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19-1247; Rev 0; 7/97
125mA, Frequency-Selectable, Switched-Capacitor Voltage Converters
_______________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: 4.7F (MAX1680), 1F (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 3.5) allows them to deliver as much as 125mA with only a 440mV drop. A shutdown feature reduces quiescent current to less than 1A. The MAX1680/MAX1681 are available in 8-pin SO packages. For devices that deliver up to 50mA in smaller MAX packages, refer to the MAX860/MAX861 data sheet.
____________________________Features
o Selectable Switching Frequencies: 125kHz/250kHz (MAX1680) 500kHz/1MHz (MAX1681) o Allow Use of Small Capacitors (1F for the MAX1681) o 125mA Output Current o 3.5 Output Impedance o 1A Logic-Controlled Shutdown o Configurable as Voltage Inverters or Doublers o +2.0V to +5.5V Input Voltage Range o Available in 8-Pin SO Packages o 90% Efficiency
MAX1680/MAX1681
________________________Applications
Local Negative Supplies Interface Power Supplies Op-Amp Power Supplies MOSFET Bias
______________Ordering Information
PART MAX1680C/D MAX1680ESA MAX1681C/D MAX1681ESA TEMP. RANGE 0C to +70C -40C to +85C 0C to +70C -40C to +85C PIN-PACKAGE Dice* 8 SO Dice* 8 SO
*Contact factory for dice specifications.
Pin Configuration appears at end of data sheet.
__________________________________________________Typical Operating Circuits
+VINPUT +3V TO +5.5V 1F CAP+ SHDN C1 1F +VINPUT +4V TO +5.5V 1F CAP+ SHDN DOUBLED OUTPUT VOLTAGE
FSEL
IN
FSEL
IN C2 1F
C1 1F
MAX1681 LV GND
INVERTED OUTPUT VOLTAGE
MAX1681
LV GND CAPOUT
CAP-
OUT C2 1F
INVERTER CONFIGURATION NOTE: USE 4.7F CAPACITORS FOR MAX1680 INPUT VOLTAGE RANGE: +2.0V TO +5.5V.
DOUBLER CONFIGURATION NOTE: USE 4.7F CAPACITORS FOR MAX1680 INPUT VOLTAGE RANGE: +2.5V TO +5.5V.
________________________________________________________________ Maxim Integrated Products
1
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125mA, Frequency-Selectable, Switched-Capacitor Voltage Converters MAX1680/MAX1681
ABSOLUTE MAXIMUM RATINGS
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 Continuous Power Dissipation (TA = +70C) SO (derate 5.88mW/C above +70C) ..........................471mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +160C Lead Temperature (soldering, 10sec) .............................+300C
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 = 10F (MAX1680), C1 = C2 = 2.2F (MAX1681), TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER SYMBOL CONDITIONS Inverter configuration, RL = 1k, LV = GND Doubler configuration, RL = 1k, LV = OUT FSEL = IN (125kHz) MAX1680 FSEL = LV (250kHz) Supply Current I+ FSEL = IN (500kHz) MAX1681 FSEL = LV (1MHz) Output Voltage Under Load (Note 2) Output Resistance (Note 2) Output Resistance to Ground in Shutdown Shutdown Current Input Bias Current (SHDN) Input Bias Current (FSEL) Shutdown, FSEL Thresholds VLOAD ROUT ROUT(SHUT) I+SHDN ISHDN IFSEL VIL VIH LV = GND (Note 3) FSEL = LV MAX1680 FSEL = IN Switching Frequency fOSC FSEL = LV MAX1681 FSEL = IN TA = +25C TA = +25C TA = +25C TA = +25C ILOAD = 125mA FSEL = IN or LV SHDN = IN OUT = GND, SHDN = IN -1 -1 4 187 157 94 79 750 570 375 285 500 1000 125 250 313 348 156 174 1250 1490 625 745 kHz MAX1680 MAX1681 MAX1680 MAX1681 TA = +25C TA = +25C TA = +25C TA = +25C MIN 2.0 3.0 2.5 4.0 2.5 5 10 20 TYP MAX 5.5 5.5 5.5 5.5 4.5 5.4 9 10.8 18 21.6 36 43.2 -3.75 -4.56 3.5 1 10 5 1 1 1 1 V A A A V mA V V UNITS
Input Voltage Range
VIN
2
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125mA, Frequency-Selectable, Switched-Capacitor Voltage Converters
ELECTRICAL CHARACTERISTICS (continued)
(Typical Operating Circuits (inverter configuration), FSEL = LV = GND, VIN = 5V, C1 = C2 = 10F (MAX1680), C1 = C2 = 2.2F (MAX1681), TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER Power Efficiency SYMBOL CONDITIONS RL = 100 to GND, FSEL = IN MAX1680 MAX1681 MIN TYP 90 80 MAX UNITS %
MAX1680/MAX1681
ELECTRICAL CHARACTERISTICS
(Typical Operating Circuits (inverter configuration), FSEL = LV = GND, VIN = 5V, C1 = C2 = 10F (MAX1680), C1 = C2 = 2.2F (MAX1681), TA = -40C to +85C, unless otherwise noted.) (Note 4) PARAMETER SYMBOL CONDITIONS Inverter configuration, RL = 1k, LV = GND Doubler configuration, RL = 1k, LV = OUT MAX1680 MAX1681 MAX1680 MAX1681 FSEL = IN (125kHz) MAX1680 FSEL = LV (250kHz) Supply Current I+ FSEL = IN (500kHz) MAX1681 FSEL = LV (1MHz) Output Voltage Under Load (Note 2) Output Resistance (Note 2) Output Resistance in Shutdown Shutdown Current Input Bias Current (SHDN) Input Bias Current (FSEL) Shutdown, FSEL Thresholds VLOAD ROUT ROUT(SHUT) I+SHDN ISHDN IFSEL VIL VIH LV = GND (Note 3) MAX1680 Switching Frequency fOSC MAX1681 FSEL = LV FSEL = IN FSEL = LV FSEL = IN -1 -1 4 157 79 570 285 348 174 1490 745 kHz ILOAD = 125mA FSEL = IN or LV SHDN = IN OUT = GND, SHDN = IN -3.75 10 5 1 1 1 1 43.2 V A A A V 21.6 10.8 mA MIN 2.0 3.0 2.5 4.0 TYP MAX 5.5 5.5 5.5 5.5 5.4 mA V UNITS
Input Voltage Range
VIN
Note 2: C1 and C2 are low-ESR (<0.2) 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 0.2 ESR. Note 3: The typical threshold for VINPUT other than +5V is 0.35VINPUT (VIL = VIH). Note 4: Specifications to -40C are guaranteed by design, not production tested.
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125mA, Frequency-Selectable, Switched-Capacitor Voltage Converters MAX1680/MAX1681
__________________________________________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 = 10F (MAX1680), C1 = C2 = 2.2F (MAX1681), and TA = +25C, unless otherwise noted. Test results are also valid for the doubler configuration with LV = OUT and TA = +25C.)
OUTPUT VOLTAGE DROP vs. LOAD CURRENT
MAX1680/81TOC01
OSCILLATOR FREQUENCY CHANGE vs. SUPPLY VOLTAGE
MAX1680/81TOC02
OSCILLATOR FREQUENCY CHANGE vs. TEMPERATURE
OSCILLATOR FREQUENCY CHANGE (%) 8 6 4 2 0 -2 -4 -6 -8 -10 -40 -20 0 20 40 60 80 100 MAX1680 MAX1681
MAX1680/81TOC03
800 700 OUTPUT VOLTAGE DROP (mV) 600 VINPUT = 3V 500 400 300 200 100 0 0 20 40 60 80 100 120 VINPUT = 5V
2 OSCILLATOR FREQUENCY CHANGE (%) 0 -2 -4 -6 -8 MAX1681 -10 -12 -14 2.0 2.5 3.0 3.5 4.0 4.5 5.0 MAX1680
10
140
5.5
LOAD CURRENT (mA)
SUPPLY VOLTAGE (V)
TEMPERATURE (C)
OUTPUT SOURCE RESISTANCE vs. SUPPLY VOLTAGE
MAX1680/81TOC04
OUTPUT SOURCE RESISTANCE vs. TEMPERATURE
VINPUT = 3V OUTPUT SOURCE RESISTANCE () 5 4 VINPUT = 5V 3 2 1 0 20
MAX1680/81TOC05
MAX1680 EFFICIENCY vs. LOAD CURRENT (INVERTER CONFIGURATION)
MAX1680/81TOC06
8.5 OUTPUT SOURCE RESISTANCE () 7.5 6.5 5.5 4.5 3.5 2.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
6
100
80 EFFICIENCY (%)
60
VINPUT = 3V VINPUT = 4V VINPUT = 5.5V
40
FSEL = IN 0 -40 -20 0 20 40 60 80 100 1 10 100 1000 TEMPERATURE (C) LOAD CURRENT (mA) 5.5
SUPPLY VOLTAGE (V)
4
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125mA, Frequency-Selectable, Switched-Capacitor Voltage Converters
____________________________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 = 10F (MAX1680), C1 = C2 = 2.2F (MAX1681), and TA = +25C, unless otherwise noted. Test results are also valid for the doubler configuration with LV = OUT and TA = +25C.)
MAX1681 EFFICIENCY vs. LOAD CURRENT (DOUBLER CONFIGURATION)
MAX1680/81TOC07
MAX1680/MAX1681
MAX1680 SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX1680/81TOC08
MAX1681 SUPPLY CURRENT vs. SUPPLY VOLTAGE
DOUBLER MODE FSEL = LV
MAX1680/81TOC09
100
9 8 SUPPLY CURRENT (mA) 7 6 5 4 3 2 1 INVERTER MODE FSEL = IN 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 DOUBLER MODE FSEL = IN INVERTER MODE FSEL = LV DOUBLER MODE FSEL = LV
30 25 SUPPLY CURRENT (mA) 20 15 10 5 0 INVERTER MODE FSEL = IN 2.5 3.0 3.5 4.0 4.5 5.0 5.5 INVERTER MODE FSEL = LV DOUBLER MODE FSEL = IN
80 EFFICIENCY (%)
60
VINPUT = 3V VINPUT = 4V
40
20
VINPUT = 5.5V FSEL = IN
0 1 10 100 1000 LOAD CURRENT (mA)
0 6.0 SUPPLY VOLTAGE (V)
6.0
SUPPLY VOLTAGE (V)
MAX1680 OUTPUT SOURCE RESISTANCE vs. CAPACITANCE (INVERTER CONFIGURATION)
MAX1680/81TOC10
MAX1680 OUTPUT SOURCE RESISTANCE vs. CAPACITANCE (DOUBLER CONFIGURATION)
VINPUT = 3V, FSEL = LV OUTPUT SOURCE RESISTANCE () 9 8 7 6 5 4 3 VINPUT = 5V, FSEL = LV VINPUT = 3V, FSEL = IN
MAX1680/81TOC11 MAX1680/81TOC13
10 OUTPUT SOURCE RESISTANCE () 9 8 7 6 5 4 3 0 2 4 6 8 VINPUT = 3V, FSEL = IN VINPUT = 5V, FSEL = IN VINPUT = 3V, FSEL = LV VINPUT = 5V, FSEL = LV
10
VINPUT = 5V, FSEL = IN
10 12 14 16 18 20
0
2
4
6
8
10 12 14 16 18 20
CAPACITANCE (F)
CAPACITANCE (F)
MAX1681 OUTPUT SOURCE RESISTANCE vs. CAPACITANCE (INVERTER CONFIGURATION)
MAX1680/81TOC12
MAX1681 OUTPUT SOURCE RESISTANCE vs. CAPACITANCE (DOUBLER CONFIGURATION)
10 OUTPUT SOURCE RESISTANCE () 9 8 7 6 5 4 3 VINPUT = 5V, FSEL = LV VINPUT = 5V, FSEL = IN VINPUT = 3V, FSEL = LV VINPUT = 3V, FSEL = IN
10 OUTPUT SOURCE RESISTANCE () 9 8 7 6 5 VINPUT = 5V, FSEL = LV 4 VINPUT = 5V, FSEL = IN 3 0 2 4 6 8 VINPUT = 3V, FSEL = LV VINPUT = 3V, FSEL = IN
10 12 14 16 18 20
0
2
4
6
8
10 12 14 16 18 20
CAPACITANCE (F)
CAPACITANCE (F)
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125mA, Frequency-Selectable, Switched-Capacitor Voltage Converters MAX1680/MAX1681
______________________________________________________________Pin Description
FUNCTION PIN NAME INVERTER 1 2 3 4 5 6 7 8 FSEL CAP+ GND CAPOUT LV SHDN IN DOUBLER 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. Positive Charge-Pump Capacitor Connection Power-Supply Ground Input Negative Charge-Pump Capacitor Connection Negative Voltage Output Logic Voltage Input. Connect LV to GND. Shutdown Input. Driving SHDN high disables the charge pump, and the output goes to 0V. SHDN is a CMOS input. Power-Supply Positive Voltage Input Power-Supply Ground Connection Connect LV to OUT. Not available; connect to OUT. Positive Voltage Output Power-Supply Positive Voltage Input
_______________Detailed Description
The MAX1680/MAX1681 switched-capacitor voltage converters either invert or double the input voltage. They have low output resistance (3.5) 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 <1A (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.
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 .
__________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
Table 1. Nominal Switching Frequencies
FREQUENCY (kHz) FSEL CONNECTION MAX1680 FSEL = LV FSEL = IN 250 125 MAX1681 1000 500
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125mA, Frequency-Selectable, Switched-Capacitor Voltage Converters
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. 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 6.4F minimum capacitor is recommended. For an output of only 62.5mA, a 3.2F capacitor is recommended. C1's value can be estimated as follows: C1 = 6.4F 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.
MAX1680/MAX1681
Table 2. Switching-Frequency Trade-Offs
ATTRIBUTE Output Ripple C1, C2 Values Supply Current LOWER FREQUENCY Larger Larger Smaller HIGHER FREQUENCY Smaller Smaller Larger
Capacitor Selection
The MAX1680/MAX1681 are tested with capacitor values of 10F and 2.2F, respectively. Capacitor size and switching speed determine output resistance. Larger C1 values decrease the output resistance until the internal switch resistance (3.5 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
Table 3. Low-ESR Capacitor Suppliers
SUPPLIER AVX Marcon/United Chemi-Con Matsuo Nichicon Sanyo Sprague TDK United Chemi-Con Vishay/Vitramon PHONE (803) 946-0690 (800) 282-4975 (847) 696-2000 (714) 969-2491 USA: (847) 843-7500 Japan: 81-7-5231-8461 USA: (619) 661-6835 Japan: 81-7-2070-6306 (603) 224-1961 (847) 390-4373 (714) 255-9500 (203) 268-6261 FAX (803) 626-3123 (847) 696-9278 (714) 960-6492 USA: (847) 843-2798 Japan: 81-7-5256-4158 USA: (619) 661-1055 Japan: 81-7-2070-1174 (603) 224-1430 (847) 390-4428 (714) 255-9400 (203) 452-5670 DEVICE TYPE Surface mount, TPS series Ceramic capacitors Surface mount, 267 series Through-hole, PL series Through-hole, OS-CON series Surface mount, 595D series Ceramic capacitors Through-hole, LXF series SMT ceramic chip capacitors
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7
125mA, Frequency-Selectable, Switched-Capacitor Voltage Converters MAX1680/MAX1681
Table 4. Minimum Recommended Capacitances for Maximum Output Current
fOSC (kHz) 125 250 500 1000 CAPACITANCE (F) (C1 = C2) VIN = 2V 2.5 1.2 0.6 0.3 VIN = 3V 3.8 1.9 0.9 0.4 VIN = 4V 5.1 2.5 1.2 0.6 VIN = 5V 6.4 3.2 1.6 0.8
+VINPUT
1F
FSEL CAP+
IN SHDN 1F
FSEL CAP+
IN SHDN
1F
MAX1681 LV GND
VOUT = -VINPUT CAPOUT 1F
MAX1681
LV GND CAPOUT VOUT = -2VINPUT 1F
NOTE: USE 4.7F 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.
device is larger than that for an individual device (20 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.
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
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125mA, Frequency-Selectable, Switched-Capacitor Voltage Converters MAX1680/MAX1681
+VINPUT
FSEL
IN 1F
FSEL
IN 1F
CAP+
SHDN
CAP+
SHDN
1F
1F
MAX1681 LV GND
MAX1681 GND LV "n"
CAPOUT VOUT
CAP-
OUT 1F
NOTE: USE 4.7F 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.
+VINPUT FSEL IN 1F CAP+ SHDN D1 IN4148
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.
1F
MAX1681 LV GND
CAP-
OUT
VOUT = -VINPUT 1F
1F
D2 IN4148 VOUT = 2VINPUT -VFD1 1F -VFD2
NOTE: USE 4.7F CAPACITORS FOR MAX1680.
Figure 3. Combined Doubler and Inverter
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9
125mA, Frequency-Selectable, Switched-Capacitor Voltage Converters MAX1680/MAX1681
Table 5. Device Comparison
PART NUMBER MAX660 MAX665 MAX860 MAX861 MAX1680 MAX1681 ICL7660 TYPICAL QUIESCENT CURRENT (mA) 0.12/1.0 0.20/1.0 0.20/0.60/1.40 0.30/1.10/2.50 2.5/5.0 10/20 0.080 OUTPUT CURRENT (mA) 100 100 50 50 125 125 10 OUTPUT RESISTANCE () 6.5 6.5 12 12 3.5 3.5 55 SWITCHING FREQUENCY (kHz) 5/40 5/40 6/50/130 13/100/250 125/250 500/1000 5
__________________Pin Configuration
___________________Chip Information
TRANSISTOR COUNT: 171
TOP VIEW
SUBSTRATE CONNECTED TO IN
FSEL CAP+ GND
1 2 3
8 7
IN SHDN LV OUT
MAX1680 MAX1681
6 5
CAP- 4
SO
10
______________________________________________________________________________________
125mA, Frequency-Selectable, Switched-Capacitor Voltage Converters
________________________________________________________Package Information
SOICN.EPS
MAX1680/MAX1681
______________________________________________________________________________________
11
125mA, Frequency-Selectable, Switched-Capacitor Voltage Converters MAX1680/MAX1681
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 (c) 1997 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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