676, CLSEL = OUT V SHDN = 0 or VOUT VLBI = 0, ISINK = 1mA V LBO = 5.5V, VLBI = 5.5V MAX1676, VBATT = 2V 3 0.8 MIN TYP 16 0.1 90 85 4 1 0.03 1 1.4 0.07 0.2 0.07 88 7 1.2 50 50 3 50 0.4 1 150 0.2VOUT MAX 35 1 UNITS A A % s s nA nA A nA V A V V
MAX1674/MAX1675/MAX1676
Note 1: Start-up voltage operation is guaranteed with the addition of a Schottky MBR0520 external diode between the input and output. Note 2: Steady-state output current indicates that the device maintains output voltage regulation under load. See Figures 5 and 6. Note 3: Device is bootstrapped (power to the IC comes from OUT). This correlates directly with the actual battery supply.
ELECTRICAL CHARACTERISTICS
(VBATT = 2V, FB = OUT, RL = , TA = -40C to +85C, unless otherwise noted.) (Note 4) PARAMETER Output Voltage Output Voltage Range Reference Voltage FB, LBI Thresholds Internal NFET, PFET On-Resistance Operating Current into OUT (Note 3) Shutdown Current into OUT LX Switch On-Time LX Switch Off-Time LX Switch Current Limit (NFET) tON tOFF ILIM RDS(ON) VFB = 1.4V, VOUT = 3.3V SHDN = GND VFB = 1V, VOUT = 3.3V VFB = 1V, VOUT = 3.3V MAX1674, MAX1676 (CLSEL = OUT) MAX1675, MAX1676 (CLSEL = GND) 2.7 0.75 0.75 0.36 VREF IREF = 0 SYMBOL VOUT FB = OUT FB = GND CONDITIONS MIN 3.13 4.75 2.20 1.2675 1.2675 MAX 3.47 5.25 5.5 1.3325 1.3325 0.6 40 1 7.0 1.25 1.25 0.69 UNITS V V V V A A s s A
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High-Efficiency, Low-Supply-Current, Compact, Step-Up DC-DC Converters MAX1674/MAX1675/MAX1676
ELECTRICAL CHARACTERISTICS (continued)
(VBATT = 2V, FB = OUT, RL = , TA = -40C to +85C, unless otherwise noted.) (Note 4) PARAMETER CLSEL Input Current SHDN Input Current LBO Off Leakage Current SYMBOL ICLSEL I SHDN I LBO CONDITIONS MAX1676, CLSEL = OUT VSHDN = 0 or VOUT V LBO = 5.5V, VLBI = 5.5V MIN MAX 3 75 1 UNITS A nA A
Note 4: Specifications to -40C are guaranteed by design, not production tested.
Typical Operating Characteristics
(L = 22H, CIN = 47F, COUT = 47F 0.1F, CREF = 0.1F, TA = +25C, unless otherwise noted.)
EFFICIENCY vs. LOAD CURRENT
MAX1674 toc01
EFFICIENCY vs. LOAD CURRENT
MAX1674 toc02
EFFICIENCY vs. LOAD CURRENT
90 80 EFFICIENCY (%) 70 60 50 40 30 20 VIN = 2.4V VIN = 1.2V
MAX1674 toc03
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0.01 0.1 1 10 VOUT = 5V ILIMIT = 500mA 100 VIN = 3.6V VIN = 2.4V VIN = 1.2V
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0.01 0.1 1 10 LOAD CURRENT (mA) VOUT = 5V ILIMIT = 1A 100 VIN = 1.2V VIN = 2.4V VIN = 3.6V
100
10 0 0.01 0.1 1 10
VOUT = 3.3V ILIMIT = 500mA 100 1000
1000
1000
LOAD CURRENT (mA)
LOAD CURRENT (mA)
EFFICIENCY vs. LOAD CURRENT
MAX1674 toc04
REFERENCE OUTPUT VOLTAGE vs. TEMPERATURE
MAX1674 toc05
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0.01 0.1 1 10 LOAD CURRENT (mA) VOUT = 3.3V ILIMIT = 1A 100 VIN = 1.2V VIN = 2.4V
1.300 REFERENCE OUTPUT VOLTAGE (V)
1.298 IREF = 0 1.296
1.294 IREF = 100A 1.292
1.290 -40 -20 0 20 40 60 80 100 TEMPERATURE (C)
1000
4
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High-Efficiency, Low-Supply-Current, Compact, Step-Up DC-DC Converters
Typical Operating Characteristics (continued)
(L = 22H, CIN = 47F, COUT = 47F 0.1F, CREF = 0.1F, TA = +25C, unless otherwise noted.)
SHUTDOWN CURRENT vs. SUPPLY VOLTAGE
MAX1674toc08
MAX1674/MAX1675/MAX1676
NO-LOAD BATTERY CURRENT vs. INPUT BATTERY VOLTAGE
MAX1674toc07
START-UP VOLTAGE vs. LOAD CURRENT
1.8 1.6 START-UP VOLTAGE (V) 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 0.01 0.1 1 10 LOAD CURRENT (mA) 100 WITH 1N5817 WITHOUT DIODE 1.0 0.8 SHUTDOWN CURRENT (A) 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 1
140 INPUT BATTERY CURRENT (A) 120 100 80 ILIMIT = 0.5A, 5.0V 60 40 20 0 0 ILIMIT = 0.5A, 3.3V ILIMIT = 1A, 3.3V ILIMIT = 1A, 5.0V
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 INPUT BATTERY VOLTAGE (V)
1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V)
SHUTDOWN THRESHOLD vs. SUPPLY VOLTAGE
MAX1674TOC10
MAXIMUM OUTPUT CURRENT vs. INPUT VOLTAGE (VOUT = 5V)
800 700 600 500 400 300 200 0.5A CURRENT LIMIT 100 0 1A CURRENT LIMIT
MAX1674toc11
MAXIMUM OUTPUT CURRENT vs. INPUT VOLTAGE (VOUT = 3.3V)
700 600 1A CURRENT LIMIT 500 400 300 200 100 0 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 INPUT VOLTAGE (V) 0.5A CURRENT LIMIT
MAX1674toc12
1.4 1.2 SHUTDOWN THRESHOLD (V) 1.0 0.8 0.6 0.4 0.2 0 0
900 MAXIMUM OUTPUT CURRENT (mA)
800 MAXIMUM OUTPUT CURRENT (mA)
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 SUPPLY VOLTAGE (V)
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
INPUT VOLTAGE (V)
HEAVY-LOAD SWITCHING WAVEFORMS
MAX1674 TOC13
SWITCH RESISTANCE vs. TEMPERATURE
0.40 VLX 5V/div ILX 0.5A/div 0.35 RESISTANCE () 0.30 0.25 0.20 0.15 0.10 0.2 0.05 0 0 -60 -40 -20 0 20 40 60 80 100 2.0 2.5 N-CHANNEL ILIM (A)
MAX1674toc13.5
LX CURRENT LIMIT vs. OUTPUT VOLTAGE
MAX1674, MAX1676 (CLSEL = OUT)
MAX1674toc14
0.45 P-CHANNEL
1.2 1.0 0.8 0.6 0.4 MAX1675, MAX1676 (CLSEL = GND)
VIN = 2.4V VOUT = 5.0V 1s/div
VOUT AC COUPLED 100mV/div
3.0
3.5
4.0
4.5
5.0
TEMPERATURE (C)
OUTPUT VOLTAGE (V)
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5
MAX167toc09
160
High-Efficiency, Low-Supply-Current, Compact, Step-Up DC-DC Converters MAX1674/MAX1675/MAX1676
Typical Operating Characteristics (continued)
(L = 22H, CIN = 47F, COUT = 47F 0.1F, CREF = 0.1F, TA = +25C, unless otherwise noted.)
LINE-TRANSIENT RESPONSE
MAX1674 TOC15
LOAD-TRANSIENT RESPONSE
MAX1674 TOC16
EXITING SHUTDOWN
MAX1674 TOC17
VIN 2V TO 3V 1V/div
VIN = 2.4V VOUT = 3.3V IOUT 200mA/div
VOUT 2V/div
ILOAD 100mA 10s/div
VOUT AC COUPLED 100mV/div
VOUT 50mV/div AC COUPLED 5s/div 500s/div
VSHDN 2V/div
Pin Description
PIN MAX1674 MAX1675 1 MAX1676 NAME FUNCTION
1
FB
Dual-ModeTM Feedback Input. Connect to GND for +5.0V output. Connect to OUT for +3.3V output. Use a resistor network to set the output voltage from +2.0V to +5.5V. Low-Battery Comparator Input. Internally set to trip at +1.30V. Open-Drain Low-Battery Comparator Output. Output is low when VLBI is <1.3V. LBO is high impedance during shutdown. Current-Limit Select Input. CLSEL = OUT sets the current limit to 1A. CLSEL = GND sets the current limit to 0.5A. 1.3V Reference Voltage. Bypass with a 0.1F capacitor. Shutdown Input. High = operating, low = shutdown. Battery Input and Damping Switch Connection. If damping switch is unused, leave BATT unconnected. Ground N-Channel and P-Channel Power MOSFET Drain Power Output. OUT provides bootstrap power to the IC.
2 3 -- 4 5 -- 6 7 8
2 3 4 5 6 7 8 9 10
LBI LBO CLSEL REF SHDN BATT GND LX OUT
Dual-Mode is a trademark of Maxim Integrated Products.
6
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High-Efficiency, Low-Supply-Current, Compact, Step-Up DC-DC Converters
Detailed Description
The MAX1674/MAX1675/MAX1676 compact, step-up DC-DC converters start up with voltages as low as 0.9V and operate with an input voltage down to 0.7V. Consuming only 16A of quiescent current, these devices offer a built-in synchronous rectifier that reduces cost by eliminating the need for an external diode and improves overall efficiency by minimizing losses in the circuit (see Synchronous Rectification section for details). The internal MOSFET resistance is typically 0.3, which minimizes losses. The current limit of the MAX1674 and MAX1675 are 1A and 0.5A, respectively. The MAX1675's lower current limit allows the use of a physically smaller inductor in space-sensitive applications. The MAX1676 features a circuit that eliminates noise due to inductor ringing. In addition, the MAX1676 offers a selectable current limit (0.5A or 1A) for design flexibility. combines the high output power and efficiency of a pulse-width-modulation (PWM) device with the ultra-low quiescent current of a traditional PFM (Figure 1). There is no oscillator; a constant-peak-current limit in the switch allows the inductor current to vary between this peak limit and some lesser value. At light loads, the switching frequency is governed by a pair of one-shots that set a typical minimum off-time (1s) and a typical maximum on-time (4s). The switching frequency depends upon the load and the input voltage, and can range up to 500kHz. The peak current of the internal Nchannel MOSFET power switch is fixed at 1A (MAX1674), at 0.5A (MAX1675), or is selectable (MAX1676). Unlike conventional pulse-skipping DC-DC converters (where ripple amplitude varies with input voltage), ripple in these devices does not exceed the product of the switch current limit and the filter-capacitor equivalent series resistance (ESR).
MAX1674/MAX1675/MAX1676
PFM Control Scheme
A unique minimum-off-time, current-limited, pulse-frequency-modulation (PFM) control scheme is a key feature of the MAX1674/MAX1675/MAX1676. This scheme
Synchronous Rectification
The internal synchronous rectifier eliminates the need for an external Schottky diode, thus reducing cost and board space. During the cycle off-time, the P-channel MOSFET turns on and shunts the MOSFET body diode.
OUT MINIMUM OFF-TIME ONE-SHOT EN TRIG Q ONE-SHOT ZERO CROSSING AMPLIFIER P LX
0.1F 47F
VOUT
SHDN
VIN 22H 47F
CLSEL (MAX1676) MAXIMUM ON-TIME ONE-SHOT VIN R3 R2 100k LBO R4 LBI VOUT TRIG Q ONE-SHOT
F/F S R
N Q GND
MAX1674 MAX1675 MAX1676
CURRENT-LIMIT AMPLIFIER BATT (MAX1676) DAMPING SWITCH FB
R1 200
R5
ERROR AMPLIFIER REFERENCE LOW-BATTERY COMPARATOR
R6 REF 0.1F
Figure 1. Simplified Functional Diagram
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High-Efficiency, Low-Supply-Current, Compact, Step-Up DC-DC Converters MAX1674/MAX1675/MAX1676
As a result, the synchronous rectifier significantly improves efficiency without the addition of an external component. Conversion efficiency can be as high as 94%, as shown in the Typical Operating Characteristics. For low-voltage inputs from single cells (Alkaline, NiCd, or NiMH), use an external Schottky diode such as the 1N5817 to ensure start-up.
VIN R1 200 BATT 22H
Voltage Reference
The voltage at REF is nominally +1.30V. REF can source up to 100A to external circuits. The reference maintains excellent load regulation (see Typical Operating Characteristics). A bypass capacitor of 0.1F is required for proper operation.
MAX1676
DAMPING SWITCH LX OUT 0.1F 47F
VOUT
Shutdown
The device enters shutdown when V SHDN is low. During shutdown, the body diode of the P-channel MOSFET allows current flow from the battery to the output. V OUT falls to approximately VIN - 0.6V and LX remains high impedance. The capacitance and load at OUT determine the rate at which V OUT decays. Shutdown can be pulled as high as 6V, regardless of the voltage at OUT.
Figure 2. Simplified Diagram of Inductor Damping Switch
Current Limit Select Pin (MAX1676)
The MAX1676 allows a selectable inductor current limit of either 0.5A or 1A. This allows flexibility in designing for higher current applications or for smaller, compact designs. Connect CLSEL to OUT for 1A or to GND for 0.5A. CLSEL draws 1.4A when connected to OUT.
VLX 1V/div
BATT/Damping Switch (MAX1676)
The MAX1676 is designed with an internal damping switch to minimize ringing at LX. The damping switch connects an external resistor (R1) across the inductor when the inductor's energy is depleted (Figure 2). Normally, when the energy in the inductor is insufficient to supply current to the output, the capacitance and inductance at LX form a resonant circuit that causes ringing. The ringing continues until the energy is dissipated through the series resistance of the inductor. The damping switch supplies a path to quickly dissipate this energy, minimizing the ringing at LX. Damping LX ringing does not reduce VOUT ripple, but does reduce EMI. R1 = 200 works well for most applications while reducing efficiency by only 1%. Larger R1 values provide less damping, but have less impact on efficiency. Generally, lower values of R1 are needed to fully damp LX when the VOUT/VIN ratio is high (Figures 2, 3, and 4).
2s/div
Figure 3. LX Ringing Without Damping Switch
VLX 1V/div
2s/div
Figure 4. LX Waveform with Damping Switch (with 200 external resistor)
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High-Efficiency, Low-Supply-Current, Compact, Step-Up DC-DC Converters
Selecting the Output Voltage
VOUT can be set to 3.3V or 5.5V by connecting the FB pin to GND (5V) or OUT (3.3V) (Figures 5 and 6). To adjust the output voltage, connect a resistor-divider from VOUT to FB to GND (Figure 7). Choose a value less than 260k for R6. Use the following equation to calculate R5: R5 = R6 [(VOUT / VREF ) - 1] where VREF = +1.3V and VOUT may range from 2V to 5V. The input bias current of FB has a maximum value of 50nA which allows large-value resistors (R6 260k) to be used.
MAX1674/MAX1675/MAX1676
Low-Battery Detection
The MAX1674/MAX1675/MAX1676 contain an on-chip comparator for low-battery detection. If the voltage at LBI falls below the internal reference voltage (1.30V), LBO (an open-drain output) sinks current to GND. The low-battery monitor threshold is set by two resistors, R3 and R4 (Figures 5, 6, and 7). Since the LBI current is less than 50nA, large resistor values (R4 260k) can be used to minimize loading of the input supply. Calculate R3 using the following equation: R3 = R4 [(VTRIP / VREF) - 1] for VTRIP 1.3V. VTRIP is the level where the low-battery detector output goes low, and V REF is the internal 1.30V reference. Connect a pull-up resistor of 100k or greater from LBO to OUT when driving CMOS circuits. LBO is an open-drain output, and can be pulled as high as 6V regardless of the voltage at OUT. When LBI is above the threshold, the LBO output is high impedance. If the low-battery comparator is not used, ground
VIN
47F 10V R1 200
22H
BATT (MAX1676)
LX OUT CLSEL (MAX1676) FB SHDN 0.1F VOUT 47F +3.3V 200mA
R3 LBI R4
REF 0.1F
MAX1674 MAX1675 MAX1676
GND
R2 100k LBO LOW-BATTERY OUTPUT
VIN
Figure 5. Preset Output Voltage of +3.3V
47F VIN R1 200 47F R1 200 BATT (MAX1676) 22H
LX OUT SHDN CLSEL (MAX1676) R2 100k 0.1F R5 LOWBATTERY OUTPUT OUTPUT 2V to 5.5V 47F
22H
R3 LBI
BATT (MAX1676)
LX OUT CLSEL (MAX1676) SHDN R2 100k REF LOWBATTERY OUTPUT 0.1F OUTPUT 5.0V, 150mA 47F R4
R3 LBI R4
MAX1674 MAX1675 MAX1676
GND 0.1F
LBO FB
REF 0.1F
MAX1674 MAX1675 MAX1676
GND
LBO FB
R6
Figure 6. Preset Output Voltage of +5V
Figure 7. Setting an Adjustable Output
9
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High-Efficiency, Low-Supply-Current, Compact, Step-Up DC-DC Converters MAX1674/MAX1675/MAX1676
VIN
VTRIP (VH, VL)
47F 22H R1 200
R3 LBI
MAX1674 MAX1675 MAX1676
OUT 0.1F R2 100k
VOUT 47F
BATT (MAX1676)
LX OUT CLSEL (MAX1676) 0.1F
VOUT
R4 LBO R7 GND
R3 LBI
47F
FB SHDN
MAX1674 MAX1675 REF MAX1676
GND 0.1F
LBO
R2 100k LOWBATTERY OUTPUT
R4
VH = 1.3V 1 + VL = 1.3V 1 +
(
)
R3 R3 + R7 R4 (VOUT - 1.3V) R 3 R3 - R4 (1.3V) (R2 + R7)
(
)
WHERE VH IS THE UPPER TRIP LEVEL VL IS THE LOWER TRIP LEVEL
Figure 8. Setting Resistor Values for the Low-Battery Indicator when VIN < 1.3V
Figure 9. Adding External Hysteresis to the Low-Battery Indicator
LBI and LBO. For VTRIP less than 1.3V, configure the comparator as shown in Figure 8. Calculate the value of the external resistors R3 and R4 as follows: R3 = R4(VREF - VTRIP) / (VOUT - VREF) Since the low-battery comparator is noninverting, external hysteresis can be added by connecting a resistor between LBO and LBI as shown in Figure 9. When LBO is high, the series combination of R2 and R7 source current into the LBI summing junction.
MAX1674, 500mA for the MAX1675, and 1A or 0.5A for the MAX1676. However, it is generally acceptable to bias the inductor into saturation by as much as 20%, although this will slightly reduce efficiency. Table 1 lists suggested components. The inductor's DC resistance significantly affects efficiency. See Table 2 for a comparison of inductor specifications. Calculate the maximum output current as follows: VOUT - VBATT VBATT ILIM - 1/ 2 L + RP t OFF = VOUT
Applications Information
Inductor Selection
An inductor value of 22H performs well in most applications. The MAX1674/MAX1675/MAX1676 will also work with inductors in the 10H to 47H range. Smaller inductance values typically offer a smaller physical size for a given series resistance, allowing the smallest overall circuit dimensions. However, due to higher peak inductor currents, the output voltage ripple (I PEAK x output filter capacitor ESR) also tends to be higher. Circuits using larger inductance values exhibit higher output current capability and larger physical dimensions for a given series resistance. The inductor's incremental saturation current rating should be greater than the peak switch-current limit, which is 1A for the IOUT(MAX)
where IOUT(MAX) = maximum output current in amps VBATT = input voltage L = inductor value in H = efficiency (typically 0.9) tOFF = LX switch's off-time in s RP = resistance of P-channel MOSFET in ILIM = 0.5A or 1.0A
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High-Efficiency, Low-Supply-Current, Compact, Step-Up DC-DC Converters
Table 1. Suggested Components
PRODUCTION METHOD INDUCTORS Sumida CD43 series Sumida CD54 series Coilcraft DT1608C Coilcraft DO1608C Coiltronics Uni-PAC Murata LQH4 series Sumida RCH654-220 CAPACITORS RECTIFIERS (OPTIONAL)
MAX1674/MAX1675/MAX1676
Surface Mount
Sprague 593D series Sprague 595D series AVX TPS series ceramic Sanyo OS-CON series
Motorola MBR0530 Nihon EC 15QS02L
Miniature Through-Hole
--
Table 2. Surface-Mount Inductor Specifications
MANUFACTURER PART NUMBER Coilcraft DT1608C-103 Coilcraft DO1608C-153 Coilcraft DO1608C-223 Coiltronics UP1B-100 Coiltronics UP1B-150 Coiltronics UP1B-220 Murata LQH4N100 Murata LQH4N220 Sumida CD43-8R2 Sumida CD43-100 Sumida CD54-100 Sumida CD54-180 Sumida CD54-220 H 10 15 22 10 15 22 10 22 8.2 10 10 18 22 (max) IPEAK (A) 0.095 0.200 0.320 0.111 0.175 0.254 0.560 0.560 0.132 0.182 0.100 0.150 0.180 0.7 0.9 0.7 1.9 1.5 1.2 0.4 0.4 1.26 1.15 1.44 1.23 1.11 HEIGHT (mm) 2.92 2.92 2.92 5.0 5.0 5.0 2.6 2.6 3.2 3.2 4.5 4.5 4.5
Table 3. Component Suppliers
COMPANY AVX Coilcraft Coiltronics Motorola Murata Nihon Sanyo Sprague Sumida Taiyo Yuden PHONE USA (803) 946-0690 USA (847) 639-6400 USA (561) 241-7876 USA (303) 675-2140 (800) 521-6274 USA (814) 237-1431 (800) 831-9172 FAX USA (803) 626-3123 USA (847) 639-1469 USA (561) 241-9339 USA (303) 675-2150 USA (814) 238-0490
USA (805) 867-2555 USA (805) 867-2556 Japan 81-3-3494-7411 Japan 81-3-3494-7414 USA (619) 661-6835 USA (619) 661-1055 Japan 81-7-2070-6306 Japan 81-7-2070-1174 USA (603) 224-1961 USA (603) 224-1430
USA (647) 956-0666 USA (647) 956-0702 Japan 81-3-3607-5111 Japan 81-3-3607-5144 USA (408) 573-4150 USA (408) 573-4159
Capacitor Selection
A 47F, 10V surface-mount tantalum (SMT) output filter capacitor provides 80mV output ripple when stepping up from 2V to 5V. Smaller capacitors (down to 10F with higher ESRs) are acceptable for light loads or in applications that can tolerate higher output ripple. Values in the 10F to 100F range are recommended. The equivalent series resistance (ESR) of both bypass and filter capacitors affects efficiency and output ripple. Output voltage ripple is the product of the peak
inductor current and the output capacitor ESR. Use low-ESR capacitors for best performance, or connect two or more filter capacitors in parallel. Low-ESR, SMT tantalum capacitors are currently available from Sprague (595D series) AVX (TPS series) and other sources. Ceramic surface-mount and Sanyo OS-CON organic-semiconductor through-hole capacitors also exhibit very low ESR, and are especially useful for operation at cold temperatures. See Table 3 for a list of suggested component suppliers.
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11
High-Efficiency, Low-Supply-Current, Compact, Step-Up DC-DC Converters MAX1674/MAX1675/MAX1676
Optional External Rectifier
Although not required, a Schottky diode (such as the MBR0520) connected between LX and OUT allows lower start-up voltages (Figure 10) and is recommended for single-cell operation. Note that adding this diode provides no significant efficiency improvement.
VIN SINGLE CELL
47F 22H R1 200
PC Board Layout and Grounding
Careful printed circuit layout is important for minimizing ground bounce and noise. Keep the IC's GND pin and the ground leads of the input and output filter capacitors less than 0.2in (5mm) apart. In addition, keep all connections to the FB and LX pins as short as possible. In particular, when using external feedback resistors, locate them as close to the FB as possible. To maximize output power and efficiency and minimize output ripple voltage, use a ground plane and solder the IC's GND directly to the ground plane.
R3
BATT (MAX1676)
LX MBR0520 OUT FB SHDN R2 100k
LBI R4
MAX1674 MAX1675 MAX1676
0.1F
47F
CLSEL (MAX1676) REF 0.1F GND
LBO
LOW-BATTERY OUTPUT
Figure 10. Adding a Schottky Diode for Single-Cell Operation
Chip Information
TRANSISTOR COUNT: 751
Package Information
10LUMAXB.EPS
12
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