19-0916; Rev 0; 3/90 SULA AL/VI CMOS Fixed/Adjustable Output Step-Up Switching Regulators General Description The MAX631, MAX632, and MAX633 are +5V, +12V, and +15V fixed output, step-up DC-DC converters for use in low-power, high-efficiency switching regulator applica- tions. The only external components required are an output filter capacitor and a low-cost inductor. Included on-chip are low battery detection circuitry and a charge pump output for generating a negative voltage in dual- supply applications. Though most simply used as fixed output regulators, the MAX631/632/633 can also be set for other output volt- ages by adding an external voltage divider. PART" TEMP. RANGE PIN-PACKAGE Maxim manufactures a broad line of step-up, step-down, MAXE31XCPA OC to +700 8 Plastic DIP and inverting DC-DC converters, with features such as MAX631XCSA Orc to +70C 8 Narrow SO logic-level shutdown, adjustable oscillator frequency, MAX631XC/D OC to +70C Dice and external MOSFET drive. MAX631XEPA -40C to +85C 8 Plastic DIP MAX631XESA -40C to +85C 8 Narrow SO Applications MAX631XEJA -40C to +85C 8 CERDIP Minimum Component, High-Efficiency MAX631XMJA 55C to +125C 8 CERDIP __ DC-DC Converters MAX632XCPA OC to +70C 8 Plastic DIP Portable Instruments MAX632XCSA O'C to +70C _ 8 Narrow SO Rechargeable and Primary Battery MAX632XC/D_ OC to +70C Dice Power Conversion MAX632XEPA -40C to +85C 8 Plastic DIP Uninterruptable On-Board Power Supplies MAX632XESA 40C to +85C 8 Narrow SO Card Level Multiple Power Conversion MAX632XEJA 40C to +85'C 8 CERDIP MAX632XMJA -55C to +125C 8 CERDIP Pin Configuration Features @ Fixed +5V, +12V, +15V Output Voltages @ Adjustable Output with 2 Resistors @ 80% Typ Efficiency @ Only 2 External Components @ Charge Pump for Negative Output @ 135A Typ Operating Current Ordering Information *X = A for 5% Output Accuracy. X = B for 10% Accuracy. Ordering information continued on last page Typical Operating Circuit Top View 330uH 4 | x VOUT SV ad 2Vto 5V ~~ Bt 1] 8 | comp MAXIM I mam 80 [2] iyaxesr |Z) ve = MAX631 = 100uF eno [a MAX632 Fe) op MAX633 GND ix [4] [5 | vour LBI VFB 1 7 DIP/SO i +5V OUTPUT DC-DC CONVERTER MAAXKI/V Maxim Integrated Products 1 Call toll free 1-800-998-8800 for free samples or literature. 9/EE9/LE9XVNMAX631/632/633 CMOS Fixed/Adjustable Output Step-Up Switching Regulators ABSOLUTE MAXIMUM RATINGS Supply Voltage, VOUT .... Output Voltage, LX and LBO Input Voltage, LBI and VFB LX Output Current . LBO Output Current .... Power Dissipation Plastic DIP (derate 8.33mW/"C above +50C) .... SO (derate 6mMW/"C above +50C) .. CERDIP (derate 8mW/"C above +50C) ... Lees +18V Operating Temperature Range beeen +18V MAX638_XC owe eee -0.3V to (VOUT + 0.3V) MAX63_XE ..... 2.0.00 eee ee 450mA Peak MAX63_XM ............ veces 5OmMA Storage Temperature .......0000.... Lead Temperature (Soldering, 10 sec.) 625mW Lene 450mWw Lee 800mWw O'C to +70C -40C to +85C -55C to +125C -65C to +160 C +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 (Ta = +25C, unless otherwise noted.) PARAMETER SYMBOL CONDITIONS TYP MAX UNITS | Voltage at VOUT Operating Voltage Range Over Temperature (C, E) 2.0 16.5 Vv Over Temperature (M) 24 16.5 | __ Voltage at VOUT | Ta = +25C 1.5 1.3 Start-up Voltage Over Temperature (C, E) 1.8 v | [| Over Temperature (M) 2.0 LX off, Over Temperature VOUT= +5V, MAX631 0.135 0.4 Supply Current Is VOUT = +12V, MAX632 0.5 20 | mA VOUT = +15V, MAX633 0.75 2.5 Reference Voltage (Internal) ie +e perature 150 131 ae Vv | No Load, VEB = GND / Over Ternperature MAX631A 4.75 5.0 5.25 MAX632A 5% Output Accuracy 11.4 12.0 126 VOUT Voltage MAX633A 14.25 15.0 15.75 Vv MAX631B 45 5.0 5.5 MAX632B 10% Output Accuracy 10.8 12.0 13.2 | MAX633B 13.5 15.0 16.5 Efficiency 80 % | Line Regulation (Note 1) +0. 5VOUT<+VS<VOUT 0.08 %VOUT Load Regulation (Note 1) So ogo 150mW | 0.2 %VOUT VOUT = +5V | MAX631A 40 45 50 MAX631B 35 45 60 VOUT = +12V Oscillator Frequency fo MAX632A 45.5 50 56 kHz MAX632B 40 50 65 VOUT = +15V MAX633A 45.5 50 56 MAX633B 40 50 65 Oscillator Frequency Tempco -60 H2/"C MAX631, VOUT = +5V 40 50 60 Oscillator Duty Cycle MAX632, VOUT = +12V 40 50 60 % MAX633, VOUT = +15V 40 50 60 T LX On Resistance | Ron | P= 100A voor Sey | 35 7 a J MAXI/VICMOS Fixed/Adjustable Output Step-Up Switching Regulators ELECTRICAL CHARACTERISTICS (continued) (Ta = +25C, unless otherwise noted.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX | UNITS V4 = +16.5V Ta = +25C 0.01 1.0 LX Leakage Current XL Over Temperature (C, E) 30 HA Over Temperature (M) 100 Diode Forward Voltage VF IF = 100mA 1.0 Vv : VOUT = +5V, IOUT = +10mA 70 140 CP On Resistance VOUT = +15V, IOUT = +30mA 30 VFB Input Bias Current IFB ; 0.01 10 1 nA Low Battery Input Threshold VLBI 1.31 Vv Low Battery Inout Bias Current ILBI 0.01 16 nA V2 = +0.4V, V1 =4+1.1V Low Battery Output Current ILBO Ta = +25C 1.0 mA Over Temperature -0.5 Low Battery Output _ _ Leakage Current ILBOL V2 = +16.5V, V1 = 41.4V 0.01 3.0 pA | Note 1: Guaranteed by correlation with DC pulse measurements. Pin Description Typical Applications PIN NAME FUNCTION | Basic Step-Up Circuits 1 LBI Low Battery Detector Input. When the Figure 1 shows the basic boost or step-up circuit for the Sots alr is Pee Oy. MAX631/632/633. The circuit corresponds to Table 1 LBO sinks current. : which shows values for typical input voltages and output 2 LBO The Low Battery Detector Output is an currents. open drain N-channel MOSFET which Table 1. Inductor Selection for Common sinks current when LBI is below 1.31V. Designs GND Ground . LX This pin drives the external inductor Vin VOUT IOUT EFF. INDUCTOR with an internal N-channel power (v) (Vv) (mA) (%) | pn. (Note 2) uH Q MOSFET. LX has an output resistance - of typically 6Q and a peak current rat- 2 5 5 78 =|CB 6860-21 470 0.4 ing of 425mA. 2 5 10 74 |G 1B253 250 0.44 5 VOUT The regulated DC-DC converter output. 2 5 15 61 |G 1B103 100 0.25 6 cP The Charge Pump output is a low im- 3 5 25 82 |cB 6860-21 470 (04 pedance buffer which swings from GND to VOUT at the oscillator fre- 3 5 40 75 |CB 7070-29 220 0.55 quency. 2 external capacitors and di- ~ : odes can be connected to generate a 3 12 5 79 'CB 6860-19 330 0.35 negative output voltage (Figure 3). 3 42 10 79 |CB 7070-28 180 0.48 7 VFB When VFB is grounded, the DC-DC con- 5 12 12 88 CB 6860-21 A470 04 verter output will be the factory preset value. When an external voltage divider 5 12 25 87 |CB 6860-19 330 0.35 is connected from VOUT to VFB and GND, this pin becomes the feedback 3 15 S 73 1CB 7070-29 220 0.55 ; input for adjustable output operation. 3 15 8 71 |CB 7070-27 150 0.43 8 COMP | The Compensation input is connected 5 15 10 85 |CB 6860-21 470 O04 to the internal voltage divider which sets the fixed voltage output. In some 5 15 15 85 |CB 6860-19 330 0.35 circuit board layouts, a lead compen- sation capacitor (100pF to 10nF) con- 8 15 35 90 |G 1B503 5000.56 Meee eee eee im Note 2: CB = Cadell-Burns, NY, (516) 746-2310 roves transient expense m- G = Gowanda Electronics Corp., NY, (716) 532-2234 Proves transi p . Other Manufacturers listed in Table 2. MAXI/VI 3 9/ECE9/LEOXVINMAX631/632/633 CMOS Fixed/Adjustable Output Step-Up Switching Regulators Typical Operating Characteristics SUPPLY CURRENT vs, OUTPUT VOLTAGE 20 400 Ta +25C ZX 3 0 5 10 16 0 05 1.0 Vout {] _. _- Detailed Description The operation of the MAX631/632/633 can best be under- stood by examining the regulating loop of Figure 1. When the output voltage drops below the preset (or externally set) value, the Error Comparator switches high and connects the internal 45kHz Oscillator to the gate of the LX output driver, N1. N1 is an N-channel MOSFET with a typical on resistance of 6Q and a current rating of 150mA. The following equation provides a good rule of thumb to see if the MAX631/632/633 can provide the desired output cur- rent without exceeding the current rating of N1: 8 (VOUT Vix) IOUT VIN Vout = 15V ww Ss Ss Ly OUTPUT CURRENT (mAj N S Ss s Ss Ly OFF <450mA LOW BATTERY 2 OUTPUT 6 4 LBO cP] Lx +5V LOW BATTERY CATCH fons +. VOUT! 5. VOUT wr T i N1 be Ri COMPARATOR LBI | i 131V | REF *300k Ccomp 100pF VEB COMP| 8 wm GND| 3 OFFSET 1 Som COMPARATOR FQR VOUT =15V L ON MAxE31 Figure 1. +3V to +5V Converter and Block Diagram 4 Lx OUTPUT CURRENT vs. VOUT OSCILLATOR FREQUENCY vs. OUTPUT VOLTAGE 55 Ta 725C 50 Vout = 10V 45 Vout = 5 40 fo (kHz) 35 30 25 0 15 202530 0 2 4 6 8 W 12 4 16 _ bx VOLTAGE (V) __ Nout {) A low output voltage turns N1 on and off at the internal clock frequency. During each on half-cycle, the current through the inductor rises linearly, storing energy in the coil. During each off half-cycle, the coils magnetic field collapses and voltage across the inductor reverses sign. The voltage at LX then rises until the internal diode is forward based, delivering power to the output. When the output voltage reaches the desired level, the Error Com- parator inhibits N1 until the load discharges the output filter capacitor (C1) to less than the desired output level. Vin, Bootstrapped Operation The MAX631/632/633 does not have a Vin pin. Input power to start the DC-DC converter is supplied via the external inductor to the VOUT pin. Once the converter has started, it is then powered from its own output. This "bootstrap" design ensures that the output MOSFET, N1, will have maximum gate drive and, hence, a minimum Ron. It also allows the converter to start at lower input voltages. Vin, Greater Than VOUT If the regulator's input voltage is more than one forward diode drop greater than the desired output voltage, N1 will not turn on. Current will still be supplied to the load directly through the inductor and the internal diode, but without regulation. As long as the input is more than 0.6V above the desired output, the actual output voltage will be equal to the input voltage minus 0.6V. Fixed or Adjustable Output For operation at one of the preset output voltages (+5V for the MAX631, +12V for the MAX632, and +15V for the MAX633), VFB is connected to GND, and no external resistors are required. For an output voltage other than the preset value, an external voltage divider (R3 and R4, Figure 2) is required. VOUT is set as follows: MAAAI/VICMOS Fixed/Adjustable Output Step-Up Switching Regulators Let R4 be any resistance in the 10kQ to 10MQ range, typically 100kQ, then: VOUT RS = Ra fen: ' Table 1 shows nominal inductor parameters for a variety of input and output voltages. Values are given for both maximum output and maximum efficiency designs. When noise is not critical, a low-cost bobbin inductor will suffice. For higher power circuits or when low EMI and noise are required, pot cores and toroids should be used. (See Tables 1 and 2 for typical part numbers and manu- facturers.) Table 2. Coil and Core Manufacturers (Note 3) DESCRIPTION TYPICAL "MANUFACTURER | PART # BOBBIN INDUCTORS Dale [ates | S00uH, 0.50 | Caddell-Burns 7070-29 220nH, 0.55Q Gowanda 1B253 250uH, 0.4402 TRW | LL-S00 5O0pH, 0.752 _| | POTTED TOROIDAL INDUCTORS Dale | TE-3Q4TA imH,0820 | TRW MH-1 600uH, 1.92 Gowanda 050AT 1003 | 100uH, 0.050 FERRITE CORES AND TOROIDS (Note 4) B64290-K38-X38 | Tor. Core, aut | Tor. Cope. Siemens Magnetics 655.130 S3nH/T | Pot Core, Stackpole 57-3215 4mm x 8mm | Magnetics G-41408-25 Pot Core, | 14x 8, 250nH/T* | Note 3: This list does not constitute an endorsement by Maxim integrated Products and is not intended to be a compre- hensive list of all manufacturers of these components. Note 4: Permag Corp. is a distributor for many of the listed core and toroid manufacturers. (616) 822-3311 Output Filter Capacitor The MAX63 1/632/633's output ripple has 2 components which are 90 out of phase. One component results from the change in the stored charge on the filter capac- itor with each LX pulse. The other is the product of the capacitor's charge-discharge current and its Equivalent Series Resistance (ESR). With low-cost aluminum elec- trolytic capacitors, the ESR produced ripple is often MA XI/VI L (SEE "INDUCTOR SELECTION") VIN 4 LX 5 VOUT _? maxim YT MAX631 is = : maxes2 | 7 CMe 100) MAX633 VFB LBl GND comp | R4 <= 100k = T1378 + ag~pq LOU", = A ty Vin VOUT Figure 2. Connections for Adjustable Output larger than that caused by the change in charge. Con- sequently, high-quality aluminum or tantalum filter ca- pacitors will minimize output ripple, even if smaller capacitance values are used. Best results at a reason- able cost are typically achieved with a high-quality aluminum electrolytic, in the 100uF to 500uF range, in parallel with a 0.1uF ceramic capacitor. Catch Diode The MAX631 series regulators contain an internal catch diode and, therefore, require no external diode for most applications. However, an external diode can be con- nected in parallel with the internal diode at the LX and VOUT pins. For example, a Schottky diode with a low forward voltage drop will provide some improvement in efficiency. Bypassing and Compensation Since the inductor charging current can be relatively large, high currents flow through the ground connection to the MAX631/632/633. To prevent unwanted feedback, the impedance of the ground path must be as low as possible, and power-supply bypassing should be used. When the value of the voltage setting resistors (R3 and R4, Figure 2) exceed 50kQ, stray capacitance at the VFB input can add a'lag' tothe feedback response, destabliz- ing the regulator, increasing low frequency ripple, and lowering efficiency. This problem can often be avoided by minimizing lead lengths and circuit board trace size at the VFB node. It can also be remedied by adding a lead" compensation capacitor (100pF to 10nF) in parallel with R3. The COMP input allows access to the internal voltage divider so that compensation can also be added when fixed output operation is used. A capacitor connected between VOUT and COMP again adds a "lead" to the regulator's response. 9/CE9/LEOXVNMAX631/632/633 CMOS Fixed/Adjustable Output Step-Up Switching Regulators Low Battery Detector The Low Battery Detector compares the voltage on the Low Battery Input, LBI, with the internal 1.31V bandgap reference. The Low Battery Detector Output, LBO, goes low whenever the input voltage at LBI is less than 1.31V. The Low Battery detection voltage is set by resistors, R1 and R2 (Figure 1). Let R2 be any resistance in the 10kQ to 10MQ range, typically 100kQ, then: VLB R1=R2 Gay 7? (VLB is the desired Low Battery detection voltage) rr. i OUF 10 uF IN4148 Vep =-(VOUT - 2VF}* *\Ve = FORWARD DIODE VOLTAGE IN4148 5 IN4148 = - Ve)" VOUT Vor = 2(VOUT - Vr) + =p 10ur + oe T T 10uF Figure 3. Using the Charge Pump (CP) output as a voltage inverter and/or doubler. Both circuits can be used together. ae +15V SV ee . 4 =~ 100uF LX 5 T VOUT = AAAXIAA MAX633 cP 10uF ~ + 10uF LBl GND VFB te oy IN4148 ( 1 8 |? IN5817) Figure 4. +5V to +15V/12V Converter 6 Negative Output Voltage The Charge Pump (CP) output is a low impedance buffer which swings from ground to VOUT at the oscillator frequency. Two external capacitors and diodes can be connected, as shown in Figure 3, to generate a negative output voltage of -(VOUT - 1.2V) or a positive output of 2(VOUT 1.2V). 1.2V is the forward drop of 2 silicon diodes. Both circuits can be used at once if desired. With 10uF capacitors, the output impedance of Vcp is about 309. If space is critical, the capacitors can be reduced, but with a slight increase in output impedance and Vcp output ripple. The circuit shown in Figure 4 provides approximately +10mA with VOUT = +15V, and 15mA if VOUT = +12V. The magnitude of the negative output is about 3V less than VOUT due to the forward voltage drop of the 1N4148 diodes and the output impedance of CP. Using Schottky diodes (IN5817) will increase the absolute value of the negative output by about 1V. The performance of the CP output is shown in Figure 5. What Value of Inductor? A General Discussion The converters in this data sheet operate by charging an inductor from a DC input and then discharging the induc- tor to generate a DC output that is greater than the input. The proper inductor for any DC-DC converter depends on three things: the desired output power, the input voltage (or range of input voltage), and the converters oscillator frequency and duty cycle. The oscillator timing is important because it determines how long the coil will be charged during each cycle. This, along with the input CHARGE PUMP NEGATIVE OUTPUT VOLTAGE vs. OUTPUT CURRENT Vout (V) oo Sx Your = 5 N a NS INS8I7 SCHOTTKY DIODES 6 (N4148 SILICON DIODES 0 -10 ~20 -30 ~40 'ouy (mA) Figure 5. Charge Pump Negative Output Voltage vs. Current MAAIICMOS Fixed/Adjustable Output Step-Up Switching Regulators voltage, determines how much energy will be stored in the coil. The inductor must meet four electrical criteria: [ ] Value- Low enough inductance so it stores ade- quate energy at the worst-case, low input voltage. High enough so excessive and potentially destructive currents are avoided under worst-case conditions for high power-switch transistor on time and high input voltage. {] Saturation- The coil must deliver the correct induc- tance value at the worst-case, high peak operating cur- rent. { ] EMI- Electromagnetic interference must not upset nearby circuitry or the regulator IC. Ferrite bobbin types work well for digital circuits; toroid or pot core types work well for EMl-sensitive analog circuits. [] DC resistance- Winding resistance must be ade- quately low so efficiency is not affected and self-heating does not occur. Values less than 0.5Q are usually more than adequate. Other inductor parameters, such as core loss or self-res- onant frequency, are not a factor at the relatively low MAX631/632/633 operating frequency. Inductor Value- Low Enough? The problem that bites designs most often, especially in the production or pre-production phase, happens when the inductor value is too high. These units fail to deliver enough load current and exhibit poor load regulation. The worst-case is: [] Maximum load current Minimum supply voltage [] Maximum inductor value, including tolerance [] Maxirnum on resistance of the switch because it reduces the excitation voltage across the inductor [ ] Worst-case low on time Inductor Value- High Enough? The inductor value must also be high enough so peak currents do not stress the transistor or cause the inductor core to saturate. All kinds of odd symptoms can be traced to excessive inductor currents: {iow efficiency, rattling heat sinks, whining coils, and increased output ripple. Very low inductor values may result in damaged power transistors. The slope of the inductor current, and therefore the peak value that it reaches in a given on time, is determined by the supply voltage and the inductor value. The worst case occurs at: [] Maximum supply voltage [] Minimum inductor value, including tolerance MM AXAI/VI [] Minimum on resistance of the switch [ ] Low switching frequency (or maximum switch on- time) Inductor Selection The inductor equations below must be calculated for both worst-case sets of conditions. The final value chosen should be between the minimum value and maximum value calculated. Within these bounds, the value can be adjusted slightly lower for extra load capability or higher for lowest ripple. _ VOUT +VplopeE -VIN 1] Ibk= IOUT MT Ik = (6.25) Win -Vew) OU? Vin -Vsw [2] L=~ ~~ (ton) pk Where Vsy is the voltage drop across the switch in the on state. Conservatively, the worst case is about 0.75V max, 0.25V min with Vip = +15V and 1.5V max, 0.5V min with Vin = +5V. Example: A +5V 10% input must be converted to +15V at 15mA. A Schottky diode (1N5817) anda MAX633B are used. Calculate maximum inductor value allowed: [= 15V+0.4V = 4.5V Pk = (9 25) (4.5V 0.75V) _ 45-075 ~ 174mA Calculate the minimum inductor value allowed: (15mA) = 174mA (8us) = 172uH Ink = 450mA (from table of max ratings) _ _ 5:5V - 0.26V ~ 450mA If this minimum value is greater than the maximum value calculated above, an external power MOSFET must be used. See the MAX641/642/643 data sheet. A value of 160uH would be a good choice for this application. The "A" grade devices, with tighter oscillator tolerance, allow more output current in a given applica- tion. (12us) = 140uH Inductor Saturation When using off-the-shelf inductors, make sure the peak current rating is observed. When designing your own inductors, observe the core manufacturer's Ampere- turns or NI ratings. Failure to observe the peak current or NI ratings may lead to saturation of the inductor. Inductor saturation leads to very high current levels caus- ing excessive power dissipation, poor efficiency, and possible damage to the chip and the catch diode. 9/EE9/LEOXVNMAX631/632/633 CMOS Fixed/Adjustable Output Step-Up Switching Regulators Test for saturation by applying the maximum load and the maximum input voltage while monitoring the inductor current with a current probe. The normal inductor current waveform is a sawtooth with a linear current ramp. Sat- uration creates a nonlinear current waveform with a very rapid increase in current once the inductor saturates. It is this rapid current increase and the resultant high peak currents that can damage the inductor and the catch diode. Chip Topography GND GND LBO LB! 0.070" (1.78mm)} Lx _ 0.096" (2.44mm)} _ Ordering Information (continued) [PART TEMP.RANGE __-PIN-PACKAGE | MAX633XCPA OC to +70C 8 Plastic DIP MAX633XCSA OC to +70C 8 Narrow SO MAX633XC/D 0C to +70C Dice MAX633XEPA -40C to +85C 8 Plastic DIP MAX633XESA -40C to +85C 8 Narrow SO MAX633XEJA -40C to +85C 8CERDIP | | MAX633xMJA -55C to +125C 8 CERDIP "X = A for 5% Output Accuracy. X = B for 10% Accuracy. 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 lime. 8 Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600 1990 Maxim Integrated Products Printed USA 3/90 MAXIM iS a registered trademark of Maxim Integrated Products Dual Mode is a trademark of Maxim Integrated Products