MAX1920/MAX1921 Low-Voltage, 400mA Step-Down DC-DC Converters in SOT23 General Description The MAX1920/MAX1921 step-down converters deliver over 400mA to outputs as low as 1.25V. These converters use a unique proprietary current-limited control scheme that achieves over 90% efficiency. These devices maintain extremely low quiescent supply current (50A), and their high 1.2MHz (max) operating frequency permits small, low-cost external components. This combination makes the MAX1920/MAX1921 excellent high-efficiency alternatives to linear regulators in space-constrained applications. Internal synchronous rectification greatly improves efficiency and eliminates the external Schottky diode required in conventional step-down converters. Both devices also include internal digital soft-start to limit input current upon startup and reduce input capacitor requirements. The MAX1920 provides an adjustable output voltage (1.25V to 4V). The MAX1921 provides factory-preset output voltages (see the Selector Guide). Both are available in space-saving 6-pin SOT23 packages. The MAX1920 is also available in a 6-pin TDFN package. Applications Next-Generation Wireless Handsets PDAs, Palmtops, and Handy-Terminals Battery-Powered Equipment CDMA Power Amplifier Supply Features 400mA Guaranteed Output Current Internal Synchronous Rectifier for > 90% Efficiency Tiny 6-Pin SOT23 Package Available in 6-Pin TDFN Package (MAX1920) Up to 1.2MHz Switching Frequency for Small External Components 50A Quiescent Supply Current 0.1A Logic-Controlled Shutdown 2V to 5.5V Input Range Fixed 1.5V, 1.8V, 2.5V, 3V, and 3.3V Output Voltages (MAX1921) Adjustable Output Voltage (MAX1920) 1.5% Initial Accuracy Soft-Start Limits Startup Current Ordering Information TEMP RANGE PIN-PACKAGE MAX1920EUT-T PART -40C to +85C 6 SOT23-6 MAX1920EUT+T -40C to +85C 6 SOT23-6 MAX1920ETT-T -40C to +85C 6 TDFN MAX1920ETT+T -40C to +85C 6 TDFN MAX1921EUT_ _-T -40C to +85C 6 SOT23-6 MAX1921EUT_ _+T -40C to +85C 6 SOT23-6 Note: The MAX1921 offers five preset output voltage options. See the Selector Guide, and then insert the proper designator into the blanks above to complete the part number. +Denotes a lead-free package. LX MAX1921 4.75k 5600pF 4.7F IN 1 AGND 2 * MAX1920 MAX1921 OFF SHDN 6 5 4 6 LX MAX1920 5 PGND PGND SHDN 3 ON LX OUTPUT 1.5V UP TO 400mA OUT 4 OUT (FB) SOT23-6 * 1 2 3 PGND AGND 4.7H IN CIN IN SHDN INPUT 2V TO 5.5V FB TOP VIEW AGND Pin Configuration Typical Operating Circuit TDFN ( ) ARE FOR MAX1920 ONLY A "+" SIGN WILL REPLACE THE FIRST PIN INDICATOR ON LEAD-FREE PACKAGES. 19-2296; Rev 3; 8/05 MAX1920/MAX1921 Low-Voltage, 400mA Step-Down DC-DC Converters in SOT23 Absolute Maximum Ratings IN, FB, SHDN to AGND............................................-0.3V to +6V OUT to AGND, LX to PGND.........................-0.3V to (IN + 0.3V) AGND to PGND.....................................................-0.3V to +0.3V OUT Short Circuit to GND...................................................... 10s Continuous Power Dissipation (TA = +70C) 6-Pin SOT23-6 (derate 8.7mW/C above +70C)........695mW 6-Pin TDFN (derate 18.2mW/C above +70C)......1454.5mW Operating Temperature Range............................ -40C to +85C Junction Temperature.......................................................+150C Storage Temperature......................................... -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 = 3.6V, SHDN = IN, TA = 0C to +85C. Typical parameters are at TA = +25C, unless otherwise noted.) (Note 1) PARAMETER Input Voltage Range SYMBOL VIN CONDITIONS MIN TYP I(LX) < 400mA 2.5 5.5 I(LX) < 200mA (MAX1921EUT15, MAX1921EUT18) 2.0 2.5 Startup Voltage UVLO Threshold 2.0 UVLO VIN rising VIN falling 1.85 1.50 UVLO Hysteresis Quiescent Supply Current Quiescent Supply Current Dropout Shutdown Supply Current 1.65 UNITS V V V mV IIN No switching, no load 50 70 A IIN SHDN = IN, OUT/FB = 0 220 300 A SHDN = GND 0.1 4.0 A ISHDN IOUT = 0, TA = +25C IOUT Output Voltage Range (MAX1920) FB Feedback Threshold (MAX1920) VFB FB Feedback Hysteresis (MAX1920) VHYS FB Bias Current (MAX1920) 1.95 200 Output Voltage Accuracy (MAX1921) OUT BIAS Current MAX -1.5 +1.5 IOUT = 0 to 400mA, TA = -40C to +85C -3 +3 IOUT = 0 to 200mA, TA = -40C to +85C -3 +3 SHDN = 0 OUT at regulation voltage 8 16 Figure 4, IN = 4.5V 1.25 TA = +25C 1.231 1.25 1.269 1.220 1.25 1.280 TA = -40C to +85C IFB 1 4.00 1.210 % A V V 1.280 5 mV FB = 1.5V 0.01 Load Regulation IOUT = 0 to 400mA 0.005 %/mA Line Regulation VIN = 2.5V to 5.5V 0.2 %/V SHDN Input Voltage High VIH SHDN Input Voltage Low VIL SHDN Leakage Current ISHDN High-Side Current Limit ILIMP www.maximintegrated.com 0.20 1.6 SHDN = GND or IN 525 A V 0.4 V 0.001 1.000 A 730 950 mA Maxim Integrated 2 MAX1920/MAX1921 Low-Voltage, 400mA Step-Down DC-DC Converters in SOT23 Electrical Characteristics (continued) (VIN = 3.6V, SHDN = IN, TA = 0C to +85C. Typical parameters are at TA = +25C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL Low-Side Current Limit CONDITIONS ILIMN MIN TYP MAX UNITS 350 550 800 mA High-Side On-Resistance RONHS ILX = -40mA, VIN = 3V 0.6 1.1 Rectifier On-Resistance RONSR ILX = 40mA, VIN = 3V 0.5 0.9 Rectifier Off-Current Threshold ILXOFF LX Leakage Current ILXLEAK IN = SHDN = 5.5V, LX = 0 to IN 0.1 5.0 A LX Reverse Leakage Current ILXLKR IN unconnected, VLX = 5.5V, SHDN = GND 0.1 5.0 A 60 mA Minimum On-Time tON(MIN) 0.28 0.4 0.5 s Minimum Off-Time tOFF(MIN) 0.28 0.4 0.5 s Note 1: All devices are 100% production tested at TA = +25C. Limits over the operating temperature range are guaranteed by design. Typical Operating Characteristics (CIN = 2.2F ceramic, Circuit of Figure 1, components of Table 1, unless otherwise noted.) EFFICIENCY (%) 60 50 40 30 VIN = 3.3V 70 VIN = 5V 100 60 50 40 30 80 70 50 30 20 10 10 100 0.1 1 10 100 0 1000 0.1 1 10 100 1000 LOAD CURRENT (mA) LOAD CURRENT (mA) OUTPUT VOLTAGE ACCURACY vs. LOAD (VOUT = 3.3V) OUTPUT VOLTAGE ACCURACY vs. LOAD (VOUT = 2.5V) OUTPUT VOLTAGE ACCURACY vs. LOAD (VOUT = 1.5V) VIN = 5V 3.300 VIN = 4.2V 3.267 VIN = 3.6V 3.234 0 50 100 150 200 250 300 350 400 LOAD (mA) www.maximintegrated.com VIN = 5V 2.525 2.500 VIN = 3V 2.475 2.450 2.425 1.530 OUTPUT VOLTAGE 3.333 2.550 1.545 MAX1920 toc05 2.575 VIN = 5V MAX1920 toc06 LOAD CURRENT (mA) 3.366 3.201 0 1000 OUTPUT VOLTAGE 3.399 10 VIN = 5V 40 10 1 VIN = 3.3V 60 20 0.1 VIN = 2.5V 90 20 0 OUTPUT VOLTAGE 80 EFFICIENCY vs. LOAD CURRENT (VOUT = 1.5V) MAX1920 toc03 VIN = 5V VIN = 4.2V 70 VIN = 2.7V 90 MAX1920 toc04 EFFICIENCY (%) 80 100 EFFICIENCY (%) VIN = 3.6V 90 MAX1920 toc01 100 EFFICIENCY vs. LOAD CURRENT (VOUT = 2.5V) MAX1920 toc02 EFFICIENCY vs. LOAD CURRENT (VOUT = 3.3V) 1.515 1.500 VIN = 3.3V 1.485 VIN = 2.5V 1.470 0 50 100 150 200 250 300 350 400 LOAD (mA) 1.455 0 50 100 150 200 250 300 350 400 LOAD (mA) Maxim Integrated 3 MAX1920/MAX1921 Low-Voltage, 400mA Step-Down DC-DC Converters in SOT23 Typical Operating Characteristics (continued) (CIN = 2.2F ceramic, Circuit of Figure 1, components of Table 1, unless otherwise noted.) 1000 100 10 1000 100 10 VIN = 3.3 VIN = 3.3 1 0.1 1 10 100 1000 1 LOAD (mA) 0.1 1 10 100 10,000 VOUT = 2.5V 1000 1000 1 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 SOFT-START AND SHUTDOWN RESPONSE MAX1920 toc12 VOUT 1V/div VOUT AC-COUPLED 5mV/div VOUT AC-COUPLED 5mV/div IIN 100mA/div VLX 2V/div VLX 2V/div 1s/div 1s/div MEDIUM-LOAD LINE-TRANSIENT RESPONSE LIGHT-LOAD LINE-TRANSIENT RESPONSE 200s/div LOAD-TRANSIENT RESPONSE MAX1920 toc15 MAX1920 toc14 VIN AC-COUPLED 200mV/div VIN AC-COUPLED 200mV/div VSHDN 5V/div VIN = 3.3V, VOUT = 1.5V, RLOAD = 6 VIN = 3.3V, VOUT = 1.5V, ILOAD = 250mA MAX1920 toc13 1.5 SUPPLY VOLTAGE (V) MAX1920 toc11 VIN = 3.3V, VOUT = 1.5V, ILOAD = 40mA VOUT = 1.5V 10 MEDIUM-LOAD SWITCHING WAVEFORM MAX1920 toc10 VOUT = 3.3V 100 LOAD (mA) LIGHT-LOAD SWITCHING WAVEFORM NO LOAD SUPPLY CURRENT vs. SUPPLY VOLTAGE MAX1920 toc09 MAX1920 toc08 10,000 SWITCHING FREQUENCY (kHz) MAX1920 toc07 SWITCHING FREQUENCY (kHz) 10,000 SWITCHING FREQUENCY vs. LOAD (VOUT = 1.5V) NO-LOAD SUPPLY CURRENT (A) SWITCHING FREQUENCY vs. LOAD (VOUT = 1.8V) VIN = 3.3V, VOUT = 1.5V, ILOAD = 20mA TO 320mA VOUT AC-COUPLED 100mV/div IL 200mA/div VIN = 3.8V to 4.2V, VOUT = 1.5V, ILOAD = 250mA 4s/div www.maximintegrated.com VOUT AC-COUPLED 5mV/div VOUT AC-COUPLED 5mV/div ILOAD 200mA/div VIN = 3.8V to 4.2V, VOUT = 1.5V, ILOAD = 20mA 4s/div 40s/div Maxim Integrated 4 MAX1920/MAX1921 Low-Voltage, 400mA Step-Down DC-DC Converters in SOT23 Pin Description PIN NAME FUNCTION SOT TDFN* 1 2 IN 2 6 AGND Analog Ground. Connect to PGND. 3 1 SHDN Active-Low Shutdown Input. Connect SHDN to IN for normal operation. In shutdown, LX becomes high-impedance and quiescent current drops to 0.1A. 4 -- OUT 4 5 FB 5 3 PGND 6 4 LX Supply voltage input for MAX1921EUT15 and MAX1921EUT18 is 2V to 5.5V. Supply voltage input for MAX1920 and other voltage versions of MAX1921 is 2.5V to 5.5V. Bypass IN to GND with a 2.2F ceramic capacitor as close as possible to IN. MAX1921 Voltage Sense Input. OUT is connected to an internal voltage-divider. MAX1920 Voltage Feedback Input. FB regulates to 1.25V nominal. Connect FB to an external resistive voltage-divider between the output voltage and GND. Power Ground. Connect to AGND. Inductor Connection *MAX1920 only. Detailed Description The MAX1920/MAX1921 step-down DC-DC converters deliver over 400mA to outputs as low as 1.25V. They use a unique proprietary current-limited control scheme that maintains extremely low quiescent supply current (50A), and their high 1.2MHz (max) operating frequency permits small, low-cost external components. Control Scheme The MAX1920/MAX1921 use a proprietary, current-limited control scheme to ensure high-efficiency, fast transient response, and physically small external components. This control scheme is simple: when the output voltage is out of regulation, the error comparator begins a switching cycle by turning on the high-side switch. This switch remains on until the minimum on-time of 400ns expires and the output voltage regulates or the current-limit threshold is exceeded. Once off, the high-side switch remains off until the minimum off-time of 400ns expires and the output voltage falls out of regulation. During this period, the lowside synchronous rectifier turns on and remains on until INPUT 2V TO 5.5V 1 CIN IN LX 6 ON OFF 3 AGND PGND SHDN OUT OUTPUT UP TO 400mA R1 MAX1921 2 L 5 CFF 4 COUT either the high-side switch turns on again or the inductor current approaches zero. The internal synchronous rectifier eliminates the need for an external Schottky diode. This control scheme allows the MAX1920/MAX1921 to provide excellent performance throughout the entire loadcurrent range. When delivering light loads, the high-side switch turns off after the minimum on-time to reduce peak inductor current, resulting in increased efficiency and reduced output voltage ripple. When delivering medium and higher output currents, the MAX1920/MAX1921 extend either the on-time or the off-time, as necessary to maintain regulation, resulting in nearly constant frequency operation with high-efficiency and low-output voltage ripple. Shutdown Mode Connecting SHDN to GND places the MAX1920/ MAX1921 in shutdown mode and reduces supply current to 0.1A. In shutdown, the control circuitry, internal switching MOSFET, and synchronous rectifier turn off and LX becomes high impedance. Connect SHDN to IN for normal operation. Soft-Start The MAX1920/MAX1921 have internal soft-start circuitry that limits current draw at startup, reducing transients on the input source. Soft-start is particularly useful for higher impedance input sources, such as Li+ and alkaline cells. Soft-start is implemented by starting with the current limit at 25% of its full current value and gradually increasing it in 25% steps until the full current limit is reached. See Soft-Start and Shutdown Response in the Typical Operating Characteristics. Figure 1. Typical Output Application Circuit (MAX1921) www.maximintegrated.com Maxim Integrated 5 MAX1920/MAX1921 Low-Voltage, 400mA Step-Down DC-DC Converters in SOT23 Design Procedure The MAX1920/MAX1921 are optimized for small external components and fast transient response. There are several application circuits (Figures 1 through 4) to allow the choice between ceramic or tantalum output capacitor and internally or externally set output voltages. The use of a small ceramic output capacitor is preferred for higher reliability, improved voltage-positioning transient response, reduced output ripple, and the smaller size and greater availability of ceramic versus tantalum capacitors. Voltage Positioning Figures 1 and 2 are the application circuits that utilize small ceramic output capacitors. For stability, the circuit obtains feedback from the LX node through R1, while load transients are fed-forward through CFF. Because there is no D.C. feedback from the output, the output voltage exhibits load regulation that is equal to the output load current multiplied by the inductor's series resistance. This small amount of load regulation is similar to voltage positioning as used by high-powered microprocessor supplies intended for personal computers. For the MAX1920/ MAX1921, voltage positioning eliminates or greatly reduces undershoot and overshoot during load transients (see the Typical Operating Characteristics), which effectively halves the peak-to-peak output voltage excursions compared to traditional step-down converters. Table 1. MAX1921 Suggested Components for Figure 1 5V 3.3V, 1 Li+, 3 x AA 3.3V 3.0V L = 10H, COUT = 10F, R1 = 8.25k, CFF = 3300pF 2.5V L = 6.8H, COUT = 6.8F, R1 = 5.62k, CFF = 4700pF 1.8V 1.5V L = 10H, COUT = 10F, R1 = 8.25k, CFF = 3300pF Induction Selection In order to calculate the smallest inductor, several calculations are needed. First, calculate the maximum duty cycle of the application as: DutyCycle( = MAX ) VIN ( MIN ) x 100% Second, calculate the critical voltage across the inductor as: if DutyCycle(MAX) < 50%, then VCRITICAL = (VIN(MIN) - VOUT), else VCRITICAL = VOUT Last, calculate the minimum inductor value as: L(MIN) = 2.5 x10-6 x VCRITICAL Select the next standard value larger than L(MIN). The L(MIN) calculation already includes a margin for inductance tolerance. Although values much larger than L(MIN) work, transient performance, efficiency, and inductor size suffer. A 550mA rated inductor is enough to prevent saturation for output currents up to 400mA. Saturation occurs when the inductor's magnetic flux density reaches the maximum level the core can support and inductance falls. Choose a low DC-resistance inductor to improve efficiency. Tables 2 and 3 list some suggested inductors and suppliers. PART NUMBER 2.5V, 2 x AA N/A L = 4.7H, COUT = 4.7F, R1 = 4.75k, CFF = 5600pF Coilcraft LPO1704 L (H) RL (ohms max) Isat (A) 4.7 0.200 1.10 6.8 0.320 0.90 10 0.410 0.80 4.7 0.080 0.90 6.8 0.095 0.73 10 0.160 0.55 Sumida CDRH2D18 4.7 0.081 0.63 6.8 0.108 0.57 Toko D312F 4.7 0.38 0.74 10 0.79 0.50 Toko D412F 4.7 0.230 0.84 10 0.490 0.55 4.7 0.087 1.14 6.8 0.105 0.95 10 0.150 0.76 Sumida CDRH3D16 Toko D52LC www.maximintegrated.com VOUT Table 2. Suggested Inductors INPUT SOURCE OUTPUT For convenience, Table 1 lists the recommended external component values for use with the MAX1921 application circuit of Figure 1 with various input and output voltages. SIZE 6.6 x 5.5 x 1.0 = 36.3mm3 3.8 x 3.8 x 1.8 = 26.0mm3 3.2 x 3.2 x 2.0 = 20.5mm3 3.6 x 3.6 x 1.2 = 15.6mm3 4.6 x 4.6 x 1.2 = 25.4mm3 5.0 x 5.0 x 2.0 = 50.0mm3 Maxim Integrated 6 MAX1920/MAX1921 Low-Voltage, 400mA Step-Down DC-DC Converters in SOT23 Capacitor Selection Tantalum Output Capacitor For nearly all applications, the input capacitor, CIN, may be as small as 2.2F ceramic with X5R or X7R dielectric. The input capacitor filters peak currents and noise at the voltage source and, therefore, must meet the input ripple requirements and voltage rating. Calculate the maximum RMS input current as: = IIN ( RMS ) I OUT ( MAX ) x VOUT ( VIN - VOUT ) VIN The output capacitor, COUT, may be either ceramic or tantalum depending upon the chosen application circuit (see Figures 1 through 4). Table 3 lists some suggested capacitor suppliers. For tantalum COUT, use the application circuit of Figure 3 or Figure 4. With tantalum COUT, the equivalent series resistance (ESR) of COUT must be large enough for stability. Generally, 25mV of ESR-ripple at the feedback node is sufficient. The simplified calculation is: ESRCOUT(MIN) = 8.0 x 10-2 x VOUT Because tantalum capacitors rarely specify minimum ESR, choose a capacitor with typical ESR that is about twice as much as ESRCOUT(MIN). Although ESRs greater than this work, output ripple becomes larger. For tantalum COUT, calculate the minimum output capacitance as: = C OUT ( MIN ) 1.25 x Ceramic Output Capacitor For ceramic COUT, use the application circuit of Figure 1 or Figure 2. Calculate the minimum capacitor value as: COUT(MIN) = 2.5 x 10-6 x VCRITICAL Select the next standard value larger than COUT(MIN). The COUT(MIN) calculation already includes a margin for capacitor tolerance. Values much larger than COUT(MIN) always improve transient performance and stability, but capacitor size and cost increase. INPUT 2V TO 5.5V 1 CIN IN LX R1 MAX1920 2 AGND L 6 PGND CFF 5 OUTPUT UP TO 400mA COUT The 1.25 multiplier is for capacitor tolerance. Select any standard value larger than COUT(MIN). Feedback and Compensation The MAX1921 has factory preset output voltages of 1.5V, 1.8V, 2.5V, 3V, and 3.3V, while the MAX1920 is externally adjusted by connecting FB to a resistive voltage-divider. When using a ceramic output capacitor, the feedback network must include a compensation feed-forward capacitor, CFF. INPUT 2V TO 5.5V 1 CIN OFF 3 SHDN FB LX AGND PGND SHDN OUT L OUTPUT UP TO 400mA COUT 5 4 ON R2 Figure 2. Typical Application Circuit (MAX1920) www.maximintegrated.com IN 6 MAX1921 2 ON L x I OUT ( MAX ) ESR COUT ( MIN ) x VCRITICAL OFF 3 4 Figure 3. MAX1921 Application Circuit Using Tantalum Output Capacitor Maxim Integrated 7 MAX1920/MAX1921 Low-Voltage, 400mA Step-Down DC-DC Converters in SOT23 Table 3. Component Suppliers SUPPLIER MAX1920 Using Ceramic COUT PHONE WEBSITE Coilcraft 847-639-6400 www.coilcraft.com Kemet 408-986-0424 www.kemet.com 814-237-1431 www.murata.com Murata Sumida Taiyo Yuden Toko USA 847-956-0666 Japan 81-3-3607-5111 www.sumida.com USA 408-573-4150 www.T-Yuden.com Japan 81-3-3833-5441 www.yuden.co.jp USA 847-297-0070 www.tokoam.com Japan 81-3-3727-1161 www.toko.co.jp MAX1921 Using Ceramic COUT When using the application circuit of Figure 1, the inductor's series resistance causes a small amount of load regulation, as desired for a voltage-positioning load transient response. Choose R1 such that VOUT is high at no load by about half of this load regulation. The simplified calculation is: R1 = 5 x 104 x RL(MAX) where RL(MAX) is the maximum series resistance of the inductor. Select a standard resistor value that is within 20% of this calculation. Next, calculate CFF for 25mV ripple at the internal feedback node. The simplified calculation is: CFF = 2.5 x 10-5/R1 where R1 is the standard resistor value that is used. Select a standard capacitor value that is within 20% of the calculated CFF. INPUT 2V TO 5.5V 1 CIN IN LX 6 OUTPUT UP TO 400mA L COUT MAX1920 2 ON OFF 3 AGND PGND SHDN FB 5 R1 4 R2 Figure 4. MAX1920 Application Circuit Using Tantalum Output Capacitor www.maximintegrated.com When using the application circuit of Figure 2, the inductor's series resistance causes a small amount of load regulation, as desired for a voltage-positioning load transient response. Choose R1 and R2 such that VOUT is high at no load by about half of this load regulation: VOUT + R L x I OUT ( MAX ) / 2 R1 = R 2 x - 1 VREF where R2 is chosen in the 50k to 500k range, VREF = 1.25V and RL is the typical series resistance of the inductor. Use 1% or better resistors. Next, calculate the equivalent resistance at the FB node as: = Req R1|| = R2 R1x R 2 R1 + R 2 Then, calculate CFF for 25mV ripple at FB. The simplified calculation is: CFF = 2.5 x 10-5/Req Select a standard capacitor value that is within 20% of the calculated CFF. MAX1920 Using Tantalum COUT When using the application circuit of Figure 4, choose R1 and R2 such as to obtain the desired VOUT: VOUT R1 = R 2 x - 1 V REF where R2 is chosen to be less than 50k and VREF = 1.25V. Use 1% or better resistors. Layout Considerations High switching frequencies make PC board layout a very important part of design. Good design minimizes excessive EMI on the feedback paths and voltage gradients in the ground plane, both of which can result in instability or regulation errors. Connect the inductor, input filter capacitor, and output filter capacitor as close to the device as possible, and keep their traces short, direct, and wide. Connect their ground pins at a single common node in a star ground configuration. The external voltage-feedback network should be very close to the FB pin, within 0.2in (5mm). Keep noisy traces, such as the LX trace, away from the voltagefeedback network; also keep them separate, using grounded copper. The MAX1920/MAX1921 evaluation kit data sheet includes a proper PC board layout and routing scheme. Maxim Integrated 8 MAX1920/MAX1921 Low-Voltage, 400mA Step-Down DC-DC Converters in SOT23 Selector Guide PART Chip Information VOUT (V) TOP MARK MAX1920EUT Adjustable ABCO MAX1920ETT Adjustable ADR MAX1921EUT33 3.3 ABCJ MAX1921EUT30 3.0 ABCK MAX1921EUT25 2.5 ABCL MAX1921EUT18 1.8 ABCM MAX1921EUT15 1.5 ABCN TRANSISTOR COUNT: 1467 Package Information For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a "+", "#", or "-" in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. -(52/'/(( www.maximintegrated.com Maxim Integrated 9 MAX1920/MAX1921 Low-Voltage, 400mA Step-Down DC-DC Converters in SOT23 Package Information (continued) For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a "+", "#", or "-" in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. -(52/'/(( www.maximintegrated.com Maxim Integrated 10 MAX1920/MAX1921 Low-Voltage, 400mA Step-Down DC-DC Converters in SOT23 Package Information (continued) For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a "+", "#", or "-" in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. www.maximintegrated.com Maxim Integrated 11 MAX1920/MAX1921 Low-Voltage, 400mA Step-Down DC-DC Converters in SOT23 Package Information (continued) For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a "+", "#", or "-" in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated's website at www.maximintegrated.com. Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance. Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc. (c) 2005 Maxim Integrated Products, Inc. 12