LM3351 Switched Capacitor Voltage Converter General Description The LM3351 is a CMOS charge-pump voltage converter which efficiently provides a 3.3V to 5V step-up, or 5V to 3.3V step-down. The LM3351 is pin for pin compatible with the LM3350 but consumes 66% less quiescent current. The LM3351 uses four small, low cost capacitors to provide the voltage conversion. It eliminates the cost, size and radiated EMI related to inductor based circuits, or the power loss of a linear regulator. Operating power conversion efficiency greater than 90% provides ideal performance for battery powered portable systems. The architecture provides a fixed voltage conversion ratio of 3/2 or 2/3. Thus it can be used for other DC-DC conversions as well. Key Specifications n 200 kHz switch frequency allows use of very small, inexpensive capacitors. n n n n n 4.2Ω typical step-up output impedance 1.8Ω typical step-down output impedance 95% typical power conversion efficiency at 50 mA 250 nA typical shutdown current Low quiescent current extends battary life Features n Conversion of 3.3V to 5V, or 5V to 3.3V n Small Mini SO-8 package n No inductor required Applications n n n n Any mixed 5V and 3.3V system Laptop computers and PDAs Handheld instrumentation PCMCIA cards Ordering Information Order Number Package Type NSC Package Drawing Package Marking LM3351MMX Mini SO-8 MUA08A S05A 3500 Units on Tape and Reel LM3351MM Mini SO-8 MUA08A S05A 1000 Units on Tape and Reel Supplied As Basic Operating Circuits Step-Up Converter Step-Down Converter DS100146-1 DS100146-2 Connection Diagram Mini SO8 Package DS100146-3 Top View © 1999 National Semiconductor Corporation DS100146 www.national.com LM3351 Switched Capacitor Voltage Converter December 1999 LM3351 Absolute Maximum Ratings (Note 1) Storage Temperature If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Lead Temperature (Soldering, 10 secs) Maximum Input Voltage, Step-Down 3.65V Power Dissipation (PD) (TA=25˚C, (Note 2)) 500 mW θja (Note 2) 250˚C/W 260˚C ESD Susceptibility (Note 3) 2kV Not short circuit protected. 5.5V Maximum Input Voltage, Step-Up −65˚C to +150˚C Operating Conditions (Note 1) Ambient Temperature Range Tj Max (Note 2) −40˚C to + 85˚C 150˚C Electrical Characteristics 3/2 Step-Up Voltage Converter Specifications in standard type face are for Tj = 25˚C, and those with boldface type apply over full operating temperature range. Unless otherwise specified, Vin = 3.3V, VEnable = 3.3V, Iload = 50 mA, C1, C2, Cin and Cout = 1 µF. Symbol Parameter Conditions Typ (Note 4) Limits (Note 5) Units VoutNL Output Voltage at No Load Iload = 0 A 5.0 V VoutFL Output Voltage at 50 mA Iload = 50 mA 4.7 V Vin Input Supply Voltage Range IQ1 IQ2 Zout fSW VEnable IEnable Pη Quiescent Current Quiescent Current 3.3 Shutdown Mode, VEnable = 0V, Iload=0 A; Current into pin Vlow V(Min) 3.65 V(Max) 3 µA(Max) 1.5 mA(Max) 6.25 Ω (Max) 125 kHz(Min) 275 kHz(Max) 1.0 V(Min) 2.5 V(Max) 1 µA(Max) 0.025 Normal Mode, IIoad = 0A; Current into pin VIow 1.1 Output Source Impedance Iload = 50 mA 4.2 Switching Frequency (Note 6) µA mA Ω 200 Enable Threshold Voltage Leakage Current V 2.5 kHz 1.7 Current into ENABLE pin; ENABLE = 5V and all other pins at ground Power Efficiency V 0.025 µA % 95 Electrical Characteristics 2/3 Step-Down Voltage Converter Specifications in standard type face are for Tj = 25˚C, and those with boldface type apply over full operating temperature range. Unless otherwise specified, Vhigh = 5V, VEnable = 5V, Iload = 50 mA, C1, C2, Cin and Cout = 1 µF. Symbol Parameter Conditions Typ (Note 4) Limits (Note 5) Units VoutNL Output Voltage at No Load Iload = 0 A 3.3 V VoutFL Output Voltage at 50 mA Iload =50 mA 3.2 V Vin Input Supply Voltage Range IQ1 Quiescent Current www.national.com 5 Shutdown Mode, VEnable = 0V, Iload=0 A; Current into pin Vhigh 2 V 2.2 V(Min) 5.5 V(Max) 3 µA(Max) 0.25 µA LM3351 Electrical Characteristics 2/3 Step-Down Voltage Converter (Continued) Specifications in standard type face are for Tj = 25˚C, and those with boldface type apply over full operating temperature range. Unless otherwise specified, Vhigh = 5V, VEnable = 5V, Iload = 50 mA, C1, C2, Cin and Cout = 1 µF. Symbol IQ2 Zout fSW VEnable IEnable Pη Parameter Conditions Typ (Note 4) Normal Mode, IIoad = 0A; Current into pin Vhigh 0.8 Output Source Impedance Iload = 50 mA 1.8 Switching Frequency (Note 6) Quiescent Current Units 1.0 mA(Max) 3 Ω (Max) 125 kHz(Min) 275 kHz(Max) 1.0 V(Min) 2.5 V(Max) 1 µA(Max) mA Ω 200 Enable Threshold Voltage Leakage Current Limits (Note 5) kHz 1.7 Current into ENABLE pin; ENABLE = 5V and all other pins at ground V 0.025 Power Efficiency µA % 95 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 Electrical Characteristics. The guaranteed specifications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test conditions. Note 2: For operation at elevated temperatures, LM3351 must be derated based on package thermal resistance of θja and Tj max, Tj = TA+ θjaPD. Note 3: The human body model is a 100 pF capacitor discharged through a 1.5 kW resistor into each pin. Note 4: Typical numbers are at 25˚C and represent the most likely parametric norm. Note 5: Limits are 100% production tested at 25˚C. Limits over the operating temperature range are guaranteed through correlation using Statistical Quality Control (SQC) methods. The limits are used to calculate National’s Averaging Outgoing Quality Level (AOQL). Note 6: The internal oscillator runs at 1.6 MHz, the output switches operate at one eighth of the oscillator frequency, fOSC = 8fSW. Typical Performance Characteristics Vout vs Iload (Step-Up) Pη vs Iload (Step-Up) Output Source Impedance vs Temperature (Step-Up) DS100146-4 DS100146-5 DS100146-6 3 www.national.com LM3351 Typical Performance Characteristics Vout vs Iload (Step-Down) (Continued) Pη vs Iload (Step-Down) DS100146-7 Output Source Impedance vs Temperature (Step-Down) DS100146-8 DS100146-9 Switching Frequency vs Temperature DS100146-10 Pin Description Detailed Operation Pin Name 1 Cap1+ Positive terminal for the first charge pump capacitor. 2 Cap1− Negative terminal for the first charge pump capacitor. 3 Cap2+ Positive terminal for the second charge pump capacitor. 4 Cap2− Negative terminal for the second charge pump capacitor. 5 Vlow In Step-Up mode, this will be the input terminal. In Step-Down mode, this will be the output terminal. 6 Gnd Ground 7 Vhigh In Step-Down mode, this will be the input terminal. In Step-Up mode, this will be the output terminal. 8 Enable www.national.com Function OPERATING PRINCIPLE The LM3351 is a charge-pump voltage converter that provides a voltage conversion ratio of 3/2 in step-up mode and a conversion ratio of 2/3 in the step-down mode. Thus it can be used in the step-down mode to provide a 3.3V output from a regulated 5V input or in the step-up mode to provide a 5V output from a regulated 3.3V input. Other values of input voltages can be used as long as they are within the limits. The LM3351 contains an array of CMOS switches which are operated in a certain sequence to provide the step-up or step-down of the input supply. An internal RC oscillator provides the timing signals. Energy transfer and storage are provided by four inexpensive ceramic capacitors. The selection of these capacitors is explained in the Capacitor Selection section under Application Information. Active high CMOS logic level Enable Input. Connect to Voltage Input terminal to enable the IC. Connect to Ground (Pin 6) to disable. 4 LM3351 Detailed Operation (Continued) STEP-UP APPLICATIONS NEED AN EXTRA DIODE The LM3351 is biased from pin Vhigh. Thus for step-up applications, an external Schottky diode (D1) is needed to supply power to Vhigh during startup (See Figure 1). Note that during shutdown, this diode will provide a DC path from Vin to Vout. The load may therefore continue to draw current from the input voltage source. This Schottky diode is not required for step-down applications (See Figure 2). SHUTDOWN MODE When ENABLE is a logic low (ground), the LM3351 enters a low power shutdown mode. In this mode, all circuitry is disabled and therefore, all switching action stops. During shutdown, the current consumption drops to 250 nA (typical). When ENABLE is a logic high, (i.e. 3.3V for step-up mode and 5.0V for step-down mode), the LM3351 returns to normal operation. Application Information CAPACITOR SELECTION The LM3351 requires four capacitors: an input bypass capacitor (connected between Vin and ground), an output hold capacitor (connected between Vout and ground), and two sampling capacitors (C1 and C2 in Figures 1, 2). 1.0 µF ( ± 20%) ceramic chip type capacitors are recommended for all four capacitors. The usable operating frequency should be greater than 5 MHz for all capacitors. The output hold capacitor value determines the output ripple. Increasing the value of the hold capacitor decreases the ripple. The value of this capacitor (Cout) can be calculated (approximately) based on the output ripple (∆Vout) requirements from: where Iload is the load current and fO is the oscillator frequency. In order to ensure superior performance over the entire operating temperature range, capacitors made of X7R dielectric material are suggested. However, capacitors made of other dielectric materials that still meet the ± 20% specification over the entire temperature range can also be used. PRECAUTIONS The LM3351 is not short circuit protected. 5 www.national.com LM3351 Typical Application Circuits DS100146-12 FIGURE 1. Step-Up Converter DS100146-13 FIGURE 2. Step-Down Converter Layout Information LAYOUT CONSIDERATIONS The LM3351’s high switching frequency (200 kHz) makes a good layout important. Figure 3 illustrates a typical layout. It is important to keep the distance short between the four capacitors and the IC. Wide traces and grounding are also recommended. These steps will minimize trace inductance and high frequency ringing. Of the four capacitors, CIN and COUT have the highest value of di/dt. It is therefore most important to keep them close to the IC. The ground lead that CIN and COUT share should also be kept wide and short. The location of the diode (D1) used in the step-up configuration is not critical. This diode is only used during the initial turn on of the IC. D1 is not needed in step-down applications. www.national.com 6 LM3351 Layout Information (Continued) DS100146-15 B. Actual Size of the Layout DS100146-14 A. Copper side (5X) DS100146-16 C. Copper side with Component Locations (5X) FIGURE 3. Typical Layout 7 www.national.com LM3351 Switched Capacitor Voltage Converter Physical Dimensions inches (millimeters) unless otherwise noted 8-Lead Mini SO (MM) Order Number LM3351MMX or LM3351MM NS Package Number MUA08A 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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