LM2682 LM2682 Switched Capacitor Voltage Doubling Inverter Literature Number: SNVS044A LM2682 Switched Capacitor Voltage Doubling Inverter General Description Features The LM2682 is a CMOS charge-pump voltage inverter capable of converting positive voltage in the range of +2.0V to +5.5V to the corresponding doubled negative voltage of -4.0V to -11.0V respectively. The LM2682 uses three low cost capacitors to provide 10 mA of output current without the cost, size, and EMI related to inductor based circuits. With an operating current of only 150 A and an operating efficiency greater than 90% with most loads, the LM2682 provides ideal performance for battery powered systems. The LM2682 offers a switching frequency of 6 kHz. n n n n Inverts then doubles input supply voltage Small MSOP-8 package (mini SO-8) and SO-8 package 90 typical output impedance 94% typical power efficiency at 10 mA Applications n n n n n LCD contrast biasing GaAs power amplifier biasing Interface power supplies Handheld instrumentation Laptop computers and PDAs Typical Operating Circuit and Pin Configuration 8-Pin MSOP or 8-Pin SOIC 10099702 10099701 Ordering Information Order Number Package Package Number Package Marking LM2682MM MSOP-8 MUA08A S11A Tape and Reel (1000 units/reel) LM2682MMX MSOP-8 MUA08A S11A Tape and Reel (3500 units/reel) LM2682M SO-8 M08A LM2682M Rail (95 units/rail) LM2682MX SO-8 M08A LM2682M Tape and Reel (2500 units/reel) (c) 2004 National Semiconductor Corporation DS100997 Supplied As www.national.com LM2682 Switched Capacitor Voltage Doubling Inverter November 1999 LM2682 Absolute Maximum Ratings (Note 1) Power Dissipation (Note 2) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Input Voltage (VIN) MSOP-8 300 mW SO-8 470 mW TJMAX +150C +5.8V VIN dV/dT 1V/sec VOUT Operating Ratings -11.6V VOUT Short-Circuit Duration ESD Susceptibility (Note 3) Continuous Storage Temperature -65C to +150C Lead Temperature Soldering +300C Human Body Model Machine Model 2 kV 200V Ambient Temp. Range -40C to +85C Junction Temp. Range -40C to +125C LM2682 Electrical Characteristics VIN = 5V and C1 = C2 = C3 = 3.3F unless otherwise specified. Limits with bold typeface apply over the full operating ambient temperature range, -40C to +85C, limits with standard typeface apply for TA = 25C. Symbol Parameter Conditions Min Typical (Note 4) Max Units 5.5 V VIN Supply Voltage Range RL = 2 k IIN Supply Current Open Circuit, No Load 150 300 400 A ROUT VOUT Source Resistance IL = 10 mA 90 150 IL=5 mA, VIN=2 V 110 250 12 30 kHz 6 15 kHz 2.0 200 fOSC Oscillator Frequency (Note 5) fSW Switching Frequency (Note 5) POWER Power Efficiency RL = 2k (Note 6) VOLTAGE Voltage Conversion Efficiency 90 93 % 99.9 % Note 1: Absolute Maximum Ratings are those values beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is intended to be functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. Note 2: The maximum power dissipation must be de-rated at elevated temperatures (only needed for TA > 85C) and is limited by TJMAX (maximum junction temperature), J-A (junction to ambient thermal resistance) and TA (ambient temperature). J-A is 140C/W for the SO-8 package and 220C/W for the MSOP-8 package. The maximum power dissipation at any temperature is: PDissMAX = (TJMAX - TA)/J-A up to the value listed in the Absolute Maximum Ratings. Note 3: The human body model is a 100 pF capacitor discharged through a 1.5 k resistor into each pin. The machine model is a 200pF capacitor discharged directly into each pin. Note 4: Typical numbers are at 25C and represent the most likely norm. Note 5: The output switches operate at one half of the oscillator frequency, fOSC = 2fSW. Note 6: The minimum specification is guaranteed by design and is not tested. Pin Description www.national.com Pin Number Symbol 1 C1- Capacitor C1 negative terminal Description 2 C2+ Capacitor C2 positive terminal 3 C2- Capacitor C2 negative terminal 4 VOUT Negative output voltage (-2VIN) 5 GND Device ground 6 VIN Power supply voltage 7 C1+ Capacitor C1 positive terminal 8 NC No Connection 2 LM2682 Typical Performance Charactistics VIN = 5V and TA = 25C unless otherwise noted. Output Resistance vs Input Voltage Output Voltage vs Load Current 10099707 10099706 Supply Current vs Input Voltage Output Resistance vs Temperature 10099708 10099709 Output Voltage Ripple vs Load Current 10099710 3 www.national.com LM2682 Basic Application Circuits 10099703 FIGURE 1. Doubling Voltage Inverter 10099704 FIGURE 2. +5V to -5V Regulated Voltage Converter Using the assumption that all four switches have the same ON resistance our equation becomes: ROUT = 16RSW + 4ESRC1 + 4ESRC2 + ESRC3 + 1/(fOSCxC1) + 1/(fOSCxC2) Application Information VOLTAGE DOUBLING INVERTER The main application of the LM2682 is to generate a negative voltage that is twice the positive input voltage. This circuit requires only three external capacitors and is connected as shown in Figure 1. It is important to keep in mind that the efficiency of the circuit is determined by the output resistance. A derivation of the output resistance is shown below: ROUT = 2(RSW1+RSW2+ESRC1+RSW3+RSW4+ESRC2) + 2(RSW1+RSW2+ESRC1+RSW3+RSW4+ESRC2) + 1/(fOSCxC1) + 1/(fOSCxC2) + ESRC3 www.national.com Output resistance is typically 90 with an input voltage of +5V, an operating temperature of 25C, and using low ESR 3.3 F capacitors. This equation shows the importance of capacitor selection. Large value, low ESR capacitors will reduce the output resistance significantly but will also require a larger overall circuit. Smaller capacitors will take up less space but can lower efficiency greatly if the ESR is large. Also to be considered is that C1 must be rated at 6 VDC or greater while C2 and C3 must be rated at 12 VDC or greater. 4 the output voltage with the input varying anywhere from 4.5V to the maximum of 5.5V. With less load the results are even better. Voltage ripple concerns are reduced in this case since the ripple at the output of the LM2682 is reduced at the output by the PSRR of the op-amp used. (Continued) The amount of output voltage ripple is determined by the output capacitor C3 and the output current as shown in this equation: VRIPPLE P-P = IOUT x (2xESRC3 + 1/[2x(fOSCxC3)]) PARALLELING DEVICES Once again a larger capacitor with smaller ESR will give better results. Any number of devices can be paralleled to reduce the output resistance. As shown in Figure 3, each device must have its own pumping capacitors, C1 and C2, but only one shared output capacitor is required. The effective output resistance is the output resistance of one device divided by the number of devices used in parallel. Paralleling devices also gives the capability of increasing the maximum output current. The maximum output current now becomes the maximum output current for one device multiplied by the number of devices used in parallel. For example, if you parallel two devices you can get 20 mA of output current and have half the output resistance of one device supplying 10 mA. +5V TO -5V REGULATED VOLTAGE CONVERTER Another application in which the LM2682 can be used is for generating a -5V regulated supply from a +5V unregulated supply. This involves using an op-amp and a reference and is connected as shown in Figure 2. The LM358 op-amp was chosen for its low cost and versatility and the LM4040-5.0 reference was chosen for its low bias current requirement. Of course other combinations may be used at the designer's discretion to fit accuracy, efficiency, and cost requirements. With this configuration the circuit is well regulated and is still capable of providing nearly 10 mA of output current. With a 9 mA load the circuit can typically maintain 5% regulation on 10099705 FIGURE 3. Paralleling Devices 5 www.national.com LM2682 Application Information LM2682 Physical Dimensions inches (millimeters) unless otherwise noted 8 Lead (0.150" Wide) Molded Small Outline Package, JEDEC NS Package Number M08A Surface Mount Mini SO-8 Package NS Package Number MUA08A www.national.com 6 LM2682 Switched Capacitor Voltage Doubling Inverter Notes National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications. For the most current product information visit us at www.national.com. LIFE SUPPORT POLICY NATIONAL'S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. 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