19-2221; Rev 1; 3/04 1.4MHz SOT23 Current-Mode Step-Up DC-DC Converter Features ♦ >90% Efficiency ♦ Adjustable Output Up to 13V ♦ Guaranteed 12V/120mA Output from 5V Input ♦ 2.6V to 5.5V Input Range ♦ LT1613 Pin Compatible ♦ 0.01µA Shutdown Current ♦ Programmable Soft-Start ♦ Space-Saving 6-Pin SOT23 Package Ordering Information Applications Notebook Computers PART LCD Displays MAX1896EUT-T TEMP RANGE PIN-PACKAGE -40°C to +85°C 6 SOT23-6 PCMCIA Cards Portable Applications Hand-Held Devices Typical Operating Circuit INPUT 2.6V TO 5.5V Pin Configuration TOP VIEW OUTPUT UP TO 13V UP TO 600mA IN LX 1 LX GND 2 MAX1896 6 IN 5 SS 4 SHDN MAX1896 R1 ON OFF SHDN SS FB FB 3 GND R2 SOT23 ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 1 MAX1896 General Description The MAX1896 step-up DC-DC converter incorporates high-performance current-mode, fixed-frequency, pulse-width modulation (PWM) circuitry and an internal 0.7Ω N-channel MOSFET to provide a highly efficient regulator with fast response. High switching frequency (1.4MHz) allows fast loop response and easy filtering with small components. The MAX1896 can produce an output voltage as high as 13V from an input as low as 2.6V. Soft-start is programmable with an external capacitor, which sets the input current ramp rate. In shutdown mode, current consumption is reduced to 0.01µA. The MAX1896 is available in a space-saving 6-pin SOT23 package. The ultra-small package and high switching frequency allow cost and space-efficient implementations. MAX1896 1.4MHz SOT23 Current-Mode Step-Up DC-DC Converter ABSOLUTE MAXIMUM RATINGS LX to GND ..............................................................-0.3V to +14V IN, SHDN, FB to GND...............................................-0.3V to +6V SS to GND ...................................................-0.3V to (VIN + 0.3V) RMS LX Pin Current ..............................................................0.6A Continuous Power Dissipation (TA = +70°C) (Note 1) 6-Pin SOT23 (derate 9.1mW/°C above +70°C)...........727mW Operating Temperature Range ...........................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+300°C Note 1: Thermal properties are specified with product mounted on PC board with one square-inch of copper area and still air. 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 = VSHDN = 3V, FB = GND, SS = open, TA = 0°C to +85°C, unless otherwise noted.) PARAMETER Input Supply Range SYMBOL Output Voltage Adjust Range VOUT VIN Undervoltage Lockout UVLO Quiescent Current CONDITIONS IIN Shutdown Supply Current MIN TYP 2.6 MAX UNITS 5.5 V 13 V 2.4 2.55 V 0.2 0.4 1 5 V SHDN = 0, TA = +25°C 0.01 0.5 V SHDN = 0 0.01 10 1.24 1.25 V 21 80 nA 0.05 0.20 %/V 1800 kHz VIN Circuit of Figure 1 VIN rising, 50mV hysteresis 2.25 VFB = 1.3V, not switching VFB = 1.0V, switching mA µA ERROR AMPLIFIER Feedback Regulation Set Point VFB FB Input Bias Current IFB 1.2 VFB = 1.24V 2.6V < VIN < 5.5V Line Regulation OSCILLATOR Frequency Maximum Duty Cycle fOSC 1000 1400 DC 82 86 0.55 0.8 % POWER SWITCH Current Limit (Note 2) ILIM On-Resistance RON Leakage Current ILXOFF VFB = 1V, duty cycle = 50% VLX = 12V, TA = +25°C A 0.7 1 0.1 1 VLX = 12V 10 Ω µA SOFT-START Reset Switch Resistance VSS = 1.2V Charge Current 1.5 4 100 Ω 7.0 µA CONTROL INPUT Input Low Voltage VIL V SHDN, VIN = 2.6V to 5.5V Input High Voltage VIH V SHDN, VIN = 2.6V to 5.5V SHDN Input Current 2 ISHDN V SHDN = 3V V SHDN = 0 0.3 1.0 V V 25 50 0.01 0.1 _______________________________________________________________________________________ µA 1.4MHz SOT23 Current-Mode Step-Up DC-DC Converter (VIN = VSHDN = 3V, FB = GND, SS = open, TA = -40°C to +85°C, unless otherwise noted.) (Note 3) PARAMETER Input Supply Range SYMBOL CONDITIONS VIN VOUT Circuit of Figure 1 VIN Undervoltage Lockout UVLO VIN rising, 50mV hysteresis. IIN Shutdown Supply Current TYP 2.6 Output Voltage Adjust Range Quiescent Current MIN 2.25 VFB = 1.3V, not switching MAX UNITS 5.5 V 13 V 2.55 V 0.4 VFB = 1.0V, switching 5 V SHDN = 0 10 mA µA ERROR AMPLIFIER Feedback Regulation Set Point VFB FB Input Bias Current IFB 1.2 VFB = 1.24V 2.6V < VIN < 5.5V Line Regulation 1.25 V 80 nA 0.20 %/V 1800 kHz OSCILLATOR Frequency Maximum Duty Cycle fOSC 1000 DC 82 % POWER SWITCH Current Limit (Note 2) ILIM On-Resistance Leakage Current RON ILXOFF VFB = 1V, duty cycle = 50% 0.55 VLX = 12V SOFT-START Reset Switch Resistance Charge Current VSS = 1.2V CONTROL INPUT Input Low Voltage VIL V SHDN = VIN = 2.6V to 5.5V Input High Voltage VIH V SHDN = VIN = 2.6V to 5.5V SHDN Input Current I SHDN 1.25 A 1 Ω 10 µA 100 Ω 7.50 µA 0.3 V 1.0 V V SHDN = 3V 50 V SHDN = 0 0.1 µA Note 2: Current limit varies with duty cycle due to slope compensation. See the Output Current Capability section. Note 3: Specifications to -40°C are guaranteed by design and not production tested. _______________________________________________________________________________________ 3 MAX1896 ELECTRICAL CHARACTERISTICS Typical Operating Characteristics (Circuit of Figure 1, VIN = 3.3V, TA = +25°C, unless otherwise noted.) EFFICIENCY vs. OUTPUT CURRENT 60 80 70 60 VIN = 3.3V, VOUT = 5V, CIRCUIT OF FIGURE 1 VIN = 3.3V, VOUT = 13V, CIRCUIT OF FIGURE 3 100 50 1 1000 10 1 OUTPUT VOLTAGE (V) 1.0 0.5 LOAD TRANSIENT (VOUT = 13V) CIRCUIT OF FIGURE 3 3.0 3.5 4.0 4.5 5.0 OUTPUT VOLTAGE AC-COUPLED 200mV/div 13.00 TA = +85°C INDUCTOR CURRENT 500mA/div TA = -40°C 5.5 0 50 100 150 LOAD TRANSIENT (VOUT = 5V) STARTUP WAVEFORM WITHOUT SOFT-START OUTPUT VOLTAGE AC-COUPLED 200mV/div SHDN 5V/div STARTUP WAVEFORM WITH SOFT-START INDUCTOR CURRENT 500mA/div 400µs/div COUT = 0.1µF CERAMIC + 22µF TANTALUM IOUT = 10mA SHDN 5V/div OUTPUT VOLTAGE 5V/div OUTPUT VOLTAGE 5V/div INDUCTOR CURRENT 500mA/div 200µs/div CFF = 100pF, COUT = 0.1µF CERAMIC + 10µF CERAMIC 200 MAX1896 toc08 OUTPUT CURRENT (mA) MAX1896 toc07 INPUT VOLTAGE (V) LOAD CURRENT 200mA/div 1000 LOAD CURRENT 100mA/div TA = +25°C 12.90 2.5 100 OUTPUT VOLTAGE vs. OUTPUT CURRENT 12.95 VOUT = 13V, CIRCUIT OF FIGURE 3 10 OUTPUT CURRENT (mA) 13.05 1.5 0 4 13.10 MAX1896 toc04 2.0 1000 OUTPUT CURRENT (mA) OUTPUT CURRENT (mA) NO LOAD SUPPLY CURRENT vs. INPUT VOLTAGE 100 MAX1896 toc06 10 VIN = 5V, VOUT = 13V, CIRCUIT OF FIGURE 3 MAX1896 toc05 1 70 60 50 50 80 INDUCTOR CURRENT 500mA/div 100µs/div VIN = 3.3V, COUT = 0.1µF CERAMIC + 3.3µF TANTALUM CIRCUIT OF FIGURE 3 2ms/div VIN = 3.3V, CSS = 33nF, COUT = 3.3µF TANTALUM + 0.1µF CERAMIC CIRCUIT OF FIGURE 3 _______________________________________________________________________________________ MAX1896 toc09 70 90 EFFICIENCY (%) 80 100 MAX1896 toc02 MAX1896 toc01 90 EFFICIENCY (%) EFFICIENCY (%) 90 EFFICIENCY vs. OUTPUT CURRENT 100 MAX1896 toc03 EFFICIENCY vs. OUTPUT CURRENT 100 NO LOAD SUPPLY CURRENT (mA) MAX1896 1.4MHz SOT23 Current-Mode Step-Up DC-DC Converter 1.4MHz SOT23 Current-Mode Step-Up DC-DC Converter STARTUP WAVEFORM WITH SOFT-START MAXIMUM OUTPUT CURRENT vs. INPUT VOLTAGE OUTPUT VOLTAGE 5V/div LX VOLTAGE 5V/div OUTPUT VOLTAGE AC-COUPLED 200mV/div INDUCTOR CURRENT 500mA/div INDUCTOR CURRENT 500mA/div MAX1896 toc12 SHDN 5V/div 600 MAXIMUM OUTPUT CURRENT (mA) IOUT = 100mA MAX1896 toc11 MAX1896 toc10 SWITCHING WAVEFORM 500 400 VOUT = 5V 300 VOUT = 12V 200 MAXIMUM OUTPUT CURRENT DEFINED AT 90% OF NO LOAD OUTPUT VOLTAGE 100 IOUT = 150mA 0 2ms/div VIN = 3.3V, CSS = 33nF, COUT = 3.3µF TANTALUM + 0.1µF CERAMIC CIRCUIT OF FIGURE 3 2.5 400ns/div VIN = 5V, COUT = 0.1µF CERAMIC + 2.2µF CERAMIC 3.0 3.5 4.0 4.5 5.0 5.5 INPUT VOLTAGE (V) Pin Description PIN NAME 1 LX 2 GND FUNCTION Power Switching Connection. Connect LX to the inductor and output rectifier. Connect components as close to LX as possible. Ground Feedback Input. Connect a resistive voltage-divider from the output to FB to set the output voltage. See the Setting the Output Voltage section. 3 FB 4 SHDN 5 SS Soft-Start Input. Connect a soft-start capacitor from SS to GND to soft-start the converter. Leave SS open to disable the soft-start function. See the Soft-Start section. 6 IN Internal Bias Voltage Input. Connect IN to the input voltage source. Bypass IN to GND with a 1µF or greater capacitor as close to IN as possible. Shutdown Input. Drive SHDN low to turn off the converter. To automatically start the converter, connect SHDN to IN. Drive SHDN with a slew rate of 0.1V/µs or greater. Do not leave SHDN unconnected. SHDN draws up to 50µA. _______________________________________________________________________________________ 5 MAX1896 Typical Operating Characteristics (continued) (Circuit of Figure 1, VIN = 3.3V, TA = +25°C, unless otherwise noted.) MAX1896 1.4MHz SOT23 Current-Mode Step-Up DC-DC Converter Detailed Description The MAX1896 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 functional diagram is shown in Figure 2. As the load varies, the error amplifier sets the inductor peak current necessary to supply the load and regulate the output voltage. To maintain stability at high duty cycle, a slope-compensation signal is internally summed with the current-sense signal. At light loads, this architecture allows the MAX1896 to skip cycles to prevent overcharging the output voltage. In this region of operation, the inductor ramps up to a peak value of about 100mA, discharges to the output and waits until another pulse is needed again. Output-Current Capability The output-current capability of the MAX1896 is a function of current limit, input voltage, 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: Soft-Start The MAX1896 can be programmed for soft-start upon power-up with an external capacitor. When the MAX1896 is turned on, the soft-start capacitor (CSS) is charged at a constant current of 4µA, ramping up to 0.5V. 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 MAX1896 is turned off, the soft-start capacitor is internally discharged to ground. Shutdown The MAX1896 shuts down to reduce the supply current to 0.01µA when SHDN is low. In this mode, the internal reference, error amplifier, comparators, biasing circuit, and N-channel MOSFET are turned off. The step-up converter’s output is still connected to IN via the external inductor and output rectifier. Applications Information The MAX1896 operates well with a variety of external components. The components in Figure 1 are suitable for most applications. See the following sections to optimize external components for a particular application. IOUT(MAX) = (ILIM x (1.45 − 0.9 x Duty)) VIN x η x VOUT − 0.5 × Duty x VIN fOSC x L where: ILIM = current limit specified at 50% (see Electrical Characteristics) DUTY = DUTY CYCLE = VOUT − VIN + VDIODE VOUT − ILIM x RON + VDIODE Inductor Selection Inductor selection depends on input voltage, output voltage, maximum current, size, and availability of inductor values. Other factors can include efficiency and ripple voltage. Inductors are specified by their inductance (L), peak current (IPK), and resistance (RL). The following step-up circuit equations are useful in choosing the inductor values based on the application. They allow the trading of peak current and inductor value while considering component availability and cost. The equation used here assumes a constant LIR, which is the ratio of the inductor peak-to-peak AC current to average DC inductor current. A good compromise between the size of the inductor versus loss and output ripple is to choose an LIR of 0.3 to 0.5. The peak inductor current is then given by: VDIODE = catch diode forward drop at ILIM, (V) fOSC = oscillator frequency, (Hz) L = inductor value, (H) η = conversion efficiency, 0.85 nominal VIN = input voltage, (V) VOUT = output voltage, (V) 6 IOUT(MAX) x VOUT LIR IPK = x 1 + η x VIN(MIN) 2 where: IOUT(MAX) = maximum output current, (A) VIN(MIN) = minimum input voltage, (V) _______________________________________________________________________________________ 1.4MHz SOT23 Current-Mode Step-Up DC-DC Converter L = [VIN(MIN)2 x η x (VOUT VOUT 2 − VIN(MIN) )] x LIR x IOUT(MAX) x fOSC The MAX1896 operates with an adjustable output from VIN to 13V. Connect a resistive voltage-divider from the output to FB (see Typical Operating Circuit). Choose a value for R2 between 10kΩ and 50kΩ. Calculate R1 using the equation: Diode Selection The output diode should be rated to handle the output voltage and the peak switch current. Make sure the diode’s peak current rating is at least IPK and that its breakdown voltage exceeds VOUT. Schottky diodes are recommended. If a junction rectifier is used, it must be an ultra-fast type (trr < 50ns) to prevent excessive loss in the rectifier. Input and Output Capacitor Selection The MAX1896 operates with both tantalum and ceramic output capacitors. When using tantalum capacitors, the zero caused by the ESR of the tantalum is used to ensure stability. When using ceramic capacitors, the zero due to the ESR will be at too high a frequency to be useful in stabilizing the control loop. When using ceramic capacitors, use a feedforward capacitor to increase the phase margin, improving the control-loop stability. Figure 3 shows the circuit with ceramic capacitors and the feedforward capacitor, CFF. Use the following equation to determine the value of the feedforward capacitor: C k1 x VOUT 2 CFF = x OUT R1 VIN 0.5 − 1 where VFB, the step-up regulator feedback set point, is 1.24V. Connect the resistive-divider as close to the IC as possible. Soft-Start Capacitor The soft-start capacitor should be large enough that the current limit does not reach final value before the output has reached regulation. Calculate CSS to be: CSS > k 2 x COUT x VOUT 2 − VIN x VOUT VIN x IINRUSH − IOUT x VOUT where: k2 = 21 x 10-6, (S) VOUT = maximum output voltage, (V) IINRUSH = peak inrush current allowed, (A) IOUT = maximum output current during power-up stage, (A) where: Ω x F k1 = 7.14 x 10−4 with units of A V R1 = R2 x OUT VFB 0.5 VIN = minimum input voltage, (V) The soft-start duration (tSS) is the time it takes the current limit to reach its final value. The soft-start duration can be calculated by the equation: R1 = see Figure 3, (Ω) COUT = total output capacitance including any bypass capacitor on the output bus, (Farads). See Figure 3. VOUT = output voltage, (V) VIN = input voltage, (V). tss = k3 ✕ CSS where: k3 = 6.67 ✕ 105Ω _______________________________________________________________________________________ 7 MAX1896 Setting the Output Voltage The inductance (H) value is then given by: MAX1896 1.4MHz SOT23 Current-Mode Step-Up DC-DC Converter Application Circuits Layout Procedure 1-Cell to 3.3V SEPIC Power Supply Figure 4 shows the MAX1896 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. L1 and L2 are two windings on a single inductor or two separate inductors. The coupling capacitor between these two windings must be a low-ESR type to achieve maximum efficiency, and must also be able to handle high ripple currents. Ceramic capacitors are best for this application. Good PC board layout and routing are required in highfrequency switching power supplies to achieve good regulation, and stability. It is strongly recommended that the evaluation kit PC board layouts be followed as closely as possible. Refer to the MAX1896 EV kit for a good layout. 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 VIN 2.6V TO 4.5V CIN C1 10µF 10V L 10µH SUMIDA CD43-100 TRANSISTOR COUNT: 970 C2 0.1µF VOUT 5V IN ON/OFF SHDN LX NIHON EC10QSO2L 0.1µF MAX1896 COUT 22µF 16V GND SS FB CSS 33nF R1 36kΩ R2 12kΩ Figure 1. Typical Application Circuit 8 _______________________________________________________________________________________ 1.4MHz SOT23 Current-Mode Step-Up DC-DC Converter MAX1896 ENABLE COMPARATOR SHDN IN 4µA BIAS SOFTSTART ENABLE TRANSCONDUCTANCE ERROR AMPLIFIER SS ERROR COMPARATOR FB LX CONTROL AND DRIVER LOGIC 1.24V N CLOCK GND SLOPE COMPENSATION OSCILLATOR CURRENT SENSE Σ MAX1896 Figure 2. Functional Diagram VIN 2.6V TO 5.5V L 10µH CD43-100 IN ON/OFF 10µF CERAMIC 0.1µF CERAMIC C1 D1 NIHON EC10QSO2L IN ON/OFF COUT 10µF CERAMIC MAX1896 L1 VOUT 13V LX SHDN VIN 2.6V TO 5.5V SHDN VOUT LX C2 MAX1896 COUT CFF 100pF SS CSS 33nF FB GND GND SS R3 10kΩ R2 12kΩ R1 115kΩ Figure 3. MAX1896 with Ceramic Output Capacitor and Feedforward Capacitor L2 FB R1 R2 Figure 4. MAX1896 in an SEPIC Configuration _______________________________________________________________________________________ 9 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.) 6LSOT.EPS MAX1896 1.4MHz SOT23 Current-Mode Step-Up DC-DC Converter PACKAGE OUTLINE, SOT-23, 6L 21-0058 F 1 1 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. 10 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.