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| LM2664 Switched Capacitor Voltage Converter January 1999 LM2664 Switched Capacitor Voltage Converter General Description 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 A (operating efficiency greater than 91% with most loads) and 1 A typical shutdown current, the LM2664 provides ideal performance for battery powered systems. The device is in SOT-23-6 package. Features n n n n n Inverts Input Supply Voltage SOT23-6 Package 12 Typical Output Impedance 91% Typical Conversion Efficiency at 40 mA 1A 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 (c) 1999 National Semiconductor Corporation DS100031 www.national.com Absolute Maximum Ratings (Note 1) 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 5.8V Continuous Power Dissipation (TA = 25C)(Note 3) TJMax(Note 3) JA (Note 3) Operating Junction Temperature Range Storage Temperature Range Lead Temp. (Soldering, 10 seconds) ESD Rating 600 mW 150C 210C/W -40 to 85C -65C to +150C 300C 2kV (GND - 0.3V) to (V+ + 0.3V) 50 mA 1 sec. V+ and OUT Continuous Output Current Output Short-Circuit Duration to GND (Note 2) Electrical Characteristics Limits in standard typeface are for TJ = 25C, and limits in boldface type apply over the full operating temperature range. Unless otherwise specified: V+ = 5V, C1 = C2 = 3.3 F. (Note 4) Symbol V+ IQ ISD VSD Parameter Supply Voltage Supply Current Shutdown Supply Current Shutdown Pin Input Voltage Normal Operation Shutdown Mode IL RSW ROUT fOSC fSW PEFF Output Current Sum of the Rds(on)of the four internal MOSFET switches Output Resistance (Note 7) Oscillator Frequency Switching Frequency Power Efficiency IL = 40 mA IL = 40 mA (Note 8) (Note 8) RL (1.0k) between GND and OUT IL = 40 mA to GND No Load 80 40 90 40 4 12 160 80 94 % 91 99 99.96 % 8 25 2.0 (Note 5) 0.8 (Note 6) No Load Condition Min 1.8 220 1 Typ Max 5.5 500 Units V A A V mA kHz kHz VOEFF Voltage Conversion Efficiency 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 85C, 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)/JA, where TJMax is the maximum junction temperature, TA is the ambient temperature, and JA is the junction-to-ambient thermal resistance of the specified package. Note 4: In the test circuit, capacitors C1 and C2 are 3.3 F, 0.3 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 Test Circuit DS100031-3 *C1 and C2 are 3.3 F, SC series OS-CON capacitors. FIGURE 1. LM2664 Test Circuit Typical Performance Characteristics Supply Current vs Supply Voltage (Circuit of Figure 1, V+ = 5V unless otherwise specified) Supply Current vs Temperature DS100031-21 DS100031-13 Output Source Resistance vs Supply Voltage Output Source Resistance vs Temperature DS100031-14 DS100031-15 3 www.national.com Typical Performance Characteristics specified) (Continued) Output Voltage Drop vs Load Current (Circuit of Figure 1, V+ = 5V unless otherwise Efficiency vs Load Current DS100031-16 DS100031-17 Oscillator Frequency vs Supply Voltage Oscillator Frequency vs Temperature DS100031-18 DS100031-19 Shutdown Supply Current vs Temperature DS100031-20 www.national.com 4 Connection Diagram 6-Lead Small Outline Package (M6) DS100031-22 Actual Size DS100031-4 Top View With Package Marking Ordering Information Order Number LM2664M6 LM2664M6X Package Number MA06A MA06A Package Marking SO3A (Note 9) SO3A (Note 9) Supplied as Tape and Reel (250 units/rail) 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 1 2 3 4 5 6 Name GND OUT CAP- SD V+ CAP+ Power supply ground input. Negative voltage output. 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. Function 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 Application Information (Continued) Capacitor Selection 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 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: 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. 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 1A. 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. AVX Corp. Sprague Sanyo Murata Taiyo Yuden Tokin Phone (708)-843-7500 (803)-448-9411 (207)-324-4140 (619)-661-6835 (800)-831-9172 (800)-348-2496 (408)-432-8020 Capacitor Type PL & PF series, through-hole aluminum electrolytic TPS series, surface-mount tantalum 593D, 594D, 595D series, surface-mount tantalum OS-CON series, through-hole aluminum electrolytic Ceramic chip capacitors Ceramic chip capacitors 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 Other Applications (Continued) DS100031-10 FIGURE 3. Lowering Output Resistance by Paralleling Devices Cascading Devices 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: 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. 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 Other Applications (Continued) DS100031-12 FIGURE 5. Combined Voltage Doubler and Inverter Regulating VOUT 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: Vout = Vref (1 + R1/R2) where, Vref = 1.23V Note that, the following conditions must be satisfied simultaneously for worst case design: 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 9 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 OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 2. A critical component in any component of a life support 1. Life support devices or systems are devices or sysdevice or system whose failure to perform can be reatems which, (a) are intended for surgical implant into sonably expected to cause the failure of the life support the body, or (b) support or sustain life, and whose faildevice or system, or to affect its safety or effectiveness. ure 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: support@nsc.com National Semiconductor Europe Fax: +49 (0) 1 80-530 85 86 Email: europe.support@nsc.com Deutsch Tel: +49 (0) 1 80-530 85 85 English Tel: +49 (0) 1 80-532 78 32 Francais Tel: +49 (0) 1 80-532 93 58 Italiano Tel: +49 (0) 1 80-534 16 80 National Semiconductor Asia Pacific Customer Response Group Tel: 65-2544466 Fax: 65-2504466 Email: sea.support@nsc.com National Semiconductor Japan Ltd. Tel: 81-3-5639-7560 Fax: 81-3-5639-7507 www.national.com 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. |
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