LM2664 Switched Capacitor Voltage Converter General Description Features The LM2664 CMOS charge-pump voltage converter inverts a positive voltage in the range of +1.8V to +5.5V to the corresponding negative voltage of −1.8V to −5.5V. The LM2664 uses two low cost capacitors to provide up to 40 mA of output current. The LM2664 operates at 160 kHz oscillator frequency to reduce output resistance and voltage ripple. With an operating current of only 220 µA (operating efficiency greater than 91% with most loads) and 1 µA typical shutdown current, the LM2664 provides ideal performance for battery powered systems. The device is in SOT-23-6 package. n n n n n Inverts Input Supply Voltage SOT23-6 Package 12Ω Typical Output Impedance 91% Typical Conversion Efficiency at 40 mA 1µA Typical Shutdown Current Applications n n n n n n Cellular Phones Pagers PDAs Operational Amplifier Power Suppliers Interface Power Suppliers Handheld Instruments Basic Application Circuits Voltage Inverter DS100031-1 +5V to −10V Converter DS100031-25 © 1999 National Semiconductor Corporation DS100031 www.national.com LM2664 Switched Capacitor Voltage Converter November 1999 LM2664 Absolute Maximum Ratings (Note 1) Continuous Power Dissipation (TA = 25˚C)(Note 3) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Supply Voltage (V+ to GND, or GND to OUT) SD 600 mW TJMax(Note 3) 150˚C θJA (Note 3) 210˚C/W Operating Junction Temperature Range 5.8V (GND − 0.3V) to (V+ + 0.3V) −40˚ to 85˚C Storage Temperature Range −65˚C to +150˚C V+ and OUT Continuous Output Current 50 mA Lead Temp. (Soldering, 10 seconds) Output Short-Circuit Duration to GND (Note 2) 1 sec. ESD Rating 300˚C 2kV Electrical Characteristics Limits in standard typeface are for TJ = 25˚C, and limits in boldface type apply over the full operating temperature range. Unless otherwise specified: V+ = 5V, C1 = C2 = 3.3 µF. (Note 4) Symbol Parameter V+ Supply Voltage IQ Supply Current ISD Shutdown Supply Current VSD Shutdown Pin Input Voltage Condition Min Typ 1.8 No Load 220 IL Output Current RSW Sum of the Rds(on)of the four internal MOSFET switches IL = 40 mA µA µA 0.8 (Note 6) 40 ROUT Output Resistance (Note 7) IL = 40 mA Oscillator Frequency (Note 8) fSW Switching Frequency (Note 8) PEFF Power Efficiency RL (1.0k) between GND and OUT IL = 40 mA to GND No Load 99 Voltage Conversion Efficiency V 500 2.0 (Note 5) fOSC 80 Units 5.5 1 Normal Operation Shutdown Mode VOEFF Max V mA 4 8 12 25 Ω Ω 160 kHz 40 80 kHz 90 94 % 91 99.96 % Note 1: Absolute maximum ratings indicate limits beyond which damage to the device may occur. Electrical specifications do not apply when operating the device beyond its rated operating conditions. Note 2: OUT may be shorted to GND for one second without damage. However, shorting OUT to V+ may damage the device and should be avoided. Also, for temperatures above 85˚C, OUT must not be shorted to GND or V+, or device may be damaged. Note 3: The maximum allowable power dissipation is calculated by using PDMax = (TJMax − TA)/θJA, where TJMax is the maximum junction temperature, TA is the ambient temperature, and θJA is the junction-to-ambient thermal resistance of the specified package. Note 4: In the test circuit, capacitors C1 and C2 are 3.3 µF, 0.3Ω maximum ESR capacitors. Capacitors with higher ESR will increase output resistance, reduce output voltage and efficiency. Note 5: The minimum input high for the shutdown pin equals 40% of V+. Note 6: The maximum input low for the shutdown pin equals 20% of V+. Note 7: Specified output resistance includes internal switch resistance and capacitor ESR. See the details in the application information for simple negative voltage converter. Note 8: The output switches operate at one half of the oscillator frequency, fOSC = 2fSW. www.national.com 2 LM2664 Test Circuit DS100031-3 *C1 and C2 are 3.3 µF, SC series OS-CON capacitors. FIGURE 1. LM2664 Test Circuit Typical Performance Characteristics (Circuit of Figure 1, V+ = 5V unless otherwise specified) Supply Current vs Supply Voltage Supply Current vs Temperature DS100031-21 Output Source Resistance vs Supply Voltage DS100031-13 Output Source Resistance vs Temperature DS100031-14 DS100031-15 3 www.national.com LM2664 Typical Performance Characteristics (Circuit of Figure 1, V+ = 5V unless otherwise specified) (Continued) Output Voltage Drop vs Load Current Efficiency vs Load Current DS100031-16 Oscillator Frequency vs Supply Voltage DS100031-17 Oscillator Frequency vs Temperature DS100031-18 DS100031-19 Shutdown Supply Current vs Temperature DS100031-20 www.national.com 4 LM2664 Connection Diagram 6-Lead Small Outline Package (M6) DS100031-22 Actual Size DS100031-4 Top View With Package Marking Ordering Information Order Number Package Number Package Marking Supplied as LM2664M6 MA06A SO3A (Note 9) Tape and Reel (1000 units/rail) LM2664M6X MA06A SO3A (Note 9) Tape and Reel (3000 units/rail) Note 9: The first letter ″S″ identifies the part as a switched capacitor converter. The next two numbers are the device number. The fourth letter ″A″ indicates the grade. Only one grade is available. Larger quantity reels are available upon request. Pin Description Pin Name 1 GND Power supply ground input. 2 OUT Negative voltage output. 3 CAP− 4 SD 5 V+ 6 CAP+ Function Connect this pin to the negative terminal of the charge-pump capacitor. Shutdown control pin, tie this pin to V+ in normal operation, and to GND for shutdown. Power supply positive voltage input. Connect this pin to the positive terminal of the charge-pump capacitor. Circuit Description The LM2664 contains four large CMOS switches which are switched in a sequence to invert the input supply voltage. Energy transfer and storage are provided by external capacitors. Figure 2 illustrates the voltage conversion scheme. When S1 and S3 are closed, C1 charges to the supply voltage V+. During this time interval, switches S2 and S4 are open. In the second time interval, S1 and S3 are open; at the same time, S2 and S4 are closed, C1 is charging C2. After a number of cycles, the voltage across C2 will be pumped to V+. Since the anode of C2 is connected to ground, the output at the cathode of C2 equals −(V+) when there is no load current. The output voltage drop when a load is added is determined by the parasitic resistance (Rds(on) of the MOSFET switches and the ESR of the capacitors) and the charge transfer loss between capacitors. Details will be discussed in the following application information section. DS100031-5 FIGURE 2. Voltage Inverting Principle Application Information Simple Negative Voltage Converter The main application of LM2664 is to generate a negative supply voltage. The voltage inverter circuit uses only two external capacitors as shown in the Basic Application Circuits. The range of the input supply voltage is 1.8V to 5.5V. The output characteristics of this circuit can be approximated by an ideal voltage source in series with a resistance. The voltage source equals −(V+). The output resistance Rout is a function of the ON resistance of the internal MOSFET switches, the oscillator frequency, the capacitance and ESR of C1 and C2. Since the switching current charging and discharging C1 is approximately twice as the output current, the 5 www.national.com LM2664 Application Information Capacitor Selection (Continued) As discussed in the Simple Negative Voltage Converter section, the output resistance and ripple voltage are dependent on the capacitance and ESR values of the external capacitors. The output voltage drop is the load current times the output resistance, and the power efficiency is effect of the ESR of the pumping capacitor C1 will be multiplied by four in the output resistance. The output capacitor C2 is charging and discharging at a current approximately equal to the output current, therefore, its ESR only counts once in the output resistance. A good approximation of Rout is: Where IQ(V+) is the quiescent power loss of the IC device, and IL2Rout is the conversion loss associated with the switch on-resistance, the two external capacitors and their ESRs. The selection of capacitors is based on the specifications of the dropout voltage (which equals Iout Rout), the output voltage ripple, and the converter efficiency. Low ESR capacitors (Table 1) are recommended to maximize efficiency, reduce the output voltage drop and voltage ripple. where RSW is the sum of the ON resistance of the internal MOSFET switches shown in Figure 2. High capacitance, low ESR capacitors will reduce the output resistance. The peak-to-peak output voltage ripple is determined by the oscillator frequency, the capacitance and ESR of the output capacitor C2: Again, using a low ESR capacitor will result in lower ripple. Shutdown Mode A shutdown (SD ) pin is available to disable the device and reduce the quiescent current to 1µA. Applying a voltage less than 20% of V+ to the SD pin will bring the device into shutdown mode. While in normal operating mode, the pin is connected to V+. Low ESR Capacitor Manufacturers Manufacturer Nichicon Corp. Phone (708)-843-7500 Capacitor Type PL & PF series, through-hole aluminum electrolytic AVX Corp. (803)-448-9411 TPS series, surface-mount tantalum Sprague (207)-324-4140 593D, 594D, 595D series, surface-mount tantalum Sanyo (619)-661-6835 OS-CON series, through-hole aluminum electrolytic Murata (800)-831-9172 Ceramic chip capacitors Taiyo Yuden (800)-348-2496 Ceramic chip capacitors Tokin (408)-432-8020 Ceramic chip capacitors Other Applications Paralleling Devices Any number of LM2664s can be paralleled to reduce the output resistance. Each device must have its own pumping capacitor C1, while only one output capacitor Cout is needed as shown in Figure 3. The composite output resistance is: www.national.com 6 LM2664 Other Applications (Continued) DS100031-10 FIGURE 3. Lowering Output Resistance by Paralleling Devices Cascading Devices Rout = nRout_1 + n/2 Rout_2 + ... + Rout_n Note that, the number of n is practically limited since the increasing of n significantly reduces the efficiency, and increases the output resistance and output voltage ripple. Cascading the LM2664s is an easy way to produce a greater negative voltage (e.g. A two-stage cascade circuit is shown in Figure 4). If n is the integer representing the number of devices cascaded, the unloaded output voltage Vout is (-nVin). The effective output resistance is equal to the weighted sum of each individual device: DS100031-11 FIGURE 4. Increasing Output Voltage by Cascading Devices Combined Doubler and Inverter In Figure 5, the LM2664 is used to provide a positive voltage doubler and a negative voltage converter. Note that the total current drawn from the two outputs should not exceed 50 mA. 7 www.national.com LM2664 Other Applications (Continued) DS100031-12 FIGURE 5. Combined Voltage Doubler and Inverter Regulating VOUT Vout = Vref (1 + R1/R2) where, Vref = 1.23V Note that, the following conditions must be satisfied simultaneously for worst case design: It is possible to regulate the negative output of the LM2664 by use of a low dropout regulator (such as LP2980). The whole converter is depicted in Figure 6. This converter can give a regulated output from −1.8V to −5.5V by choosing the proper resistor ratio: Vin_min > Vout_min +Vdrop_max (LP2980) + Iout_max x Rout_max (LM2664) Vin_max < Vout_max +Vdrop_min (LP2980) + Iout_min x Rout_min (LM2664) DS100031-24 FIGURE 6. Combining LM2664 with LP2980 to Make a Negative Adjustable Regulator www.national.com 8 LM2664 Switched Capacitor Voltage Converter Physical Dimensions inches (millimeters) unless otherwise noted 6-Lead Small Outline Package (M6) NS Package Number MA06A For Order Numbers, refer to the table in the ″Ordering Information″ section of this document. 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. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. National Semiconductor Corporation Americas Tel: 1-800-272-9959 Fax: 1-800-737-7018 Email: [email protected] www.national.com National Semiconductor Europe Fax: +49 (0) 1 80-530 85 86 Email: [email protected] Deutsch Tel: +49 (0) 1 80-530 85 85 English Tel: +49 (0) 1 80-532 78 32 Français Tel: +49 (0) 1 80-532 93 58 Italiano Tel: +49 (0) 1 80-534 16 80 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. 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