19-0374; Rev 1; 5/96 KIT ATION EVALU BLE A IL A V A 3.3V/5V or Adjustable-Output, Single-Cell DC-DC Converters ____________________________Features 0.8V to 6.0V Input Supply Voltage 0.9V Guaranteed Start-Up Supply Voltage >80% Efficiency Over Wide Load Range 100A No-Load Battery Current (VOUT = 3.3V) 1A Shutdown Mode Up to 250kHz Switching Frequency 1.5% Reference Tolerance Low-Battery Detector (LBI/LBO) Available in Ultra-Small 8-Pin MAX Package (1.11mm high) Circuit Fits in 0.2in2 ______________Ordering Information ________________________Applications Pagers Remote Controls Detectors 1-Cell Battery-Operated Equipment Backup Supplies PART TEMP. RANGE PIN-PACKAGE MAX866C/D 0C to +70C Dice* MAX866ESA -40C to +85C 8 SO MAX866EUA MAX867C/D MAX867ESA MAX867EUA -40C to +85C 0C to +70C -40C to +85C -40C to +85C 8 MAX Dice* 8 SO 8 MAX * Dice are tested at TA = +25C only. __________Typical Operating Circuit INPUT 0.8V TO VOUT TOP VIEW 330H OUTPUT 5V OR 3.3V ON/OFF _________________Pin Configurations SHDN LX MBRS0520LTI OR 1N5817 SHDN 1 8 LX 3/5 2 7 GND 6 OUT 5 LBI REF 3 MAX866 LBO 4 SO/MAX 47F MAX866 3V/5V SELECT LOW-BATTERY DETECTOR INPUT 3/5 OUT LBI REF GND LBO LOW-BATTERY DETECTOR OUTPUT SHDN 1 8 LX FB 2 7 GND 6 OUT 5 LBI REF 3 MAX867 LBO 4 0.22F SO/MAX ________________________________________________________________ Maxim Integrated Products 1 For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800 MAX866/MAX867 _______________General Description The MAX866 and MAX867 are ultra-small, high-efficiency, CMOS, step-up, DC-DC switching regulators for 1-cell battery-powered systems. The MAX866 accepts a positive input voltage between 0.8V and VOUT and converts it to a higher, pin-selectable output voltage of 3.3V or 5V. The MAX867 adjustable version accepts 0.8V to 6.0V input voltages and generates a higher adjustable output voltage in the 2.7V to 6.0V range. Typical efficiencies are greater than 80%. Typical no-load supply current is 100A (1A in shutdown). The MAX866/MAX867 combine ultra-low quiescent supply current and high efficiency to give maximum battery life. Its high switching frequency permits the use of small, low-cost inductors and capacitors. Additionally, internal peak-current limiting protects the IC. MAX866/MAX867 3.3V/5V or Adjustable-Output, Single-Cell DC-DC Converters ABSOLUTE MAXIMUM RATINGS Supply Voltage (OUT to GND) ...................................-0.3V, +7V Switch Voltage (LX to GND) .......................................-0.3V, +7V ------- SHDN , LBO to GND ....................................................-0.3V, +7V -- LBI, REF, 3/ 5, FB to GND ............................-0.3V, (VOUT + 0.3V) Reference Current (IREF) ..................................................2.5mA Continuous Power Dissipation (TA = +70C) SO (derate 5.88mW/C above +70C) .........................471mW MAX (derate 4.1mW/C above +70C) ......................330mW Reverse Battery Current (TA +45C) (Note 1)................750mA Operating Temperature Ranges MAX86_C/D .......................................................0C to +70C MAX86_E_A ....................................................-40C to +85C Junction Temperature .....................................................+150C Storage Temperature Range ............................-65C to +160C Lead Temperature (soldering, 10sec) ............................+300C Note 1: Reverse battery current is measured from the Typical Operating Circuit's battery input terminal to GND when the battery is connected backwards. A reverse current of 750mA will not exceed the package dissipation limits but, if left for an extended time (more than ten 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 (Circuit of Figure 2, VIN = 1.2V, ILOAD = 0mA, TA = +25C, unless otherwise noted.) PARAMETER CONDITIONS MIN TYP MAX UNITS 0.8 0.9 V 4.80 5.0 5.20 3.17 3.3 3.43 4.80 5.0 5.20 4.75 5.0 5.25 3.13 3.3 3.47 4.75 5.0 5.25 4.80 5.0 5.20 Minimum Start-Up Supply Voltage 0.9V VIN 3V Output Voltage (Note 2) -- MAX866, 3/ 5 = 0V, 0mA ILOAD 6mA -- MAX866, 3/ 5 = 3V, 0mA ILOAD 8mA MAX867, VOUT = 5V, 0mA ILOAD 6mA -- MAX866, 3/ 5 = 0V, 0mA ILOAD 6mA 0.9V VIN 3V, -- TA =TMIN TO TMAX MAX866, 3/ 5 = 3V, 0mA ILOAD 8mA (Note 3) MAX867, V = 5V, 0mA I 6mA OUT 1.2V VIN 3V -- MAX866, 3/ 5 = 0V, 0mA ILOAD 10mA -- MAX866, 3/ 5 = 3V, 0mA ILOAD 15mA 3.17 3.3 3.43 4.80 5.0 5.20 6 9 0.9V VIN 3V MAX867, VOUT = 5V, 0mA ILOAD 10mA -- MAX866, 3/ 5 = 0V, 4.8V VLOAD 5.2V -- MAX866, 3/ 5 = 3V, 3.17V VLOAD 3.43V 8 13 6 9 10 15 1.2V VIN 3V MAX867, VOUT = 5V, 4.8V VLOAD 5.2V -- MAX866, 3/ 5 = 0V, 4.8V VLOAD 5.2V -- MAX866, 3/ 5 = 3V, 3.17V VLOAD 3.43V 15 23 MAX867, VOUT = 5V, 4.8V VLOAD 5.2V 10 15 Maximum Load Current (Note 2) Quiescent Supply Current in 3.3V mode (Note 4) No-Load Battery Current Shutdown Quiescent Current (Note 4) LOAD -- ILOAD = 0mA, 3/ 5 = 3V, LBI = 1.5V, VOUT = 3.47V, FB = 1.5V 27 Output set for 3.3V, measured at VIN in Figure 2, VIN = 1.5V ------- -- SHDN = 0V, 3/ 5 = 3V, LBI = 1.5V, VOUT = 3.47V, FB = 1.5V Reference Voltage 60 500 1.22 Reference Load Regulation LBI Input Threshold With falling edge 1.22 A A 1 No REF load -- 3/ 5 = 3V, -20A REF load 250A, CREF = 0.22F 2 mA 100 Peak Inductor Current Limit V A mA 1.25 1.28 V 0.8 2.0 % 1.25 1.28 V _______________________________________________________________________________________ 3.3V/5V or Adjustable-Output, Single-Cell DC-DC Converters MAX866/MAX867 ELECTRICAL CHARACTERISTICS (continued) (Circuit of Figure 2, VIN = 1.2V, ILOAD = 0mA, TA = +25C, unless otherwise noted.) CONDITIONS PARAMETER MIN TYP LBI Input Hysteresis MAX UNITS 25 LBO Output Voltage Low ISINK = 2mA, open-drain output LBO Output Leakage Current -------- -- SHDN , 3/ 5 Input Voltage Low ------- -- SHDN , 3/ 5 Input Voltage High ------- -- SHDN , 3/ 5, FB, LBI Input Current LBO = 5V FB Voltage MAX867, output in regulation 1.22 Output Voltage Range MAX867 2.7 mV 0.4 V 1 A 0.08 x VOUT V 0.32 x VOUT -------- -- LBI = 1.5V, FB = 1.5V, SHDN = 0V or 3V, 3/ 5 = 0V or 3V V 40 100 nA 1.25 1.28 V 6.0 V Note 2: Output current specified with circuit of Figure 2 and CoilCraft D01608-334 inductor for test purposes only. More (or less) output current can be supplied with other coil types depending on inductance value and coil resistance. See Typical Operating Characteristics for other coil types. Output voltage and output current are guaranteed over this VIN operating range once the device has started up. Actual VIN start-up voltage depends on load current. Note 3: Output voltage specifications over temperature are guaranteed by design to limits that are 6 sigma from either side of the mean. Note 4: Current measured into OUT. VOUT is forced to 3.47V to maintain LX off when measuring device current. __________________________________________Typical Operating Characteristics (Circuits of Figure 2, TA = +25C, unless otherwise noted.) EFFICIENCY vs. LOAD CURRENT (VOUT = 3.3V) L = COILCRAFT D01608-334 (330H, 2.9) 70 70 70 TOP TO BOTTOM: VIN = 2.0V VIN = 1.5V VIN = 1.25V VIN = 1.0V VIN = 0.75V VIN = 0.5V 40 30 20 10 60 TOP TO BOTTOM: VIN = 2.0V VIN = 1.5V VIN = 1.25V VIN = 1.0V VIN = 0.75V 50 40 30 20 10 100 0 0.01 1000 0.1 L = COILCRAFT D01608-334 (330H, 2.9) 60 50 TOP TO BOTTOM: VIN = 2.0V VIN = 1.5V VIN = 1.25V VIN = 1.0V VIN = 0.75V 10 1200 BATTERY CURRENT (A) EFFICIENCY (%) 80 70 20 100 DECREASING BATTERY VOLTAGE 1000 INCREASING BATTERY VOLTAGE 1 10 LOAD CURRENT (mA) 100 100 1000 4000 3500 DECREASING BATTERY VOLTAGE 3000 2500 2000 1500 INCREASING BATTERY VOLTAGE 1000 500 0 0.1 10 NO-LOAD BATTERY CURRENT vs. BATTERY VOLTAGE (VOUT = 5V) 600 400 1 0.1 LOAD CURRENT (mA) 800 200 0 0.01 0.01 NO-LOAD BATTERY CURRENT vs. BATTERY VOLTAGE (VOUT = 3.3V) MAX866/67-04 100 30 10 LOAD CURRENT (mA) EFFICIENCY vs. LOAD CURRENT (VOUT = 5.0V) 40 1 BATTERY CURRENT (A) 10 MAX866/67-05 1 0.1 LOAD CURRENT (mA) 90 20 0 0.01 TOP TO BOTTOM: VIN = 2.0V VIN = 1.5V VIN = 1.25V VIN = 1.0V VIN = 0.75V VIN = 0.5V 40 30 10 0 60 50 MAX866/67-06 50 EFFICIENCY (%) 80 60 L = SUMIDA CD73-331 (330H, 1.5) 90 80 MAX866/667-03 90 EFFICIENCY vs. LOAD CURRENT (VOUT = 5.0V) 100 80 EFFICIENCY (%) EFFICIENCY (%) MAX866/667-01 L = SUMIDA CD73-331 (330H, 1.5) 90 100 MAX866/67-02 EFFICIENCY vs. LOAD CURRENT (VOUT = 3.3V) 100 0 0 0.2 0.4 0.6 0.8 1.0 1.2 BATTERY VOLTAGE (V) 1.4 1.6 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 BATTERY VOLTAGE (V) _______________________________________________________________________________________ 3 ____________________________Typical Operating Characteristics (continued) (Circuits of Figure 2, TA = +25C, unless otherwise noted.) START-UP INPUT VOLTAGE vs. LOAD CURRENT (VOUT = 5V) 47H 1.2 100H 1.1 1.0 0.9 0.8 220H 0.7 330H 0.6 1.4 100H 2.5 1.3 1.2 47H 1.1 1.0 0.9 100H 0.8 0.7 330H 220H 1mH 330H 2.0 1.5 22H 1.0 0.5 0.5 0.5 10 1 0 0.1 100 1 10 100 INPUT VOLTAGE (V) 330H 1.5 47H 1.0 22H 0.5 MAX866/67-11 10 9 VREF LOAD REGULATION (mV) 100H 2.5 100 REFERENCE VOLTAGE vs. REFERENCE CURRENT MAX186-14AMAX866/67-10 3.0 10 LOAD CURRENT (mA) INPUT VOLTAGE vs. LOAD CURRENT (VOUT = 5V) 2.0 1 LOAD CURRENT (mA) LOAD CURRENT (mA) 8 7 6 5 4 3 2 1 0 0 1 10 100 1000 LOAD CURRENT (mA) MAX866 LINE-TRANSIENT RESPONSE (3.3V MODE) 0 100 200 50 150 REFERENCE LOAD CURRENT (A) 250 MAX866 LINE-TRANSIENT RESPONSE (5V MODE) A A B B 1ms/div A: 3.3V OUTPUT VOLTAGE, AC COUPLED 20mV/div B: INPUT VOLTAGE (0.9V AND 1.4V) 500mV/div ILOAD = 10mA, COUT = 47F 4 47H 0.6 1mH 0.1 3.0 INPUT VOLTAGE (V) 1.3 1.5 MAX866/67-08 MAX186-14A 1.4 START-UP INPUT VOLTAGE (V) MAX186-14AMAX866/67-07 1.5 INPUT VOLTAGE vs. LOAD CURRENT (VOUT = 3.3V) MAX186-14AMAX866/67-09 START-UP INPUT VOLTAGE vs. LOAD CURRENT (VOUT = 3.3V) START-UP INPUT VOLTAGE (V) MAX866/MAX867 3.3V/5V or Adjustable-Output, Single-Cell DC-DC Converters 1ms/div A: 5.0V OUTPUT VOLTAGE, AC COUPLED 20mV/div B: INPUT VOLTAGE (0.9V AND 1.4V) 500mV/div ILOAD = 10mA, COUT = 47F _______________________________________________________________________________________ 1000 3.3V/5V or Adjustable-Output, Single-Cell DC-DC Converters MAX866 LOAD-TRANSIENT RESPONSE (3.3V MODE) MAX866 LOAD-TRANSIENT RESPONSE (5V MODE) A A B B 1ms/div A: 5.0V OUTPUT VOLTAGE, AC COUPLED 20mV/div B: OUTPUT CURRENT (0mA AND 10mA) 5mV/div (TEKTRONIX P6042 CURRENT PROBE) ILOAD = 5mA, COUT = 47F, VIN = 1.25V 1ms/div A: 3.3V OUTPUT VOLTAGE, AC COUPLED 20mV/div B: OUTPUT CURRENT (0mA AND 10mA) 5mV/div (TEKTRONIX P6042 CURRENT PROBE) ILOAD = 5mA, COUT = 47F, VIN = 1.25V MAX866 SHUTDOWN RESPONSE (5V MODE) MAX866 SHUTDOWN RESPONSE (3.3V MODE) A A B B 10ms/div 10ms/div A: 5.0V OUTPUT VOLTAGE, 2V/div B: SHDN INPUT VOLTAGE (0V AND 5V) 5V/div ILOAD = 10mA MAX867 LBI AND FB THRESHOLD vs. TEMPERATURE VFB (MAX867) 1.240 -60 -40 -20 0 20 40 60 TEMPERATURE (C) 80 100 1.0 3.3V MODE ILOAD = 0A START-UP VOLTAGE (V) 1.250 START-UP VOLTAGE vs. TEMPERATURE MAX866/67-25 MAX866/67-24 LBI 0.5 OUTPUT VOLTAGE ERROR (%) LBI, FB VOLTAGE (V) 1.260 MAX866 OUTPUT VOLTAGE ERROR vs. TEMPERATURE 0 5V MODE MAX866/67-26 A: 3.3V OUTPUT VOLTAGE, 2V/div B: SHDN INPUT VOLTAGE (0V AND 5V) 2V/div ILOAD = 10mA 0.9 0.8 0.7 0.6 ILOAD= OA -0.5 -60 -40 -20 0 20 40 60 TEMPERATURE (C) 80 100 0.5 -60 -40 -20 0 20 40 60 TEMPERATURE (C) 80 100 _______________________________________________________________________________________ 5 MAX866/MAX867 ____________________________Typical Operating Characteristics (continued) (Circuits of Figure 2, TA = +25C, unless otherwise noted.) ____________________________Typical Operating Characteristics (continued) (Circuits of Figure 2, TA = +25C, unless otherwise noted.) 20 VIN = 0.9V 15 3.3V MODE 10 -60 -40 -20 0 20 40 60 TEMPERATURE (C) 80 100 26 IOUT 24 MAX866/67-29 VOUT = 3.47V 28 REFERENCE VOLTAGE (V) 25 30 1.255 MAX866/67-28 VIN = 1.2V QUIESCENT SUPPLY CURRENT (A) MAX866/67-27 30 REFERENCE VOLTAGE vs. TEMPERATURE QUIESCENT SUPPLY CURRENT vs. TEMPERATURE OUTPUT CURRENT CAPABILITY vs. TEMPERATURE OUTPUT CURRENT (mA) MAX866/MAX867 3.3V/5V or Adjustable-Output, Single-Cell DC-DC Converters 1.250 IREF = 0A 22 20 -60 -40 -20 0 20 40 60 TEMPERATURE (C) 80 100 1.245 -60 -40 -20 0 20 40 60 TEMPERATURE (C) 80 100 ______________________________________________________________Pin Description PIN 6 NAME FUNCTION MAX866 MAX867 1 1 -------- SHDN 2 -- -- 3/ 5 Selects the output voltage; connect to GND for 5V output, and to OUT for 3.3V output. -- 2 FB Feedback Input for adjustable-output operation. Connect to an external resistor voltage divider between OUT and GND. 3 3 REF 1.25V Reference Voltage Output. Bypass with 0.22F to GND (0.1F if there is no external reference load). Maximum load capability is 250A source, 20A sink. 4 4 LBO Low-Battery Output. An open-drain N-channel MOSFET sinks current when the voltage at LBI drops below 1.25V. 5 5 LBI Low-Battery Input. When the voltage on LBI drops below 1.25V, LBO sinks current. If not used, connect to VIN. 6 6 OUT Connect OUT to the regulator output. OUT provides bootstrap power to the IC. 7 7 GND Power Ground. Must be low impedance; solder directly to ground plane. 8 8 LX Shutdown Input. When low, the entire circuit is off and VOUT = VIN - VD, where VD is the forward voltage drop of the external Schottky rectifier. N-Channel Power-MOSFET Drain _______________________________________________________________________________________ 3.3V/5V or Adjustable-Output, Single-Cell DC-DC Converters MAX866/MAX867 MINIMUM OFF-TIME ONE-SHOT VBATT TRIG Q ONE-SHOT SHDN LX VOUT F/F S N Q R 3/5* MAXIMUM ON-TIME ONE-SHOT GND Q TRIG ONE-SHOT CURRENT-LIMIT COMPARATOR OUT MAX866/MAX867 ** * FB** ** * ERROR COMPARATOR LBO REF N LBI COMPARATOR LBI REFERENCE *MAX866 ONLY **MAX867 ONLY Figure 1. Block Diagram _______________Detailed Description Operating Principle The MAX866/MAX867 combine a switch-mode regulator, N-channel power MOSFET, precision voltage reference, and power-fail detector in a single monolithic device. The MOSFET is a "sense-FET" type for best efficiency, and has a very low gate threshold voltage to ensure start-up with low battery voltages (0.8V typ). PFM Control Scheme The MAX866/MAX867 control scheme (Figure 1) combines low-voltage efficiency (80% typ) with low battery drain (100A typ). There is no oscillator; switching is accomplished by a pair of one shots that set a maximum LX on-time (4.5s typ) and a minimum LX off-time (1s). LX on-time will be terminated early if the inductor current reaches 0.5A before 4.5s elapses. With the standard application circuit (Figure 2a), LX current is typically less than 50mA, so LX on-time is normally not terminated by the 0.5A limit and lasts the complete 4.5s. The LX on-resistance is typically 1 to minimize switch losses. The MAX866/MAX867 switching frequency depends on load, input voltage, and inductor value, and it can range up to 250kHz with typical component values. _______________________________________________________________________________________ 7 MAX866/MAX867 3.3V/5V or Adjustable-Output, Single-Cell DC-DC Converters Voltage Reference The precision voltage reference is suitable for driving external loads, such as an analog-to-digital converter. The voltage-reference output changes less than 2% when sourcing up to 250A and sinking up to 20A. If the reference drives an external load, bypass it with 0.22F to GND. If the reference is unloaded, bypass it with at least 0.1F. Logic Inputs and Outputs The 3/5 input is internally diode clamped to GND and OUT, and should not be connected to signals outside this range. The SHDN input and LBO output (opendrain) are not clamped to V+ and can be pulled as high as 7V regardless of the voltage at OUT. Do not leave control inputs (3/5, LBI, or SHDN) floating. __________________Design Procedure Output Voltage Selection For the MAX866, you can select a 3.3V or 5V output voltage under logic control, or by tying 3/5 to GND or OUT. The MAX867's output voltage is set by two resistors, R1 and R2 (Figure 2b), which form a voltage divider between the output and FB. Use the following equation to determine the output voltage: R1 + R2 VOUT = VREF ( ________ ) R2 where VREF = 1.25V. To simplify resistor selection: VOUT - 1 R1 = R2 ( _____ ) VREF VIN VIN C1 47F 5 LX LBI MAX866 OUT 1 3 C3 0.1F 3/5 SHDN LBO REF 8 6 2 D1 R1 VOUT 5 MAX867 OUT 1 4 GND L1 = COILCRAFT DO1608-334 D1 = MOTOROLA MBR0520LTI Figure 2a. Standard Application Circuit--Preset Output Voltage LX LBI C2 47F OUTPUT SELECT 7 8 C1 47F L1 330H 3 C3 0.1F FB SHDN LBO REF L1 330F 8 D1 6 R1 VOUT C2 47F 2 4 R2 GND 7 L1 = COILCRAFT DO1608-334 D1 = MOTOROLA MBR0520LTI Figure 2b. Standard Application Circuit--Adjustable Output Voltage _______________________________________________________________________________________ 3.3V/5V or Adjustable-Output, Single-Cell DC-DC Converters FOR VTH < 1.25V VIN OUT Q1 MMDFZP02E VOUT (3.3V/5V) 6 R9 1M R5 MAX866 MAX866 LBI R3 LBI VIN MAX866 5 LBO R10 1M R7 R6 Q2 2N3904 5 OUT 6 LBI R11 1M 4 5 R4 MAX866/MAX867 FOR VTH > 1.25V (1.25V) R8 1M ( ) VTH -1 VREF WHERE VTH = THE VIN TRIP THRESHOLD R3 = R4 ( LOAD ) VREF - VTH VOUT - VREF WHERE VTH = THE VIN TRIP THRESHOLD R5 = R6 Figure 3. Low-Battery Detector Circuits Figure 4. Low-Voltage Start-Up Circuit Since the input bias current at FB has a maximum value of 100nA, large values (10k to 300k) can be used for R1 and R2 with no significant accuracy loss. For 1% error, the current through R1 should be at least 100 times FB's bias current. Figure 3. This circuit uses VOUT (3.3V or 5.0V in the MAX866, adjustable in MAX867) as a reference. The voltage divider formed by R5 and R6 allows the effective trip point of VIN to be set below 1.25V. R6 is usually set to approximately 100k, and R5 is given by the formula: R5 = [R6 x (VREF - VTH)] / (VOUT - VREF) Note that LBI drops below the 1.25V LBI threshold trip point when either VIN or VOUT is low. Since VOUT regulation and the LBI threshold are derived from the same internal voltage reference, they track together over temperature. Low-Battery Detection, VTH > 1.25V The MAX866 series contains an on-chip comparator for low-battery detection. If the voltage at LBI falls below the regulator's internal reference voltage (1.25V), LBO (an open-drain output) sinks current to GND. The lowbattery monitor's threshold is set by two resistors, R3 and R4 (Figure 3). Set the threshold voltage using the following equation: Low-Battery Start-Up VTH R3 = R4 (____ - 1) VREF where VTH is the desired threshold of the low-battery detector and VREF is the internal 1.25V reference. Since the LBI current is less than 100nA, large resistor values (typically 10k to 300k) can be used for R3 and R4 to minimize loading of the input supply. When the voltage at LBI is below the internal threshold, LBO sinks current to GND. Connect a pull-up resistor of 100k or more from LBO to OUT when driving CMOS circuits. When LBI is above the threshold, the LBO output is off. If the low-battery comparator is not used, connect LBI to VIN and leave LBO open. Low-Battery Detection, VTH < 1.25V When the low-battery detection threshold voltage is below 1.25V, use the circuit shown on the right in The MAX866/MAX867 are bootstrapped circuits; they can start under no-load conditions at much lower battery voltages than under full load. Once started, the output can maintain a moderate load as the battery voltage decreases below the start-up voltage (see Typical Operating Characteristics). The circuit shown in Figure 4 allows the circuit to start with no load, then uses the LBI circuit and an external low-threshold P-channel MOSFET switch to apply the load after the output has started. Resistors R7 and R8 are selected to trip the LBI detector at about 90% of the output voltage. On start-up, LBI and LBO are low, Q2 is off, and transistor Q1's gate is held high by R11. This disconnects the load, allowing the MAX866 to bootstrap itself at the lowest possible voltage. When the output reaches its final output voltage, LBI and LBO go high, turning on Q2, Q1, and the load. _______________________________________________________________________________________ 9 MAX866/MAX867 3.3V/5V or Adjustable-Output, Single-Cell DC-DC Converters Table 1. Component Suppliers PRODUCTION METHOD INDUCTORS Surface Mount See Table 2 Miniature Through Hole Sumida RCH654-220 COMPANY CAPACITORS RECTIFIERS Matsuo 267 series Sprague 595D series AVX TPS series Motorola MBR 0530 Nihon EC15QS02L Sanyo OS-CON series low-ESR organic semiconductor Motorola 1N5017 PHONE FAX AVX USA: (803) 946-0690 (803) 626-3123 Coilcraft USA: (847) 639-6400 (847) 639-1469 Matsuo USA: (714) 969-2491 (714) 960-6492 Motorola USA: (602) 244-5303 (602) 244-4015 Murata-Erie USA: (800) 831-9172 (814) 238-0490 Nihon USA: (805) 867-2555 Japan: 81-3-3494-7411 (805) 867-2698 81-3-3494-7414 Sanyo USA: (619) 661-6835 Japan: 81-7-2070-6306 (619) 661-1055 81-7-2070-1174 Sumida USA: (847) 956-0666 Japan: 81-3-3607-5111 (847) 956-0702 81-3-3607-5144 TDK USA: (847) 390-4461 (847) 390-4405 J.W. Miller USA: (310) 515-1720 (310) 515-1962 Inductor Selection An inductor value of 330H works well in most applications, supplying loads over 10mA and allowing typical start-up voltages of 0.8V. The inductor value is not critical, and the MAX866/MAX867 can operate with values from 22H to 1mH. In general, smaller inductor values supply more output current while larger values start with lower input voltage. Several inductor suppliers and part numbers are listed in Tables 1 and 2. The peak inductor current should not exceed the inductor's current rating. Since the MAX866/MAX867 current limit of 0.5A will not be reached in most applications, the peak coil current (IPK) is: IPK = (VIN(max) x 4.5s) / L For a typical 1-cell alkaline design, VIN(max) is 1.55V, so: IPK = (1.55V x 4.5s) / 330H = 21.14mA 10 which is well within the ratings of most surface-mount coils. Higher efficiency and output current are achieved with lower inductor resistance, but unfortunately this is inversely related to physical size. Table 2 indicates resistance and height for each coil. Some of the smallest coils have resistances over 10, and will not provide the same output power or efficiency of a 1 coil. At light loads however (below 5mA), the efficiency differences between low- and high-resistance coils may be only a percent or two. The Typical Operating Characteristics graphs show efficiency and output current plots for 1.5 and 2.9, 330H coils. Capacitor Selection A 47F, 6V, 0.85, surface-mount tantalum (SMT) output filter capacitor typically provides 15mV output ripple when stepping up from 0.9V to 1.4V at 10mA. Smaller capacitors (down to 10F with higher ESRs) are acceptable for light loads or in applications that can ______________________________________________________________________________________ 3.3V/5V or Adjustable-Output, Single-Cell DC-DC Converters MAX866/MAX867 Table 2. Surface-Mount Inductor Information INDUCTANCE (mH) RESISTANCE (W) RATED CURRENT (A) HEIGHT (mm) Sumida CD73-331 330 1.5 0.28 3.5 Sumida CD104-331 330 1.1 0.42 4 Murata-Erie LQH4N331K04M00** 330 8.2 0.095 2.6 TDK NLC565050T-331K** 330 4.9 0.14 5 Coilcraft D01608-334 330 2.9 0.16 3.2 Coilcraft DT1608-334 330* 2.9 0.16 3.2 Coilcraft D03316-334 330 0.7 0.6 5.4 Coilcraft DT3316-334 330* 0.7 0.6 5.4 J.W. Miller PM105-331K 330 1.1 0.52 5.4 MANUFACTURER /PART * Shielded ** Low cost tolerate higher output ripple. Values in the 10F to 47F range are recommended. The equivalent series resistance (ESR) of both bypass and filter capacitors affects efficiency and output ripple. 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) and AVX (TPS series). See Table 1 for a list of suggested capacitor suppliers. ___________________Chip Topography LX SHDN 3/5 OR FB* GND 0.084" (2.1336mm) Rectifier Diode For optimum performance, a switching Schottky diode (such as the 1N5817 or MBR0520LTI) is recommended. Refer to Table 1 for a list of component suppliers. For low output power applications, a PN-junction switching diode (such as the 1N4148) will also work well, although its greater forward voltage drop will reduce efficiency and raise the start-up voltage. PC Layout and Grounding The circuit's high-frequency operation makes PC layout important for minimizing ground bounce and noise. Keep the IC's GND pin and the ground leads of C1 and C2 (Figure 2) less than 0.2in (5mm) apart. Also keep all connections to the FB and LX pins as short as possible. To maximize output power and efficiency and minimize output ripple voltage, use a ground plane and solder the IC's GND (pin 7) directly to the ground plane. REF OUT LBI LBO 0.058" (1.4732mm) *3/5 FOR MAX866; FB FOR MAX867. TRANSISTOR COUNT: 357; SUBSTRATE IS CONNECTED TO OUT. ______________________________________________________________________________________ 11 MAX866/MAX867 3.3V/5V or Adjustable-Output, Single-Cell DC-DC Converters ________________________________________________________Package Information DIM C A 0.101mm 0.004 in e B A1 E L A A1 B C D E e H L INCHES MAX MIN 0.044 0.036 0.008 0.004 0.014 0.010 0.007 0.005 0.120 0.116 0.120 0.116 0.0256 0.198 0.188 0.026 0.016 6 0 MILLIMETERS MIN MAX 0.91 1.11 0.10 0.20 0.25 0.36 0.13 0.18 2.95 3.05 2.95 3.05 0.65 4.78 5.03 0.41 0.66 0 6 H 8-PIN MAX MICROMAX SMALL OUTLINE PACKAGE D DIM D 0-8 A 0.101mm 0.004in. e B A1 E C L Narrow SO SMALL-OUTLINE PACKAGE (0.150 in.) H A A1 B C E e H L INCHES MAX MIN 0.069 0.053 0.010 0.004 0.019 0.014 0.010 0.007 0.157 0.150 0.050 0.244 0.228 0.050 0.016 DIM PINS D D D 8 14 16 MILLIMETERS MIN MAX 1.35 1.75 0.10 0.25 0.35 0.49 0.19 0.25 3.80 4.00 1.27 5.80 6.20 0.40 1.27 INCHES MILLIMETERS MIN MAX MIN MAX 0.189 0.197 4.80 5.00 0.337 0.344 8.55 8.75 0.386 0.394 9.80 10.00 21-0041A 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. 12 __________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600 (c) 1996 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products. 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