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for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim?s website at www.maxim integrated .com. _______________general description the max1044 and icl7660 are monolithic, cmos switched-capacitor voltage converters that invert, dou- ble, divide, or multiply a positive input voltage. they are pin compatible with the industry-standard icl7660 and ltc1044. operation is guaranteed from 1.5v to 10v with no external diode over the full temperature range. they deliver 10ma with a 0.5v output drop. the max1044 has a boost pin that raises the oscillator frequency above the audio band and reduces external capacitor size requirements. the max1044/icl7660 combine low quiescent current and high efficiency. oscillator control circuitry and four power mosfet switches are included on-chip. applications include generating a -5v supply from a +5v logic supply to power analog circuitry. for applica- tions requiring more power, the max660 delivers up to 100ma with a voltage drop of less than 0.65v. ________________________applications -5v supply from +5v logic supplypersonal communications equipment portable telephones op-amp power supplies eia/tia-232e and eia/tia-562 power supplies data-acquisition systems hand-held instruments panel meters ____________________________features ? miniature max package ? 1.5v to 10.0v operating supply voltage range ? 98% typical power-conversion efficiency ? invert, double, divide, or multiply input voltages ? boost pin increases switching frequencies(max1044) ? no-load supply current: 200a max at 5v ? no external diode required for higher-voltageoperation ______________ordering information ordering information continued at end of data sheet. * contact factory for dice specifications. switched-capacitor voltage converters max1044 icl7660 4 3 2 1 cap- gnd cap+ (n.c.) boost 5 6 7 8 v out lv osc v+ top view ( ) are for icl7660 dip/so/max to-99 icl7660 n.c. cap+ gnd cap- v out lv osc v+ and case 1 2 3 4 5 6 7 8 _________________pin configurations negative voltage converter cap+cap- v+ v out gnd inputsupply voltage negativeoutput voltage max1044 icl7660 __________typical operating circuit dice* 8 so 8 plastic dip pin-package temp. range 0c to +70c 0c to +70c 0c to +70c max1044c/d max1044csa max1044 cpa part 8 plastic dip -40c to +85c max1044epa 19-4667; rev 1; 7/94 max1044/icl7660 downloaded from: http:/// available
switched-capacitor voltage converters absolute maximum ratings electrical characteristics(circuit of figure 1, v+ = 5.0v, lv pin = 0v, boost pin = open, i load = 0ma, t a = t min to t max , unless otherwise noted.) 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. note 1: the maxim icl7660 and max1044 can operate without an external output diode over the full temperature and voltageranges. the maxim icl7660 can also be used with an external output diode in series with pin 5 (cathode at v out ) when replacing the intersil icl7660. tests are performed without diode in circuit. note 2: f osc is tested with c osc = 100pf to minimize the effects of test fixture capacitance loading. the 1pf frequency is correlat- ed to this 100pf test point, and is intended to simulate pin 7?s capacitance when the device is plugged into a test socketwith no external capacitor. for this test, the lv pin is connected to gnd for comparison to the original manufacturer?s device, which automatically connects this pin to gnd for (v+ > 3v). supply voltage (v+ to gnd, or gnd to v out )....................10.5v input voltage on pins 1, 6, and 7 .........-0.3v v in (v+ + 0.3v) lv input current ..................................................................20a output short-circuit duration (v+ 5.5v)..................continuous continuous power dissipation (t a = +70c) plastic dip (derate 9.09mw/c above +70c) ............727mw so (derate 5.88mw/c above +70c) .........................471mw max (derate 4.1mw/c above +70c) ......................330mw cerdip (derate 8.00mw/c above +70c) .................640mw to-99 (derate 6.67mw/c above +70c) ....................533mw operating temperature ranges max1044c_ _ /icl7660c_ _ ..............................0c to +70c max1044e_ _ /icl7660e_ _ ............................-40c to +85c max1044m_ _ /icl7660m_ _ ........................-55c to +125c storage temperature range ............................-65c to + 150c lead temperature (soldering, 10sec) .............................+300c khz t a = 0c to +70c t a = +25c t a = -55c to +125c v osc = 0v or v+, lv open r l = 5k , t a = +25c, f osc 5khz, lv open t a = -40c to +85c r l = 10k , lv open r l = 10k , lv to gnd f osc = 2.7khz (icl7660) , f osc = 1khz (max1044) , v+ = 2v, i l = 3ma, lv to gnd 30 200 r l = , pins 1 and 7 no connection, lv open a 10 supply current 20 pin 1 = 0v pin 1 = v+ 3 oscillator sink orsource current % 95 98 power efficiency c osc = 1pf, lv to gnd (note 2) 400 1 325 output resistance i l = 20ma, f osc = 5khz, lv open 200 t a = 0c to +70c t a = -40c to +85c 200 units max1044 min typ max parameter 325 t a = +25c 130 325 130 150 200 v 1.5 10 supply voltagerange (note 1) 65 100 5 oscillator frequency 100 v+ = 2v v+ = 5v m 1.0 oscillator impedance 80 175 95 98 400 300 250 225 icl7660 min typ max 300 140 250 120 150 250 3.0 10.0 1.5 3.5 55 100 10 100 1.0 t a = -55c to +125c r l = , pins 1 and 7 = v+ = 3v t a = +25c t a = +25c t a = 0c to +70c t a = -40c to +85c t a = -55c to +125c v+ = 5v v+ = 2v r l = , t a = +25c, lv open 99.0 99.9 % 97.0 99.9 voltage conversion efficiency a k conditions max1044/icl7660 2 maxim integrated downloaded from: http:///
80 90 100 30 10 1 efficiency vs. oscillator frequency 70 max1044-fig 7 oscillator frequency (hz) efficiency (%) 10 4 5040 10 2 10 3 6x10 5 60 10 5 c1, c2 = 100f c1, c2 = 10f c1, c2 = 1f externalhcmos oscillator 10,000 100,000 0.1 1 oscillator frequency vs. external capacitance 1000 max1044-fig 8 c osc (pf) oscillator frequency (hz) 1000 10 1 10 100 100,000 100 10,000 icl7660 andmax1044 with boost = open max1044 withboost -v+ 100 1 oscillator frequency vs. supply voltage max1044-fig 9 supply voltage (v) oscillator frequency (hz) 4 10,000 1000 23 678910 100,000 5 from top to bottom at 5vmax1044, boost = v+, lv = gnd max1044, boost = v+, lv = open icl7660, lv = gnd icl7660, lv = open max1044, boost = open, lv = gnd max1044, boost = open, lv = open 0 012345678910 output voltage and output ripple vs. load current -0.5 -2.0 max1044-fig 1 load current (ma) output voltage (v) output ripple (mvp-p) -1.5-1.0 0 250200 150 100 50 400350 300 outputvoltage v+ = 2vlv = gnd output ripple a: max1044 with boost = v+ b: icl7660 c: max1044 with boost = open a b c 0 0 5 10 15 20 25 30 35 40 output voltage and output ripple vs. load current -0.5 -2.0 -2.5 -3.0 -3.5 -4.0 -4.5 -5.0 max1044-fig 2 load current (ma) output voltage (v) output ripple (mvp-p) -1.5-1.0 0 720640 560 480 400 320 240 160 80 800 output voltage output ripple v+ = 5vlv = open a a b c b c a: max1044 with boost = v+ b: icl7660 c: max1044 with boost = open 0 0 5 10 15 20 25 30 35 40 output voltage and output ripple vs. load current -1 -4 -5 -6 -7 -8 -9 -10 max1044-fig 3 load current (ma) output voltage (v) output ripple (mvp-p) -3-2 0 700630 560 490 420 350 280 210 140 70 v+ = 10vlv = open outputripple a b a: max1044 with boost = v+ b: icl7660 c: max1044 with boost = open c b c a outputvoltage 0 012345678910 efficiency and supply current vs. load current 10 40 50 60 70 80 90 100 max1044-fig 4 load current (ma) efficiency (%) supply current (ma) 3020 0 7 8 9 106 5 4 3 2 1 supply current efficiency v+ = 2vlv = gnd 0 0 5 10 15 20 25 30 35 40 efficiency and supply current vs. load current 10 40 50 60 70 80 90 100 max1044-fig 5 load current (ma) efficiency (%) supply current (ma) 3020 0 35 40 45 5030 25 20 15 10 5 v+ = 5vlv = open efficiency a: max1044 with boost = v+ b: icl7660 c: max1044 with boost = open supply current b c a 0 0 5 10 15 20 25 30 35 40 efficiency and supply current vs. load current 10 40 50 60 70 80 90 100 max1044-fig 6 load current (ma) efficiency (%) supply current (ma) 3020 0 35 40 45 5030 25 20 15 10 5 v+ = 10vlv = open a: max1044 with boost = v+ b: icl7660 c: max1044 with boost = open supply current b, c efficiency a switched-capacitor voltage converters __________________________________________typical operating characteristics (v+ = 5v; c bypass = 0.1f; c1 = c2 = 10f; lv = open; osc = open; t a = +25c; unless otherwise noted.) max1044/icl7660 maxim integrated 3 downloaded from: http:///
0.1 1 2345678910 quiescent current vs. supply voltage max1044-fig 12 supply voltage (v) quiescent current (a) 10 1 100 1000 2000 a b d c a: max1044, boost = v+, lv = gndb: max1044, boost = v+, lv = open c: icl7660 and max1044 with boost = open, lv = gnd; above 5v, max1044 only d: icl7660 and max1044 with boost = open, lv = open 0 10 1 10 2 10 3 10 4 10 5 output resistance vs. oscillator frequency max1044-fig 14 frequency (hz) resistance ( ) 200100 300 400 500 600 700 800 900 1000 c1, c2 = 100f c1, c2 = 1f c1, c2 = 10f externalhcmos oscillator 0 -50 -25 0 25 50 75 100 125 quiescent current vs. temperature max1044-fig 13 temperature (c) quiescent current (a) 200100 300 400 500 icl7660, max1044 with boost = open max1044 withboost = v+ 0 12345678910 output resistance vs. supply voltage max1044-fig 15 supply voltage (v) output resistance ( ) 4020 60 80 100 120 140 160 180 200 20 -60 -40 -20 0 20 40 60 80 100 120 140 output resistance vs. temperature max1044-fig 16 temperature (c) output resistance ( ) 4030 50 60 70 80 icl7660,max1044 with boost = open max1044 withboost = v+ switched-capacitor voltage converters ____________________________typical operating characteristics (continued) (v+ = 5v; c bypass = 0.1f; c1 = c2 = 10f; lv = open; osc = open; t a = +25c; unless otherwise noted.) 0 -50 oscillator frequency vs. temperature max1044-fig 10 temperature (c) oscillator frequency (khz) 25 4020 -25 0 75 100 125 60 80 100 50 a: max1044 with boost = v+ b: icl7600 c: max1044 with boost = open b a c 1 10 0 10 1 10 2 10 3 10 4 10 5 5x10 5 quiescent current vs. oscillator frequency max1044-fig 11 oscillator frequency (hz) quiescent current (a) 100 10 1000 10,000 usingexternal hcmos oscillator usingexternal capacitor max1044/icl7660 4 maxim integrated downloaded from: http:///
_______________detailed description the max1044/icl7660 are charge-pump voltage con-verters. they work by first accumulating charge in a bucket capacitor and then transfer it into a reservoir capacitor. the ideal voltage inverter circuit in figure 2 illustrates this operation. during the first half of each cycle, switches s1 & s3close and switches s2 & s4 open, which connects the bucket capacitor c1 across v+ and charges c1. during the second half of each cycle, switches s2 & s4 close and switches s1 & s3 open, which connects the positive terminal of c1 to ground and shifts the nega- tive terminal to v out . this connects c1 in parallel with the reservoir capacitor c2. if the voltage across c2 issmaller than the voltage across c1, then charge flows from c1 to c2 until the voltages across them are equal. during successive cycles, c1 will continue pouring charge into c2 until the voltage across c2 reaches - (v+). in an actual voltage inverter, the output is less than - (v+) since the switches s1?s4 have resistance and the load drains charge from c2. additional qualities of the max1044/icl7660 can be understood by using a switched-capacitor circuit model. switching the bucket capacitor, c1, between the input and output of the circuit synthesizes a resis- tance (figures 3a and 3b.) when the switch in figure 3a is in the left position, capacitor c1 charges to v+. when the switch moves to the right position, c1 is discharged to v out . the charge transferred per cycle is: q = c1(v+ - v out ). if the switch is cycled at frequency f, then the resulting switched-capacitor voltage converters max1044 icl7660 boostcap+ gnd c bypass = 0.1f v+ r l cap- v+ osc c1 10 f lv v out c2 10 f c osc externaloscillator v out _____________________________________________________________ pin description name function boost (max1044) frequency boost. connecting boost to v+ increases the oscillator frequency by a factor of six. when theoscillator is driven externally, boost has no effect and should be left open. pin 1 n.c. (icl7660) no connection 3 gnd ground. for most applications, the positive terminal of the reservoir capacitor is connected to this pin. 2 cap+ connection to positive terminal of charge-pump capacitor 6 lv low-voltage operation. connect to ground for supply voltages below 3.5v.icl7660: leave open for supply voltages above 5v. 5 v out negative voltage output. for most applications, the negative terminal of the reservoir capacitor isconnected to this pin. 4 cap- connection to negative terminal of charge-pump capacitor 7 osc oscillator control input. connecting an external capacitor reduces the oscillator frequency. minimize straycapacitance at this pin. 8 v+ power-supply positive voltage input. (1.5v to 10v). v+ is also the substrate connection. figure 1. maxim max1044/icl7660 test circuit max1044/icl7660 maxim integrated 5 downloaded from: http:///
current is: i = f x q = f x c1(v+ - v out ). rewriting this equation in ohm?s law form defines an equivalent resis-tance synthesized by the switched-capacitor circuit where: where f is one-half the oscillator frequency. this resis- tance is a major component of the output impedance of switched-capacitor circuits like the max1044/icl7660. as shown in figure 4, the max1044/icl7660 contain mosfet switches, the necessary transistor drive cir- cuitry, and a timing oscillator. ________________design information the max1044/icl7660 are designed to provide a simple, compact, low-cost solution where negative or doubled supply voltages are needed for a few low- power components. figure 5 shows the basic negative voltage converter circuit. for many applications, only two external capacitors are needed. the type of capacitor used is not critical. proper use of the low-voltage (lv) pin figure 4 shows an internal voltage regulator inside themax1044/icl7660. use the lv pin to bypass this regulator, in order to improve low-voltage performance i (v+ - v ) 1 / (f x c1) r 1 f x c1 out equiv = = and switched-capacitor voltage converters s1 v+ s2 s3 s4 c1 c2 v out = -(v+) figure 2. ideal voltage inverter v+ c1 f c2 r load v out figure 3a. switched capacitor model r equiv = r equiv v out r load 1 v+ f c1 c2 figure 3b. equivalent circuit 1m boost pin 1 osc pin 7 lv pin 6 gnd pin 3 cap- pin 4 s2 s1 s4 s3 cap+ pin 2 v+ pin 8 v out pin 5 2 q oscillator internal regulator q figure 4. max1044 and icl7660 functional diagram max1044/icl7660 6 maxim integrated downloaded from: http:///
and allow operation down to 1.5v. for low-voltageoperation and compatibility with the industry-standard ltc1044 and icl7660, the lv pin should be connect- ed to ground for supply voltages below 3.5v and left open for supply voltages above 3.5v. the max1044?s lv pin can be grounded for all operat- ing conditions. the advantage is improved low-voltage performance and increased oscillator frequency. the disadvantage is increased quiescent current and reduced efficiency at higher supply voltages. for maxim?s icl7660, the lv pin must be left open for supply voltages above 5v. when operating at low supply voltages with lv open, connections to the lv, boost, and osc pins should be short or shielded to prevent emi from causing oscillator jitter. oscillator frequency considerations for normal operation, leave the boost and osc pinsof the max1044/icl7660 open and use the nominal oscillator frequency. increasing the frequency reduces audio interference, output resistance, voltage ripple, and required capacitor sizes. decreasing frequency reduces quiescent current and improves efficiency. oscillator frequency specifications the max1044/icl7660 do not have a precise oscillatorfrequency. only minimum values of 1khz and 5khz for the max1044 and a typical value of 10khz for the icl7660 are specified. if a specific oscillator frequency is required, use an external oscillator to drive the osc pin. increasing oscillator frequency using the boost pin for the max1044, connecting the boost pin to the v+pin raises the oscillator frequency by a factor of about 6. figure 6 shows this connection. higher frequency oper-ation lowers output impedance, reduces output ripple, allows the use of smaller capacitors, and shifts switch- ing noise out of the audio band. when the oscillator is driven externally, boost has no effect and should be left open. the boost pin should also be left open for normal operation. reducing the oscillator frequency using c osc an external capacitor can be connected to the osc pinto lower the oscillator frequency (figure 6). lower frequency operation improves efficiency at low load currents by reducing the ic?s quiescent supply current. it also increases output ripple and output impedance. this can be offset by using larger values for c1 and c2. connections to the osc pin should be short to prevent stray capacitance from reducing the oscillator frequency. overdriving the osc pin with an external oscillator driving osc with an external oscillator is useful whenthe frequency must be synchronized, or when higher frequencies are required to reduce audio interference. the max1044/icl7660 can be driven up to 400khz. the pump and output ripple frequencies are one-half the external clock frequency. driving the max1044/icl7660 at a higher frequency increases the ripple frequency and allows the use of smaller capacitors. it also increases the quiescent current. the osc input threshold is v+ - 2.5v when v+ 5v, and is v+ / 2 for v+ < 5v. if the external clock does notswing all the way to v+, use a 10k pull-up resistor (figure 7). output voltage considerations the max1044/icl7660 output voltage is not regulated.the output voltages will vary under load according to the output resistance. the output resistance is primarily switched-capacitor voltage converters max1044 icl7660 4 3 c1 10f *required for v+ < 3.5v v out = -(v+) c210f v+ 2 1 5 6 7 8 * c bypass figure 5. basic negative voltage converter max1044 4 3 10f c osc v out = -(v+) 10f v+ 2 1 5 6 7 8 connectionfrom v+ to boost figure 6. negative voltage converter with c osc and boost max1044/icl7660 maxim integrated 7 downloaded from: http:///
a function of oscillator frequency and the capacitorvalue. oscillator frequency, in turn, is influenced by temperature and supply voltage. for example, with a 5v input voltage and 10f charge-pump capacitors, the output resistance is typically 50 . thus, the output voltage is about -5v under light loads, and decreasesto about -4.5v with a 10ma load current. minor supply voltage variations that are inconsequential to digital circuits can affect some analog circuits. therefore, when using the max1044/icl7660 for powering sensitive analog circuits, the power-supply rejection ratio of those circuits must be considered. the output ripple and output drop increase under heavy loads. if necessary, the max1044/icl7660 out- put impedance can be reduced by paralleling devices, increasing the capacitance of c1 and c2, or connect- ing the max1044?s boost pin to v+ to increase the oscillator frequency. inrush current and emi considerations during start-up, pump capacitors c1 and c2 must be charged. consequently, the max1044/icl7660 devel- op inrush currents during start-up. while operating, short bursts of current are drawn from the supply to c1, and then from c1 to c2 to replenish the charge drawn by the load during each charge-pump cycle. if the voltage converters are being powered by a high- impedance source, the supply voltage may drop too low during the current bursts for them to function prop- erly. furthermore, if the supply or ground impedance is too high, or if the traces between the converter ic and charge-pump capacitors are long or have large loops, switching noise and emi may be generated. to reducethese effects: 1) power the max1044/icl7600 from a low-impedance source. 2) add a power-supply bypass capacitor with low effective series resistance (esr) close to the icbetween the v+ and ground pins. 3) shorten traces between the ic and the charge-pump capacitors. 4) arrange the components to keep the ground pins of the capacitors and the ic as close as possible. 5) leave extra copper on the board around the voltage converter as power and ground planes. this is easily done on a double-sided pc board. efficiency, output ripple, and output impedance the power efficiency of a switched-capacitor voltageconverter is affected by the internal losses in the con- verter ic, resistive losses of the pump capacitors, and conversion losses during charge transfer between the capacitors. the total power loss is: the internal losses are associated with the ic?s internal functions such as driving the switches, oscillator, etc. these losses are affected by operating conditions such as input voltage, temperature, frequency, and connec- tions to the lv, boost, and osc pins. the next two losses are associated with the output resistance of the voltage converter circuit. switch losses occur because of the on-resistances of the mosfet switches in the ic. charge-pump capacitor losses occur because of their esr. the relationship between these losses and the output resistance is as follows: where: and f osc is the oscillator frequency. r 1 (f / 2) x c1 4 2r esr esr out osc switches c1 c2 ?+ + () + p p i x r out 2 out += p = p +p +p +p switched-capacitor voltage converters max1044 icl7660 4 3 10f v out = -(v+) 10f v+ v+ cmos orttl gate 10k requiredfor ttl 2 1 5 6 7 8 figure 7. external clocking loss internal losses switchlosses pumpcapacitor losses conversionlosses pumpcapacitor losses switchlosses max1044/icl7660 8 maxim integrated downloaded from: http:///
the first term is the effective resistance from theswitched-capacitor circuit. conversion losses occur during the transfer of charge between capacitors c1 and c2 when there is a voltage difference between them. the power loss is: increasing efficiency efficiency can be improved by lowering output voltageripple and output impedance. both output voltage rip- ple and output impedance can be reduced by using large capacitors with low esr. the output voltage ripple can be calculated by noting that the output current is supplied solely from capacitor c2 during one-half of the charge-pump cycle. slowing the oscillator frequency reduces quiescent cur- rent. the oscillator frequency can be reduced by con- necting a capacitor to the osc pin. reducing the oscillator frequency increases the ripple voltage in the max1044/icl7660. compensate by increasing the values of the bucket and reservoir capacitors. for example, in a negative voltage converter, the pump frequency is around 4khz or 5khz. with the recommended 10f bucket and reservoir capacitors, the circuit consumes about 70a of quiescent current while providing 20ma of output current. setting the oscillator to 400hz by connecting a 100pf capacitor toosc reduces the quiescent current to about 15a. maintaining 20ma output current capability requires increasing the bucket and reservoir capacitors to 100f. note that lower capacitor values can be used for lower output currents. for example, setting the oscillator to 40hz by connecting a 1000pf capacitor to osc pro- vides the highest efficiency possible. leaving the bucket and reservoir capacitors at 100f gives a maximum i out of 2ma, a no-load quiescent current of 10a, and a power conversion efficiency of 98%. general precautions 1) connecting any input terminal to voltages greater than v+ or less than ground may cause latchup. donot apply any input sources operating from external supplies before device power-up. 2) never exceed maximum supply voltage ratings.3) do not connect c1 and c2 with the wrong polarity. 4) do not short v+ to ground for extended periods with supply voltages above 5.5v present on other pins. 5) ensure that v out (pin 5) does not go more positive than gnd (pin 3). adding a diode in parallel withc2, with the anode connected to v out and cathode to lv, will prevent this condition. ________________application circuits negative voltage converter figure 8 shows a negative voltage converter, the mostpopular application of the max1044/icl7660. only two external capacitors are needed. a third power-supply bypass capacitor is recommended (0.1f to 10f) v 1 2 x f x c2 2 x esr i ripple osc c2 out ?+ ?? ? ?? ? p 1 2 c1 (v v 1 2 c2 v 2v v x f / 2 conv.loss out 2 ripple 2 out ripple osc ) =+ ?? ?? + ?? ? ?? ?? ?? ? 2 switched-capacitor voltage converters max1044 icl7660 4 3 c1 10f v out = -(v+) c bypass 0.1f 2 1 5 6 7 8 c210f v+ boost lv figure 8. negative voltage converter with boost and lv connections max1044 icl7660 4 3 v out = 2(v+) - 2v d 2 1 5 6 7 8 c1 c2 v+ figure 9. voltage doubler max1044/icl7660 maxim integrated 9 downloaded from: http:///
positive voltage doubler figure 9 illustrates the recommended voltage doublercircuit for the max1044/icl7660. to reduce the voltage drops contributed by the diodes (v d ), use schottky diodes. for true voltage doubling or higher output cur-rents, use the max660. voltage divider the voltage divider shown in figure 10 splits the powersupply in half. a third capacitor can be added between v+ and v out . combined positive multiplication and negative voltage conversion figure 11 illustrates this dual-function circuit.capacitors c1 and c3 perform the bucket and reser- voir functions for generating the negative voltage. capacitors c2 and c4 are the bucket and reservoir capacitors for the doubled positive voltage. this circuithas higher output impedances resulting from the use of a common charge-pump driver. cascading devices larger negative multiples of the supply voltage can beobtained by cascading max1044/icl7660 devices (figure 12). the output voltage is nominally v out = -n(v+) where n is the number of devices cascaded. the out-put voltage is reduced slightly by the output resistance of the first device, multiplied by the quiescent current of the second, etc. three or more devices can be cascaded in this way, but output impedance rises dramatically. for example, the output resistance of two cascaded max1044s is approximately five times the output resis- tance of a single voltage converter. a better solution may be an inductive switching regulator, such as the max755, max759, max764, or max774. switched-capacitor voltage converters max1044 icl7660 4 3 2 1 5 6 7 8 c210f c1 10f v+ v out = v+ 12 lv figure 10. voltage divider max1044 icl7660 4 3 v out = 2(v+) - 2v d 2 1 5 6 7 8 c4 c1 c2 v+ v out = -(v+) c3 lv figure 11. combined positive and negative converter max1044 icl7660 4 3 2 1 5 6 7 8 max1044 icl7660 4 3 2 1 5 6 7 8 10f 10f v+ 10f 10f 10f v out = -n(v+) 10f max1044 icl7660 4 3 2 1 5 6 7 8 123 figure 12. cascading max1044/icl7660 for increased output voltage max1044/icl7660 10 maxim integrated downloaded from: http:///
paralleling devices paralleling multiple max1044/icl7660s reduces outputresistance and increases current capability. as illus- trated in figure 13, each device requires its own pump capacitor c1, but the reservoir capacitor c2 serves all devices. the equation for calculating output resistance is: shutdown schemes figures 14a?14c illustrate three ways of adding shut- down capability to the max1044/icl7660. when using these circuits, be aware that the additional capacitive loading on the osc pin will reduce the oscillator fre- quency. the first circuit has the least loading on the osc pin and has the added advantage of controlling shutdown with a high or low logic level, depending on the orientation of the switching diode. r r (of max1044 or icl7660) n (number of devices) out out = switched-capacitor voltage converters max1044 icl7660 4 3 v out = -(v+) 2 1 5 6 7 8 c2 c1 v+ max1044 icl7660 4 3 2 1 5 6 7 8 c1 1n figure 13. paralleling max1044/icl7660 to reduce output resistance max1044 icl7660 4 3 10f v out = -(v+) 10f cmos orttl gate 1n4148 v+ 2 1 5 6 7 8 v+ 10k required for ttl figure 14a-14c. shutdown schemes for max1044/icl7660 outputenable 74hc126 or 74ls126 tri-state buffer v+ 7 max1044 icl7660 74hc03open-drain or 74ls03 open-collector nand gates v+ max1044 icl7660 7 a)b) c) 8 cerdip** 8 so pin-package temp. range -40c to +85c -55c to +125c max1044mja max1044esa part 8 plastic dip 0c to +70c icl7660 cpa 8 so 0c to +70c icl7660csa 8 max 0c to +70c icl7660cua dice* 0c to +70c icl7660c/d 8 plastic dip -40c to +85c icl7660epa 8 so -40c to +85c icl7660esa 8 cerdip** -55c to +125c icl7660amja ? 8 to-99** -55c to +125c icl7660amtv ? _ordering information (continued) * contact factory for dice specifications. ** contact factory for availability. ? the maxim icl7660 meets or exceeds all ?a? and ?s? specifications. max1044/icl7660 maxim integrated 11 downloaded from: http:///
switched-capacitor voltage converters __________________________________________________________chip topographies gnd cap- lvv out transistor count: 71substrate connected to v+ cap+ 0.084" (2.1mm) 0.060" (1.5mm) v+ osc icl7660 gnd cap+ boost 0.076" (1.930mm) 0.076" (1.930mm) cap- v out v+ osc lv transistor count: 72substrate connected to v+ max1044 l c a1 b dim a a1 b cd e e h l min 0.0360.004 0.010 0.005 0.116 0.116 0.188 0.016 0 max 0.0440.008 0.014 0.007 0.120 0.120 0.198 0.026 6 min 0.910.10 0.25 0.13 2.95 2.95 4.78 0.41 0 max 1.110.20 0.36 0.18 3.05 3.05 5.03 0.66 6 inches millimeters 8-pin max package 0.65 0.0256 21-0036 a e e h d 0.127mm0.004 in ________________________________________________________package information max1044/icl7660 12 maxim integrated downloaded from: http:///
switched-capacitor voltage converters max1044/icl7660 13 maxim integrated 160 rio robles, san jose, ca 95134 usa 1-408-601-1000 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. the parametric values (min and max limits) shown in the electrical characteristics table are guaranteed. other parametric values quoted in this data sheet are provided for guidance. ? 1994 maxim integrated the maxim logo and maxim integrated are trademarks of maxim integrated products, inc. downloaded from: http:///

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