19-1360; Rev 0; 7/98 KIT ATION EVALU LE B A IL A AV High-Efficiency, Low-Supply-Current, Compact, Step-Up DC-DC Converters ____________________________Features ♦ 94% Efficient at 200mA Output Current The input voltage ranges from 0.7V to VOUT, where VOUT can be set from 2V to 5.5V. Start-up is guaranteed from 1.1V inputs. The MAX1674/MAX1675/ MAX1676 have a preset, pin-selectable output for 5V or 3.3V. The outputs can also be adjusted to other voltages using two external resistors. All three devices have a 0.3Ω N-channel MOSFET power switch. The MAX1674 has a 1A current limit. The MAX1675 has a 0.5A current limit, which permits the use of a smaller inductor. The MAX1676 comes in a 10-pin µMAX package and features an adjustable current limit and circuitry to reduce inductor ringing. ♦ LBI/LBO Low-Battery Detector ________________________Applications Pagers Wireless Phones Medical Devices Hand-Held Computers ♦ 16µA Quiescent Supply Current ♦ Internal Synchronous Rectifier (no external diode) ♦ 0.1µA Logic-Controlled Shutdown ♦ Selectable Current Limit for Reduced Ripple ♦ Low-Noise, Anti-Ringing Feature (MAX1676) ♦ 8-Pin and 10-Pin µMAX Packages ♦ Preassembled Evaluation Kit (MAX1676EVKIT) _______________Ordering Information PART TEMP. RANGE PIN-PACKAGE MAX1674EUA MAX1675EUA MAX1676EUB -40°C to +85°C -40°C to +85°C -40°C to +85°C 8 µMAX 8 µMAX 10 µMAX PDAs RF Tags Pin Configurations 1 to 3-Cell Hand-Held Devices TOP VIEW Typical Operating Circuit FB 1 INPUT 0.7V TO VOUT LBI 2 LBO 3 MAX1674 MAX1675 REF 4 ON SHDN OFF LX MAX1674 OUT MAX1675 OUTPUT 3.3V, 5V, OR ADJ (2V TO 5.5V) UP TO 300mA FB 1 LBI REF 0.1µF LBO FB GND LOW-BATTERY DETECT OUT OUT 7 LX 6 GND 5 SHDN µMAX 10 OUT LBI 2 LOW-BATTERY DETECT IN 8 LBO 3 MAX1676 9 LX 8 GND CLSEL 4 7 BATT REF 5 6 SHDN 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. MAX1674/MAX1675/MAX1676 General Description The MAX1674/MAX1675/MAX1676 compact, high-efficiency, step-up DC-DC converters fit in small µMAX packages. They feature a built-in synchronous rectifier, which improves efficiency and reduces size and cost by eliminating the need for an external Schottky diode. Quiescent supply current is only 16µA. MAX1674/MAX1675/MAX1676 High-Efficiency, Low-Supply-Current, Compact, Step-Up DC-DC Converters ABSOLUTE MAXIMUM RATINGS Supply Voltage (OUT to GND) ..............................-0.3V to +6.0V Switch Voltage (LX to GND) .....................-0.3V to (VOUT + 0.3V) Battery Voltage (BATT to GND).............................-0.3V to +6.0V SHDN, LBO to GND ..............................................-0.3V to +6.0V LBI, REF, FB, CLSEL to GND ...................-0.3V to (VOUT + 0.3V) Switch Current (LX) ...............................................-1.5A to +1.5A Output Current (OUT) ...........................................-1.5A to +1.5A Continuous Power Dissipation (TA = +70°C) 8-Pin µMAX (derate 4.1mW/°C above +70°C) .............330mW 10-Pin µMAX (derate 5.6mW/°C above +70°C) ...........444mW Operating Temperature Range ...........................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +165°C Lead Temperature (soldering, 10sec) .............................+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 (VBATT = 2V, FB = OUT (VOUT = 3.3V), RL = ˙∞, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN VIN Start-Up Voltage 1.1 TA = +25°C 0.9 TA = +25°C, RL = 3kΩ (Note 1) VOUT Reference Voltage Tempco FB = GND 4.80 5 5.20 2 IOUT VREF mV/°C 3.43 5.5 MAX1674, MAX1676 (CLSEL = OUT) 300 420 MAX1675, MAX1676 (CLSEL = GND) 150 220 V V mA MAX1674, MAX1676 (CLSEL = OUT) 180 285 MAX1675, MAX1676 (CLSEL = GND) 90 130 1.274 1.30 IREF = 0 1.326 0.024 TEMPCO V mV/°C Reference Voltage Load Regulation VREF_LOAD IREF = 0 to 100µA 3 15 mV Reference Voltage Line Regulation VREF_LINE VOUT = 2V to 5.5V 0.08 2.5 mV/V 1.30 1.326 V 0.3 0.6 Ω 1.274 FB, LBI Input Threshold Internal NFET, PFET On-Resistance LX Switch Current Limit (NFET) LX Leakage Current 2 V 3.30 FB = GND (VOUT = 5V) Reference Voltage V 1.1 3.17 FB = OUT (VOUT = 3.3V) Steady-State Output Current (Note 2) V FB = OUT Output Voltage Range UNITS 5.5 -2 Start-Up Voltage Tempco Output Voltage MAX 0.7 Minimum Input Voltage Operating Voltage TYP RDS(ON) ILIM ILEAK ILX = 100mA MAX1674, MAX1676 (CLSEL = OUT) 0.80 1 1.20 MAX1675, MAX1676 (CLSEL = GND) 0.4 0.5 0.65 0.05 1 VLX = 0, 5.5V; VOUT = 5.5V _______________________________________________________________________________________ A µA High-Efficiency, Low-Supply-Current, Compact, Step-Up DC-DC Converters MAX1674/MAX1675/MAX1676 ELECTRICAL CHARACTERISTICS (continued) (VBATT = 2V, FB = OUT (VOUT = 3.3V), RL = ˙∞, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER Operating Current into OUT (Note 3) Shutdown Current into OUT SYMBOL Efficiency CONDITIONS MIN TYP MAX UNITS VFB = 1.4V, VOUT = 3.3V 16 35 µA SHDN = GND 0.1 1 µA VOUT = 3.3V, ILOAD = 200mA 90 VOUT = 2V, ILOAD = 1mA 85 LX Switch On-Time tON VFB = 1V, VOUT = 3.3V 3 LX Switch Off-Time tOFF VFB = 1V, VOUT = 3.3V 0.8 FB Input Current IFB VFB = 1.4V LBI Input Current ILBI VLBI = 1.4V 1 % 4 7 1 1.2 µs 0.03 50 nA 50 nA µs CLSEL Input Current ICLSEL MAX1676, CLSEL = OUT 1.4 3 µA SHDN Input Current I SHDN V SHDN = 0 or VOUT 0.07 50 nA VLBI = 0, ISINK = 1mA 0.2 0.4 V V LBO = 5.5V, VLBI = 5.5V 0.07 1 µA 88 150 Ω LBO Low Output Voltage LBO Off Leakage Current I LBO Damping Switch Resistance SHDN Input Voltage CLSEL Input Voltage MAX1676, VBATT = 2V VIL 0.2VOUT VIH 0.8VOUT VIL 0.2VOUT VIH 0.8VOUT V V Note 1: Start-up voltage operation is guaranteed with the addition of a Schottky MBR0520 external diode between the input and output. Note 2: Steady-state output current indicates that the device maintains output voltage regulation under load. See Figures 5 and 6. Note 3: Device is bootstrapped (power to the IC comes from OUT). This correlates directly with the actual battery supply. ELECTRICAL CHARACTERISTICS (VBATT = 2V, FB = OUT, RL = ∞, TA = -40°C to +85°C, unless otherwise noted.) (Note 4) PARAMETER Output Voltage SYMBOL VOUT CONDITIONS MIN MAX FB = OUT 3.13 3.47 FB = GND 4.75 5.25 2.20 5.5 V 1.2675 1.3325 V 1.2675 1.3325 V 0.6 Ω Output Voltage Range Reference Voltage VREF IREF = 0 FB, LBI Thresholds Internal NFET, PFET On-Resistance RDS(ON) UNITS V Operating Current into OUT (Note 3) VFB = 1.4V, VOUT = 3.3V 40 µA Shutdown Current into OUT SHDN = GND 1 µA LX Switch On-Time tON VFB = 1V, VOUT = 3.3V 2.7 7.0 µs LX Switch Off-Time tOFF VFB = 1V, VOUT = 3.3V 0.75 1.25 µs MAX1674, MAX1676 (CLSEL = OUT) 0.75 1.25 MAX1675, MAX1676 (CLSEL = GND) 0.36 0.69 LX Switch Current Limit (NFET) ILIM A _______________________________________________________________________________________ 3 ELECTRICAL CHARACTERISTICS (continued) (VBATT = 2V, FB = OUT, RL = ∞, TA = -40°C to +85°C, unless otherwise noted.) (Note 4) PARAMETER SYMBOL CONDITIONS MIN MAX UNITS CLSEL Input Current ICLSEL MAX1676, CLSEL = OUT 3 µA SHDN Input Current I SHDN VSHDN = 0 or VOUT 75 nA V LBO = 5.5V, VLBI = 5.5V 1 µA LBO Off Leakage Current I LBO Note 4: Specifications to -40°C are guaranteed by design, not production tested. Typical Operating Characteristics (L = 22µH, CIN = 47µF, COUT = 47µF 0.1µF, CREF = 0.1µF, TA = +25°C, unless otherwise noted.) EFFICIENCY vs. LOAD CURRENT 90 80 EFFICIENCY (%) VIN = 2.4V 70 VIN = 1.2V 60 50 40 80 VIN = 2.4V 70 VIN = 3.6V VIN = 1.2V 60 50 40 30 30 VOUT = 5V ILIMIT = 500mA 10 0 0.01 0.1 1 10 100 0 0.01 0.1 1 10 100 VOUT = 3.3V ILIMIT = 500mA 0 1000 0.01 0.1 VIN = 2.4V 60 50 40 30 20 VOUT = 3.3V ILIMIT = 1A 10 0 1 10 LOAD CURRENT (mA) 100 10 100 1000 1.300 MAX1674 toc05 80 VIN = 1.2V 1 LOAD CURRENT (mA) REFERENCE OUTPUT VOLTAGE (V) MAX1674 toc04 90 EFFICIENCY (%) 40 REFERENCE OUTPUT VOLTAGE vs. TEMPERATURE 100 0.1 50 10 EFFICIENCY vs. LOAD CURRENT 0.01 60 LOAD CURRENT (mA) LOAD CURRENT (mA) 70 VIN = 1.2V 20 VOUT = 5V ILIMIT = 1A 10 1000 VIN = 2.4V 70 30 20 20 4 90 EFFICIENCY (%) VIN = 3.6V 80 100 MAX1674 toc02 MAX1674 toc01 90 EFFICIENCY vs. LOAD CURRENT 100 MAX1674 toc03 EFFICIENCY vs. LOAD CURRENT 100 EFFICIENCY (%) MAX1674/MAX1675/MAX1676 High-Efficiency, Low-Supply-Current, Compact, Step-Up DC-DC Converters 1.298 IREF = 0 1.296 1.294 IREF = 100µA 1.292 1.290 -40 -20 0 20 40 60 TEMPERATURE (°C) _______________________________________________________________________________________ 80 100 1000 High-Efficiency, Low-Supply-Current, Compact, Step-Up DC-DC Converters NO-LOAD BATTERY CURRENT vs. INPUT BATTERY VOLTAGE 100 80 ILIMIT = 0.5A, 5.0V 60 ILIMIT = 0.5A, 3.3V 20 ILIMIT = 1A, 3.3V 0 1.0 0.8 0.6 WITH 1N5817 -1.0 0.01 0.1 1 100 MAXIMUM OUTPUT CURRENT vs. INPUT VOLTAGE (VOUT = 3.3V) 0.6 0.4 0.2 MAX1674toc11 1A CURRENT LIMIT 600 500 400 300 200 0.5A CURRENT LIMIT 800 MAXIMUM OUTPUT CURRENT (mA) 0.8 800 700 100 0 1.0 1.5 2.0 MAX1674 TOC13 2.5 3.0 3.5 4.0 200 0.5A CURRENT LIMIT 100 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 LX CURRENT LIMIT vs. OUTPUT VOLTAGE 1.2 MAX1674toc13.5 P-CHANNEL 0.35 MAX1674, MAX1676 (CLSEL = OUT) 1.0 0.8 0.30 ILIM (A) RESISTANCE (Ω) 300 4.5 N-CHANNEL 0.25 0.20 0.6 0.4 0.15 MAX1675, MAX1676 (CLSEL = GND) 0.10 0.2 0.05 0 0 1µs/div 400 SWITCH RESISTANCE vs. TEMPERATURE 0.40 VOUT AC COUPLED 100mV/div 1A CURRENT LIMIT 500 INPUT VOLTAGE (V) 0.45 VLX 5V/div ILX 0.5A/div 600 INPUT VOLTAGE (V) SUPPLY VOLTAGE (V) HEAVY-LOAD SWITCHING WAVEFORMS 700 0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V) 900 MAXIMUM OUTPUT CURRENT (mA) MAX1674TOC10 SHUTDOWN THRESHOLD (V) 1 10 LOAD CURRENT (mA) MAXIMUM OUTPUT CURRENT vs. INPUT VOLTAGE (VOUT = 5V) 1.0 VIN = 2.4V VOUT = 5.0V -0.4 -0.8 SHUTDOWN THRESHOLD vs. SUPPLY VOLTAGE 0 0 -0.2 -0.6 INPUT BATTERY VOLTAGE (V) 1.2 0.2 0.2 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 1.4 0.4 0.4 0 0 MAX167toc09 MAX1674toc08 WITHOUT DIODE 0.6 MAX1674toc12 40 1.4 1.2 0.8 MAX1674toc14 ILIMIT = 1A, 5.0V 1.0 SHUTDOWN CURRENT (µA) 120 1.6 START-UP VOLTAGE (V) 140 INPUT BATTERY CURRENT (µA) 1.8 MAX1674toc07 160 SHUTDOWN CURRENT vs. SUPPLY VOLTAGE START-UP VOLTAGE vs. LOAD CURRENT -60 -40 -20 0 20 40 TEMPERATURE (°C) 60 80 100 2.0 2.5 3.0 3.5 4.0 4.5 5.0 OUTPUT VOLTAGE (V) _______________________________________________________________________________________ 5 MAX1674/MAX1675/MAX1676 Typical Operating Characteristics (continued) (L = 22µH, CIN = 47µF, COUT = 47µF 0.1µF, CREF = 0.1µF, TA = +25°C, unless otherwise noted.) MAX1674/MAX1675/MAX1676 High-Efficiency, Low-Supply-Current, Compact, Step-Up DC-DC Converters Typical Operating Characteristics (continued) (L = 22µH, CIN = 47µF, COUT = 47µF 0.1µF, CREF = 0.1µF, TA = +25°C, unless otherwise noted.) LOAD-TRANSIENT RESPONSE LINE-TRANSIENT RESPONSE MAX1674 TOC17 VIN = 2.4V VOUT = 3.3V VIN 2V TO 3V 1V/div VOUT 2V/div IOUT 200mA/div VSHDN 2V/div VOUT 50mV/div AC COUPLED VOUT AC COUPLED 100mV/div ILOAD 100mA EXITING SHUTDOWN MAX1674 TOC16 MAX1674 TOC15 5µs/div 10µs/div 500µs/div Pin Description PIN NAME FUNCTION MAX1674 MAX1675 MAX1676 1 1 FB Dual-Mode™ Feedback Input. Connect to GND for +5.0V output. Connect to OUT for +3.3V output. Use a resistor network to set the output voltage from +2.0V to +5.5V. 2 2 LBI Low-Battery Comparator Input. Internally set to trip at +1.30V. 3 3 LBO Open-Drain Low-Battery Comparator Output. Output is low when VLBI is <1.3V. LBO is high impedance during shutdown. — 4 CLSEL 4 5 REF 5 6 SHDN Shutdown Input. High = operating, low = shutdown. — 7 BATT Battery Input and Damping Switch Connection. If damping switch is unused, leave BATT unconnected. 6 8 GND Ground 7 9 LX 8 10 OUT Current-Limit Select Input. CLSEL = OUT sets the current limit to 1A. CLSEL = GND sets the current limit to 0.5A. 1.3V Reference Voltage. Bypass with a 0.1µF capacitor. N-Channel and P-Channel Power MOSFET Drain Power Output. OUT provides bootstrap power to the IC. Dual-Mode is a trademark of Maxim Integrated Products. 6 _______________________________________________________________________________________ High-Efficiency, Low-Supply-Current, Compact, Step-Up DC-DC Converters The MAX1674/MAX1675/MAX1676 compact, step-up DC-DC converters start up with voltages as low as 0.9V and operate with an input voltage down to 0.7V. Consuming only 16µA of quiescent current, these devices offer a built-in synchronous rectifier that reduces cost by eliminating the need for an external diode and improves overall efficiency by minimizing losses in the circuit (see Synchronous Rectification section for details). The internal MOSFET resistance is typically 0.3Ω, which minimizes losses. The current limit of the MAX1674 and MAX1675 are 1A and 0.5A, respectively. The MAX1675’s lower current limit allows the use of a physically smaller inductor in space-sensitive applications. The MAX1676 features a circuit that eliminates noise due to inductor ringing. In addition, the MAX1676 offers a selectable current limit (0.5A or 1A) for design flexibility. PFM Control Scheme A unique minimum-off-time, current-limited, pulse-frequency-modulation (PFM) control scheme is a key feature of the MAX1674/MAX1675/MAX1676. This scheme combines the high output power and efficiency of a pulse-width-modulation (PWM) device with the ultra-low quiescent current of a traditional PFM (Figure 1). There is no oscillator; a constant-peak-current limit in the switch allows the inductor current to vary between this peak limit and some lesser value. At light loads, the switching frequency is governed by a pair of one-shots that set a typical minimum off-time (1µs) and a typical maximum on-time (4µs). The switching frequency depends upon the load and the input voltage, and can range up to 500kHz. The peak current of the internal Nchannel MOSFET power switch is fixed at 1A (MAX1674), at 0.5A (MAX1675), or is selectable (MAX1676). Unlike conventional pulse-skipping DC-DC converters (where ripple amplitude varies with input voltage), ripple in these devices does not exceed the product of the switch current limit and the filter-capacitor equivalent series resistance (ESR). Synchronous Rectification The internal synchronous rectifier eliminates the need for an external Schottky diode, thus reducing cost and board space. During the cycle off-time, the P-channel MOSFET turns on and shunts the MOSFET body diode. OUT MINIMUM OFF-TIME ONE-SHOT SHDN EN TRIG Q ONE-SHOT 0.1µF 47µF ZERO CROSSING AMPLIFIER P VIN LX 22µH F/F S R CLSEL (MAX1676) GND Q MAX1674 MAX1675 MAX1676 BATT CURRENT-LIMIT AMPLIFIER TRIG Q ONE-SHOT VOUT DAMPING SWITCH FB ERROR AMPLIFIER LOW-BATTERY COMPARATOR R4 R5 R6 REFERENCE LBO R1 200Ω (MAX1676) R3 R2 100k 47µF N MAXIMUM ON-TIME ONE-SHOT VIN VOUT REF 0.1µF LBI Figure 1. Simplified Functional Diagram _______________________________________________________________________________________ 7 MAX1674/MAX1675/MAX1676 Detailed Description MAX1674/MAX1675/MAX1676 High-Efficiency, Low-Supply-Current, Compact, Step-Up DC-DC Converters As a result, the synchronous rectifier significantly improves efficiency without the addition of an external component. Conversion efficiency can be as high as 94%, as shown in the Typical Operating Characteristics. For low-voltage inputs from single cells (Alkaline, NiCd, or NiMH), use an external Schottky diode such as the 1N5817 to ensure start-up. Voltage Reference The voltage at REF is nominally +1.30V. REF can source up to 100µA to external circuits. The reference maintains excellent load regulation (see Typical Operating Characteristics). A bypass capacitor of 0.1µF is required for proper operation. VIN R1 200Ω BATT 22µH MAX1676 DAMPING SWITCH LX 0.1µF Shutdown The device enters shutdown when V SHDN is low. During shutdown, the body diode of the P-channel MOSFET allows current flow from the battery to the output. V OUT falls to approximately VIN - 0.6V and LX remains high impedance. The capacitance and load at OUT determine the rate at which V OUT decays. Shutdown can be pulled as high as 6V, regardless of the voltage at OUT. VOUT OUT 47µF Figure 2. Simplified Diagram of Inductor Damping Switch Current Limit Select Pin (MAX1676) The MAX1676 allows a selectable inductor current limit of either 0.5A or 1A. This allows flexibility in designing for higher current applications or for smaller, compact designs. Connect CLSEL to OUT for 1A or to GND for 0.5A. CLSEL draws 1.4µA when connected to OUT. VLX 1V/div BATT/Damping Switch (MAX1676) The MAX1676 is designed with an internal damping switch to minimize ringing at LX. The damping switch connects an external resistor (R1) across the inductor when the inductor’s energy is depleted (Figure 2). Normally, when the energy in the inductor is insufficient to supply current to the output, the capacitance and inductance at LX form a resonant circuit that causes ringing. The ringing continues until the energy is dissipated through the series resistance of the inductor. The damping switch supplies a path to quickly dissipate this energy, minimizing the ringing at LX. Damping LX ringing does not reduce VOUT ripple, but does reduce EMI. R1 = 200Ω works well for most applications while reducing efficiency by only 1%. Larger R1 values provide less damping, but have less impact on efficiency. Generally, lower values of R1 are needed to fully damp LX when the VOUT/VIN ratio is high (Figures 2, 3, and 4). 2µs/div Figure 3. LX Ringing Without Damping Switch VLX 1V/div 2µs/div Figure 4. LX Waveform with Damping Switch (with 200Ω external resistor) 8 _______________________________________________________________________________________ High-Efficiency, Low-Supply-Current, Compact, Step-Up DC-DC Converters R5 = R6 [(VOUT / VREF ) - 1] VIN 47µF 10V R1 200Ω BATT (MAX1676) 22µH LX VOUT OUT R3 CLSEL (MAX1676) LBI 0.1µF +3.3V 200mA 47µF FB R4 SHDN REF MAX1674 MAX1675 MAX1676 R2 100k where VREF = +1.3V and VOUT may range from 2V to 5V. The input bias current of FB has a maximum value of 50nA which allows large-value resistors (R6 ≤ 260kΩ) to be used. Low-Battery Detection The MAX1674/MAX1675/MAX1676 contain an on-chip comparator for low-battery detection. If the voltage at LBI falls below the internal reference voltage (1.30V), LBO (an open-drain output) sinks current to GND. The low-battery monitor threshold is set by two resistors, R3 and R4 (Figures 5, 6, and 7). Since the LBI current is less than 50nA, large resistor values (R4 ≤ 260kΩ) can be used to minimize loading of the input supply. Calculate R3 using the following equation: R3 = R4 [(VTRIP / VREF) - 1] for VTRIP ≥ 1.3V. VTRIP is the level where the low-battery detector output goes low, and V REF is the internal 1.30V reference. Connect a pull-up resistor of 100kΩ or greater from LBO to OUT when driving CMOS circuits. LBO is an open-drain output, and can be pulled as high as 6V regardless of the voltage at OUT. When LBI is above the threshold, the LBO output is high impedance. If the low-battery comparator is not used, ground LOW-BATTERY OUTPUT LBO VIN GND 0.1µF Figure 5. Preset Output Voltage of +3.3V 47µF 22µH VIN R1 200Ω 47µF R1 200Ω R3 22µH LX OUTPUT 5.0V, 150mA OUT R3 CLSEL (MAX1676) 0.1µF MAX1674 MAX1675 MAX1676 47µF REF 0.1µF LBO REF LOWBATTERY OUTPUT 0.1µF R2 100k R2 100k MAX1674 MAX1675 MAX1676 OUTPUT 2V to 5.5V SHDN CLSEL (MAX1676) R4 SHDN R4 LX OUT LBI BATT (MAX1676) LBI BATT (MAX1676) 47µF R5 LOWBATTERY OUTPUT LBO FB GND 0.1µF R6 FB GND Figure 6. Preset Output Voltage of +5V Figure 7. Setting an Adjustable Output _______________________________________________________________________________________ 9 MAX1674/MAX1675/MAX1676 Selecting the Output Voltage VOUT can be set to 3.3V or 5.5V by connecting the FB pin to GND (5V) or OUT (3.3V) (Figures 5 and 6). To adjust the output voltage, connect a resistor-divider from VOUT to FB to GND (Figure 7). Choose a value less than 260kΩ for R6. Use the following equation to calculate R5: MAX1674/MAX1675/MAX1676 High-Efficiency, Low-Supply-Current, Compact, Step-Up DC-DC Converters VIN VTRIP (VH, VL) MAX1674 MAX1675 MAX1676 R3 47µF 22µH R1 200Ω VOUT OUT 0.1µF 47µF LBI BATT (MAX1676) LX VOUT OUT R3 CLSEL (MAX1676) LBI R2 100k R4 LBO 47µF 0.1µF FB GND R7 SHDN MAX1674 MAX1675 REF MAX1676 GND LBO R2 100k LOWBATTERY OUTPUT R4 0.1µF VH = 1.3V 1 + VL = 1.3V 1 + ( ) R3 R3 + R7 R4 ( ) (VOUT − 1.3V) R 3 R3 − R4 (1.3V) (R2 + R7) WHERE VH IS THE UPPER TRIP LEVEL VL IS THE LOWER TRIP LEVEL Figure 8. Setting Resistor Values for the Low-Battery Indicator when VIN < 1.3V LBI and LBO. For VTRIP less than 1.3V, configure the comparator as shown in Figure 8. Calculate the value of the external resistors R3 and R4 as follows: R3 = R4(VREF - VTRIP) / (VOUT - VREF) Since the low-battery comparator is noninverting, external hysteresis can be added by connecting a resistor between LBO and LBI as shown in Figure 9. When LBO is high, the series combination of R2 and R7 source current into the LBI summing junction. Figure 9. Adding External Hysteresis to the Low-Battery Indicator MAX1674, 500mA for the MAX1675, and 1A or 0.5A for the MAX1676. However, it is generally acceptable to bias the inductor into saturation by as much as 20%, although this will slightly reduce efficiency. Table 1 lists suggested components. The inductor’s DC resistance significantly affects efficiency. See Table 2 for a comparison of inductor specifications. Calculate the maximum output current as follows: Applications Information Inductor Selection An inductor value of 22µH performs well in most applications. The MAX1674/MAX1675/MAX1676 will also work with inductors in the 10µH to 47µH range. Smaller inductance values typically offer a smaller physical size for a given series resistance, allowing the smallest overall circuit dimensions. However, due to higher peak inductor currents, the output voltage ripple (I PEAK x output filter capacitor ESR) also tends to be higher. Circuits using larger inductance values exhibit higher output current capability and larger physical dimensions for a given series resistance. The inductor’s incremental saturation current rating should be greater than the peak switch-current limit, which is 1A for the 10 IOUT(MAX) VOUT – VBATT η VBATT ILIM – 1/ 2 L + R P t OFF = VOUT where IOUT(MAX) = maximum output current in amps VBATT = input voltage L = inductor value in µH η= efficiency (typically 0.9) tOFF = LX switch’s off-time in µs RP = resistance of P-channel MOSFET in Ω ILIM = 0.5A or 1.0A ______________________________________________________________________________________ High-Efficiency, Low-Supply-Current, Compact, Step-Up DC-DC Converters PRODUCTION METHOD INDUCTORS RECTIFIERS (OPTIONAL) CAPACITORS Surface Mount Sumida CD43 series Sumida CD54 series Coilcraft DT1608C Coilcraft DO1608C Coiltronics Uni-PAC Murata LQH4 series Sprague 593D series Sprague 595D series AVX TPS series ceramic Miniature Through-Hole Sumida RCH654-220 Sanyo OS-CON series Table 2. Surface-Mount Inductor Specifications — Table 3. Component Suppliers COMPANY MANUFACTURER PART NUMBER µH Coilcraft DT1608C-103 10 0.095 0.7 2.92 Coilcraft DO1608C-153 15 0.200 0.9 2.92 Coilcraft DO1608C-223 22 0.320 0.7 2.92 Coiltronics UP1B-100 10 0.111 1.9 5.0 Coiltronics UP1B-150 15 0.175 1.5 5.0 Coiltronics UP1B-220 22 0.254 1.2 5.0 Murata LQH4N100 10 0.560 0.4 2.6 Murata LQH4N220 22 0.560 0.4 2.6 Sumida CD43-8R2 8.2 0.132 1.26 3.2 Sumida CD43-100 10 0.182 1.15 3.2 Sumida CD54-100 10 0.100 1.44 4.5 Sumida CD54-180 18 0.150 1.23 4.5 Sumida CD54-220 22 0.180 1.11 4.5 Ω (max) IPEAK (A) Motorola MBR0530 Nihon EC 15QS02L HEIGHT (mm) Capacitor Selection A 47µF, 10V surface-mount tantalum (SMT) output filter capacitor provides 80mV output ripple when stepping up from 2V to 5V. Smaller capacitors (down to 10µF with higher ESRs) are acceptable for light loads or in applications that can tolerate higher output ripple. Values in the 10µF to 100µF range are recommended. The equivalent series resistance (ESR) of both bypass and filter capacitors affects efficiency and output ripple. Output voltage ripple is the product of the peak PHONE FAX AVX USA (803) 946-0690 USA (803) 626-3123 Coilcraft USA (847) 639-6400 USA (847) 639-1469 Coiltronics USA (561) 241-7876 USA (561) 241-9339 Motorola USA (303) 675-2140 (800) 521-6274 USA (303) 675-2150 Murata USA (814) 237-1431 (800) 831-9172 USA (814) 238-0490 Nihon USA (805) 867-2555 USA (805) 867-2556 Japan 81-3-3494-7411 Japan 81-3-3494-7414 Sanyo USA (619) 661-6835 USA (619) 661-1055 Japan 81-7-2070-6306 Japan 81-7-2070-1174 Sprague Sumida Taiyo Yuden USA (603) 224-1961 USA (603) 224-1430 USA (647) 956-0666 USA (647) 956-0702 Japan 81-3-3607-5111 Japan 81-3-3607-5144 USA (408) 573-4150 USA (408) 573-4159 inductor current and the output capacitor ESR. Use low-ESR capacitors for best performance, or connect two or more filter capacitors in parallel. Low-ESR, SMT tantalum capacitors are currently available from Sprague (595D series) AVX (TPS series) and other sources. Ceramic surface-mount and Sanyo OS-CON organic-semiconductor through-hole capacitors also exhibit very low ESR, and are especially useful for operation at cold temperatures. See Table 3 for a list of suggested component suppliers. ______________________________________________________________________________________ 11 MAX1674/MAX1675/MAX1676 Table 1. Suggested Components Optional External Rectifier VIN SINGLE CELL Although not required, a Schottky diode (such as the MBR0520) connected between LX and OUT allows lower start-up voltages (Figure 10) and is recommended for single-cell operation. Note that adding this diode provides no significant efficiency improvement. 47µF 22µH R1 200Ω PC Board Layout and Grounding Careful printed circuit layout is important for minimizing ground bounce and noise. Keep the IC’s GND pin and the ground leads of the input and output filter capacitors less than 0.2in (5mm) apart. In addition, keep all connections to the FB and LX pins as short as possible. In particular, when using external feedback resistors, locate them as close to the FB as possible. To maximize output power and efficiency and minimize output ripple voltage, use a ground plane and solder the IC’s GND directly to the ground plane. BATT (MAX1676) LX MBR0520 OUT R3 LBI MAX1674 MAX1675 MAX1676 FB 0.1µF 47µF SHDN R4 R2 100k CLSEL (MAX1676) LOW-BATTERY OUTPUT LBO REF 0.1µF GND Figure 10. Adding a Schottky Diode for Single-Cell Operation Chip Information TRANSISTOR COUNT: 751 Package Information 10LUMAXB.EPS MAX1674/MAX1675/MAX1676 High-Efficiency, Low-Supply-Current, Compact, Step-Up DC-DC Converters 12 ______________________________________________________________________________________