19-1563; Rev 0; 1/00 NUAL KIT MA ATION EET H S A EVALU T WS DA FOLLO Low-Noise Step-Up DC-DC Converter Features ♦ 90% Efficiency ♦ Adjustable Output from VIN to 12V ♦ 1.6A, 0.21Ω, 14V Power MOSFET ♦ +2.6V to +5.5V Input Range ♦ Pin-Selectable 640kHz or 1.2MHz Switching Frequency ♦ 0.1µA Shutdown Current ♦ Programmable Soft-Start ♦ Small 8-Pin µMAX Package Applications LCD Displays Ordering Information PART PCMCIA Cards MAX1790EUA TEMP. RANGE PIN-PACKAGE -40°C to +85°C 8 µMAX Portable Applications Hand-Held Devices Typical Operating Circuit Pin Configuration VIN 2.6V TO 5V TOP VIEW COMP 1 IN ON/OFF LX SHDN 8 SS 7 FREQ 3 6 IN GND 4 5 LX VOUT FB 2 MAX1790 SHDN MAX1790 FREQ GND SS µMAX FB COMP ________________________________________________________________ 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 1-800-835-8769. MAX1790 General Description The MAX1790 boost converter incorporates high-performance (at 1.2MHz), current-mode, fixed-frequency, pulsewidth modulation (PWM) circuitry with a built-in 0.21Ω N-channel MOSFET to provide a highly efficient regulator with fast response. High switching frequency (640kHz or 1.2MHz selectable) allows 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 12V from an input as low as 2.6V. Soft-start is programmed with an external capacitor, which sets the input current ramp rate. In shutdown mode, current consumption is reduced to 0.1µA. The MAX1790 is available in a space-saving 8-pin µMAX package. The ultra-small package and high switching frequency allow the total solution to be less than 1.1mm high. MAX1790 Low-Noise Step-Up DC-DC Converter ABSOLUTE MAXIMUM RATINGS LX to GND ..............................................................-0.3V to +14V IN, SHDN, FREQ, FB to GND ...................................-0.3V to +6V SS, COMP to GND .......................................-0.3V to (VIN + 0.3V) RMS LX Pin Current ..............................................................1.2A Continuous Power Dissipation (TA = +70°C) 8-Pin µMAX (derate 4.1mW/°C above +70°C) ...........330mW Operating Temperature Range MAX1790EUA ................................................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+300°C 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 = GND, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER Input Supply Range VIN Undervoltage Lockout SYMBOL CONDITIONS UVLO MIN TYP MAX UNITS 5.5 V 2.38 2.52 V 0.18 0.35 2 5 0.1 10 1.24 1.258 V 0 40 nA 0.05 0.15 %/V 70 140 700 240 µmhos V/V 540 1000 79 640 1220 85 84 740 1500 92 1.2 0.3 1.6 0.21 0.01 0.45 2.3 0.5 20 0.65 A Ω µA V/A 1.5 4 100 7 Ω µA 2.6 VIN VIN rising, typical hysteresis is 40mV, LX remains off below this level 2.25 VFB = 1.3V, not switching Quiescent Current IIN Shutdown Supply Current IIN SHDN = GND Feedback Voltage VFB Level to produce VCOMP = 1.24V FB Input Bias Current IFB VFB = 1.24V VFB = 1.0V, switching mA µA ERROR AMPLIFIER Feedback-Voltage Line Regulation Transconductance Voltage Gain OSCILLATOR Frequency Maximum Duty Cycle N-CHANNEL SWITCH Current Limit (Note 1) On-Resistance Leakage Current Current-Sense Transresistance SOFT-START Reset Switch Resistance Charge Current CONTROL INPUTS Input Low Voltage Input High Voltage Hysteresis FREQ Pull-Down Current SHDN Input Current 2 1.222 Level to produce VCOMP = 1.24V, 2.6V < VIN < 5.5V gm AV fOSC DC ILIM RON ILXOFF RCS ∆I = 5µA FREQ = GND FREQ = IN FREQ = GND FREQ = IN VFB = 1V, duty cycle = 65% ILX = 1.2A VLX = 12V VSS = 1.2V VIL VIH IFREQ I SHDN SHDN, FREQ; VIN = 2.6V to 5.5V SHDN, FREQ; VIN = 2.6V to 5.5V SHDN, FREQ 0.3 · VIN 0.7 · VIN 1.8 0.1 · VIN 5 0.001 _______________________________________________________________________________________ 9 1 kHz % V V V µA µA Low-Noise Step-Up DC-DC Converter (VIN = SHDN = 3V, FREQ = GND, TA = -40°C to +85°C, unless otherwise noted.) (Note 2) PARAMETER Input Supply Range VIN Undervoltage Lockout SYMBOL CONDITIONS VIN UVLO VIN rising, typical hysteresis is 40mV, LX remains off below this level MIN MAX UNITS 2.6 5.5 V 2.25 2.52 V VFB = 1.3V, not switching Quiescent Current IIN Shutdown Supply Current IIN SHDN = GND Feedback Voltage VFB Level to produce VCOMP = 1.24V FB Input Bias Current IFB VFB = 1.24V VFB = 1.0V, switching TYP 0.2 0.35 4 5 10 mA µA ERROR AMPLIFIER Feedback-Voltage Line Regulation 1.215 Level to produce VCOMP = 1.24V, 2.6V < VIN < 5.5V 1.26 V 40 nA 0.15 %/V 260 µmhos ∆I = 5µA 70 FREQ = GND 490 770 FREQ = IN 900 1500 DC FREQ = GND 78 92 Current Limit ILIM VFB = 1V, duty cycle = 65% 1.2 On-Resistance RON ILX = 1.2A Current-Sense Transresistance RCS Transconductance gm OSCILLATOR Frequency fOSC Maximum Duty Cycle kHz % N-CHANNEL SWITCH 2.3 A 0.5 Ω 0.65 V/A 0.3 · VIN V 0.3 CONTROL INPUTS Input Low Voltage VIL SHDN, FREQ, VIN = 2.6V to 5.5V Input High Voltage VIH SHDN, FREQ, VIN = 2.6V to 5.5V 0.7 · VIN V Note 1: Current limit varies with duty cycle due to slope compensation. See the Output Current Capability section. Note 2: Specifications to -40°C are guaranteed by design and not production tested. _______________________________________________________________________________________ 3 MAX1790 ELECTRICAL CHARACTERISTICS Typical Operating Characteristics (Circuit of Figure 1, VIN = 3.3V, fOSC = 640kHz, TA = +25°C, unless otherwise noted.) 75 fOSC = 1.2MHz L = 2.7µH 70 65 fOSC = 1.2MHz L = 5.4µH 75 70 65 50 1 10 100 VIN = 3.3V VOUT = 12V 55 50 1 1000 0.6 10 100 1 0.4 fOSC = 1.2MHz 0.3 0.2 LOAD-TRANSIENT RESPONSE TA = +85°C 200mA CH1 11.95 10mA 11.90 0 1000 RCOMP = 120kΩ CCOMP = 1200pF CCOMP2 = 56pF TA = +25°C 11.85 TA = -40°C 11.80 CH2 11.75 CH3 11.65 VOUT = 12V 100 OUTPUT VOLTAGE vs. OUTPUT CURRENT 11.70 0.1 10 OUTPUT CURRENT (mA) 12.05 OUTPUT VOLTAGE (V) 0.5 VIN = 5V VOUT = 12V 50 12.00 fOSC = 640kHz MAX1790-03 65 1000 12.10 MAX1790-04 0.7 70 OUTPUT CURRENT (mA) OUTPUT CURRENT (mA) NO-LOAD SUPPLY CURRENT vs. INPUT VOLTAGE fOSC = 1.2MHz L = 5.4µH 75 55 MAX1790-05 VIN = 3.3V VOUT = 5V 55 fOSC = 640kHz L = 10µH 60 60 60 fOSC = 640kHz 11.60 2.5 3.0 3.5 4.0 4.5 INPUT VOLTAGE (V) 4 85 80 MAX1790-06 80 80 90 fOSC = 640kHz L = 10µH EFFICIENCY (%) 85 95 MAX1790-02 90 85 EFFICIENCY (%) EFFICIENCY (%) 95 MAX1790-01 fOSC = 640kHz L = 5.4µH 90 EFFICIENCY vs. OUTPUT CURRENT EFFICIENCY vs. OUTPUT CURRENT EFFICIENCY vs. OUTPUT CURRENT 95 NO-LOAD SUPPLY CURRENT (mA) MAX1790 Low-Noise Step-Up DC-DC Converter 5.0 5.5 0 20 40 60 80 100 120 140 160 180 200 OUTPUT CURRENT (mA) 100µs/div CH1 = LOAD CURRENT, 100mA/div CH2 = OUTPUT VOLTAGE, AC-COUPLED, 200mV/div CH3 = INDUCTOR CURRENT, 1A/div VIN = 3V VOUT = 12V, fOSC = 640kHz, COUT = 33µF + 0.1µF _______________________________________________________________________________________ Low-Noise Step-Up DC-DC Converter MAX1790-09 MAX1790-08 RCOMP = 62kΩ CCOMP = 820pF CCOMP2 = 56pF MAX1790-07 500mA CH1 20mA STARTUP WAVEFORM WITH SOFT-START STARTUP WAVEFORM WITHOUT SOFT-START LOAD-TRANSIENT RESPONSE CH1 CH1 CH2 CH2 CH3 CH3 CH2 CH3 1ms/div 100µs/div CH1 = SHDN, 5V/div CH2 = OUTPUT VOLTAGE, 5V/div CH3 = INDUCTOR CURRENT, 200mA/div VOUT = 12V, IOUT = 10mA, fOSC = 640kHz, CSS = 0.027µF, COUT = 33µF CH1 = SHDN, 5V/div CH2 = OUTPUT VOLTAGE, 5V/div CH3 = INDUCTOR CURRENT, 1A/div VIN = 3.3V, VOUT = 12V, IOUT = 10mA, fOSC = 640kHz NO SOFT-START CAPACITOR, COUT = 33µF STARTUP WAVEFORM WITH SOFT-START MAXIMUM OUTPUT CURRENT vs. INPUT VOLTAGE CH1 CH1 CH2 CH2 CH3 CH3 1800 MAXIMUM OUTPUT CURRENT (mA) MAX1790-11 MAX1790-10 SWITCHING WAVEFORM MAX1790-12 100µs/div CH1 = LOAD CURRENT, 500mA/div CH2 = OUTPUT VOLTAGE, AC-COUPLED, 200mV/div CH3 = INDUCTOR CURRENT, 1A/div VOUT = 5V, fOSC = 640kHz, COUT = 47µF + 0.1µF 1600 1400 VOUT = 5V 1200 1000 800 600 VOUT = 12V 400 200 fOSC = 640kHz 0 2ms/div CH1 = SHDN, 5V/div CH2 = VOUT, 5V/div CH3 = INDUCTOR CURRENT, 500mA/div VOUT = 12V, IOUT = 200mA, fOSC = 640kHz, CSS = 0.027µF 500ns/div CH1 = LX SWITCHING WAVEFORM, 5V/div CH2 = OUTPUT VOLTAGE, AC-COUPLED, 200mV/div CH3 = INDUCTOR CURRENT, 1A/div VOUT = 12V, IOUT = 200mA, fOSC = 640kHz, L = 10µH; COUT = 33µF + 0.1µF 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 INPUT VOLTAGE (V) _______________________________________________________________________________________ 5 MAX1790 Typical Operating Characteristics (continued) (Circuit of Figure 1, VIN = 3.3V, fOSC = 640kHz, TA = +25°C, unless otherwise noted.) Low-Noise Step-Up DC-DC Converter MAX1790 Pin Description PIN NAME 1 COMP 2 FB 3 SHDN Shutdown Control Input. Drive SHDN low to turn off the MAX1790. 4 GND Ground 5 LX Switch Pin. Connect the inductor/catch diode to LX and minimize the trace area for lowest EMI. 6 IN Supply Pin. Bypass IN with at least a 1µF ceramic capacitor directly to GND. 7 FREQ 8 SS 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. 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 5µA pull-down 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 4µA. Full current limit is reached after t = 2.5 · 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. Detailed Description The MAX1790 is a highly efficient power supply that employs a current-mode, fixed-frequency pulse-width modulation (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 MAX1790 to “skip” cycles to prevent overcharging the output voltage. In this region of operation, the inductor ramps up to a peak value of about 50mA, discharges to the output, and waits until another pulse is needed again. VIN 2.6V TO 5.5V CIN L 6.3V IN ON/OFF D1 MBRS130LT1 0.1µF* VIN MAX1790 COUT FREQ GND 640kHz SS 0.027µF FB R1 COMP R2 CCOMP2 RCOMP CCOMP Figure 1. Typical Application Circuit 6 VOUT LX SHDN 1.2MHz C1 10µF 10V 10µF _______________________________________________________________________________________ * OPTIONAL Low-Noise Step-Up DC-DC Converter 4µA MAX1790 ENABLE COMPARATOR SHDN IN BIAS ENABLE COMP ERROR AMPLIFIER SOFTSTART SS ERROR COMPARATOR FB ∞ LX CONTROL AND DRIVER LOGIC 1.24V N CLOCK GND OSCILLATOR FREQ SLOPE COMPENSATION Σ CURRENT SENSE 5µA MAX1790 Figure 2. Functional Diagram Output Current Capability The output current capability of the MAX1790 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 · (1.26 - 0.4 · Duty) 0.5 · Duty · VIN / (fOSC · L)] · η · VIN / VOUT where: ILIM = current limit specified at 65% (see Electrical Characteristics) Duty = duty cycle = (VOUT - VIN + VDIODE) / (VOUT - ILIM · RON + VDIODE) VDIODE = catch diode forward voltage at ILIM η =conversion efficiency, 85% nominal cycle is completed. When the shutdown pin is taken low, the soft-start capacitor is discharged to ground. Frequency Selection The MAX1790’s frequency can be user selected to operate at either 640kHz or 1.2MHz. Tie FREQ to GND for 640kHz operation. For a 1.2MHz switching frequency, tie FREQ to IN. This allows the use of small, minimum-height external components while maintaining low output noise. FREQ has an internal pull-down, allowing the user the option of leaving FREQ unconnected for 640kHz operation. Shutdown Soft-Start The MAX1790 shuts down to reduce the supply current to 0.1µA 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 via the external inductor and catch diode. The MAX1790 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 4µA (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 Boost DC-DC converters using the MAX1790 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. Applications Information _______________________________________________________________________________________ 7 MAX1790 Low-Noise Step-Up DC-DC Converter Table 1. Component Selection VIN (V) VOUT (V) fOSC (Hz) L (µH) COUT (µF) RCOMP (kΩ) CCOMP (pF) CCOMP2 (pF) TYPICAL IOUT(MAX) (mA) 3.3 12 640k 10 (Sumida CDRH5D18-100NC) 33 tantalum (AVX TPSD336020R0200) 120 1200 33 250 3.3 12 1.2M 5.4 (Sumida CDRH5D18-5R4NC) 33 tantalum (AVX TPSD336020R0200) 180 650 20 250 3.3 5 640k 5.4 (Sumida CDRH5D18-5R4NC) 47 tantalum (6TPA47M) 62 820 56 800 3.3 5 1.2M 2.7 (Sumida CDRH4018-2R7) 47 tantalum (6TPA47M) 91 390 33 800 Table 2. Component Suppliers SUPPLIER PHONE FAX Coilcraft 847-639-6400 847-639-1469 Coiltronics 561-241-7876 561-241-9339 Sumida USA 847-956-0666 847-956-0702 Toko 847-297-0070 847-699-1194 AVX 803-946-0690 803-626-3123 Kemet 408-986-0424 408-986-1442 Sanyo 619-661-6835 619-661-1055 Taiyo Yuden 408-573-4150 408-573-4159 516-435-1110 516-435-1824 Inductors Capacitors Diodes Central Semiconductor The equation used here includes a constant LIR, which is the ratio of the inductor peak-peak AC current to maximum average DC inductor current. A good compromise between size of the inductor and loss and output ripple is to choose an LIR of 0.3 to 0.5. The peak inductor current is then given by: ( IOUT(MAX) ⋅ VOUT IPK = η ⋅ VIN(MIN) ) ⋅ 1 + LIR 2 The inductance value is then given by: L = International Rectifier 310-322-3331 310-322-3332 Motorola 602-303-5454 602-994-6430 Nihon 847-843-7500 847-843-2798 Zetex 516-543-7100 516-864-7630 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. Inductor Selection Inductor selection depends on input voltage, output voltage, maximum current, switching frequency, size, and availability of inductor values. Other factors can include efficiency and ripple voltage. Inductors are 8 specified by their inductance (L), peak current (IPK), and resistance (Lr). The following boost-circuit equations are useful in choosing the inductor values based on the application. They allow the trading of peak current and inductor value while allowing for consideration of component availability and cost. (VIN(MIN) )2 ⋅ η ⋅ (VOUT − VIN(MIN) ) VOUT 2 ⋅ LIR ⋅ IOUT(MAX) ⋅ fOSC Considering the typical application circuit, the maximum DC load current (IOUT(MAX)) is 500mA with a 5V output. The inductance value is then chosen to be 5.4µH, based on the above equations and using 85% efficiency and a 640kHz operating frequency. The inductor saturation current rating should be greater than I PK . The resistance of the inductor windings should be less than 0.5Ω. To minimize radiated noise in sensitive applications, use a shielded inductor. 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 _______________________________________________________________________________________ Low-Noise Step-Up DC-DC Converter 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. Sanyo OS-CON types are also recommended for their low ESR. Avoid standard aluminum electrolytic capacitors. A simple equation to estimate input and output capacitor values for a given voltage ripple is as follows: L ⋅ VRIPPLE ⋅ 0.5 C≥ ⋅ 2 IPK VOUT where VRIPPLE is the peak-to-peak ripple voltage on the capacitor. Output Voltage The MAX1790 operates with an adjustable output from VIN to 12V. Connect a resistor voltage divider to FB (Typical Operating Circuit) from the output to GND. Select the resistor values as follows: V R1 = R2 OUT − 1 V FB where VFB, the boost-regulator feedback set point, is 1.24V. Since the input bias current into FB is typically 0, R2 can have a value up to 100kΩ without sacrificing accuracy. Connect the resistor-divider as close to the IC as possible. 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 (RCOMP) and capacitor (CCOMP) in series from COMP to GND, and another capacitor (CCOMP2) from 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 ≅ (200Ω / A2) · VOUT2 · COUT / L CCOMP ≅ (0.4 · 10 -3 A / Ω) L / VIN CCOMP2 ≅ (0.005 A2 / Ω) RESR · L / VOUT2 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 MAX1790. Adjust RCOMP and CCOMP as necessary to obtain optimal transient performance. 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: CSS > 21 ⋅ 10−6 VOUT 2 − VIN ⋅ VOUT V I − I V ⋅ ⋅ INRUSH OUT OUT IN ⋅ COUT 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 = 6.77 · 105 CSS Application Circuits 1-Cell to 3.3V SEPIC Power Supply Figure 3 shows the MAX1790 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 +5.5V. 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 _______________________________________________________________________________________ 9 MAX1790 breakdown voltage exceeds VOUT. Schottky diodes are recommended. MAX1790 Low-Noise Step-Up DC-DC Converter for secondary outputs (V2 and V3) depends on the load characteristics of all three outputs. VIN 2.6V TO 5.5V Layout Procedure Good PC board layout and routing are required in highfrequency switching power supplies to achieve good regulation, high efficiency, and stability. It is strongly recommended that the evaluation kit PC board 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 coper, then connect the star ground to internal ground using multiple vias. Chip Information C1 10µF 10V L1A 5.3µH C2 10µF IN LX SHDN L1B 5.3µH MAX1790 FREQ VOUT 3.3V COUT 22µF 20V GND SS 0.027µF FB R1 1M CC R2 605k TRANSISTOR COUNT: 1012 CCOMP2 56pF RCOMP 22k CCOMP 330pF L1 = CTX8-1P COUT = TPSD226025R0200 Figure 3. MAX1790 in a SEPIC Configuration 10 D1 ______________________________________________________________________________________ Low-Noise Step-Up DC-DC Converter 0.1µF D3 3.3µF D4 0.1µF MAX1790 D2 V2 +26V 5mA V3 -9V 10mA 1µF 1µF 1µF D1 3.0V TO 3.6V C1 L1 0.47µF C2 C3 C4 V1 9V 150mA 274k LX FB IN MAX1790 FREQ 44.2k SHDN GND COMP 150k SS 27nF 18pF 470pF C1, C2, C3, C4: TAIYO YUDEN LMK325BJ335MD (3.3µF, 10V) D1: ZETEX ZHCS1000 (20V, 1A, SCHOTTKY) OR MOTOROLA MBRM120ET3 D2, D3, D4: ZETEX BAT54S (30V, 200mA, SCHOTTKY) L1: SUMIDA CLQ4D10-6R8 (6.8µH, 0.8A) OR SUMITOMO CXLM120-6R8 Figure 4. Multiple-Output, Low-Profile (1.2mm max) TFT LCD Power Supply ______________________________________________________________________________________ 11 Low-Noise Step-Up DC-DC Converter 8LUMAXD.EPS MAX1790 Package Information 12 ______________________________________________________________________________________