19-1247; Rev 0; 7/97 125mA, Frequency-Selectable, Switched-Capacitor Voltage Converters ________________________Applications Local Negative Supplies ____________________________Features ♦ Selectable Switching Frequencies: 125kHz/250kHz (MAX1680) 500kHz/1MHz (MAX1681) ♦ Allow Use of Small Capacitors (1µF for the MAX1681) ♦ 125mA Output Current ♦ 3.5Ω Output Impedance ♦ 1µA Logic-Controlled Shutdown ♦ Configurable as Voltage Inverters or Doublers ♦ +2.0V to +5.5V Input Voltage Range ♦ Available in 8-Pin SO Packages ♦ 90% Efficiency ______________Ordering Information PART Interface Power Supplies Op-Amp Power Supplies MOSFET Bias TEMP. RANGE PIN-PACKAGE MAX1680C/D 0°C to +70°C Dice* MAX1680ESA MAX1681C/D MAX1681ESA -40°C to +85°C 0°C to +70°C -40°C to +85°C 8 SO Dice* 8 SO *Contact factory for dice specifications. Pin Configuration appears at end of data sheet. __________________________________________________Typical Operating Circuits FSEL +VINPUT +3V TO +5.5V IN FSEL IN C2 1µF 1µF CAP+ C1 1µF SHDN CAP+ C1 1µF MAX1681 LV GND CAP- C2 1µF INVERTER CONFIGURATION SHDN MAX1681 LV OUT NOTE: USE 4.7µF CAPACITORS FOR MAX1680 INPUT VOLTAGE RANGE: +2.0V TO +5.5V. DOUBLED OUTPUT VOLTAGE INVERTED OUTPUT VOLTAGE +VINPUT +4V TO +5.5V 1µF GND CAP- OUT DOUBLER CONFIGURATION NOTE: USE 4.7µF CAPACITORS FOR MAX1680 INPUT VOLTAGE RANGE: +2.5V TO +5.5V. ________________________________________________________________ Maxim Integrated Products 1 For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800. For small orders, phone 408-737-7600 ext. 3468. MAX1680/MAX1681 _______________General Description The MAX1680/MAX1681 inductorless switched-capacitor voltage converters either invert an input voltage of +2.0V to +5.5V or double it while supplying up to 125mA output current. They have a selectable-frequency option that allows the use of small capacitors: 4.7µF (MAX1680), 1µF (MAX1681). With their high output current capability, these charge-pump devices are suitable replacements for inductor-based regulators, which require more expensive external components and additional board space. The devices’ equivalent output resistance (typically 3.5Ω) allows them to deliver as much as 125mA with only a 440mV drop. A shutdown feature reduces quiescent current to less than 1µA. The MAX1680/MAX1681 are available in 8-pin SO packages. For devices that deliver up to 50mA in smaller µMAX packages, refer to the MAX860/MAX861 data sheet. MAX1680/MAX1681 125mA, Frequency-Selectable, Switched-Capacitor Voltage Converters ABSOLUTE MAXIMUM RATINGS Continuous Power Dissipation (TA = +70°C) SO (derate 5.88mW/°C above +70°C) ..........................471mW Operating Temperature Range ...........................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +160°C Lead Temperature (soldering, 10sec) .............................+300°C IN ..............................................................................-0.3V to +6V LV....................................................(VOUT - 0.3V) to (VIN + 0.3V) CAP+ ...........................................................-0.3V to (VIN + 0.3V) SHDN, FSEL ......................................(VLV - 0.3V) to (VIN + 0.3V) OUT, CAP- ..................................................................-6V to 0.3V Continuous Output Current ..............................................135mA Output Short-Circuit Duration to GND (Note 1) ...................1sec Note 1: Shorting OUT to IN may damage the device and should be avoided. 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 (Typical Operating Circuits (inverter configuration), FSEL = LV = GND, VIN = 5V, C1 = C2 = 10µF (MAX1680), C1 = C2 = 2.2µF (MAX1681), TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER Input Voltage Range SYMBOL VIN CONDITIONS 5.5 MAX1681 3.0 5.5 Doubler configuration, RL = 1kΩ, LV = OUT MAX1680 2.5 5.5 MAX1681 4.0 5.5 FSEL = IN (125kHz) TA = +25°C FSEL = LV (250kHz) TA = +25°C FSEL = IN (500kHz) TA = +25°C 10 FSEL = LV (1MHz) TA = +25°C 20 I+ Output Voltage Under Load (Note 2) VLOAD ILOAD = 125mA Output Resistance (Note 2) ROUT FSEL = IN or LV Shutdown Current ROUT(SHUT) I+SHDN 2.5 5 SHDN = IN IFSEL -1 LV = GND (Note 3) V 3.5 10 Ω 1 5 Ω 1 µA 1 µA 1 µA 4 FSEL = IN fOSC FSEL = LV MAX1681 FSEL = IN mA 36 1 MAX1680 2 18 -4.56 OUT = GND, SHDN = IN Input Bias Current (FSEL) Switching Frequency 9 43.2 -3.75 FSEL = LV V 21.6 -1 VIH V 4.5 10.8 ISHDN Shutdown, FSEL Thresholds UNITS 5.4 Input Bias Current (SHDN) VIL MAX 2.0 MAX1681 Output Resistance to Ground in Shutdown TYP MAX1680 MAX1680 Supply Current MIN Inverter configuration, RL = 1kΩ, LV = GND TA = +25°C 187 250 313 125 156 1000 1250 157 TA = +25°C 94 TA = +25°C 750 348 79 174 570 TA = +25°C 375 V 1490 500 285 _______________________________________________________________________________________ 625 745 kHz 125mA, Frequency-Selectable, Switched-Capacitor Voltage Converters (Typical Operating Circuits (inverter configuration), FSEL = LV = GND, VIN = 5V, C1 = C2 = 10µF (MAX1680), C1 = C2 = 2.2µF (MAX1681), TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL Power Efficiency CONDITIONS RL = 100Ω to GND, FSEL = IN MIN TYP MAX1680 90 MAX1681 80 MAX UNITS % ELECTRICAL CHARACTERISTICS (Typical Operating Circuits (inverter configuration), FSEL = LV = GND, VIN = 5V, C1 = C2 = 10µF (MAX1680), C1 = C2 = 2.2µF (MAX1681), TA = -40°C to +85°C, unless otherwise noted.) (Note 4) PARAMETER Input Voltage Range SYMBOL VIN CONDITIONS MIN TYP MAX Inverter configuration, RL = 1kΩ, LV = GND MAX1680 2.0 5.5 MAX1681 3.0 5.5 Doubler configuration, RL = 1kΩ, LV = OUT MAX1680 2.5 5.5 MAX1681 4.0 5.5 FSEL = IN (125kHz) 5.4 FSEL = LV (250kHz) 10.8 MAX1680 Supply Current UNITS V mA I+ mA FSEL = IN (500kHz) 21.6 FSEL = LV (1MHz) 43.2 MAX1681 Output Voltage Under Load (Note 2) VLOAD ILOAD = 125mA Output Resistance (Note 2) ROUT FSEL = IN or LV 10 Ω SHDN = IN 5 Ω OUT = GND, SHDN = IN 1 µA 1 µA µA Output Resistance in Shutdown Shutdown Current ROUT(SHUT) I+SHDN -3.75 V Input Bias Current (SHDN) ISHDN Input Bias Current (FSEL) IFSEL -1 1 VIL -1 1 Shutdown, FSEL Thresholds VIH LV = GND (Note 3) MAX1680 Switching Frequency fOSC MAX1681 4 FSEL = LV 157 FSEL = IN 79 174 FSEL = LV 570 1490 FSEL = IN 285 745 V 348 kHz Note 2: C1 and C2 are low-ESR (<0.2Ω) capacitors. Capacitor ESR adds to the circuit’s output resistance. Using capacitors with higher ESR reduces output voltage and efficiency. The specified output resistance includes the C1 and C2 0.2Ω ESR. Note 3: The typical threshold for VINPUT other than +5V is 0.35VINPUT (VIL = VIH). Note 4: Specifications to -40°C are guaranteed by design, not production tested. _______________________________________________________________________________________ 3 MAX1680/MAX1681 ELECTRICAL CHARACTERISTICS (continued) __________________________________________Typical Operating Characteristics (All curves generated using the inverter configuration shown in the Typical Operating Circuits with LV = GND, FSEL = IN or LV, C1 = C2 = 10µF (MAX1680), C1 = C2 = 2.2µF (MAX1681), and TA = +25°C, unless otherwise noted. Test results are also valid for the doubler configuration with LV = OUT and TA = +25°C.) OUTPUT VOLTAGE DROP vs. LOAD CURRENT 400 VINPUT = 5V 200 100 0 -2 -4 MAX1680 -6 -8 MAX1681 -10 -12 20 40 60 80 100 120 140 8 6 4 MAX1681 2 0 MAX1680 -2 -4 -6 -8 -10 -14 2.0 2.5 3.0 3.5 4.0 4.5 5.0 -40 5.5 -20 0 20 40 60 80 100 LOAD CURRENT (mA) SUPPLY VOLTAGE (V) TEMPERATURE (°C) OUTPUT SOURCE RESISTANCE vs. SUPPLY VOLTAGE OUTPUT SOURCE RESISTANCE vs. TEMPERATURE MAX1680 EFFICIENCY vs. LOAD CURRENT (INVERTER CONFIGURATION) 6.5 5.5 4.5 3.5 100 5 4 VINPUT = 5V 3 MAX1680/81TOC06 VINPUT = 3V 80 EFFICIENCY (%) 7.5 6 MAX1680/81TOC05 MAX1680/81TOC04 8.5 OUTPUT SOURCE RESISTANCE (Ω) 0 MAX1680/81TOC03 0 10 OSCILLATOR FREQUENCY CHANGE (%) VINPUT = 3V 500 MAX1680/81TOC02 600 2 OSCILLATOR FREQUENCY CHANGE (%) MAX1680/81TOC01 OUTPUT VOLTAGE DROP (mV) 700 300 OSCILLATOR FREQUENCY CHANGE vs. TEMPERATURE OSCILLATOR FREQUENCY CHANGE vs. SUPPLY VOLTAGE 800 OUTPUT SOURCE RESISTANCE (Ω) MAX1680/MAX1681 125mA, Frequency-Selectable, Switched-Capacitor Voltage Converters 60 VINPUT = 3V VINPUT = 4V 40 2 VINPUT = 5.5V 20 1 FSEL = IN 2.0 2.5 3.0 3.5 4.0 4.5 SUPPLY VOLTAGE (V) 4 0 0 2.5 5.0 5.5 -40 -20 0 20 40 60 TEMPERATURE (°C) 80 100 1 10 100 LOAD CURRENT (mA) _______________________________________________________________________________________ 1000 125mA, Frequency-Selectable, Switched-Capacitor Voltage Converters MAX1680 SUPPLY CURRENT vs. SUPPLY VOLTAGE VINPUT = 3V VINPUT = 4V 40 INVERTER MODE FSEL = LV 6 5 DOUBLER MODE FSEL = IN 4 3 FSEL = IN 100 10 1000 DOUBLER MODE FSEL = IN 15 10 2.5 3.0 3.5 4.0 4.5 5.0 5.5 2.5 3.0 VINPUT = 3V, FSEL = LV VINPUT = 5V, FSEL = LV 7 VINPUT = 3V, FSEL = IN VINPUT = 5V, FSEL = IN 3.5 4.0 4.5 5.0 5.5 6.0 SUPPLY VOLTAGE (V) MAX1680 OUTPUT SOURCE RESISTANCE vs. CAPACITANCE (DOUBLER CONFIGURATION) 10 VINPUT = 3V, FSEL = LV OUTPUT SOURCE RESISTANCE (Ω) 9 MAX1680/81TOC10 10 5 6.0 SUPPLY VOLTAGE (V) MAX1680 OUTPUT SOURCE RESISTANCE vs. CAPACITANCE (INVERTER CONFIGURATION) 6 INVERTER MODE FSEL = IN 5 0 2.0 LOAD CURRENT (mA) 9 8 7 VINPUT = 5V, FSEL = LV VINPUT = 3V, FSEL = IN 6 5 VINPUT = 5V, FSEL = IN 4 4 3 3 0 2 4 6 8 0 10 12 14 16 18 20 2 4 6 8 10 12 14 16 18 20 CAPACITANCE (µF) CAPACITANCE (µF) MAX1681 OUTPUT SOURCE RESISTANCE vs. CAPACITANCE (INVERTER CONFIGURATION) MAX1681 OUTPUT SOURCE RESISTANCE vs. CAPACITANCE (DOUBLER CONFIGURATION) 9 8 7 VINPUT = 3V, FSEL = LV 6 VINPUT = 3V, FSEL = IN 5 VINPUT = 5V, FSEL = LV 4 VINPUT = 5V, FSEL = IN 3 10 OUTPUT SOURCE RESISTANCE (Ω) MAX1680/81TOC12 10 MAX1680/81TOC13 OUTPUT SOURCE RESISTANCE (Ω) INVERTER MODE FSEL = LV 20 0 0 8 DOUBLER MODE FSEL = LV 25 INVERTER MODE FSEL = IN 1 1 MAX1680/81TOC09 MAX1680/81TOC08 7 30 2 VINPUT = 5.5V 20 DOUBLER MODE FSEL = LV 8 MAX1680/81TOC11 60 OUTPUT SOURCE RESISTANCE (Ω) EFFICIENCY (%) 80 9 SUPPLY CURRENT (mA) MAX1680/81TOC07 100 MAX1681 SUPPLY CURRENT vs. SUPPLY VOLTAGE SUPPLY CURRENT (mA) MAX1681 EFFICIENCY vs. LOAD CURRENT (DOUBLER CONFIGURATION) 9 8 VINPUT = 3V, FSEL = LV 7 VINPUT = 3V, FSEL = IN 6 VINPUT = 5V, FSEL = LV 5 VINPUT = 5V, FSEL = IN 4 3 0 2 4 6 8 10 12 14 16 18 20 CAPACITANCE (µF) 0 2 4 6 8 10 12 14 16 18 20 CAPACITANCE (µF) _______________________________________________________________________________________ 5 MAX1680/MAX1681 ____________________________Typical Operating Characteristics (continued) (All curves generated using the inverter configuration shown in the Typical Operating Circuits with LV = GND, FSEL = IN or LV, C1 = C2 = 10µF (MAX1680), C1 = C2 = 2.2µF (MAX1681), and TA = +25°C, unless otherwise noted. Test results are also valid for the doubler configuration with LV = OUT and TA = +25°C.) MAX1680/MAX1681 125mA, Frequency-Selectable, Switched-Capacitor Voltage Converters ______________________________________________________________Pin Description FUNCTION PIN NAME INVERTER 1 FSEL Selects operating frequency. MAX1680: 250kHz when FSEL is low, 125kHz when FSEL is high. MAX1681: 1MHz when FSEL is low, 500kHz when FSEL is high. 2 CAP+ Positive Charge-Pump Capacitor Connection 3 GND Power-Supply Ground Input 4 CAP- Negative Charge-Pump Capacitor Connection 5 OUT Negative Voltage Output Power-Supply Ground Connection 6 LV Logic Voltage Input. Connect LV to GND. Connect LV to OUT. Shutdown Input. Driving SHDN high disables the charge pump, and the output goes to 0V. SHDN is a CMOS input. Not available; connect to OUT. Power-Supply Positive Voltage Input Positive Voltage Output 7 SHDN 8 IN _______________Detailed Description The MAX1680/MAX1681 switched-capacitor voltage converters either invert or double the input voltage. They have low output resistance (3.5Ω) and can deliver up to 125mA output current. These devices operate at one of two selectable frequencies: 125kHz/250kHz (MAX1680) and 500kHz/1MHz (MAX1681). This provides the flexibility to optimize capacitor size, operating supply current, and overall circuit efficiency. Frequency selection also allows for minimizing coupling into other sensitive circuits. These devices contain no internal divider; the oscillator frequency equals the switching frequency. The devices can easily be cascaded to produce a higher output voltage, or paralleled to deliver more current. The MAX1680/MAX1681 feature a shutdown mode that reduces supply current to <1µA (SHDN = high). OUT, in the inverter configuration, pulls to ground in shutdown mode. Shutdown is not available in the doubler configuration; connect SHDN to OUT. __________Applications Information Voltage Inverter A simple voltage inverter is the most common MAX1680/MAX1681 application. It requires three external capacitors (including the input bypass capacitor) as shown in the Typical Operating Circuits (inverter configuration). Although the output is not regulated, low 6 DOUBLER Power-Supply Positive Voltage Input output resistance produces a typical drop of only 0.44V with a 125mA load. This low output resistance makes the devices fairly insensitive to changes in load (see the graphs for Output Source Resistance vs. Temperature and Supply Voltage in the Typical Operating Characteristics section). Voltage Doubler The MAX1680/MAX1681 can be configured as a voltage doubler with two external capacitors as shown in the Typical Operating Circuits (doubler configuration). When loaded, the output voltage drop is similar to that of the voltage inverter. The minimum input supply range is slightly higher than in the inverter configuration. Calculate ripple voltage using the equation in the Capacitor Selection section. Frequency Control A frequency-control pin, FSEL, provides design flexibility. Each device has two selectable frequencies: 125kHz/250kHz (MAX1680) and 500kHz/1MHz (MAX1681). This allows optimization of capacitor size and supply current for a given output load. Table 1 summarizes the frequency options . Table 1. Nominal Switching Frequencies FREQUENCY (kHz) FSEL CONNECTION MAX1680 MAX1681 FSEL = LV 250 1000 FSEL = IN 125 500 _______________________________________________________________________________________ 125mA, Frequency-Selectable, Switched-Capacitor Voltage Converters Table 2. Switching-Frequency Trade-Offs LOWER FREQUENCY HIGHER FREQUENCY Larger Smaller C1, C2 Values Larger Smaller Supply Current Smaller Larger ATTRIBUTE Output Ripple Capacitor Selection The MAX1680/MAX1681 are tested with capacitor values of 10µF and 2.2µF, respectively. Capacitor size and switching speed determine output resistance. Larger C1 values decrease the output resistance until the internal switch resistance (3.5Ω typ) becomes the dominant term. Low-ESR capacitors minimize output resistance and ripple voltage. The entire circuit’s output resistance can be approximated by the following equation: ROUT ≅ RO + 4 x ESRC1 + ESRC2 + [1 / (fOSC x C1)] + [1 / (fOSC x C2)] where RO is the device’s internal effective switch resistance and f OSC is the switching frequency. Output resistance is a critical circuit component, as it determines the voltage drop that will occur at the output from the ideal value of -VINPUT (or 2VINPUT when doubling). To optimize performance, minimize overall resistance in the system. In particular, equivalent series resistance (ESR) in the capacitors produces significant losses as large currents flow through them. Therefore, choose a low-ESR capacitor for highest efficiency. Table 3 lists recommended capacitors and their suppliers. Calculate the output ripple voltage as follows: VRIPPLE = [(IOUT) / (2 x fOSC x C2)] + 2 x (IOUT x ESRC2) where IOUT is the load current, fS is the charge pump’s operating frequency, C2 is the output capacitor, and ESRC2 is the output capacitor’s ESR. Table 4 lists the minimum recommended capacitances that allow for the maximum output current. The output capacitor, C2, is normally equal to or greater than the charge-pump capacitor, C1. Capacitor values can be scaled directly proportional to the input voltage, frequency, and load current. For example, for VINPUT = 5V, ILOAD = 125mA at fOSC = 125kHz, a 6.4µF minimum capacitor is recommended. For an output of only 62.5mA, a 3.2µF capacitor is recommended. C1’s value can be estimated as follows: C1 = 6.4µF x (VINPUT / 5.0V) x (125kHz / fOSC) x (ILOAD / 125mA) where fOSC is the switching frequency (kHz) and ILOAD is the output current (mA) required. Table 3. Low-ESR Capacitor Suppliers SUPPLIER PHONE FAX DEVICE TYPE AVX (803) 946-0690 (800) 282-4975 (803) 626-3123 Surface mount, TPS series Marcon/United Chemi-Con (847) 696-2000 (847) 696-9278 Ceramic capacitors Matsuo (714) 969-2491 (714) 960-6492 Surface mount, 267 series Nichicon USA: (847) 843-7500 Japan: 81-7-5231-8461 USA: (847) 843-2798 Japan: 81-7-5256-4158 Through-hole, PL series Sanyo USA: (619) 661-6835 Japan: 81-7-2070-6306 USA: (619) 661-1055 Japan: 81-7-2070-1174 Through-hole, OS-CON series Sprague (603) 224-1961 (603) 224-1430 Surface mount, 595D series TDK (847) 390-4373 (847) 390-4428 Ceramic capacitors United Chemi-Con (714) 255-9500 (714) 255-9400 Through-hole, LXF series Vishay/Vitramon (203) 268-6261 (203) 452-5670 SMT ceramic chip capacitors _______________________________________________________________________________________ 7 MAX1680/MAX1681 Operating Frequency Trade-Offs It is important to recognize the trade-offs between switching frequency, power consumption, noise, cost, and performance. Higher frequency switching reduces capacitor size while maintaining the same output impedance, thus saving capacitor cost and board space. Lower frequency designs use less supply current. Table 2 summarizes the relative trade-offs. MAX1680/MAX1681 125mA, Frequency-Selectable, Switched-Capacitor Voltage Converters Table 4. Minimum Recommended Capacitances for Maximum Output Current CAPACITANCE (µF) (C1 = C2) fOSC (kHz) VIN = 2V VIN = 3V VIN = 4V VIN = 5V 125 2.5 3.8 5.1 6.4 250 1.2 1.9 2.5 3.2 500 0.6 0.9 1.2 1.6 1000 0.3 0.4 0.6 0.8 +VINPUT 1µF 1µF FSEL IN FSEL IN CAP+ SHDN CAP+ SHDN 1µF MAX1681 LV GND LV GND VOUT = -VINPUT CAP- MAX1681 CAP- OUT 1µF OUT VOUT = -2VINPUT 1µF NOTE: USE 4.7µF CAPACITORS FOR MAX1680. Figure 1. Cascading MAX1680/MAX1681s to Increase Output Voltage Bypass Capacitor Bypass the input voltage to reduce AC impedance and to prevent internal switching noise. Bypassing depends on the source impedance location. The AC ripple current is 2 x IOUT for the doubler and the inverter. Use a large bypass capacitor (equal to C1) if the supply has high AC impedance. Cascading Devices To produce larger negative voltages, cascade two devices (Figure 1). For two devices, the unloaded output voltage is approximately -2 x VINPUT, but this value is reduced slightly by the first device’s output resistance multiplied by the second device’s quiescent current. The effective output resistance for a cascaded 8 device is larger than that for an individual device (20Ω for two devices). Cascading several devices increases output resistance and reduces efficiency. If a large negative voltage is required for several stages, an inductive inverting switching regulator such as the MAX629 or MAX774 may offer more advantages. Paralleling Devices Parallel two or more MAX1680/MAX1681s to reduce output resistance voltage drop under a given load. With reduced output resistance, paralleled devices deliver higher load currents. Figure 2 shows two MAX1680/MAX1681s connected in parallel. Output resistance is inversely proportional to the number of devices. _______________________________________________________________________________________ 125mA, Frequency-Selectable, Switched-Capacitor Voltage Converters MAX1680/MAX1681 +VINPUT FSEL IN 1µF FSEL IN CAP+ SHDN CAP+ 1µF 1µF MAX1681 GND LV "n" 1µF MAX1681 LV GND CAP- SHDN CAP- OUT VOUT OUT 1µF NOTE: USE 4.7µF CAPACITORS FOR MAX1680. VOUT = -VINPUT ROUT = ROUT OF SINGLE DEVICE NUMBER OF DEVICES (n) Figure 2. Paralleling MAX1680/MAX1681s to Increase Output Current Combined Doubler and Inverter Figure 3 shows a single MAX1680/MAX1681 as an inverter and a doubler. The maximum output current is the sum of the loads on the two outputs and is still limited to 125mA. As the device is loaded, the output voltages move toward ground. In this particular configuration, connect LV to GND (inverter). The diodes used in the circuit cause a drop of approximately 0.7V in the doubler’s output voltage, impacting efficiency. Compatibility with the MAX660 and MAX860/MAX861 The MAX1680/MAX1681 can be used in place of the MAX860/MAX861, except for the SHDN and FSEL pins. The MAX1680/MAX1681 shut down with a high input voltage, compared with the MAX860/MAX861. The MAX1680/MAX1681 have only two frequency choices. Replacing the MAX660 with the MAX1680/MAX1681 involves a wiring change, as the external oscillator pin is replaced by the shutdown feature. Table 5 compares the devices. +VINPUT FSEL IN CAP+ SHDN 1µF 1µF D1 IN4148 MAX1681 LV GND CAP- OUT VOUT = -VINPUT 1µF 1µF D2 IN4148 NOTE: USE 4.7µF CAPACITORS FOR MAX1680. VOUT = 2VINPUT -VFD1 1µF -VFD2 Figure 3. Combined Doubler and Inverter _______________________________________________________________________________________ 9 MAX1680/MAX1681 125mA, Frequency-Selectable, Switched-Capacitor Voltage Converters Table 5. Device Comparison TYPICAL QUIESCENT CURRENT (mA) OUTPUT CURRENT (mA) OUTPUT RESISTANCE (Ω) SWITCHING FREQUENCY (kHz) 0.12/1.0 100 6.5 5/40 MAX665 0.20/1.0 100 6.5 5/40 MAX860 0.20/0.60/1.40 50 12 6/50/130 MAX861 0.30/1.10/2.50 50 12 13/100/250 MAX1680 2.5/5.0 125 3.5 125/250 MAX1681 10/20 125 3.5 500/1000 ICL7660 0.080 10 55 5 PART NUMBER MAX660 __________________Pin Configuration ___________________Chip Information TRANSISTOR COUNT: 171 SUBSTRATE CONNECTED TO IN TOP VIEW FSEL 1 CAP+ 2 GND 3 MAX1680 MAX1681 CAP- 4 8 IN 7 SHDN 6 LV 5 OUT SO 10 ______________________________________________________________________________________ 125mA, Frequency-Selectable, Switched-Capacitor Voltage Converters SOICN.EPS ______________________________________________________________________________________ 11 MAX1680/MAX1681 ________________________________________________________Package Information MAX1680/MAX1681 125mA, Frequency-Selectable, Switched-Capacitor Voltage Converters NOTES Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. 12 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 1997 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.