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19-3106; Rev 0; 1/08
KIT ATION EVALU BLE AVAILA
Low-Noise Step-Up DC-DC Converter
General Description Features
o 90% Efficiency o Adjustable Output from VIN to 18V o 2.4A, 0.15, 22V Power MOSFET o +2.6V to +4.0V Input Range o Pin-Selectable 640kHz or 1.2MHz Switching Frequency o Programmable Soft-Start o Small 8-Pin MAX Package o Integrated Input Voltage Clamp Circuit
MAX17067
The MAX17067 boost converter incorporates highperformance (at 1.2MHz), current-mode, fixed-frequency, pulse-width modulation (PWM) circuitry with a built-in 0.15 n-channel MOSFET to provide a highly efficient regulator with fast response. High switching frequency (640kHz or 1.2MHz selectable) allows for easy filtering and faster loop performance. An external compensation pin provides the user flexibility in determining loop dynamics, allowing the use of small, low equivalent-series-resistance (ESR) ceramic output capacitors. The device can produce an output voltage as high as 18V. Soft-start is programmed with an external capacitor, which sets the input-current ramp rate. The MAX17067 is available in a space-saving 8-pin MAX(R) package. The ultrasmall package and high switching frequency allow the total solution to be less than 1.1mm high.
Application
LCD Displays
PART MAX17067EUA+
Ordering Information
TEMP RANGE -40C to +85C PINPACKAGE 8 MAX PKG CODE U8+1
Typical Operating Circuit
VIN 2.6V TO 4V
+ Denotes a lead-free package.
Pin Configuration
TOP VIEW
IN VOUT LX COMP 1 FB 2 SHDN 3 GND 4 SS
FB
ON/OFF
SHDN
8 7
SS FREQ IN LX
MAX17067 FREQ GND
MAX17067
6 5
COMP
MAX
MAX is a registered trademark of Maxim Integrated Products, Inc.
________________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
Low-Noise Step-Up DC-DC Converter MAX17067
ABSOLUTE MAXIMUM RATINGS
LX to GND ..............................................................-0.3V to +22V SHDN, FREQ to GND ............................................-0.3V to +7.5V IN to GND (Note 1) ...................................................-0.3V to +6V SS, COMP, FB to GND ................................-0.3V to (VIN + 0.3V) RMS LX Pin Current ..............................................................1.2A Continuous Power Dissipation (TA = +70C) 8-Pin MAX (derate 4.1mW/C above +70C) ............330mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+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
(VIN = SHDN = 3V, FREQ = 3V, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 2)
PARAMETER Input Supply Range Output Voltage Input Supply Clamp Voltage VIN Undervoltage Lockout Quiescent Current Shutdown Supply Current ERROR AMPLIFIER Feedback Voltage FB Input Bias Current Feedback-Voltage Line Regulation Transconductance Voltage Gain OSCILLATOR Frequency Maximum Duty Cycle n-CHANNEL SWITCH Current Limit On-Resistance Leakage Current Current-Sense Transresistance SOFT-START Reset Switch Resistance Charge Current VSS = 1.2V 2.5 4.5 100 6.5 A ILIM R ON ILXOFF RCS VLX = 20V 0.2 VFB = 1V, duty cycle = 68% (Note 4) 1.8 2.4 150 10 0.3 3.4 275 20 0.4 A m A V/A f OSC DC FREQ = GND FREQ = IN FREQ = GND, FREQ = IN 500 1000 89 640 1200 92 780 1400 95 kHz % gm AV VFB IFB Level to produce VCOMP = 1.24V VFB = 1.24V Level to produce VCOMP = 1.24V, 2.6V < VIN < 5.5V I = 5A 100 1.23 50 1.24 125 0.05 240 3800 1.25 200 0.15 440 V nA %/V S V/V UVLO I IN I IN Use external limiting resistor; RIN = 100 , VIN = 10V (Note 3) VIN rising, typical hysteresis is 50mV, LX remains off below this level VFB = 1.3V, not switching VFB = 1.0V, switching SHDN = GND, TA = +25C SHDN = GND, TA = +85C 6.05 2.30 6.40 2.45 0.3 1.5 30 30 SYMBOL VIN VOUT < 18V CONDITIONS MIN 2.6 TYP MAX 4.0 18 6.60 2.57 0.6 2.5 60 UNITS V V V V mA A
2
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Low-Noise Step-Up DC-DC Converter
ELECTRICAL CHARACTERISTICS (continued)
(VIN = SHDN = 3V, FREQ = 3V, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 2)
PARAMETER CONTROL INPUTS Input Low Voltage Input High Voltage Hysteresis FREQ Pulldown Current SHDN Input Current Thermal Shutdown IFREQ I SHDN SHDN = GND, TA = +25C SHDN = GND, TA = +85C Temperature rising Hysteresis VIL VIH SHDN, FREQ, VIN = 2.6V to 4.0V SHDN, FREQ, VIN = 2.6V to 4.0V SHDN, FREQ 3 -1 0 160 20 0.7 x VIN 0.1 x VIN 6 9 +1 0.3 x VIN V V V A A C SYMBOL CONDITIONS MIN TYP MAX UNITS
MAX17067
ELECTRICAL CHARACTERISTICS
(VIN = SHDN = 3V, FREQ = 3V, TA = -40C to +85C, unless otherwise noted.) (Note 2)
PARAMETER Input Supply Range Output Voltage Range Input Supply Clamp Voltage VIN Undervoltage Lockout Quiescent Current ERROR AMPLIFIER Feedback Voltage FB Input Bias Current Feedback-Voltage Line Regulation Transconductance OSCILLATOR Frequency Maximum Duty Cycle f OSC DC FREQ = GND FREQ = IN FREQ = GND, FREQ = VIN 450 950 89 830 1500 95 kHz % gm VFB IFB Level to produce VCOMP = 1.24V VFB = 1.24V Level to produce VCOMP = 1.24V, 2.6V < VIN < 4.0V I = 5A 100 1.227 1.253 200 0.15 440 V nA %/V S UVLO I IN Use external limiting resistor; RIN = 100 , VIN = 10V (Note 3) VIN rising, typical hysteresis is 80mV, LX remains off below this level VFB = 1.3V, not switching VFB = 1.0V, switching 6.03 2.30 SYMBOL VIN VOUT < 18V CONDITIONS MIN 2.6 TYP MAX 4.0 18 6.60 2.57 0.6 2.5 UNITS V V V V mA
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3
Low-Noise Step-Up DC-DC Converter MAX17067
ELECTRICAL CHARACTERISTICS (continued)
(VIN = SHDN = 3V, FREQ = 3V, TA = -40C to +85C, unless otherwise noted.) (Note 1)
PARAMETER n-CHANNEL SWITCH Current Limit On-Resistance Current-Sense Transresistance SOFT-START Reset Switch Resistance Charge Current CONTROL INPUTS Input Low Voltage Input High Voltage VIL VIH SHDN, FREQ, VIN = 2.6V to 4.0V SHDN, FREQ, VIN = 2.6V to 4.0V 0.7 x VIN 0.3 x VIN V V VSS = 1.2V 2.5 100 6.5 A ILIM R ON RCS VFB = 1V, duty cycle = 68% (Note 4) VIN = 3V 0.19 1.8 3.4 275 0.40 V/A A SYMBOL CONDITIONS MIN TYP MAX UNITS
Note 1: Limit on IN absolute maximum ratings is for operation without the use of an external resistor for the internal clamp circuit. See the IN Supply Clamp Circuit section for IN voltage limits during clamping circuit operation. Note 2: Limits are 100% production tested at TA = +25C. Maximum and minimum limits over temperature are guaranteed by design and characterization. Note 3: See the IN Supply Clamp Circuit section to properly size the external resistor. Note 4: Current limit varies with duty-cycle slope compensation. See the Output-Current Capability section.
Typical Operating Characteristics
(Circuit of Figure 1, VIN = 3.3V, fOSC = 640kHz, TA = +25C, unless otherwise noted.)
EFFICIENCY vs. L0AD CURRENT (VIN = 3.3V, VOUT = 9V)
MAX17067 toc01
STEP-UP CONVERTER LOAD REGULATION
MAX17067 toc02
SWITCHING FREQUENCY vs. INPUT VOLTAGE
1300 SWITCHING FREQUENCY (kHz) 1200 FREQ = IN 1100 1000 900 800 700 600 FREQ = GND
MAX17067 toc03
100
1.0
1400
90 EFFICIENCY (%)
fOSC = 640kHz L = 4.7H
REGULATION (%)
0.5 L = 3.3H 0
80 fOSC = 1.2MHz L = 3.3H
70
60
50 1 10 100 1000 LOAD CURRENT (mA)
-0.5 1 10 100 1000 LOAD CURRENT (mA)
500 2.5 3.0 3.5 4.0 4.5 5.0 5.5 INPUT VOLTAGE (V)
4
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Low-Noise Step-Up DC-DC Converter
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN = 3.3V, fOSC = 640kHz, TA = +25C, unless otherwise noted.)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX17067 toc04
MAX17067
SOFT-START (RLOAD = 18)
MAX17067 toc05
4.0 3.5 SUPPLY CURRENT (mA) 3.0 2.5 2.0 1.5 1.0 0.5 0 2.5 2.7 2.9 3.1 3.3 3.5 3.7 3.9 SUPPLY VOLTAGE (V) NONSWITCHING SWITCHING
VOUT 5V/div
0V INDUCTOR CURRENT 1A/div 0A
2ms/div
LOAD-TRANSIENT RESPONSE (ILOAD = 10mA TO 200mA)
MAX17067 toc06
PULSED LOAD-TRANSIENT RESPONSE (ILOAD = 40mA TO 1.1A)
MAX17067 toc07
IOUT 200mA/div 10mA VOUT 500mA/div AC-COUPLED 0V
IOUT 1A/div 0.1A 9V VOUT 200mV/div AC-COUPLED 0V
INDUCTOR CURRENT 500mA/div 0A 100s/div L = 3.3H RCOMP = 39k CCOMP1 = 620pF L = 3.3H RCOMP = 39k CCOMP1 = 620pF 10s/div
INDUCTOR CURRENT 1A/div 0A
SWITCHING WAVEFORMS (ILOAD = 500mA)
MAX17067 toc08
LX 5V/div 0V INDUCTOR CURRENT 1A/div 0A
1s/div
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5
Low-Noise Step-Up DC-DC Converter MAX17067
Pin Description
PIN 1 2 3 4 5 6 7 NAME COMP FB SHDN GND LX IN FREQ FUNCTION Compensation Pin for Error Amplifier. Connect a series RC from COMP to ground. See the Loop Compensation section for component selection guidelines. Feedback Pin. Reference voltage is 1.24V nominal. Connect an external resistor-divider tap to FB and minimize the trace area. Set VOUT according to: VOUT = 1.24V (1 + R1 / R2). See Figure 1. Active-Low Shutdown Control Input. Drive SHDN low to turn off the MAX17067. Ground Switch Pin. Connect the inductor/catch diode to LX and minimize the trace area for lowest EMI. Supply Pin. Bypass IN with at least a 1F ceramic capacitor directly to GND. Frequency Select Input. When FREQ is low, the oscillator frequency is set to 640kHz. When FREQ is high, the frequency is 1.2MHz. This input has a 5A pulldown current. Soft-Start Control Pin. Connect a soft-start capacitor (CSS) to this pin. Leave open for no soft-start. The softstart capacitor is charged with a constant current of 4A. Full current limit is reached after t = 2.5 x 105 CSS. The soft-start capacitor is discharged to ground when SHDN is low. When SHDN goes high, the soft-start capacitor is charged to 0.5V, after which soft-start begins.
8
SS
VIN 2.6V TO 4.0V
CIN C1 10F 6.3V IN
Detailed Description
The MAX17067 is a highly efficient power supply that employs a current-mode, fixed-frequency PWM architecture for fast-transient response and low-noise operation. The device regulates the output voltage through a combination of an error amplifier, two comparators, and several signal generators (Figure 2). The error amplifier compares the signal at FB to 1.24V and varies the COMP output. The voltage at COMP determines the current trip point each time the internal MOSFET turns on. As the load varies, the error amplifier sources or sinks current to the COMP output accordingly to produce the inductor peak current necessary to service the load. To maintain stability at high duty cycle, a slope-compensation signal is summed with the current-sense signal. At light loads, this architecture allows the ICs to "skip" cycles to prevent overcharging the output voltage. In this region of operation, the inductor ramps up to a fixed peak value, discharges to the output, and waits until another pulse is needed again.
L VOUT LX D1 MBRS130LT1 COUT
ON/OFF VIN 1.2MHz
SHDN
MAX17067
FREQ GND
640kHz SS 0.027F COMP R2 CCOMP2 RCOMP CCOMP FB R1
Figure 1. Typical Application Circuit
6
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Low-Noise Step-Up DC-DC Converter MAX17067
SHDN BIAS
SKIP COMPARATOR SKIP SOFTSTART
4A
IN
SS
COMP ERROR AMPLIFIER FB ERROR COMPARATOR CONTROL AND DRIVER LOGIC CLOCK
LX N
1.24V
GND FREQ OSCILLATOR SLOPE COMPENSATION CURRENT SENSE
5A
MAX17067
Figure 2. Functional Diagram
IN Supply Clamp Circuit
The MAX17067 features an internal clamp to allow applications where there is overvoltage stress on the supply line. In many cases, high-voltage spikes happen on production lines and are difficult to protect against. The MAX17067's internal clamp circuit can solve this problem. The internal clamp circuit limits the voltage at the IN pin to 6.4V (typ) to protect the IN pin from a continuous or transient overvoltage stress condition on the supply line. To use the clamp circuit, put a series resistor (RIN) between supply and IN, and a decoupling capacitor (1F typical) from IN to GND. To properly size the external resistor, several factors should be considered: * The maximum current for the clamp is 40mA, and the clamp voltage at the IN pin is 6.05V (min). Therefore, the external resistor is: RIN ( VIN - 6.05) 0.04 * Power dissipation in the clamp is in addition to the total power loss.
*
The external resistor causes a DC voltage drop in the IN supply line. The voltage at the IN pin has to be properly maintained when clamping is used. The worst-case quiescent current of the IN pin is 2.5mA; therefore, the worst-case voltage drop is 2.5mA multiplied by RIN.
Output-Current Capability
The output-current capability of the MAX17067 is a function of current limit, input voltage, operating frequency, and inductor value. Because of the slope compensation used to stabilize the feedback loop, the duty cycle affects the current limit. The output-current capability is governed by the following equation: IOUT(MAX) = [ILIM x (1.26 - 0.4 x Duty) 0.5 x Duty x VIN/(fOSC x L)] x x VIN/VOUT where: ILIM = current limit specified at 68% (see the Electrical Characteristics): Duty = duty cycle = (VOUT - VIN + VDIODE)/ (VOUT - ILIM x RON + VDIODE) VDIODE = catch diode forward voltage at ILIM = conversion efficiency, 85% nominal
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7
Low-Noise Step-Up DC-DC Converter MAX17067
Soft-Start
The MAX17067 can be programmed for soft-start upon power-up with an external capacitor. When the shutdown pin is taken high, the soft-start capacitor (CSS) is immediately charged to 0.5V. Then the capacitor is charged at a constant current of 4.5A (typ). During this time, the SS voltage directly controls the peak inductor current, allowing 0A at VSS = 0.5V to the full current limit at VSS = 1.5V. The maximum load current is available after the soft-start cycle is completed. When the shutdown pin is taken low, the soft-start capacitor is discharged to ground.
Thermal-Overload Protection
Thermal-overload protection prevents excessive power dissipation from overheating the MAX17067. When the junction temperature exceeds TJ = +160C, a thermal sensor immediately activates the fault protection, which shuts down the MAX17067, allowing the device to cool down. Once the device cools down by approximately 20C, it returns to normal operation.
Applications Information
Boost DC-DC converters using the MAX17067 can be designed by performing simple calculations for a first iteration. All designs should be prototyped and tested prior to production. Table 1 provides a list of components for a range of standard applications. Table 2 lists component suppliers. External component value choice is primarily dictated by the output voltage and the maximum load current, as well as maximum and minimum input voltages. Begin by selecting an inductor value. Once L is known, choose the diode and capacitors.
Frequency Selection
The MAX17067's frequency can be user selected to operate at either 640kHz or 1.2MHz. Connect FREQ to GND for 640kHz operation. For a 1.2MHz switching frequency, connect FREQ to IN. This allows the use of small, minimum-height external components while maintaining low output noise. FREQ has an internal pulldown, allowing the user the option of leaving FREQ unconnected for 640kHz operation.
Shutdown
The MAX17067 is shut down to reduce the supply current to 30A when SHDN is low. In this mode, the internal reference, error amplifier, comparators, and biasing circuitry turn off while the n-channel MOSFET is turned off. The boost converter's output is connected to IN by the external inductor and catch diode.
Inductor Selection
The minimum inductance value, peak current rating, and series resistance are factors to consider when selecting the inductor. These factors influence the converter's efficiency, maximum output load capability, transientresponse time, and output voltage ripple. Physical size and cost are also important factors to be considered.
Table 1. Component Selection
VIN (V) 3.3 3.3 VOUT (V) 9 9 fOSC (Hz) 1.2M 640k L (H) 3.3 4.7 COUT (F) 10 10 RCOMP (k ) 121 82 CCOMP (pF) 620 1000 CCOMP2 (pF) 10 10 IOUT(MAX) (mA) 250 250
Table 2. Component Suppliers
SUPPLIER Inductors Coilcraft Coiltronics Sumida USA TOKO Capacitors AVX KEMET SANYO Taiyo Yuden 8 803-946-0690 408-986-0424 619-661-6835 408-573-4150 803-626-3123 408-986-1442 619-661-1055 408-573-4159 PHONE 847-639-6400 561-241-7876 847-956-0666 847-297-0070 FAX 847-639-1469 561-241-9339 847-956-0702 847-699-1194 SUPPLIER Diodes Central Semiconductor International Rectifier Motorola Nihon Zetex PHONE FAX
516-435-1110 310-322-3331 602-303-5454 847-843-7500 516-543-7100
516-435-1824 310-322-3332 602-994-6430 847-843-2798 516-864-7630
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Low-Noise Step-Up DC-DC Converter
The maximum output current, input voltage, output voltage, and switching frequency determine the inductor value. Very high inductance values minimize the current ripple and therefore reduce the peak current, which decreases core losses in the inductor and I2R losses in the entire power path. However, large inductor values also require more energy storage and more turns of wire, which increase physical size and can increase I2R losses in the inductor. Low inductance values decrease the physical size but increase the current ripple and peak current. Finding the best inductor involves choosing the best compromise between circuit efficiency, inductor size, and cost. The equations used here include a constant LIR, which is the ratio of the inductor peak-to-peak ripple current to the average DC inductor current at the full load current. The best trade-off between inductor size and circuit efficiency for step-up regulators generally has an LIR between 0.3 and 0.5. However, depending on the AC characteristics of the inductor core material and the ratio of inductor resistance to other power path resistances, the best LIR can shift up or down. If the inductor resistance is relatively high, more ripple can be accepted to reduce the number of turns required and increase the wire diameter. If the inductor resistance is relatively low, increasing inductance to lower the peak current can decrease losses throughout the power path. If extremely thin high-resistance inductors are used, as is common for LCD-panel applications, the best LIR can increase to between 0.5 and 1.0. Once a physical inductor is chosen, higher and lower values of the inductor should be evaluated for efficiency improvements in typical operating regions. Calculate the approximate inductor value using the typical input voltage (VIN), the maximum output current (IMAIN(MAX)), the expected efficiency (TYP) taken from an appropriate curve in the Typical Operating Characteristics, and an estimate of LIR based on the above discussion:
2 VIN VMAIN - VIN TYP L= I VMAIN MAIN(MAX) x fOSC LIR
Choose an available inductor value from an appropriate inductor family. Calculate the maximum DC input current at the minimum input voltage VIN(MIN) using conservation of energy and the expected efficiency at that operating point (MIN) taken from an appropriate curve in the Typical Operating Characteristics: IIN(DC,MAX) = IMAIN(MAX) x VMAIN VIN(MIN) x MIN
MAX17067
Calculate the ripple current at that operating point and the peak current required for the inductor: IRIPPLE = VIN(MIN) x (VMAIN - VIN(MIN) ) L x VMAIN x fOSC
I IPEAK = IIN(DC,MAX) + RIPPLE 2 The inductor's saturation current rating and the MAX17067s' LX current limit (ILIM) should exceed IPEAK and the inductor's DC current rating should exceed IIN(DC,MAX). For good efficiency, choose an inductor with less than 0.1 series resistance. Considering the application circuit in Figure 4, the maximum load current (IMAIN(MAX)) is 250mA with a 9V output and a typical input voltage of 3.3V. Choosing an LIR of 0.7 and estimating efficiency of 85% at this operating point: 3.3V 9V - 3.3V 0.85 3.3H L= 9V 0.25A x 1.2MHz 0.7 Using the application's minimum input voltage (3V) and estimating efficiency of 80% at that operating point: IIN(DC,MAX) = 0.25A x 9V 0.94 A 3V x 0.8
2
The ripple current and the peak current are: IRIPPLE = 3V x (9V - 3V) 0.51A 3.3H x 9V x 1.2MHz 0.51A 1.19 A 2
IPEAK = 0.94 A +
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9
Low-Noise Step-Up DC-DC Converter MAX17067
Diode Selection
The output diode should be rated to handle the output voltage and the peak switch current. Make sure that the diode's peak current rating is at least IPK and that its breakdown voltage exceeds VOUT. Schottky diodes are recommended. COMP to GND. RCOMP is chosen to set the high-frequency integrator gain for fast-transient response, while CCOMP is chosen to set the integrator zero to maintain loop stability. The second capacitor, CCOMP2, is chosen to cancel the zero introduced by output-capacitance ESR. For optimal performance, choose the components using the following equations: RCOMP = (274/A2 x VIN x VOUT x COUT/(L x IOUT) CCOMP (0.36 x 10 -3 A/) x L/VIN CCOMP2 (0.0036 A/) x RESR x L x IOUT/(VIN x VOUT) For the ceramic output capacitor, where ESR is small, CCOMP2 is optional. Table 1 shows experimentally verified external component values for several applications. The best gauge of correct loop compensation is by inspecting the transient response of the MAX17067. Adjust RCOMP and CCOMP as necessary to obtain optimal transient performance.
Input and Output Capacitor Selection
Low-ESR capacitors are recommended for input bypassing and output filtering. Low-ESR tantalum capacitors are a good compromise between cost and performance. Ceramic capacitors are also a good choice. Avoid standard aluminum electrolytic capacitors. A simple equation to estimate input and outputcapacitor values for a given voltage ripple is as follows: 0.5 x L x IPK 2 C VRIPPLE x VOUT where VRIPPLE is the peak-to-peak ripple voltage on the capacitor.
Soft-Start Capacitor
The soft-start capacitor should be large enough that it does not reach final value before the output has reached regulation. Calculate CSS to be:
VOUT 2 - VIN x VOUT CSS > 21 x 10 -6 x COUT VIN x IINRUSH - IOUT x VOUT
Output Voltage
The MAX17067 operates with an adjustable output from VIN to 20V. Connect a resistor voltage-divider to FB (see the Typical Operating Circuit) from the output to GND. Select the resistor values as follows: V R1 = R2 OUT - 1 VFB where VFB, the boost-regulator feedback set point, is 1.24V. Since the input bias current into FB is typically zero, R2 can have a value up to 100k without sacrificing accuracy. Connect the resistor-divider as close to the IC as possible.
where: COUT = total output capacitance including any bypass capacitor on the output bus VOUT = maximum output voltage IINRUSH = peak inrush current allowed IOUT = maximum output current during power-up stage VIN = minimum input voltage The load must wait for the soft-start cycle to finish before drawing a significant amount of load current. The duration after which the load can begin to draw maximum load current is: tMAX = 2.5 x 105 CSS
Loop Compensation
The voltage feedback loop needs proper compensation to prevent excessive output ripple and poor efficiency caused by instability. This is done by connecting a resistor (R COMP ) and capacitor (C COMP ) in series from COMP to GND, and another capacitor (CCOMP2) from
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Low-Noise Step-Up DC-DC Converter
Application Circuits 1-Cell to 3.3V SEPIC Power Supply
Figure 3 shows the MAX17067 in a single-ended primary inductance converter (SEPIC) topology. This topology is useful when the input voltage can be either higher or lower than the output voltage, such as when converting a single lithium-ion (Li+) cell to a 3.3V output. L1A and L1B are two windings on a single inductor. The coupling capacitor between these two windings must be a lowESR type to achieve maximum efficiency, and must also be able to handle high ripple currents. Ceramic capacitors are best for this application. The circuit in Figure 3 provides 400mA output current at 3.3V output when operating with an input voltage from +2.6V to +4.0V.
MAX17067
VIN 2.6V TO 4.0V L1A 5.3H IN
SHDN
C1 10F 10V C2 10F
D1
LX
VOUT 3.3V
MAX17067
FREQ GND SS 0.027F CC
FB
L1B 5.3H
COUT 22F 20V
AMLCD Application Figure 4 shows a power supply for active matrix (TFTLCD) flat-panel displays. Output-voltage transient performance is a function of the load characteristic. Add or remove output capacitance (and recalculate compensation-network component values) as necessary to meet transient performance. Regulation performance for secondary outputs (VGOFF and VGON) depends on the load characteristics of all three outputs.
D4 3 2 C9 0.1F
R2 605k CCOMP2 RCOMP CCOMP
R1 1M
L1 = CTX8-1P COUT = TPSD226025R0200
Figure 3. MAX17067 in a SEPIC Configuration
C11 0.1F 3 1 C10 0.1F D3 3 2 C12 1F C13 1F D2 2 VGON +27V
VGOFF -9V C14 4.7F
1
VIN 2.6V TO 4.0V
L1 3.3H 6 R3 10 C4 1F R6 100k 3 5
1
D1
VOUT +9V/250mA C7 10F 25V
C1 10F 10V
IN U1
MAX17067
LX
C15 27nF
4 SHDN GND 7 FREQ 8 SS 2 FB COMP 1 R5 121k C5 620pF C6 OPEN
R1 274k
R2 44.2k
Figure 4. Multiple-Output, Low-Profile (1.2mm max) TFT-LCD Power Supply
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Low-Noise Step-Up DC-DC Converter MAX17067
Layout Procedure
Good PCB layout and routing are required in high-frequency switching power supplies to achieve good regulation, high efficiency, and stability. It is strongly recommended that the evaluation kit PCB layouts be followed as closely as possible. Place power components as close together as possible, keeping their traces short, direct, and wide. Avoid interconnecting the ground pins of the power components using vias through an internal ground plane. Instead, keep the power components close together and route them in a star ground configuration using component-side copper, then connect the star ground to internal ground using multiple vias.
Chip Information
TRANSISTOR COUNT: 3657
12
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Low-Noise Step-Up DC-DC Converter MAX17067
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.)
8LUMAXD.EPS
MAX17067
4X S
8
8
INCHES DIM A A1 A2 b MIN 0.002 0.030 MAX 0.043 0.006 0.037
MILLIMETERS MAX MIN 0.05 0.75 1.10 0.15 0.95
O0.500.1
E
H
0.60.1
c D e E H L
1
1
0.60.1
S
D
BOTTOM VIEW
0.010 0.014 0.005 0.007 0.116 0.120 0.0256 BSC 0.116 0.120 0.188 0.198 0.016 0.026 6 0 0.0207 BSC
0.25 0.36 0.13 0.18 2.95 3.05 0.65 BSC 2.95 3.05 5.03 4.78 0.66 0.41 0 6 0.5250 BSC
TOP VIEW
A2
A1
A
c e b L
SIDE VIEW
FRONT VIEW
PROPRIETARY INFORMATION TITLE:
PACKAGE OUTLINE, 8L uMAX/uSOP
APPROVAL DOCUMENT CONTROL NO. REV.
21-0036
1 1
J
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.
13 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2008 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.

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