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19-1563; Rev 0; 1/00
NUAL KIT MA ATION ET EVALU TA SHE WS DA FOLLO
Low-Noise Step-Up DC-DC Converter
Features
o 90% Efficiency o Adjustable Output from VIN to 12V o 1.6A, 0.21, 14V Power MOSFET o +2.6V to +5.5V Input Range o Pin-Selectable 640kHz or 1.2MHz Switching Frequency o 0.1A Shutdown Current o Programmable Soft-Start o Small 8-Pin MAX Package
General Description
The MAX1790 boost converter incorporates high-performance (at 1.2MHz), current-mode, fixed-frequency, pulsewidth modulation (PWM) circuitry with a built-in 0.21 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 0.1A. The MAX1790 is available in a space-saving 8-pin MAX package. The ultra-small package and high switching frequency allow the total solution to be less than 1.1mm high.
MAX1790
Applications
LCD Displays PCMCIA Cards Portable Applications Hand-Held Devices
PART MAX1790EUA
Ordering Information
TEMP. RANGE -40C to +85C PIN-PACKAGE 8 MAX
Typical Operating Circuit
VIN 2.6V TO 5V
Pin Configuration
TOP VIEW
IN ON/OFF
SHDN
COMP 1
VOUT LX
8 7
SS FREQ IN LX
FB SHDN
2
MAX1790
3 6 5
MAX1790 FREQ GND
GND 4
MAX
SS COMP
FB
________________________________________________________________ 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.
Low-Noise Step-Up DC-DC Converter MAX1790
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 = +70C) 8-Pin MAX (derate 4.1mW/C above +70C) ...........330mW Operating Temperature Range MAX1790EUA ................................................-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 = GND, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER Input Supply Range 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 (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 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 70 1.222 1.24 0 0.05 140 700 640 1220 85 84 1.6 0.21 0.01 0.45 1.258 40 0.15 240 V nA %/V mhos V/V SYMBOL VIN UVLO IIN IIN VIN rising, typical hysteresis is 40mV, LX remains off below this level VFB = 1.3V, not switching VFB = 1.0V, switching SHDN = GND CONDITIONS MIN 2.6 2.25 2.38 0.18 2 0.1 TYP MAX 5.5 2.52 0.35 5 10 UNITS V V mA A
fOSC DC
FREQ = GND FREQ = IN FREQ = GND FREQ = IN VFB = 1V, duty cycle = 65% ILX = 1.2A VLX = 12V
540 1000 79
740 1500 92
kHz %
ILIM RON ILXOFF RCS
1.2
0.3
2.3 0.5 20 0.65 100 7 0.3 * VIN
A A V/A A V V V A A
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
1.5
4
0.7 * VIN 1.8 0.1 * VIN 5 0.001 9 1
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Low-Noise Step-Up DC-DC Converter
ELECTRICAL CHARACTERISTICS
(VIN = SHDN = 3V, FREQ = GND, TA = -40C to +85C, unless otherwise noted.) (Note 2) PARAMETER Input Supply Range VIN Undervoltage Lockout Quiescent Current Shutdown Supply Current ERROR AMPLIFIER Feedback Voltage FB Input Bias Current Feedback-Voltage Line Regulation Transconductance OSCILLATOR Frequency Maximum Duty Cycle N-CHANNEL SWITCH Current Limit On-Resistance Current-Sense Transresistance CONTROL INPUTS Input Low Voltage Input High Voltage VIL VIH SHDN, FREQ, VIN = 2.6V to 5.5V SHDN, FREQ, VIN = 2.6V to 5.5V 0.7 * VIN 0.3 * VIN V V ILIM RON RCS VFB = 1V, duty cycle = 65% ILX = 1.2A 0.3 1.2 2.3 0.5 0.65 A V/A fOSC DC FREQ = GND FREQ = IN FREQ = GND 490 900 78 770 1500 92 kHz % gm VFB IFB Level to produce VCOMP = 1.24V VFB = 1.24V Level to produce VCOMP = 1.24V, 2.6V < VIN < 5.5V I = 5A 70 1.215 1.26 40 0.15 260 V nA %/V mhos SYMBOL VIN UVLO IIN IIN VIN rising, typical hysteresis is 40mV, LX remains off below this level VFB = 1.3V, not switching VFB = 1.0V, switching SHDN = GND CONDITIONS MIN 2.6 2.25 0.2 4 TYP MAX 5.5 2.52 0.35 5 10 UNITS V V mA A
MAX1790
Note 1: Current limit varies with duty cycle due to slope compensation. See the Output Current Capability section. Note 2: Specifications to -40C are guaranteed by design and not production tested.
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Low-Noise Step-Up DC-DC Converter MAX1790
Typical Operating Characteristics
(Circuit of Figure 1, VIN = 3.3V, fOSC = 640kHz, TA = +25C, unless otherwise noted.)
EFFICIENCY vs. OUTPUT CURRENT
90 85 EFFICIENCY (%) EFFICIENCY (%) 80 75 70 65 60 55 50 1 10 100 VIN = 3.3V VOUT = 5V 1000 fOSC = 1.2MHz L = 2.7H fOSC = 640kHz L = 5.4H
MAX1790-01
EFFICIENCY vs. OUTPUT CURRENT
MAX1790-02
EFFICIENCY vs. OUTPUT CURRENT
90 85 EFFICIENCY (%) 80 75 70 65 60 fOSC = 640kHz L = 10H fOSC = 1.2MHz L = 5.4H
MAX1790-03
95
95 90 85 80 75 70 65 60 55 50 1 10 100 VIN = 3.3V VOUT = 12V fOSC = 640kHz L = 10H fOSC = 1.2MHz L = 5.4H
95
55 50 1 10 100 OUTPUT CURRENT (mA)
VIN = 5V VOUT = 12V 1000
1000
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
NO-LOAD SUPPLY CURRENT vs. INPUT VOLTAGE
MAX1790-04
OUTPUT VOLTAGE vs. OUTPUT CURRENT
MAX1790-05
LOAD-TRANSIENT RESPONSE
200mA CH1 10mA RCOMP = 120k CCOMP = 1200pF CCOMP2 = 56pF
MAX1790-06
0.7 NO-LOAD SUPPLY CURRENT (mA) 0.6 0.5 0.4 0.3 0.2 0.1 0 2.5 3.0 3.5 4.0 4.5 INPUT VOLTAGE (V) VOUT = 12V 5.0 fOSC = 1.2MHz fOSC = 640kHz
12.10 12.05 12.00 OUTPUT VOLTAGE (V) 11.95 11.90 11.85 11.80 11.75 11.70 11.65 11.60 fOSC = 640kHz 0 TA = +25C TA = -40C TA = +85C
CH2
CH3
5.5
20 40 60 80 100 120 140 160 180 200 OUTPUT CURRENT (mA)
100s/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 = 33F + 0.1F
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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.)
STARTUP WAVEFORM WITHOUT SOFT-START
MAX1790-07 MAX1790-08
MAX1790
LOAD-TRANSIENT RESPONSE
500mA CH1 20mA
STARTUP WAVEFORM WITH SOFT-START
MAX1790-09
RCOMP = 62k CCOMP = 820pF CCOMP2 = 56pF
CH1
CH1
CH2 CH2 CH2
CH3
CH3
CH3
100s/div CH1 = LOAD CURRENT, 500mA/div CH2 = OUTPUT VOLTAGE, AC-COUPLED, 200mV/div CH3 = INDUCTOR CURRENT, 1A/div VOUT = 5V, fOSC = 640kHz, COUT = 47F + 0.1F
100s/div 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 = 33F
1ms/div CH1 = SHDN, 5V/div CH2 = OUTPUT VOLTAGE, 5V/div CH3 = INDUCTOR CURRENT, 200mA/div VOUT = 12V, IOUT = 10mA, fOSC = 640kHz, CSS = 0.027F, COUT = 33F
STARTUP WAVEFORM WITH SOFT-START
MAX1790-10
SWITCHING WAVEFORM
MAX1790-11
MAXIMUM OUTPUT CURRENT vs. INPUT VOLTAGE
1600 1400 1200 1000 800 600 400 200 fOSC = 640kHz 0 VOUT = 12V VOUT = 5V
MAX1790-12
1800 MAXIMUM OUTPUT CURRENT (mA)
CH1 CH1 CH2 CH2 CH3 CH3 2ms/div CH1 = SHDN, 5V/div CH2 = VOUT, 5V/div CH3 = INDUCTOR CURRENT, 500mA/div VOUT = 12V, IOUT = 200mA, fOSC = 640kHz, CSS = 0.027F 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 = 10H; COUT = 33F + 0.1F
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)
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Low-Noise Step-Up DC-DC Converter MAX1790
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. Shutdown Control Input. Drive SHDN low to turn off the MAX1790. 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 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 4A. 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.
8
SS
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 C1 10F 10V 6.3V LX D1 MBRS130LT1 0.1F*
L
10F
IN ON/OFF VIN 1.2MHz SHDN
VOUT
MAX1790
FREQ
COUT
640kHz
GND
SS 0.027F COMP
FB R1 R2
CCOMP2
RCOMP CCOMP * OPTIONAL
Figure 1. Typical Application Circuit
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Low-Noise Step-Up DC-DC Converter MAX1790
SHDN BIAS
ENABLE COMPARATOR ENABLE 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
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)] * * 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 =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
The MAX1790 shuts down to reduce the supply current to 0.1A 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.
Soft-Start
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 4A (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
Applications Information
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.
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Low-Noise Step-Up DC-DC Converter MAX1790
Table 1. Component Selection
VIN (V) 3.3 3.3 3.3 3.3 VOUT (V) 12 12 5 5 fOSC (Hz) 640k 1.2M 640k 1.2M L (H) 10 (Sumida CDRH5D18-100NC) 5.4 (Sumida CDRH5D18-5R4NC) 5.4 (Sumida CDRH5D18-5R4NC) 2.7 (Sumida CDRH4018-2R7) COUT (F) 33 tantalum (AVX TPSD336020R0200) 33 tantalum (AVX TPSD336020R0200) 47 tantalum (6TPA47M) 47 tantalum (6TPA47M) RCOMP (k) 120 180 62 91 CCOMP (pF) 1200 650 820 390 CCOMP2 (pF) 33 20 56 33 TYPICAL IOUT(MAX) (mA) 250 250 800 800
Table 2. Component Suppliers
SUPPLIER Inductors Coilcraft Coiltronics Sumida USA Toko Capacitors AVX Kemet Sanyo Taiyo Yuden Diodes Central Semiconductor International Rectifier Motorola Nihon Zetex 516-435-1110 310-322-3331 602-303-5454 847-843-7500 516-543-7100 516-435-1824 803-946-0690 408-986-0424 619-661-6835 408-573-4150 803-626-3123 408-986-1442 619-661-1055 408-573-4159 847-639-6400 561-241-7876 847-956-0666 847-297-0070 847-639-1469 561-241-9339 847-956-0702 847-699-1194 PHONE FAX
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. 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 = VIN(MIN)
(
) 1 + LIR
2
The inductance value is then given by: L=
310-322-3332 602-994-6430 847-843-2798 516-864-7630
(VIN(MIN) )2 (VOUT - VIN(MIN) )
VOUT
2
LIR
IOUT(MAX)
fOSC
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.
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 5.4H, 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 0.5. To minimize radiated noise in sensitive applications, use a shielded inductor.
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
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
breakdown voltage exceeds VOUT. Schottky diodes are recommended. 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.
MAX1790
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: 0.5 C
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
L

2 IPK VOUT
COUT
VOUT 2 - VIN VOUT VIN IINRUSH - IOUT VOUT
VRIPPLE
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 VFB 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 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 = 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
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 (200 / A2) * VOUT2 * COUT / L CCOMP (0.4 * 10 -3 A / ) L / VIN CCOMP2 (0.005 A2 / ) RESR * L / VOUT2
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Low-Noise Step-Up DC-DC Converter MAX1790
for secondary outputs (V2 and V3) depends on the load characteristics of all three outputs.
VIN 2.6V TO 5.5V C1 10F 10V C2 10F LX
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.
L1A 5.3H IN
SHDN
D1
VOUT 3.3V
MAX1790
FREQ GND
L1B 5.3H
COUT 22F 20V
SS 0.027F CC
FB
Chip Information
TRANSISTOR COUNT: 1012
R2 605k CCOMP2 56pF RCOMP 22k CCOMP 330pF
R1 1M
L1 = CTX8-1P COUT = TPSD226025R0200
Figure 3. MAX1790 in a SEPIC Configuration
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Low-Noise Step-Up DC-DC Converter MAX1790
V2 +26V 5mA 1F 1F
D2
0.1F 3.3F
D3
0.1F 1F
D4
V3 -9V 10mA
D1
3.0V TO 3.6V C1 0.47F
L1 274k IN
MAX1790
C2 LX FB
C3
C4
V1 9V 150mA
FREQ
SHDN
44.2k
GND
COMP 150k
SS
27nF 18pF C1, C2, C3, C4: TAIYO YUDEN LMK325BJ335MD (3.3F, 10V) D1: ZETEX ZHCS1000 (20V, 1A, SCHOTTKY) OR MOTOROLA MBRM120ET3 D2, D3, D4: ZETEX BAT54S (30V, 200mA, SCHOTTKY) L1: SUMIDA CLQ4D10-6R8 (6.8H, 0.8A) OR SUMITOMO CXLM120-6R8
470pF
Figure 4. Multiple-Output, Low-Profile (1.2mm max) TFT LCD Power Supply
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11
Low-Noise Step-Up DC-DC Converter MAX1790
Package Information
8LUMAXD.EPS
12
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