LM2665 Switched Capacitor Voltage Converter General Description Features The LM2665 CMOS charge-pump voltage converter operates as a voltage doubler for an input voltage in the range of +2.5V to +5.5V. Two low cost capacitors and a diode (needed during start-up) are used in this circuit to provide up to 40 mA of output current. The LM2665 can also work as a voltage divider to split a voltage in the range of +1.8V to +11V in half. The LM2665 operates at 160 kHz oscillator frequency to reduce output resistance and voltage ripple. With an operating current of only 650 µA (operating efficiency greater than 90% with most loads) and 1µA typical shutdown current, the LM2665 provides ideal performance for battery powered systems. The device is in SOT-23-6 package. n n n n n Doubles or Splits Input Supply Voltage SOT23-6 Package 12Ω Typical Output Impedance 90% 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 Doubler DS100049-1 Splitting Vin in Half DS100049-2 © 1999 National Semiconductor Corporation DS100049 www.national.com LM2665 Switched Capacitor Voltage Converter November 1999 LM2665 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 2.5 No Load 650 Max V 1250 µA 1 Shutdown Mode IL Output Current RSW Sum of the Rds(on)of the four internal MOSFET switches IL = 40 mA µA 2.0 (Note 5) Normal Operation Units 5.5 0.8 (Note 6) 40 V mA 3.5 8 12 25 Ω Ω ROUT Output Resistance (Note 7) IL = 40 mA fOSC Oscillator Frequency (Note 8) 80 160 kHz fSW Switching Frequency (Note 8) 40 80 kHz PEFF Power Efficiency RL (1.0k) between GND and OUT IL = 40 mA to GND 86 93 VOEFF Voltage Conversion Efficiency No Load % 90 99 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 of 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 positive voltage doubler. Note 8: The output switches operate at one half of the oscillator frequency, fOSC = 2fSW. www.national.com 2 LM2665 Test Circuit DS100049-3 FIGURE 1. LM2665 Test Circuit Typical Performance Characteristics (Circuit of Figure 1, V+ = 5V unless otherwise specified) Supply Current vs Supply Voltage Supply Current vs Temperature DS100049-4 Output Source Resistance vs Supply Voltage DS100049-5 Output Source Resistance vs Temperature DS100049-6 DS100049-7 3 www.national.com LM2665 Typical Performance Characteristics (Circuit of Figure 1, V+ = 5V unless otherwise specified) (Continued) Output Voltage Drop vs Load Current Efficiency vs Load Current DS100049-9 DS100049-8 Oscillator Frequency vs Supply Voltage Oscillator Frequency vs Temperature DS100049-10 DS100049-11 Shutdown Supply Current vs Temperature DS100049-12 www.national.com 4 LM2665 Connection Diagram 6-Lead SOT (M6) DS100049-22 Actual Size DS100049-13 Top View With Package Marking Ordering Information Order Number Package Number Package Marking Supplied as LM2665M6 MA06A SO4A (Note 9) Tape and Reel (1000 units/rail) LM2665M6X MA06A SO4A (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 Function Voltage Doubler 1 V+ Voltage Split Power supply positive voltage input. Positive voltage output. 2 GND Power supply ground input Same as doubler 3 CAP− Connect this pin to the negative terminal of the charge-pump capacitor Same as doubler. 4 SD Shutdown control pin, tie this pin to ground in normal operation. Same as doubler. 5 OUT Positive voltage output. Power supply positive voltage input 6 CAP+ Connect this pin to the positive terminal of the charge-pump capacitor. Same as doubler Circuit Description The LM2665 contains four large CMOS switches which are switched in a sequence to double the input supply voltage. Energy transfer and storage are provided by external capacitors. Figure 2 illustrates the voltage conversion scheme. When S2 and S4 are closed, C1 charges to the supply voltage V+. During this time interval, switches S1 and S3 are open. In the next time interval, S2 and S4 are open; at the same time, S1 and S3 are closed, the sum of the input voltage V+ and the voltage across C1 gives the 2V+ output voltage when there is no load. 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. DS100049-14 FIGURE 2. Voltage Doubling Principle Application Information Positive Voltage Doubler The main application of the LM2665 is to double the input voltage. The range of the input supply voltage is 2.5V to 5.5V. The output characteristics of this circuit can be approximated by an ideal voltage source in series with a resistance. The 5 www.national.com LM2665 Application Information Split V+ in Half Another interesting application shown in the Basic Application Circuits is using the LM2665 as a precision voltage divider. . This circuit can be derived from the voltage doubler by switching the input and output connections. In the voltage divider, the input voltage applies across the OUT pin and the GND pin (which are the power rails for the internal oscillator), therefore no start-up diode is needed. Also, since the off-voltage across each switch equals Vin/2, the input voltage can be raised to +11V. (Continued) voltage source equals 2V+. 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 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: Shutdown Mode A shutdown (SD) pin is available to disable the device and reduce the quiescent current to 1 µA. In normal operating mode, the SD pin is connected to ground. The device can be brought into the shutdown mode by applying to the SD pin a voltage greater than 40% of the V+ pin voltage. where RSW is the sum of the ON resistance of the internal MOSFET switches shown in Figure 2. Capacitor Selection As discussed in the Positive Voltage Doubler 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 The peak-to-peak output voltage ripple is determined by the oscillator frequency, the capacitance and ESR of the output capacitor C2: High capacitance, low ESR capacitors can reduce both the output resistance and the voltage ripple. The Schottky diode D1 is only needed for start-up. The internal oscillator circuit uses the OUT pin and the GND pin. Voltage across OUT and GND must be larger than 1.8V to insure the operation of the oscillator. During start-up, D1 is used to charge up the voltage at the OUT pin to start the oscillator; also, it protects the device from turning-on its own parasitic diode and potentially latching-up. Therefore, the Schottky diode D1 should have enough current carrying capability to charge the output capacitor at start-up, as well as a low forward voltage to prevent the internal parasitic diode from turning-on. A Schottky diode like 1N5817 can be used for most applications. If the input voltage ramp is less than 10V/ ms, a smaller Schottky diode like MBR0520LT1 can be used to reduce the circuit size. 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. 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 LM2665s 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 LM2665 Other Applications (Continued) DS100049-19 FIGURE 3. Lowering Output Resistance by Paralleling Devices Cascading Devices Note that, the increasing of the number of cascading stages is pracitically limited since it significantly reduces the efficiency, increases the output resistance and output voltage ripple. Cascading the LM2665s is an easy way to produce a greater voltage (A two-stage cascade circuit is shown in Figure 4). The effective output resistance is equal to the weighted sum of each individual device: Rout = 1.5Rout_1 + Rout_2 DS100049-20 FIGURE 4. Increasing Output Voltage by Cascading Devices Regulating VOUT Note that, the following conditions must be satisfied simultaneously for worst case design: It is possible to regulate the output of the LM2665 by use of a low dropout regulator (such as LP2980-5.0). The whole converter is depicted in Figure 5. A different output voltage is possible by use of LP2980-3.3, LP2980-3.0, or LP2980-adj. 2Vin_min > Vout_min +Vdrop_max (LP2980) + Iout_max x Rout_max (LM2665) 2Vin_max < Vout_max +Vdrop_min (LP2980) + Iout_min x Rout_min (LM2665) DS100049-21 FIGURE 5. Generate a Regulated +5V from +3V Input Voltage 7 www.national.com LM2665 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. 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