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| LM2685 Dual Output Regulated Switched Capacitor Voltage Converter July 1999 LM2685 Dual Output Regulated Switched Capacitor Voltage Converter General Description The LM2685 CMOS charge-pump voltage converter operates as an input voltage doubler, +5V regulator and inverter for an input voltage in the range of +2.85V to +6.5V. Five low cost capacitors are used in this circuit to provide up to 50mA of output current at +5V ( 5%), and 15mA at -5V. The LM2685 operates at a 130 kHz switching frequency to reduce output resistance and voltage ripple. With an operating current of only 800A (operating efficiency greater than 80% with most loads) and 6A typical shutdown current, the LM2685 is ideal for use in battery powered systems. The device is in a small 14-pin TSSOP package. Features n n n n n n n +5V regulated output Inverts V05(+5V) to VNEG(-5V) Doubles input supply voltage TSSOP-14 package 80% typical conversion efficiency at 25mA Input voltage range of 2.85V to 6.5V Independent shutdown control pins Applications n n n n n Cellular phones Pagers PDAs Handheld instrumentation 3.3V to 5V voltage conversion applications Typical Application and Connection Diagram DS101100-2 14-Pin TSSOP DS101100-1 Ordering Information Order Number LM2685MTC LM2685MTCX Package Type TSSOP-14 TSSOP-14 NSC Package Drawing MTC14 MTC14 Supplied As 94 Units, Rail 2.5k Units, Tape and Reel (c) 1999 National Semiconductor Corporation DS101100 www.national.com Pin Description Pin No. 1 2 3 4 5 6 Name VIN GND VNEG VNSW CE SDP Power supply input voltage. Power supply ground. Negative output voltage created by inverting V05. VNEG output connected through a series switch, NSW. Chip enable input. This pin is high for normal operation and low for shutdown. (See Shutdown and Load Disconnect section in the Detailed Device Description division). Positive side shutdown input. This pin is low for normal operation and high for positive side shutdown and VPSW load disconnect. (See Shutdown and Load Disconnect section in the Detailed Device Description division). Negative side shutdown input. This pin is low for normal operation and high for negative side shutdown and VNSW load disconnect. (See Shutdown and Load Disconnect section in the Detailed Device Description division). The negative terminal of inverting charge-pump capacitor, C2. The positive terminal of inverting charge-pump capacitor, C2. Regulated +5V output. V05 output connected through a series switch, PSW. Voltage Doubler Output. (2.85V VIN 5.4V. See Voltage Doubler section). The positive terminal of doubling charge-pump capacitor, C1. The negative terminal of doubling charge-pump capacitor, C1. Function 7 SDN 8 9 10 11 12 13 14 C2- C2+ V05 VPSW VDBL C1+ C1- www.national.com 2 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 (VIN to GND or GND to VNEG) SDN, SDP, CE V05 Continuous Output Current V05 Short-Circuit Duration to GND (Note 2) 6.8V (GND - 0.3V) to (VIN + 0.3V) 80mA Indefinite Continuous Power Dissipation (TA = 25C) (Note 3) TJMAX (Note 3) JA (Note 3) Operating Ambient Temp. Range Operating Junction Temp. Range Storage Temp. Range Lead Temp. (Soldering, 10 sec.) ESD Rating (Note 4) 600mW 150C 140C/W -40C to 85C -40C to 125C -65C to 150C 300C 2kV Electrical Characteristics Limits with standard typeface apply for TJ = 25C, and limits in boldface type apply over the full temperature range. Unless otherwise specified VIN = 3.6V, C1 = C2 = C3 = C5 = 2.2F. C4 = 4.7F (Note 5) Symbol V+ IQ ISD VSD IL (+5V) RO (-5V) FSW PEFF V05 GLINE GLOAD RSW Parameter Supply Voltage Supply Current Shutdown Supply Current Shutdown Pin Input Voltage for CE, SDP, SDN Output Current at V05 Output Resistance at VNEG Switch Frequency Average Power Efficiency at V05 Output Regulation Line Regulation Load Regulation Series Switch Resistance VNEG to VNSW V05 to VPSW 2.85V VIN 6.5V IL = 25mA to GND 1mA < IL < 50mA (Note 7) 1mA < IL < 50mA (Note 7) 2.85V < VIN < 3.6V 1mA < IL < 50mA VIN > 2.85V 4.896 4.845 No Load No Load, VIN = 6.5V VIN = 6.5V Logic Input High @ 6.5V Logic Input Low @ 6.5V 2.85V < VIN < 6.5V IL = 15mA (Note 6) 85 20 130 82 5.10 5.10 0.25 0.3 1.5 5.0 1.0 5.304 5.355 2.4 0.8 50 40 180 Conditions Min 2.85 800 300 6 Typ Max 6.5 1600 600 30 Units V A A V mA kHz % V %/V % Note 1: Absolute Maximum Ratings indicate limits 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: V05 may be shorted to GND without damage. However, shorting VNEG to V05 may damage the device and must be avoided. Also, for temperature above 85C, V05 must not be shorted to GND 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: The human body model is a 100 pF capacitor discharged through a 1.5k resistor into each pin. Note 5: In the typical operating circuit, capacitors C1 and C2 are 2.2F, 0.3 maximum ESR capacitors. Capacitors with higher ESR will increase output resistance, reduce output voltage and efficiency. Note 6: Specified output resistance includes internal switch resistance and ESR of capacitors. See the Detailed Device Description section. Note 7: The 50 mA maximum current assumes no current is drawn from VDBL pin. See Voltage Doubler section in the Detailed Device Description. 3 www.national.com Typical Performance Characteristics Supply Current vs Input Voltage Unless otherwise specified, TA = 25C, VIN = 3.6V. Efficiency vs Load Current Supply Current vs Temperature DS101100-6 DS101100-7 DS101100-8 Output Voltage (V05) vs. Load Current Output Resistance (VNEG) vs. Temperature Output Resistance (VDBL) vs. Input Voltage DS101100-9 DS101100-10 DS101100-11 Output Resistance (VDBL) vs. Temperature Switch Frequency vs. Temperature Line Transient Response (with 5mA Load) DS101100-13 DS101100-12 DS101100-14 A: INPUT VOLTAGE: VIN = 3.2V to 6.0V, 5V/div B: OUTPUT VOLTAGE: VPSW: 100mV/div C: OUTPUT VOLTAGE: VNSW: 100mV/div www.national.com 4 Typical Performance Characteristics 3.6V. (Continued) V05 Load Transient Response Unless otherwise specified, TA = 25C, VIN = VNSW Load Transient Response VPSW and VNSW Response to CE (with 5mA Load) DS101100-15 DS101100-16 A: LOAD CURRENT: ILOAD = 5mA to 39.6mA, 10mA/div B: OUTPUT VOLTAGE: V05: 10mV/div A: LOAD CURRENT: ILOAD = 4.4mA to -9.4mA, 10mA/div B: OUTPUT VOLTAGE: VNSW: 50mV/div DS101100-17 A: CE INPUT: 5V/div B: OUTPUT VOLTAGE: VPSW: 5V/div C: OUTPUT VOLTAGE: VNSW: 5V/div V05 Response to SDP (with 5mA Load) VNSW Response to SDP (with 5mA Load) VNSW Response to SDN (with 5mA Load) DS101100-18 DS101100-19 DS101100-20 A: SDP INPUT: 5V/div B: OUTPUT VOLTAGE: 5V/div A: SDP INPUT: 5V/div B: OUTPUT VOLTAGE (VNSW): 5V/div A: SDN INPUT: 5V/div B: OUTPUT VOLTAGE (VNSW): 5V/div 5 www.national.com Detailed Device Description DS101100-3 FIGURE 1. Functional Block Diagram The LM2685 CMOS charge pump voltage converter operates as an input voltage doubler, +5V regulator and inverter for an input voltage in the range of +2.85V to +6.5V. It delivers maximum load currents of 50mA and 15mA for the regulated +5V and the inverted output voltages respectively, with an operating current of only 800A. It also has a typical shutdown current of 6A. All these performance qualities make the LM2685 an ideal device for battery powered systems. The LM2685 has three main functional blocks: a voltage doubler, a low dropout (LDO) regulator, and a voltage inverter. Figure 1 shows the LM2685 functional block diagram. Voltage Doubler The voltage doubler stage doubles the input voltage VIN, within the range of +2.85V to +5.4V. For VIN above 5.4V, the doubler shuts off and the input voltage is passed directly to VDBL via an internal power switch. The doubler contains four large CMOS switches which are switched in a sequence to double the input supply voltage. Figure 2 illustrates the voltage conversion scheme. When S2 and S4 are closed, C1 charges to the supply voltage VIN. During this time interval, switches S1 and S3 are open. In the next time interval, S2 and S4 are opened at the same time, S1 and S3 are closed, the sum of the input voltage VIN and the voltage across C1 gives the 2VIn and the voltage across C1 gives the 2VIN at VDBL output. VDBL supplies the LDO regulator. It is recommended not to load VDBL when V05 has a load of 50mA. For proper operation, the sum of VDBL and V05 loads must not be more than 50mA. DS101100-4 FIGURE 2. Voltage Doubler Principle +5 LDO Regulator VDBL is the input to an LDO regulator that regulates it to a +5 output voltage at V05. VPSW is tied to V05 through a series switch PSW. The LDO output capacitor (4.7F Tantalum) may be tied to either V05 or VPSW. Inverter From the V05 output, a -5V output is created at VNEG by means of an inverting charge pump. This negative output is unregulated, meaning that it's output will droop as the load current at VNEG increases. The inverter contains four large CMOS switches which are in a sequence to invert the input supply voltage. Figure 3 illustrates the voltage conversion scheme. When S1 and S3 are closed, C1 charges to the supply voltage V05. 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 cross C2 will be pumped to V05. Since the anode of C2 is connected to ground, the output at the cathode of C2 equals -(V05) when there is no load current. The output voltage drop when a load www.national.com 6 Detailed Device Description (Continued) 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. Shutdown and Load Disconnect In addition to the nominal charge pump and regulator functions, the LM2685 features shutdown and load disconnect circuitry. CE (chip enable) and SDP (shutdown positive) perform the same task with opposite input polarities. When CE is low or SDP is high, all circuit blocks are disabled and V05 falls to ground potential. This is the same result as when the die temperature exceeds 150C (typical), and the device's internal thermal shutdown is triggered. Forcing SDN (shutdown negative) high disables only the inverting charge pump. The doubling charge pump and the LDO regulator continue to operate, so the V05 and the VPSW remain at 5V. The LM2685 incorporates two low impedance switches tied to the V05 and VNEG outputs, because some special applications require load disconnect and this is achievable via the switches. Switch PSW connects V05 to VPSW, and switch NSW connects VNEG to VNSW. In normal operation, these switches are closed, allowing 5V loads to be tied to either V05 or VPSW and -5V loads to be tied to either VNEG or VNSW. Driving SDN high opens switch NSW only, while forcing CE low or SDP high, opens both the PSW and NSW. DS101100-5 FIGURE 3. Voltage Inverter Principle 7 www.national.com LM2685 Dual Output Regulated Switched Capacitor Voltage Converter Physical Dimensions inches (millimeters) unless otherwise noted TSSOP-14 Package 14-Lead Thin Shrink Small-Outline Package For Ordering, Refer to Ordering Information Table NS Package Number MTC14 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: support@nsc.com www.national.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 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. 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 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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