19-35 12; Rev 0, 5/86 General Description Maxims MAX634 and MAX4391 CMOS DC-DC regu- Jators are designed for simple, efficient, inverting DC-DC converter circuits. The MAX634 and MAX4391 switching regulators provide all contro! and power handling functions in a compact 8 pin package: a 1.25V bandgap reference, an oscillator, a comparator for output voltage regulation, and a 525mA P-channel output MOSFET. A second comparator is also pro- vided for convenient low battery detection. The operating current is typically 100A and is nearly independent of output switch current and duty cycle, thus ensuring high efficiency even in low power battery operated systems. Operating in the inverting MAAIL/SVI CMOS Micropower inverting Switching Regulator Features @ Converts Positive Voltage to Negative Voltage @ Low Operating Current100uA @ Compact 8 Pin MiniDIP and SO Packages @ High Efficiency85% Typical @ Low Battery Detector # 4% Output Voltage Accuracy (MAX634) @ +3V to +16.5V Input Voltage Range # Adjustable Output Voltage Up to -20V with Simple Coil Virtually Unlimited Voltage with configuration, the MAX634 and MAX4391 can convert Transformer a positive input voltage in the range of +8V to 16.5V i , i, to any negative output voltage up to -20V. Ordering Information These devices are pin compatible enhancements of TEMP. RANGE PACKAGE 7 the Raytheon bipolar circuit, RC4391. Improvements PART 5 . 4 include significantly higher efficiency, extended low MAX634C/D orc to+70C Dice voltage operation and improved output voltage MAX634CPA 0C to +70C 8 Lead Plastic DIP_ accuracy (MAX634). MAX634CSA 0Cto+70C 8 Lead Small Outline Maxim manufactures a broad line of DC-DC conver- MAX634EPA -40C to +85C 8 Lead Plastic DIP ters, including the MAX635, MAX636, and MAX637; ae - which reduce the external component count in fixed MAX6S4ESA -40C to *85C BB Lead Small Outline -5V, -12V, and -15V output DC-DC converter circuits. MAX634EJA -40C to +85C 8 Lead CERDIP See Table 2 on the last page of this data sheet for a MAX634MJA.-55G to +125C. 8 Lead CERDIP summary of other Maxim DC-DC converters. : A lications MAX4391C/D orc to +70C Dice ; | ; _ PP MAX4391CPA 0C to +70C 8 Lead Plastic DIP High Efficiency Battery Powered DC-DC MAX4391CSA O to+70C~Ss 8 Lead Small Outline Converters - Board Level. Local P Supply G fi MAX4391EPA = -40C to +85C 8 Lead Plastic DIP oara Level, ova ower Supply enera ton MAX4391ESA -40C to +85C 8 Lead Small Outline Regulated Negative Output Power Supplies MAX4391EJA 40C to -85C 8 Lead CERDIP +5V to +12V or +15V Power Conversion MAX4391MJA-55C to+125C 8 Lead CERDIP Regulated Voltage Inverters : Typical Operating Circuit Pin Configuration ue 1 +OVIN + Top View 6 a a LBR Vs Vea -5V OUT = e LBR]1 sly MAXIM 6 2 MAX634 a0 VREF MAXIM 2 7TIV LBD EI MAX634 7 | Veer MAX4391 ex [2] fs] *s =o GNO eno [| 5] kx + L +5V to -5V Converter | MAXIM Maxim Integrated Products 1 Call toll free 1-800-998-8800 for free samples or literature. L6EPXVIN/VEOSXVWMAX634/MAX4391 CMOS Micropower Inverting Switching Regulator ABSOLUTE MAXIMUM RATINGS Supply Voltage (Note 1)... cece cece eee +18V Power Dissipation Storage Temperature Range .............. -65C to +160C Plastic DIP (derate 8.33mW/C above +50C) ...... 625mW Lead Temperature (Soldering, 10 seconds) ............ +300C Small Outline (derate 6mW/C above -50C) ...... 450mW Operating Temperature Range CERDIP (derate 8mMW/C above +50C) ........... 800mWw MAX634C, MAX4391C oo... eee eee 0C to -70C Input Voltage, Pins 1.3.8 (Note 2) .......... -0.3V to +Vo 40.3V MAX634E, MAX4391E .. 0.0... eee -40C to +85C Ly Output Current 0.0... eee 525mA Peak MAX634M, MAX4391M ... 0... 0 cece eee -55C to +125C LBD Output Current 0.00. eee eee 50mA Stresses above 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 above those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum ratings conditions for extended periods may atfect device reliability. ELECTRICAL CHARACTERISTICS (+Vg = +6.0V, Ta = +25C, unless otherwise noted) MAX634 MAX4391 PARAMETER SYMBOL CONDITIONS MIN. TYP MAX. | MIN. TYR MAX. UNITS Supply Voltage (Note 1) +Vs 2.3 16.5 4.0 16.5 Vv No External Loads Supply Current lin Vg =4.0V 70 150 90 250 BA +Vg = 16.5V 150 500 170 500 Vout nom = 72-0V -5.20 -4.80 | -5.35 -4.65 Output Voltage Vout | yup" = -15.0V -15.70 14.30 |-15.85 1415) . Vout nom = 79-0V 9 Line Regulation (Note 4) Vig = BOV to 15V 2.0 3.0 Vou Vout nom = 79.0V +Vg = 4.5V, Cy = 350pF 0.4 04 Load Regulation (Note 4) Proap = Omw to 75mW %VeuT Vout nom = 715.0V +V5 = 4.5V, Cy = 350pF 0.14 0.14 PLoap = OMW to 75mW Reference Voltage 1.22 1.25 1.28 1.18 1.25 1.32 Vv Switch Current low Pin S =5.0V 75 150 75 150 mA Switch Leakage Current log Pin 5 = -18V, +V. = 6V 0.01 1.0 0.01 5.0 BA Capacitor Charging Current lex 30 30 BA C, + Threshold Voltage +Vg - 0.1 +V5 - 01 V Cy - Threshold Voltage 04 O41 7 Operating Frequency Range (Note 3) Fo OA 75 0.1 75 kHz Low Battery Output Current lip Vg = 0.4V, V,=1.1V 500 1000 250 600 | HA Low Battery Output Leakage lLBpo Vg = 16.5V, Vy = 1.4V 0.04 3.0 0.01 5.0 uA | Low Battery Input Threshold Vigra 1.25 1.25 Vv Low Battery Input Bias Current lLer 0.01 10 0.01 10 nA Feedback Input Bias Current lie 0.01 10 0.01 10 nA Efficiency | Figure 2 | 80 80 % Note 1: In addition to the Absolute Maximum rating of +18V. the input voltage also must not exceed 24 -|-Voy jj. Note 2: The input voltage limit may be exceeded provided input current is limited to less than 1mA Note 3: The operating frequency range is guaranteed by design and verified with sample testing. Note 4: Guaranteed by correlation with DC pulse measurements. 2 MAAIWVIELECTRICAL CHARACTERISTICS (+Vg = +6.0V, full operating temperature range unless otherwise noted) CMOS Micropower Inverting Switching Regulator MAX4391 MAX634 PARAMETER SYMBOL CONDITIONS MIN. TYP MAX. | MIN. TYR MAX. UNITS Supply Voltage (Note 5) +Vs 26 16.5 4.0 16.5 Vv No External Loads Supply Current lin Veg = 4.0V 150 250 pA +Vg = 16.5V 500 500 Reference Voltage Veer 1.18 1.25 1.32 1.13 1.25 1.36 v V, = -5.0V -$.25 -4.75 | 5.5 -45 Output Voltage Vv OUT nom Vv ouT Vout nom = -15.0V -16.0 -14.0 ] -16.5 -13.5. Vv = -5.0V Line Regulation _ We = 50V to 15V 3.0 4.0 | %Vous Vout nom = ~5.0V +Vg = 4.5V, Cy = 350pF 0.5 0.5 Load Regulation Proap =omW to 7amW %VeuT OUT nom -15.0V +Vg = 4.5V, Cy = S50pF 0.3 03 PLoap = OMW to 75mW Switch Leakage Current leo Pin 5 = -18V, +V, = 6V 0.01 20 30 uA Low Battery Output Current ILBp Vg = 0.4V, V,=1.1V 500 250 uA Low Battery Output Leakage lLgpo Vg = 16.5V, V, = 1.4V 3 5 pA Note 5: In addition to the Absolute Maximum rating of +18V, the input voltage also must not exceed 24 -| Voy Pin Description PIN NAME FUNCTION PIN NAME FUNCTION 1 LBR Low Battery Detection comparator input. 6 +Vs The positive supply voltage, from +3V to The LBD output, pin 2, sinks current +16.5V (MAX634). The total voltage when this pin is below the low battery difference between the negative output detector threshold of 1.25V voltage and the positive input voltage 2 LBD | The Low Battery Detector output is an must be less than 24V, open drain N-channel MOSFET which sinks current when the LBR input, pin 1, 7 Vacr | The Voltage REFerence output is 1.25V, is below 1.25V. generated by an on-chip bandgap 3 Cy An external capacitor connected reference. between this terminal and ground sets the oscillator frequency. 47pF = 40kHz 8 VeB The output voltage is set by an external 4 GND | Ground. resistive divider connected to the 5 Ly External Inductor output driver. The Voltage Feedback input, pin 8. The internal P-channel MOSFET which drives MAX634/MAX4391 will pulse the Ly this pin has an output resistance of 8 ouput whenever the voltage at this L and a peak current rating of 525mA. terminal is above Ground. aa | . MAXAL/VI L6EPXVIN/PESXVNMAX634/MAX4391 CMOS Micropower Inverting Switching Regulator Typical Operating Characteristics Lx ON RESISTANCE vs. TEMPERATURE 2 +Vs|= #2! La 15 Tt = I = 10 = at = = Vs} +5 2 a Lae Lt | 5 7 0 50-25 0 2 50 78 TEMPERATURE (C) 100 125 -50 25 Detailed Description Principle of Operation Figure 1 shows a simplified buck-boost voltage inverter, sometimes called an inverting or flyback converter. When the switch is closed a charging cur- rent flows through the inductor, creating a magnetic field. When the switch opens, the current continues to flow through the inductor in the same direction as the charging current. Since the switch is now open, the current must flow through the diode, thereby charging the capacitor with a negative voltage. The current linearly decays to zero and the magnetic field collapses as the energy stored in the inductor is transferred to the output filter capacitor. The MAX634 controls the magnitude of the negative output voltage by turning the switch on and off only when the output voltage has fallen below the desired value. Basic Circuit Operation Figure 2 shows the standard circuit for converting a positive input voltage into a negative voltage. When the feedback voltage at pin 8 is above ground, the P-channel MOSFET at pin 5 turns on during the next low-going period of the oscillator. The P-channel MOSFET delivers current to the external inductor, storing energy in its magnetic field. When the oscil- lator output goes high, the P-channel MOSFET turns off, and the kickback of the inductor pulls current through diode D1, negatively charging the output fil- ter capacitor, C1. This cycle repeats until the output voltage pulls the feedback input, pin 8, below ground. SUPPLY CURRENT vs. TEMPERATURE SUPPLY CURRENT vs. SUPPLY VOLTAGE Taf 25 oo fs {aA} 0 2 sO 75 TEMPERATURE (C] 100 125 Figure 1. Simplified Voltage Inverter The NOR gate latch prevents high frequency oscilla- tions by not allowing Ly to switch repeatedly during an oscillator cycle. The output voltage is determined by the internal 1.25V reference and the ratio of the resistors R1 and R2. - Aq Vout =1.25V x R2 Capacitor C1 is the output filter capacitor. The capac- itance and ESR (equivalent series resistance) of C1 determine the output ripple. C2 and C3 are bypass capacitors; while Cy sets the oscillator frequency. MVIAALWVICMOS Micropower inverting Switching Regulator ! | 4<23 = r > BATTERY { = fa COMPARATOR a Ot 2 if ier Wok t- 4 1 BR > 1 260K.) > \ + LBD LOW BATTERY 2 quIPUY --+--- a Des 47pF FOR 40kHz c 200pF FOR 10kH2 x 4) GNO Ve +1.25V | FEEDBACK COMPARATOR p -VouT +1.25V BANDGAP REFERENCE Vaer IN914 y O +g L DALE 2 TesvaTa 3 |-OmH OUTPUT RI ; VOLTAGE -5.0V 300kQ -9.0V 536k 1) -12.0V 720KQ. -15.0V 900k LL Figure 2. Standard Application Circuit Oscillator The MAX634/MAX4391 oscillator uses only one external component, a capacitor Cy connected between pin 3 and Ground. A value of 47pF sets the oscillator frequency to approximately 40kHz. The oscillator can also be externally driven with a CMOS gate which swings from ground to +Vs. The Ly output is always off when the Cy pin is externally driven high. Low Battery Detector The Low Battery Detector (LBD) Output (pin 2, Fig- ure 2} sinks current whenever the input voltage at Low Battery Resistor (pin 1} is less than +1.25V. The LBR input is a high impedance CMOS input, with less than 10nA Jeakage current. The LBD output is an open drain N-channel MOSFET with about 5000 of output resistance. The operating voltage of the low battery detector can be adjusted using an exter- nal voltage divider as shown in Figure 2. If hysteresis is desired, add a resistor between pins 1 and 2. R4 Viopatt = 1.25V x (1+ 53) or, _ VLOBATT R4=R3x (Sosy - 1) MAXAL/VI where Viogatt is the operating voltage of the low battery detector, and R3 is usually between 10kQ and 10MQ, with a typical value being 470k{). _____ External Component Selection Inductor Value The available output current from an inverting DC- DC voltage converter is determined by the value of the external inductor, the output voltage, the input voltage, and the operating frequency. The inductor must 1) have the correct inductance, 2) be able to handle the peak currents, and 3) have acceptable series resistance and core losses. Lax = (Vin Ton)? f 2 Pout Vin Ton Luin = ra MAX where Imax is the maximum allowable peak Lx current (525mA). Contrary to what most people would expect at first glance, reducing the inductor value increases the available output current: lower L increases the peak current, thereby increasing the available power. lf the inductance is too high, the MAX634/MAX4391 will not be able to deliver the desired output power, L6EVXVIN/PESXVINMAX634/MAX4391 CMOS Micropower Inverting Switching Regulator even with the Ly output turned on with each oscilla- tor cycle. The available output power can be increased by either decreasing the inductance or by decreas- ing the frequency. Decreasing the frequency increases the on period of the Ly output, thereby increasing the peak inductor current, which in turn increases the available output power since the output power is proportional to the square of the peak inductor current. The most common MAX634 circuit is the buck-boost voltage inverter (Figure 2). When the P-channel out- put device is on, the current in the inductor linearly rises since: di _v di oL At the end of the on period the current is VIN Ton 5V x 50us In. = A - = A pk L 1mH 250m assuming a 10kHz, 50% duty cycle oscillator and Vs =5V The energy in the coil is: 1 E= aL Ip? = 31.2uJ At maximum load this cycle is repeated 10,000 times per second, and the power transferred through the coil is 10,000 x 31.2uJ = 312mW. If the output voltage is -5V, then 312/5 = 62.5mA of output current is avail- able, ignoring losses and component tolerances. Ina practical circuit, 50mA of output current is available at -5V. The external inductor required by the MAX634/ MAX4391 is readily obtained from a variety of sup- pliers. (See Table 1.) Types of Inductors Molded Inductors These are cylindrically wound coils which look similar to 1 watt resistors. They have the advantages of low cost and ease of handling, but have higher resistance, higher losses, and lower power handling capability than other types. Potted Toroidal Inductors A typical 1mH, 0.82 ohm potted toroidal inductor (Dale TE-3Q4TA) is 0.685" in diameter by 0.385 high and mounts directly onto a printed circuit board by its leads. Such devices offer high efficiency and mounting ease, but at a somewhat higher cost than molded inductors. Ferrite Cores (Pot Cores) Pot cores are very popular as switch-mode inductors since they offer high performance and ease of design. The coils are generally wound on a plastic bobbin, which is then placed between two pot core sections. A simple clip to hold the core sections together completes the inductor. Smaller pot cores mount directly onto printed circuit boards via the bobbin terminals. Cores come in a wide variety of sizes, often with the center posts ground down to provide an air gap. The gap prevents saturation while accurately defining the inductance per turn squared. Pot cores are suitable for all DC-DC converters, but are usually used in the higher power applications. They are also useful for experimentation since it is easy to wind coils onto the plastic bobbins. Toroidal Cores In volume production the toroidal core offers high performance, low size and weight, and low cost. They are, however, slightly more difficult for proto- typing, in that manually winding turns onto a toroid is more tedious than on the plastic bobbins used with pot cores. Toroids are more efficient for a given size since the flux is more evenly distributed than in a pot core, where the effective cross sectional area differs between the post, side, top and bottom. Since it is difficult to gap a toroid, manufacturers produce toroids using a mixture of ferromagnetic powder (typically iron or Mo-Permalloy powder) and a binder. The permeability is controlled by varying the amount of binder, which changes the effective gap between the ferromagnetic particles. Mo-Permalloy powder (MPP) cores have lower losses and are recom- mended for the highest efficiency, while iron powder cores are lower cost. Table 1. Coil and Core Manufacturers MANUFACTURER racae DESCRIPTION MOLDED INDUCTORS __ : / Dale IHA-104. 500pzH, 0.5 ohms Caddell-Burns 6860-19 3304H. 0.33 ohms. | | TRW : LL-500 5004H, 0.75 ohms | POTTED TOROIDAL INDUCTORS Dale TE-3Q4TA || 1mH,0.820hms_| | TRW MH-l | 600zH, 1.9 ohms Torotel Prod. PT53-18 | 500uH,50nhms | FERRITE CORES AND TOROIDS Allen Bradley T0451100A ieepa | Siemens ; B64290-K38-X38 Tor. Core, 4uH/T? Magnetics 555130 ror ae L- 4 Stackpole 57-3215 reer am Magnetics 6-41408-25 14 x8. 280nH/T? | Note 1: This list does not constitute an endorsement by Maxim Integrated Products and is not intended to be a comprehensive list of all manufacturers of these components. MAXICMOS Micropower inverting Switching Regulator External Diode In most MAX634 circuits the inductor current returns to zero before Ly turns on for the next output pulse. This allows the use of slow turn-off diodes. On the other hand, the diode current abruptly goes from zero to full peak current each time Ly switches off (Figure 2, D1). To avoid excessive losses during turn- on, the diode must have a fast turn-on time. The 1N914 or 1N4148 is suitable for low power appli- cations. The 1N5817 series of Schottky diodes or their equivalent are suitable for higher power applica- tions. Rectifier diodes such as the 1N4001 series are unacceptable since their slow turn-on results in ex- cessive losses. Filter Capacitor The output filter capacitor (C1 in Figure 2) stores the energy delivered by the inductor, and delivers current to the load. The output voltage ripple is directly affected by the capacitance and the equivalent series resistance (ESR) of the output filter capacitor. The output voltage ripple has two components, with approximately 90 phase difference. One ripple com- ponent is created by the change in stored charge in the capacitor with each output pulse. The other ripple component is the product of the capacitor charge/ discharge current times the ESR (effective series resistance) of the capacitor. With low cost aluminum electrolytic capacitors, the ESR produced ripple is generally larger than the ripple from the change in charge. Vegr = Ip x ESR (Volts P-P) =| Vin 2LF }) x ESR (Volts P-P) where Vin is the input voltage to the coil, L is the inductance of the coil, f is the oscillator frequency, and ESR is the equivalent series resistance of the output filter capacitor. The output ripple resulting from the change in charge on the filter capacitor is: | Vaaq -2 where: Q = tois Xx ~peak ; - Vin and: Ineak = tcHG x TL _ VinftcHe){tois) 2Lc where tcHq and tpjs are the charge and discharge times for the inductor (1/(2f) can be used for norminal calculations). Vga MAAIL/VI Oscillator Capacitor, Cy The oscillator capacitor can be a low cost ceramic capacitor. If the circuit will be operated over a wide temperature range, an capacitor with a low tempera- ture coefficient of capacitance should be used. The value of Cy can be calculated using the formula: 2.14 x 10-6 Cy = = Cit where f is the desired operating frequency in Hertz. and Ciyrz is the sum of the stray capacitance on the Cx pin and the internal capacitance of the package. The internal capacitance is about 1pF for the plastic package and 3pF for the CERDIP package. Typical stray capacitance is about 3pF for normal printed circuit board layouts, but will be significantly higher if a socket is used. _tt(tCSC*C Aisin Hints Inductor Saturation When using off-the-shelf inductors, make sure that the peak current rating is observed. When designing your own inductors, observe the core manufacturers Ampere-turns or NI ratings. Failure to observe the peak current or NI ratings may lead to saturation of the inductor, especially in circuits with external cur- rent boosting transistors. Inductor saturation leads to very high current levels through the external boost transistors, causing excessive power dissipation, poor efficiency, and possible damage to the inductor and the external transistor. Test for saturation by applying the maximum load. the maximum input voltage, and (for a safety mar- gin) lowering the clock frequency by 25%. Monitor the inductor current using a current probe. The normal inductor current waveform is a sawtooth with a linear current ramp. Saturation 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 cur- rents that can damage the inductor and the external boost transistor. Bypassing and Compensation The high operating current pulses in the Ly output and the external inductor can cause erratic opera- tion unless the MAX4391/MAX634 is properly by- passed. Connect a 10uF bypass capacitor directly across the MAX4391 between pin 6 (+Vs) and pin 4 (Ground) to minimize the inductance and high fre- quency impedance of the power source. Make sure that the high current ground return path of the inductor does not cause a voltage drop in the MAX4391 ground line. L6EPXVIN/PEOXVNMAX634/MAX4391 CMOS Micropower Inverting Switching Regulator The reference voltage output, pin 7, should also be bypassed to ground to avoid coupling to the high current path that includes the L, output, the inductor, and its ground return. With light loads, coupling from the high power cir- cuit into the control circuitry may cause the output pulses to occur in bursts, thereby increasing low frequency ripple and degrading the line and load regulation. Normal operation with evenly distributed output pulses can be restored by adding a 100pF to 1O0nF compensation capacitor across the feedback resistor, R1. Minimizing the stray capacitance on the Vep terminal will often eliminate the need for this compensation capacitor. e _____ Typical Applications -5V Output Regulated Voltage Inverter The standard circuit in Figure 2 will deliver 50mA at -5V. Efficiency is 85% when using a low loss pot core or toroidal inductor such as the Dale TE3Q4TA series. Using a low cost molded inductor with several ohms series resistance reduces the efficiency to 70%. -12V and -15V Output DC-DC Inverters The circuit of Figure 2 can also be used for -12V or 15V outputs by simply changing the value of R1 in the feedback network using the formula 720k0 FOR +12 SO0DkO FOR +15 Wise 2 NM Vea He iL cl ey = J mr aR -15V 2 = OUTPUT NG. ] 60 Veer 1Ng148 MAXIM MAX634 3 MAX4391 cy" Vs 47pF ==6 +2 9 r% HA +BY IN4148 OUTPUT E T oat GND Ly cae 14m x 8mm POT CORE 220uH PRIMARY Figure 3. Dual Output, +12V or +18V DC-DC Converter Dual Output, +12V or +15V DC-DC Converters The buck-boost configuration of the MAX634 is well suited for dual output DC-DC converters. As shown in Figure 3, all that is needed is a second winding on the inductor. Typically, this second winding is bifilar (primary and secondary are wound simultaneously RI _ Vout Re using two wires in parallel). The inductor core Is 1.25V usually a toroid or a pot core, see Table 1. INPUT, 9V BATTERY Ra R4 100k!) 100k! Y -wv. WA INg14 500.H INgIa NEGOUT 4 db} Toaaa" >! 9 ye POS OUT -12, 15mA L isnt mt nF mt + +12V, 45mA ye q . 330uF + 250uH NC at] ; =e a = 5 {a {7 [6 5 = (3 BkO ~ lx Vee Vner +Vs Py Vs ud, GNO Ic Vee SMIAAISVI MAXI * Ra MAX634 , MAX630 ea Cx LBD LER 3 zt { 190pF Figure 4. =12V Dual Tracking Regulator MAAI/WICMOS Micropower Inverting Switching Regulator The negative output voltage is fully regulated by the MAX634. The positive voltage is semi-regulated, and will vary slightly with load changes on either the pos- itive or negative outputs. See the MAX630 data sheet for a similar circuit with a fully regulated positive output and a semi-regulated negative output. If both outputs must be fully regulated use both a MAX634 and a MAX630, as shown in Figure 4. Voltage Inverter In Figure 5, the negative output voltage tracks the positive input voltage. This circuit performs the same function as Maxim's ICL7660, but with better output regulation and higher output current capability. With the circuit components shown, Figure 5 will deliver approximately 50mA at -9V when the input is +9V, and about 30mA at -5V when the input is +5V. Input voltage tracking is achieved by using the posi- tive input voltage as the reference instead of the onboard bandgap reference. The output voltage is set by the input voltage. R17. and R2 as follows: R2 Vout = Ry x Vs Low Power Shutdown Unlike the MAX630, the MAX634 and MAX4391 do not have a logic level shutdown pin, but a low power mode can easily be implemented as shown in Figure 6. Since the operating current is only 250uA maxi- S MAKIN MAX634 MAX4391 LOW = SHUTDOWN HIGH = OPERATE -~- NCHANNEL FET = = = SUCH AS 2N7000 | OR IRFOI20 L Figure 6. Low Power Shutdown GND mum, the GND pin can be driven directly by a CMOS gate or N-channel FET. Drive GND low for normal operation; let it float or drive it high to enter the low power shutdown mode. In low power shut- down the MAX634 circuit draws only the leakage current of the Ly output. The Ground pin should be well bypassed and any voltage drop across the CMOS gate adds to the ref- erence voltage, slightly increasing the regulated out- | | I bag put voltage. 3 i 47pF FOR 40KHz c 150pF FOR 14kH2 x 4 GND . I 3A RS i 5 1 VS Tooke 3 +, ier Veg 1k > 1 260k > ' _ v = LOW BATTERY 4 = ge = 1 veo v REF OUTPUT MAXIM MAX634 MAX4391 Nour -in 1N4148 ol Figure 5. Regulated Voltage inverter MAAIM L6EPXVI/PEOXVNMAX634/MAX4391 CMOS Micropower Inverting Switching Regulator 4 s Vin 4 1 . I 2 Ra RS S < ! A ~Vour 100k 11 3 $~ tar we va Lf _- UR OF 1 260KQ s ae ~ 2 LOW BATTERY w-4 ~~ 7 Leo Vree (NS8I7 MAKIN or MA X634 3 MAX4391 [| Cy Vs OUTPUT 4?pF FOR 40kKz c , x NPN VOLTAGE R1 BOF FOR }4kH2 POWER - 4 TRANSISTOR -5.0V 300ki2 GNO ly -9.0V. 549k -12.0V 720k9 | -15.0V 900k 1k. Ly 47H Figure 7. Boosting Output Power With External NPN Power Transistor Boosting Output Power With External Power Devices The MAX634 and MAX4391 are limited to a maxi- mum switch current of 525mA. If higher current, or output resistance less than the 6 ohms of the MAX634 is required, the circuits of Figures 7, 8, or 9 can be used, The circuit of Figure 7 uses an NPN bipolar transis- tor to boost the output current. All of the NPN transistor base current is used to drive the inductor, but the voltage drop across the transistor will be approxmately 0.7V. The circuit of Figure 8 uses a low resistance N- channel MOSFET in a transformer coupled voltage inverter circuit. This circuit has the advantage that a positive output voltage can also be obtained by simply adding a diode and an output filter capacitor. The -15V output is fully regulated for both line and load variations; the +20V output voltage will varies with changes in load on either the +20V or -15V output, as well as changes in the +5V input. This variation is normally less than 10%. High Output Voltage The circuit in Figure 9 converts any positive voltage from +3V to +16V to any desired output voltage. as long as the voltage breakdown of the external P-Channel MOSFET is not exceeded. This circuit is also useful for generating a high power, high effi-~ ciency -12V or -15V output using a simple one wind- ing coil. I LBR ll NC. 4 LBD VreF MAXI! MAX634 GNO 3 MAX4397 oc tx Cy = 4 LBRO 0 VREF MAKIM MAX634 MAX4391 Cx 4 Tl GND Figure 8. High Power +6V to -15V DC-DC Converter 10 Figure 9. Boosting Voltage External P-Channel MOSFET MAAI/VICMOS Micropower Inverting Switching Regulator Operating with Wide Input Voitage Range The available output power varies as the square of the input voltage. The Low Battery Detector can compensate for a reduction in input voltage by lower- ing the oscillator frequency, as shown in Figure 10. With the values shown, the oscillator frequency is 40kHz when the input voltage is above 6V. When the input falls below 6V, the Low Battery Detector (LBD) output goes low, placing the 100pF capacitor in parallel with Cy, reducing the oscillator frequency to 14kHz. This increases the available output power by a factor of 3. This circuit can be used with any of the other appli- cation circuits in this data sheet. LBD MAKIN Cup MAX634 100pF 3 MAX4391 Cx | Figure 10. Wide Input Voltage Range Operation with Variable Frequency Oscilator. _.____________ Chip Topography GND Cx LBD LBR . | | LX Yo MAAN! 1 L6EPXVIN/PESXVUNMAX634/MAX4391 CMOS Micropower inverting Switching Regulator Table 2. Maxim DC-DC Converters DEVICE DESCRIPTION INPUT VOLTAGE OUTPUT VOLTAGE COMMENTS ICL7660 Charge Pump Voltage Inverter 1.5V to 10V -Vin Not regulated ne MAX4193 | DC-DC Boost Converter 2.4V to 16.5V Vout = Vin RC4193 2nd source | | mAx630 | DC-DC Boost Converter 2.0V to 16.5V ~Vour> Vin Improved RC4191 2nd source MAX631 DC-DC Boost Converter 1.5V to 5.6V +5V Only 2 external components | | MAX632 DC-DC Boost Converter 1.5V to 12.6V : +412V Only 2 external components MAX633 DC-DC Boost Converter 1.5V to 15.6V +15V : Only 2 external components MAXx4391 | DC-DG Voltage Inverter 4V to 16.5V up to -20V RC4391 2nd source | MAX634 | DC-DC Voltage Inverter 2.3V to 16.5V upto -20V_ Improved RC4391 2nd source _| [ MAX635 DC-DC Voltage Inverter 2.3V to 16.5V -5V Only 3 external components | MAX636 DC-DC Voltage Inverter 2.3V to 16.5V -12V Only 3 external components | | MAX637 DC-DC Voltage Inverter 2.3V to 16.5V ~15V- Only 3 external components | MAX638 DC-DC Voltage Stepdown 3V to 16.5V Vout < Vin, Only 3 external components ~ MAX641 High Power Boost Converter 1.5V to 5.6V +5V Drives external MOSFET MAX642 High Power Boost Converter 1.5V to 12.6V +12V Drives external MOSFET MAX643 High Power Boost Converter 1.5V to 15.6V +15V "Drives external MOSFET Package Information ogy MAX in0160 MAX sean a1 LEAD #1 a 0.030 - 0.110 0.026 RAD zi 008 le gS 7ad AAD temo Le (0.635) TOU east l- : oT gt Hats me ot a TYR tr ren 8 928 me: (0508) 308 azo - . Ga) a 125 wn ko y tosh 764 a o 0.020 wnt tie a220= sat i 0.008 - 0.012 (0.508) 0.100 yaqy (0.203 - 0.305) um (2540) _ 0.002 seat ei ose ci 0.100 = ge fh 0807 Q05t1 11385 + 0025 le.255 0635 (2540 = 0.254) (9779 = 0.835) 8 Lead Plastic DIP (PA) 8 Lead CERDIP (JA) Aja = 160C/W Oa = 125C/W Ajo = 75C/W Ajc = 55C/W Maxim cannot assume responsibility for use of any circuitry other than cucuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications withaut notice at any time Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600 12 1986 Max im Integrated Products Printed USA MAXIMA 5 4 segistered trademark of Maxim Integrated Products