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Rev 19-4667; 1; 7/94 Switched-Capacitor Voltage Converters _______________General Description The MAX1044 and ICL7660 are monolithic, CMOS switched-capacitor voltage converters that invert, double, 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 applications requiring more power, the MAX660 delivers up to 100mA with a voltage drop of less than 0.65V. ____________________________Features o Miniature MAX Package o 1.5V to 10.0V Operating Supply Voltage Range o 98% Typical Power-Conversion Efficiency o Invert, Double, Divide, or Multiply Input Voltages o BOOST Pin Increases Switching Frequencies (MAX1044) o No-Load Supply Current: 200A Max at 5V o No External Diode Required for Higher-Voltage Operation MAX1044/ICL7660 ______________Ordering Information PART MAX1044CPA MAX1044CSA MAX1044C/D MAX1044EPA TEMP. RANGE 0C to +70C 0C to +70C 0C to +70C -40C to +85C PIN-PACKAGE 8 Plastic DIP 8 SO Dice* 8 Plastic DIP ________________________Applications -5V Supply from +5V Logic Supply Personal 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 Ordering Information continued at end of data sheet. * Contact factory for dice specifications. _________________Pin Configurations TOP VIEW (N.C.) BOOST CAP+ GND CAP1 2 3 4 8 V+ OSC LV VOUT MAX1044 ICL7660 7 6 5 __________Typical Operating Circuit DIP/SO/MAX CAP+ V+ INPUT SUPPLY VOLTAGE N.C. 1 V+ AND CASE 8 7 OSC MAX1044 ICL7660 CAP+ CAPVOUT GND NEGATIVE OUTPUT VOLTAGE 2 ICL7660 6 LV GND 3 4 5 VOUT NEGATIVE VOLTAGE CONVERTER CAP( ) ARE FOR ICL7660 TO-99 1 ________________________________________________________________ Maxim Integrated Products Call toll free 1-800-998-8800 for free samples or literature. Switched-Capacitor Voltage Converters MAX1044/ICL7660 ABSOLUTE MAXIMUM RATINGS Supply Voltage (V+ to GND, or GND to VOUT)....................10.5V Input Voltage on Pins 1, 6, and 7 .........-0.3V VIN (V+ + 0.3V) LV Input Current ..................................................................20A Output Short-Circuit Duration (V+ 5.5V)..................Continuous Continuous Power Dissipation (TA = +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 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 1, V+ = 5.0V, LV pin = 0V, BOOST pin = open, ILOAD = 0mA, TA = TMIN to TMAX, unless otherwise noted.) PARAMETER RL = , pins 1 and 7 no connection, LV open CONDITIONS TA = +25C TA = 0C to +70C TA = -40C to +85C TA = -55C to +125C 10 3.0 1.5 TA = +25C TA = 0C to +70C TA = -40C to +85C TA = -55C to +125C Output Resistance fOSC = 2.7kHz (ICL7660), TA = +25C fOSC = 1kHz (MAX1044), TA = 0C to +70C V+ = 2V, IL = 3mA, TA = -40C to +85C LV to GND TA = -55C to +125C V+ = 5V COSC = 1pF, Oscillator Frequency LV to GND (Note 2) V+ = 2V Power Efficiency RL = 5k, TA = +25C, fOSC 5kHz, LV open Voltage Conversion Efficiency RL = , TA = +25C, LV open Pin 1 = 0V Oscillator Sink or VOSC = 0V or V+, LV open Source Current Pin 1 = V+ V+ = 2V Oscillator Impedance TA = +25C V+ = 5V IL = 20mA, fOSC = 5kHz, LV open 65 10 100 130 130 150 325 325 325 400 5 1 95 98 97.0 99.9 3 20 1.0 100 1.0 100 10 95 98 99.0 99.9 1.5 55 10.0 3.5 100 120 140 150 250 300 300 400 V MAX1044 MIN TYP MAX 30 200 200 200 200 ICL7660 MIN TYP MAX 80 175 225 250 250 A UNITS Supply Current RL = , pins 1 and 7 = V+ = 3V Supply Voltage Range (Note 1) RL = 10k, LV open RL = 10k, LV to GND kHz % % A M k Note 1: The Maxim ICL7660 and MAX1044 can operate without an external output diode over the full temperature and voltage ranges. The Maxim ICL7660 can also be used with an external output diode in series with pin 5 (cathode at VOUT) when replacing the Intersil ICL7660. Tests are performed without diode in circuit. Note 2: fOSC is tested with COSC = 100pF to minimize the effects of test fixture capacitance loading. The 1pF frequency is correlated to this 100pF test point, and is intended to simulate pin 7's capacitance when the device is plugged into a test socket with 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). 2 _______________________________________________________________________________________ Switched-Capacitor Voltage Converters MAX1044/ICL7660 __________________________________________Typical Operating Characteristics (V+ = 5V; CBYPASS = 0.1F; C1 = C2 = 10F; LV = open; OSC = open; TA = +25C; unless otherwise noted.) OUTPUT VOLTAGE and OUTPUT RIPPLE vs. LOAD CURRENT MAX1044-Fig 1 OUTPUT VOLTAGE and OUTPUT RIPPLE vs. LOAD CURRENT MAX1044-Fig 2 OUTPUT VOLTAGE and OUTPUT RIPPLE vs. LOAD CURRENT 720 OUTPUT RIPPLE (mVp-p) OUTPUT VOLTAGE (V) 640 -9 -8 -7 -6 -5 -4 -3 -2 -1 A 0 0 5 10 15 20 25 30 35 40 LOAD CURRENT (mA) 0 OUTPUT RIPPLE B C V+ = 10V LV = OPEN OUTPUT VOLTAGE A: MAX1044 with BOOST = V+ B: ICL7660 C: MAX1044 with BOOST = OPEN A B C MAX1044-Fig 3 -2.0 OUTPUT VOLTAGE OUTPUT VOLTAGE (V) -1.5 A: MAX1044 with BOOST = V+ B: ICL7660 C: MAX1044 with BOOST = OPEN C -0.5 B V+ = 2V LV = GND 400 350 OUTPUT VOLTAGE (V) 300 250 200 150 100 50 OUTPUT RIPPLE (mVp-p) -5.0 -4.5 -4.0 -3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 A 0 0 5 10 15 B 800 -10 700 630 OUTPUT RIPPLE (mVp-p) SUPPLY CURRENT (mA) 560 490 420 350 280 210 140 70 OUTPUT VOLTAGE A A: MAX1044 with BOOST = V+ B: ICL7660 C: MAX1044 with BOOST = OPEN C B 560 480 C 400 320 -1.0 V+ = 5V LV = OPEN 240 160 80 A 0 0 1 2 3 4 5 6 OUTPUT RIPPLE 7 8 9 10 0 OUTPUT RIPPLE 20 25 30 35 40 0 LOAD CURRENT (mA) LOAD CURRENT (mA) EFFICIENCY and SUPPLY CURRENT vs. LOAD CURRENT MAX1044-Fig 4 EFFICIENCY and SUPPLY CURRENT vs. LOAD CURRENT MAX1044-Fig 5 EFFICIENCY and SUPPLY CURRENT vs. LOAD CURRENT 45 SUPPLY CURRENT (mA) 40 35 30 25 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0 5 10 15 20 25 30 35 40 LOAD CURRENT (mA) V+ = 10V LV = OPEN B, C A EFFICIENCY A: MAX1044 with BOOST = V+ B: ICL7660 C: MAX1044 with BOOST = OPEN SUPPLY CURRENT MAX1044-Fig 6 100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0 1 2 3 4 5 6 7 8 V+ = 2V LV = GND SUPPLY CURRENT EFFICIENCY 10 9 SUPPLY CURRENT (mA) 8 7 6 5 4 3 2 1 0 100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0 5 10 15 20 25 30 35 V+ = 5V LV = OPEN A: MAX1044 with BOOST = V+ B: ICL7660 C: MAX1044 with BOOST = OPEN C EFFICIENCY A B 50 100 50 45 40 35 30 25 20 15 10 5 0 SUPPLY CURRENT 20 15 10 5 0 9 10 40 LOAD CURRENT (mA) LOAD CURRENT (mA) EFFICIENCY vs. OSCILLATOR FREQUENCY MAX1044-Fig 7 OSCILLATOR FREQUENCY vs. EXTERNAL CAPACITANCE MAX1044-Fig 8 OSCILLATOR FREQUENCY vs. SUPPLY VOLTAGE MAX1044-Fig 9 100 90 EFFICIENCY (%) 80 70 60 50 40 30 101 102 103 104 105 EXTERNAL HCMOS OSCILLATOR 100,000 OSCILLATOR FREQUENCY (Hz) 10,000 1000 100 10 1 0.1 ICL7660 and MAX1044 with BOOST = OPEN MAX1044 with BOOST -V+ 100,000 OSCILLATOR FREQUENCY (Hz) C1, C2 = 100F C1, C2 = 10F C1, C2 = 1F 10,000 1000 6x105 100 1 10 100 1000 10,000 100,000 1 2 COSC (pF) FROM TOP TO BOTTOM AT 5V MAX1044, 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 3 4 5 6 7 8 9 10 OSCILLATOR FREQUENCY (Hz) SUPPLY VOLTAGE (V) _______________________________________________________________________________________ 3 Switched-Capacitor Voltage Converters MAX1044/ICL7660 ____________________________Typical Operating Characteristics (continued) (V+ = 5V; CBYPASS = 0.1F; C1 = C2 = 10F; LV = open; OSC = open; TA = +25C; unless otherwise noted.) OSCILLATOR FREQUENCY vs. TEMPERATURE MAX1044-Fig 10 QUIESCENT CURRENT vs. OSCILLATOR FREQUENCY MAX1044-Fig 11 100 OSCILLATOR FREQUENCY (kHz) A: MAX1044 with BOOST = V+ B: ICL7600 C: MAX1044 with BOOST = OPEN 10,000 QUIESCENT CURRENT (A) 80 A 60 1000 100 40 USING EXTERNAL CAPACITOR USING EXTERNAL HCMOS OSCILLATOR 101 102 103 104 105 5x105 20 C 0 -50 B -25 0 25 50 75 100 125 10 1 100 TEMPERATURE (C) OSCILLATOR FREQUENCY (Hz) QUIESCENT CURRENT vs. SUPPLY VOLTAGE MAX1044-Fig 12 QUIESCENT CURRENT vs. TEMPERATURE 400 QUIESCENT CURRENT (A) MAX1044-Fig 13 2000 1000 QUIESCENT CURRENT (A) A B C D 500 100 300 MAX1044 with BOOST = V+ 10 A: MAX1044, BOOST = V+, LV = GND B: 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 200 1 100 ICL7660, MAX1044 with BOOST = OPEN 0.1 1 2 0 -50 -25 0 25 50 75 100 125 TEMPERATURE (C) 3 4 5 6 7 8 9 10 SUPPLY VOLTAGE (V) OUTPUT RESISTANCE vs. OSCILLATOR FREQUENCY MAX1044-Fig 14 OUTPUT RESISTANCE vs. SUPPLY VOLTAGE MAX1044-Fig 15 OUTPUT RESISTANCE vs. TEMPERATURE MAX1044-Fig 16 1000 900 800 RESISTANCE () 700 C1, C2 = 100F EXTERNAL HCMOS OSCILLATOR 200 180 OUTPUT RESISTANCE () 160 140 120 100 80 60 40 20 0 80 70 60 50 40 30 20 -60 -40 -20 0 MAX1044 with BOOST = V+ ICL7660, MAX1044 with BOOST = OPEN 600 500 400 300 200 100 0 101 102 103 FREQUENCY (Hz) 104 105 1 2 3 4 5 6 7 8 9 10 OUTPUT RESISTANCE () C1, C2 = 10F C1, C2 = 1F 20 40 60 80 100 120 140 SUPPLY VOLTAGE (V) TEMPERATURE (C) 4 _______________________________________________________________________________________ Switched-Capacitor Voltage Converters _____________________________________________________________ Pin Description PIN NAME BOOST (MAX1044) 1 N.C. (ICL7660) 2 3 4 5 CAP+ GND CAPVOUT No Connection Connection to positive terminal of Charge-Pump Capacitor Ground. For most applications, the positive terminal of the reservoir capacitor is connected to this pin. Connection to negative terminal of Charge-Pump Capacitor Negative Voltage Output. For most applications, the negative terminal of the reservoir capacitor is connected to this pin. Low-Voltage Operation. Connect to ground for supply voltages below 3.5V. ICL7660: Leave open for supply voltages above 5V. Oscillator Control Input. Connecting an external capacitor reduces the oscillator frequency. Minimize stray capacitance at this pin. Power-Supply Positive Voltage Input. (1.5V to 10V). V+ is also the substrate connection. FUNCTION Frequency Boost. Connecting BOOST to V+ increases the oscillator frequency by a factor of six. When the oscillator is driven externally, BOOST has no effect and should be left open. MAX1044/ICL7660 6 LV 7 8 OSC V+ V+ BOOST V+ CBYPASS = 0.1F EXTERNAL OSCILLATOR OSC COSC GND LV RL MAX1044 CAP+ ICL7660 C1 10F CAP- VOUT C2 10F VOUT Figure 1. Maxim MAX1044/ICL7660 Test Circuit _______________Detailed Description The MAX1044/ICL7660 are charge-pump voltage converters. 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 & S3 close 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 negative terminal to VOUT. This connects C1 in parallel with the reservoir capacitor C2. If the voltage across C2 is smaller 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 S1S4 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 resistance (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 VOUT . The charge transferred per cycle is: Q = C1(V+ - VOUT). If the switch is cycled at frequency f, then the resulting 5 _______________________________________________________________________________________ Switched-Capacitor Voltage Converters MAX1044/ICL7660 current is: I = f x Q = f x C1(V+ - VOUT). Rewriting this equation in Ohm's law form defines an equivalent resistance synthesized by the switched-capacitor circuit where: I= (V+ - VOUT ) 1 / (f x C1) and 1 REQUIV = f x C1 S1 V+ C1 S2 S3 S4 C2 VOUT = -(V+) Figure 2. Ideal Voltage Inverter where f is one-half the oscillator frequency. This resistance 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 circuitry, and a timing oscillator. ________________Design Information f V+ VOUT The MAX1044/ICL7660 are designed to provide a simple, compact, low-cost solution where negative or doubled supply voltages are needed for a few lowpower 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. C1 C2 RLOAD Proper Use of the Low-Voltage (LV) Pin Figure 4 shows an internal voltage regulator inside the MAX1044/ICL7660. Use the LV pin to bypass this regulator, in order to improve low-voltage performance Figure 3a. Switched Capacitor Model V+ pin 8 S1 CAP+ pin 2 S2 REQUIV V+ REQUIV = 1 f C1 C2 RLOAD VOUT 1M OSCILLATOR BOOST pin 1 OSC pin 7 Q 2 Q S3 INTERNAL REGULATOR S4 CAPpin 4 VOUT pin 5 LV pin 6 GND pin 3 Figure 3b. Equivalent Circuit 6 Figure 4. MAX1044 and ICL7660 Functional Diagram _______________________________________________________________________________________ Switched-Capacitor Voltage Converters MAX1044/ICL7660 CONNECTION FROM V+ TO BOOST 1 C1 10F 2 3 4 8 V+ CBYPASS VOUT = -(V+) 10F C2 1 2 10F 3 4 *REQUIRED FOR V+ < 3.5V 6 VOUT = -(V+) 5 10F 8 V+ MAX1044 ICL7660 7 6 5 MAX1044 7 COSC * Figure 5. Basic Negative Voltage Converter Figure 6. Negative Voltage Converter with COSC and BOOST and allow operation down to 1.5V. For low-voltage operation and compatibility with the industry-standard LTC1044 and ICL7660, the LV pin should be connected 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 operating 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. Figure 6 shows this connection. Higher frequency operation lowers output impedance, reduces output ripple, allows the use of smaller capacitors, and shifts switching 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 COSC An external capacitor can be connected to the OSC pin to 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 when the 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 not swing all the way to V+, use a 10k pull-up resistor (Figure 7). Oscillator Frequency Considerations For normal operation, leave the BOOST and OSC pins of 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 oscillator frequency. 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. 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 _______________________________________________________________________________________ 7 Switched-Capacitor Voltage Converters MAX1044/ICL7660 switching noise and EMI may be generated. To reduce these 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 IC between 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. V+ 10k REQUIRED FOR TTL CMOS or V+ TTL GATE 1 2 10F 3 4 8 MAX1044 ICL7660 7 6 5 VOUT = -(V+) 10F Figure 7. External Clocking a function of oscillator frequency and the capacitor value. 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 decreases to 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 output impedance can be reduced by paralleling devices, increasing the capacitance of C1 and C2, or connecting the MAX1044's BOOST pin to V+ to increase the oscillator frequency. Efficiency, Output Ripple, and Output Impedance The power efficiency of a switched-capacitor voltage converter is affected by the internal losses in the converter IC, resistive losses of the pump capacitors, and conversion losses during charge transfer between the capacitors. The total power loss is: P LOSS = P INTERNAL +P SWITCH +P PUMP LOSSES LOSSES +P CONVERSION LOSSES CAPACITOR LOSSES Inrush Current and EMI Considerations During start-up, pump capacitors C1 and C2 must be charged. Consequently, the MAX1044/ICL7660 develop 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 highimpedance source, the supply voltage may drop too low during the current bursts for them to function properly. 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, 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 connections 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: PPUMP CAPACITOR LOSSES + PSWITCH = IOUT x ROUT LOSSES 2 where: ROUT 1 + (fOSC / 2) x C1 4 2RSWITCHES + ESRC1 + ESRC2 and fOSC is the oscillator frequency. ( ) 8 _______________________________________________________________________________________ Switched-Capacitor Voltage Converters MAX1044/ICL7660 The first term is the effective resistance from the switched-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: 1 2 PCONV.LOSS = C1 (V+ ) 2 - VOUT + 2 1 2 C2 VRIPPLE - 2VOUT VRIPPLE x fOSC / 2 2 Increasing Efficiency Efficiency can be improved by lowering output voltage ripple and output impedance. Both output voltage ripple 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. 1 VRIPPLE + 2 x ESRC2 IOUT 2 x fOSC x C2 Slowing the oscillator frequency reduces quiescent current. The oscillator frequency can be reduced by connecting 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 to OSC 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 provides the highest efficiency possible. Leaving the bucket and reservoir capacitors at 100F gives a maximum IOUT 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. Do not 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+ ...