19-1183; Rev 0; 6/97 ANUAL N KIT M EET IO T A U EVAL TA SH WS DA FOLLO High-Efficiency, Step-Up DC-DC Converters for 1V Inputs ____________________________Features ♦ Built-In Synchronous Rectifier Each device consists of an internal 1Ω, N-channel MOSFET power switch; a built-in synchronous rectifier that acts as the catch diode; an oscillator; a reference; and pulse-frequency-modulation (PFM) control circuitry. Both devices feature an independent undervoltage comparator (PFI/PFO). The MAX1642 also includes a 2µA logic-controlled shutdown mode. The MAX1643 offers a dedicated low-battery detector (BATTLO) in lieu of shutdown. The output voltage for each device is preset to 3.3V ±4%, or can be adjusted from +2V to +5.2V using only two resistors. ♦ 4µA Quiescent Supply Current into BATT Pin ________________________Applications Pagers ♦ 0.88V Guaranteed Start-Up ♦ Ultra-Small µMAX Package: 1.1mm High ♦ 83% Efficiency ♦ 2µA Logic-Controlled Shutdown (MAX1642) ♦ Two Undervoltage Detectors (MAX1643) ♦ 2V to 5.2V Output Range ♦ 20mA Output Current at 1.2V Input ♦ Reverse Battery Protection ______________Ordering Information PART TEMP. RANGE MAX1642C/D 0°C to +70°C MAX1642EUA MAX1643C/D MAX1643EUA -40°C to +85°C 0°C to +70°C -40°C to +85°C PIN-PACKAGE Dice* 8 µMAX Dice* 8 µMAX *Dice are tested at TA = +25°C. Note: To order these devices shipped in tape and reel, add a -T to the part number. Remote Controls Pointing Devices Personal Medical Monitors Single-Cell Battery-Powered Devices _________________Pin Configurations TOP VIEW BATT 1 __________Typical Operating Circuit INPUT 0.88V TO 1.65V 100µH OUT LX 22µF SHDN LOW-BATTERY DETECTOR INPUT PFI GND 7 LX PFO 3 6 GND SHDN 4 5 FB 8 OUT 7 LX BATTLO 3 6 GND PFO 4 5 FB PFI 2 MAX1642 µMAX 22µF MAX1642 OFF OUT OUTPUT 3.3V BATT ON 8 BATT 1 PFO FB LOW-BATTERY DETECTOR OUTPUT PFI 2 MAX1643 µMAX ________________________________________________________________ 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 408-737-7600 ext. 3468. MAX1642/MAX1643 _______________General Description The MAX1642/MAX1643 are high-efficiency, low-voltage, step-up DC-DC converters intended for devices powered by a single alkaline cell. They feature low quiescent supply currents and are supplied in the ultra-small µMAX package, which is only 1.1mm high. The guaranteed start-up voltage is 0.88V. MAX1642/MAX1643 High-Efficiency, Step-Up DC-DC Converters for 1V Inputs ABSOLUTE MAXIMUM RATINGS BATT to GND ...........................................................-0.3V to 6.0V BATT Forward Current ..........................................................0.5A OUT to GND.............................................................-0.3V to 6.0V OUT, LX Current.......................................................................1A LX to GND................................................................-0.3V to 6.0V SHDN, FB, BATTLO, PFO to GND ...........................-0.3V to 6.0V PFI to GND ............................................................-0.3V to VBATT Reverse Battery Current (TA = +25°C) (Note 1) ...............220mA Continuous Power Dissipation µMAX (derate 4.1mW/°C above 70°C)..........................330mW Operating Temperature Range MAX1642EUA/MAX1643EUA ............................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +165°C Lead Temperature (soldering, 10sec) .............................+300°C Note 1: The reverse battery current is measured from the Typical Operating Circuit’s input terminal to GND when the battery is connected backward. A reverse current of 220mA will not exceed package dissipation limits but, if left for an extended time (more than 10 minutes), may degrade performance. 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 (VBATT = V SHDN = 1.3V, ILOAD = 0mA, FB = GND, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL Minimum Operating Input Voltage VBATT(MIN) CONDITIONS MIN TYP Maximum Operating Input Voltage RL = 3kΩ, TA = +25°C 0.88 Start-Up Voltage Tempco VOUT FB Set Voltage 3.16 External feedback 2.0 External feedback 1.18 3.30 mV/°C 3.44 V 5.2 V 1.225 1.27 V N-Channel On-Resistance VOUT = 3.3V 1 1.5 Ω P-Channel On-Resistance VOUT = 3.3V 1.5 2.2 Ω P-Channel Catch-Diode Voltage IDIODE = 100mA, P-channel switch off 0.8 35 V-µs On-Time Constant VFB VFB < 0.1V V V -2 Output Voltage Range UNITS V 1.65 Start-Up Voltage (Note 2) Output Voltage MAX 0.7 K 0.9V < VBATT < 1.5V (tON = K / VBATT) 17 1 25 V Off-Time Tracking Ratio (Note 3) RATIO 0.9V < VBATT < 1.5V, VOUT = 3.3V Quiescent Current into OUT IQOUT VOUT = 3.5V 11 1.5 18 µA 4 6.5 µA 0.1 1 µA 3.5 µA 10 nA Quiescent Current into BATT IQBATT Shutdown Current into OUT ISHDN,OUT VOUT = 3.5V (MAX1642) Shutdown Current into BATT ISHDN,BATT VBATT = 1.0V (MAX1642) 2 ILOAD = 20mA 80 Efficiency η % FB Input Current VFB = 1.3V PFI Trip Voltage Falling PFI, hysteresis = 1% 632 mV PFI Input Current VPFI = 650mV 10 nA VPFI = 0V, VOUT = 3.3V, ISINK = 1mA 0.4 V 1 µA PFO, BATTLO Low Output Voltage VOL PFO, BATTLO Leakage Current VOUT = 3.3V, hysteresis = 2% (MAX1643) SHDN Input Low Voltage VIL % of VBATT (MAX1642) SHDN Input High Voltage VIH % of VBATT (MAX1642) 2 614 VPFI = 650mV, V PFO = 6V BATTLO Trip Voltage SHDN Input Current 590 0.96 1.0 1.04 V 20 % 80 (MAX1642) _______________________________________________________________________________________ % 10 nA High-Efficiency, Step-Up DC-DC Converters for 1V Inputs MAX1642/MAX1643 ELECTRICAL CHARACTERISTICS (VBATT = V SHDN = 1.3V, ILOAD = 0mA, FB = GND, TA = -40°C to +85°C, unless otherwise noted.) (Note 4) PARAMETER SYMBOL Output Voltage VOUT FB Set Voltage VFB N-Channel On-Resistance MIN MAX UNITS VFB < 0.1V CONDITIONS 2.99 3.56 V External feedback 1.11 1.32 V 1.5 Ω VOUT = 3.3V P-Channel On-Resistance VOUT = 3.3V On-Time Constant K 0.9V < VBATT < 1.5V (tON = K / VBATT) Quiescent Current into OUT IQOUT Quiescent Current into BATT IQBATT Shutdown Current into OUT ISHDN,OUT VOUT = 3.5V (MAX1642) Shutdown Current into BATT ISHDN,BATT VBATT = 1.0V (MAX1642) 12.4 VOUT = 3.5V 2.2 Ω 38.2 V-µs 18 µA 6.5 µA 1 µA 3.5 µA PFI Trip Voltage Falling PFI, hysteresis = 1% 550 662 mV BATTLO Trip Voltage Falling VBATT, VOUT = 3.3V, hysteresis = 2% (MAX1643) 0.93 1.06 V Note 2: Start-up guaranteed by correlation to measurements of device parameters (i.e., switch on-resistance, on-times, off-times, and output voltage trip points). t x VBATT tOFF = ON x RATIO. This guarantees discontinuous conduction. VOUT - VBATT Note 3: Note 4: Specifications to -40°C are guaranteed by design, not production tested. __________________________________________Typical Operating Characteristics (Circuit of Figure 4, VBATT = 1.2V, R1 + R2 = 1MΩ, TA = +25°C, unless otherwise noted.) EFFICIENCY vs. OUTPUT CURRENT (VOUT = 2.4V) 70 60 50 VIN = 1.0V 40 VIN = 1.2V VIN = 0.85V 30 70 60 50 VIN = 1.0V 40 VIN = 1.2V VIN = 0.85V 10 0.01 0.1 1 10 OUTPUT CURRENT (mA) 100 80 70 60 50 VIN = 1.2V VIN = 1.0V 40 VIN = 0.85V 20 L1 = 150µH TDK NLC565050T-151K 10 0 0 VIN = 1.6V 90 30 20 L1 = 100µH SUMIDA CD54-101 100 MAX1642/43 TOC02A 80 30 20 10 VIN = 1.6V 90 EFFICIENCY (%) EFFICIENCY (%) 80 100 EFFICIENCY (%) VIN = 1.6V 90 MAX1642/43 TOC01A 100 EFFICIENCY vs. OUTPUT CURRENT (VOUT = 3.3V) MAX1642/43 TOC01B EFFICIENCY vs. OUTPUT CURRENT (VOUT = 2.4V) L1 = 100µH SUMIDA CD54-101 0 0.01 0.1 1 10 OUTPUT CURRENT (mA) 100 0.01 0.1 1 10 100 OUTPUT CURRENT (mA) _______________________________________________________________________________________ 3 ____________________________Typical Operating Characteristics (continued) (Circuit of Figure 4, VBATT = 1.2V, R1 + R2 = 1MΩ, TA = +25°C, unless otherwise noted.) EFFICIENCY vs. OUTPUT CURRENT (VOUT = 5.0V) EFFICIENCY (%) 60 50 VIN = 1.2V VIN = 1.0V 40 VIN = 0.85V 30 20 L1 = 150µH TDK NLC565050T-151K 0.1 1 10 0.1 1 10 100 0.01 1 10 OUTPUT CURRENT (mA) NO-LOAD BATTERY CURRENT vs. INPUT VOLTAGE NO-LOAD BATTERY CURRENT vs. TEMPERATURE BATT AND OUT PIN QUIESCENT CURRENTS vs. TEMPERATURE 30 100 80 60 40 20 15 IOUT 10 5 20 VOUT = 2.5V OR 3.3V 0 10 1.0 1.4 1.2 1.6 1.8 0 -40 -20 0 20 40 60 80 100 -20 0 40 VOUT = 5V 1.2 1.1 1.0 VOUT = 2.4V, 3.3V 0.8 1.6 L1 = 150µH TDK NLC565050T-151K 1.5 START-UP INPUT VOLTAGE (V) L1 = 100µH SUMIDA CD54-101 20 60 MINIMUM START-UP INPUT VOLTAGE vs. OUTPUT CURRENT MAX1642/43 TOC07a 1.6 0.9 -40 TEMPERATURE (°C) MINIMUM START-UP INPUT VOLTAGE vs. OUTPUT CURRENT 1.3 IBATT TEMPERATURE (°C) INPUT VOLTAGE (V) 1.4 VBATT = 1.2V VOUT = 3.6V 25 QUIESCENT CURRENT (µA) 120 QUIESCENT CURRENT (µA) 100 VBATT = 1.2V VOUT = 3.3V MAX1642/43 TOC06 140 MAX1642/43 TOC04 VOUT = 5.0V 1.4 VOUT = 5V 1.3 1.2 1.1 1.0 0.9 VOUT = 2.4V, 3.3V 0.8 0.7 0.7 0.6 0.6 0 100 OUTPUT CURRENT (mA) 1000 1.5 0.1 OUTPUT CURRENT (mA) 10,000 0.8 L1 = 150µH TDK NLC565050T-151K 10 0 0.01 100 VIN = 1.2V 40 0 0.01 5 10 15 OUTPUT CURRENT (mA) 4 50 20 L1 = 100µH SUMIDA CD54-101 10 0 VIN = 0.85V 60 30 20 10 QUIESCENT CURRENT (mA) VIN = 1.2V 40 70 MAX1642/43 TOC07b 30 VIN = 0.85V 50 VIN = 1.0V 80 70 60 VIN = 1.6V 90 MAX1642/43 TOC05 EFFICIENCY (%) 70 VIN = 1.0V 80 EFFICIENCY (%) 80 VIN = 1.6V 90 100 MAX1642/43 TOC03a VIN = 1.6V 90 100 MAX1642/43 TOC02B 100 EFFICIENCY vs. OUTPUT CURRENT (VOUT = 5.0V) MAX1642/43 TOC03b EFFICIENCY vs. OUTPUT CURRENT (VOUT = 3.3V) START-UP INPUT VOLTAGE (V) MAX1642/MAX1643 High-Efficiency, Step-Up DC-DC Converters for 1V Inputs 20 25 0 2 4 6 8 10 12 OUTPUT CURRENT (mA) _______________________________________________________________________________________ 14 16 80 100 High-Efficiency, Step-Up DC-DC Converters for 1V Inputs MAXIMUM OUTPUT CURRENT vs. INPUT VOLTAGE 25 20 15 VOUT = 3.3V VOUT = 5V 10 L1 = 100µH SUMIDA CD54-101 5 SWITCHING WAVEFORMS 16 MAX1642/43 TOC09 MAX1642/43 TOC08c VOUT = 2.4V 18 MAXIMUM OUTPUT CURRENT (mA) MAX1642/43 TOC08b VOUT = 2.4V 30 20 A 14 12 VOUT = 3.3V B 10 8 VOUT = 5V 6 C 4 L1 = 150µH TDK NLC565050T-151K 2 0 0 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 0.8 INPUT VOLTAGE (V) 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 10ms/div INPUT VOLTAGE (V) VOUT = 3.3V, VIN = 1.2V, IOUT = 12mA A: LX, 2V/div, L1 = TDK NLC565050T-151K B: OUT, 20mV/div, 3.3V DC OFFSET C: INDUCTOR CURRENT, 100mA/div SHUTDOWN RESPONSE AND INDUCTOR CURRENT LINE-TRANSIENT RESPONSE MAX1642/43 TOC12 MAX1642/43 TOC11 LOAD-TRANSIENT RESPONSE MAX1642/43 TOC10 MAXIMUM OUTPUT CURRENT (mA) 35 MAXIMUM OUTPUT CURRENT vs. INPUT VOLTAGE A A A B B B C 400µs/div VOUT = 3.3V, VBATT = 1.2V A: OUT, 20mV/div, 3.3V DC OFFSET B: LOAD, 2mA to 20mA, 10mA/div 400µs/div VOUT = 3.3V, LOAD = 15mA A: OUT, 50mV/div, 3.3V DC OFFSET B: VBATT, 1V to 1.5V, 500mV/div 10ms/div VOUT = 3.3V, VBATT = 1.2V, IOUT = 5mA A: OUT, 1V/div B: INDUCTOR CURRENT, 200mA/div C: SHDN, 2V/div _______________________________________________________________________________________ 5 MAX1642/MAX1643 ____________________________Typical Operating Characteristics (continued) (Circuit of Figure 4, VBATT = 1.2V, R1 + R2 = 1MΩ, TA = +25°C, unless otherwise noted.) MAX1642/MAX1643 High-Efficiency, Step-Up DC-DC Converters for 1V Inputs ______________________________________________________________Pin Description PIN NAME MAX1642 MAX1643 1 1 BATT 2 2 PFI — 3 BATTLO 3 4 PFO 4 — SHDN 5 5 FB 6 6 GND 7 7 LX 8 8 OUT FUNCTION IC Battery-Power Input. Sense input for BATTLO comparator (MAX1643 only). Power-Fail Input. When the voltage on PFI drops below 614mV, PFO sinks current. Open-Drain Battery-Low Output. When the voltage at BATT drops below 1V, BATTLO sinks current. Open-Drain Power-Fail Output. Sinks current when PFI drops below 614mV. Active-Low Shutdown Input. Connect to BATT for normal operation. Feedback Input for adjustable-output operation. Connect FB to an external resistor voltage divider between OUT and GND. Connect to GND for fixed-output operation. Ground N-Channel MOSFET Switch Drain and P-Channel Synchronous-Rectifier Drain Power Output. Feedback input for fixed 3.3V operation and IC power input. Connect filter capacitor close to OUT. _______________Detailed Description The MAX1642/MAX1643 each consist of an internal 1Ω, N-channel MOSFET power switch, a built-in synchronous rectifier that acts as the catch diode, an oscillator, a reference, and PFM control circuitry (Figure 1). These devices are optimized for applications with power-management features that operate from one alkaline cell, such as pagers, remote controls, and battery-powered instruments. They are designed to meet the specific demands of the operating states characteristic of such systems: 1) Primary battery is good and the load is active: In this state, the system draws tens of milliamperes, and the MAX1642/MAX1643 typically offer 80% efficiency. 2) Primary battery is good and the load is sleeping: In this state, the load is drawing hundreds of microamperes, and the DC-DC converter IC draws very low quiescent current. In many applications, the load is expected to be in this state most of the time. 6 Operating Principle The MAX1642/MAX1643 employ a proprietary pulsefrequency-modulation (PFM) control scheme that combines the ultra-low quiescent current traditional of pulse-skipping PFM converters with the high-load efficiency of pulse-width-modulation (PWM) converters. The on-time and minimum off-times are varied as a function of the input and output voltages: t ON = K VBATT t OFF(MIN) = 1.2 x K VOUT - VBATT where K is typically 25V-µs. This enables the MAX1642/MAX1643 to maintain high efficiency over a wide range of loads and input/output voltages. The DCDC converter is powered from the OUT pin. _______________________________________________________________________________________ High-Efficiency, Step-Up DC-DC Converters for 1V Inputs Bootstrap DC-DC Block The bootstrap block contains a low-voltage start-up oscillator. This oscillator pumps up the output voltage to approximately 1.7V, where the main DC-DC converter can operate. The oscillator is powered from the BATT input and drives an NPN switch. During start-up, the P-channel synchronous rectifier remains off and either its body diode or an external diode is used as an output rectifier. Reduce the load as needed to allow start-up with input voltages below 2V (see Typical Operating Characteristics). Shutdown (MAX1642) Pulling SHDN low places the MAX1642 in shutdown mode (ISHDN = 2µA typical). In shutdown, the internal switching MOSFET turns off, PFO goes highimpedance, and the synchronous rectifier turns off to prevent reverse current from flowing from the output back to the input. However, there is still a forward current path through the synchronous-rectifier body diode from the input to the output. Thus, in shutdown, the output remains one diode drop below the battery voltage (V BATT ). To disable the shutdown feature, connect SHDN (a logic input) to BATT. BATT OUT TIMING TON 0.5REF EN PFI TOFF LOGIC PDRV NDRV P MAX1642 LX PFO FB REF RFRDY N START-UP OSCILLATOR REF REF 0.5REF GND OUT 1.7V SHDN Figure 1. MAX1642 Functional Diagram _______________________________________________________________________________________ 7 MAX1642/MAX1643 When the error comparator detects that the output voltage is too low, it turns on the internal N-channel MOSFET switch until the on-time is satisfied (see Figure 1 and the Standard Application Circuits, Figures 2 and 3). During the on-time, current ramps up in the inductor, storing energy in a magnetic field. When the MOSFET turns off, during the second half of each cycle, the magnetic field collapses, causing the inductor voltage to force current through the synchronous rectifier, transferring the stored energy to the output filter capacitor and load. The output filter capacitor stores charge while current from the inductor is high, then holds up the output voltage until the second half of the next switching cycle, smoothing power flow to the load. MAX1642/MAX1643 High-Efficiency, Step-Up DC-DC Converters for 1V Inputs BATTLO (MAX1643) The MAX1643 contains an on-chip comparator for lowbattery detection. If the voltage at BATT drops below 1V, BATTLO sinks current. BATTLO is an open-drain output. In combination with PFI/PFO, this allows monitoring of both the input and output voltages. 100µH, 350mA 0.88V to 1.65V INPUT 22µF 0.1µF OUT PFI OUT Reverse-Battery Protection MAX1642 The MAX1642/MAX1643 can sustain/survive single-cell battery reversal up to the package power-dissipation limit. An internal 5Ω resistor in series with a diode limits reverse current to less than 220mA, which prevents damage to the MAX1642/MAX1643. Prolonged operation above 220mA reverse-battery current can degrade the devices’ performance. ________________Design Information LX BATT 3.3VOUT 0.1µF 22µF PF0 SHDN GND FB Figure 2. MAX1642 3.3V Standard Application Circuit Output Voltage Selection The MAX1642/MAX1643 operate with a 3.3V ±4% or adjustable output. To select fixed-voltage operation, connect FB to GND. For an adjustable output between 2V and 5.2V, connect FB to a resistor voltage divider between OUT and GND (Figure 4). FB regulates to 1.23V. Since FB leakage is 10nA max, select feedback resistor R2 in the 100kΩ to 1MΩ range. R1 is given by: V R1 = R2 OUT - 1 VREF where VREF = 1.23V. 0.88V to 1.65V INPUT 100µH, 350mA 22µF 0.1µF LX BATT 3.3VOUT OUT OUT MAX1643 0.1µF 22µF PFI BATTLO PFO GND FB Power-Fail Detection The MAX1642/MAX1643 have an on-chip comparator for power-fail detection. This comparator can detect loss of power at the input or output. If the voltage at PFI falls below 614mV, the PFO output sinks current to GND. Hysteresis at the power-fail input is 1%. The power-fail monitor’s threshold is set by two resistors: R3 and R4 (Figure 5). Set the threshold using the following equation: V R3 = R4 TH - 1 VPFI where VTH is the desired threshold of the power-fail detector, and VPFI is the 614mV reference of the powerfail comparator. Since PFI leakage is 10nA max, select feedback resistor R4 in the 100kΩ to 1MΩ range. Low-Battery Start-Up The MAX1642/MAX1643 are bootstrapped circuits with a low-voltage start-up oscillator. They can start under low-load conditions at lower battery voltages than at full load. Once started, the output can maintain the load as 8 Figure 3. MAX1643 3.3V Standard Application Circuit the battery voltage decreases below the start-up voltage (see Typical Operating Characteristics). Inductor Selection A 100µH inductor is recommended for most applications. The use of lower inductor values (down to 68µH) increases maximum output current. Higher values (up to 220µH) reduce peak inductor current and consequent ripple and noise. The inductor’s saturationcurrent rating must exceed the peak current limit synthesized by the MAX1642/MAX1643’s timing algorithms: IPEAK = KMAX LMIN where KMAX = 35V-µs. The maximum recommended IPEAK is 350mA. For best efficiency, inductor series resistance should be less than 1Ω. _______________________________________________________________________________________ High-Efficiency, Step-Up DC-DC Converters for 1V Inputs 100µH 0.88V to 1.65V INPUT 22µF MAX1642/MAX1643 Capacitor Selection Choose input and output capacitors to service input and output peak currents with acceptable voltage ripple. A 22µF, 6V, low-ESR, surface-mount tantalum output filter capacitor typically provides 60mV output ripple when stepping up from 1.3V to 3.3V at 20mA. The input filter capacitor (CIN) also reduces peak currents drawn from the battery and improves efficiency. Low equivalent series resistance (ESR) capacitors are recommended. Capacitor ESR is a major contributor to output ripple (usually more than 60%). Ceramic capacitors have the lowest ESR, but low-ESR tantalums represent a good balance between cost and performance. Low-ESR aluminum electrolytic capacitors are tolerable, and standard aluminum electrolytic capacitors should be avoided. Do not exceed tantalum capacitors’ ripplecurrent ratings; select capacitors with a rating exceeding the peak inductor current (IPEAK). 0.1µF BATT LX PFI OUT VOUT = 2V TO 5.2V OUT 100pF* MAX1642 R1 FB PF0 SHDN R2 GND *OPTIONAL COMPENSATION Figure 4. Adjustable-Output Circuit PC Board Layout and Grounding High switching frequencies and large peak currents make PC board layout an important part of design. Poor design can result in excessive EMI on the feedback paths and voltage gradients in the ground plane. Both of these factors can result in instability or regulation errors. The OUT pin must be bypassed directly to GND as close to the IC as possible (within 0.2 in. or 5mm). Place power components—such as the MAX1642/ MAX1643, inductor, input filter capacitor, and output filter capacitor—as close together as possible. Keep their traces short, direct, and wide (≥50 mil or 1.25mm), and place their ground pins close together in a star-ground configuration. Keep the extra copper on the board and integrate it into ground as a pseudo-ground plane. On multilayer boards, route the star ground using component-side copper fill, then connect it to the internal ground plane using vias. Place the external voltage-feedback network very close to the FB pin (within 0.2 in. or 5mm). Noisy traces, such as from the LX pin, should be kept away from the voltagefeedback network and separated from it using grounded copper. The evaluation kit manual shows an example PC board layout, routing, and pseudo-ground plane. Noise and Voltage Ripple EMI and output voltage ripple can be minimized by following a few simple design rules. 1) Place the DC-DC converter and digital circuitry on an opposite corner of the PC board, away from sensitive RF and analog input stages. VTH MAX1642 MAX1643 R3 PFI R4 Figure 5. Power-Fail Detection Circuit 2) Use a closed-core inductor, such as toroid or shielded bobbin, to minimize fringe magnetic fields. 3) Choose the largest inductor value that satisfies the load requirement to minimize peak switching current and resulting ripple and noise. 4) Use low-ESR input and output filter capacitors. 5) Follow sound circuit-board layout and grounding rules (see the PC Board Layout and Grounding section). 6) Where necessary, add LC pi filters, linear post-regulators such as the MAX8863 and MAX8864 (SOT23 package), or shielding. The LC pi filter’s cutoff frequency should be at least a decade or two below the DC-DC converter’s switching frequency for the specified load and input voltage. _______________________________________________________________________________________ 9 MAX1642/MAX1643 High-Efficiency, Step-Up DC-DC Converters for 1V Inputs __________________ Chip Information Table 1. Component Suppliers SUPPLIER AVX USA Coilcraft Coiltronics Dale USA USA USA USA Japan USA Japan USA USA Japan USA Nichicon Sanyo Sprague Sumida TDK PHONE FAX (803) 946-0690 (800) 282-4975 (847) 639-6400 (561) 241-7876 (605) 668-4131 (847) 843-7500 81-7-5231-8461 (619) 661-6835 81-7-2070-6306 (603) 224-1961 (847) 956-0666 81-3-3607-5111 (847) 390-4373 (803) 626-3123 TRANSISTOR COUNT: 594 SUBSTRATE CONNECTED TO GND (847) 639-1469 (561) 241-9339 (605) 665-1627 (847) 843-2798 81-7-5256-4158 (619) 661-1055 81-7-2070-1174 (603) 224-1430 (847) 956-0702 81-3-3607-5144 (847) 390-4428 Table 2. Surface-Mount Inductor Information INDUCTOR SPECIFICATION INDUCTANCE (µH) 68 100 150 220 10 VENDOR/PART RESISTANCE (Ω) ISAT (mA) Coilcraft DO1608-683 0.75 400 Sumida CD54-680 0.46 610 Coilcraft DO1608-104 1.1 310 Sumida CD54-101 0.7 520 TDK NLC565050T-101K 1.6 250 Coilcraft DO1608-154 1.7 270 Sumida CD54-151 1.1 400 TDK NLC565050T-151K 2.2 210 Coilcraft DO1608-224 2.3 220 Sumida CD54-221 1.57 350 ______________________________________________________________________________________ High-Efficiency, Step-Up DC-DC Converters for 1V Inputs 8LUMAXD.EPS ______________________________________________________________________________________ 11 MAX1642/MAX1643 ________________________________________________________Package Information MAX1642/MAX1643 High-Efficiency, Step-Up DC-DC Converters for 1V Inputs NOTES 12 ______________________________________________________________________________________