19-1240; Rev 1; 2/04 Switched-Capacitor Voltage Inverters Features The ultra-small MAX870/MAX871 monolithic, CMOS charge-pump inverters accept input voltages ranging from +1.4V to +5.5V. The MAX870 operates at 125kHz, and the MAX871 operates at 500kHz. Their high efficiency (90%) and low operating current (0.7mA for the MAX870) make these devices ideal for both battery-powered and board-level voltage-conversion applications. 5-Pin SOT23-5 Package Oscillator control circuitry and four power MOSFET switches are included on-chip. A typical MAX870/ MAX871 application is generating a -5V supply from a +5V logic supply to power analog circuitry. Both parts come in a 5-pin SOT23-5 package and can deliver 25mA with a voltage drop of 500mV. Require Only Two Capacitors For a similar device with logic-controlled shutdown, refer to the MAX1720/MAX1721. For applications requiring more power, the MAX860 delivers up to 50mA with a voltage drop of 600mV, in a space-saving MAX package. ________________________Applications 99% Voltage Conversion Efficiency Invert Input Supply Voltage 0.7mA Quiescent Current (MAX870) +1.4V to +5.5V Input Voltage Range 25mA Output Current Shutdown Control Ordering Information PART TEMP RANGE PINPACKAGE SOT TOP MARK MAX870EUK -40C to +85C 5 SOT23-5 ABZN MAX871EUK -40C to +85C 5 SOT23-5 ABZO Local -5V Supply from 5V Logic Supply Small LCD Panels Cell Phones Medical Instruments Handy-Terminals, PDAs Battery-Operated Equipment Pin Configuration Typical Operating Circuit 5 IN C1+ 2 INPUT SUPPLY VOLTAGE MAX870 MAX871 3 C1OUT 4 1 NEGATIVE OUTPUT VOLTAGE TOP VIEW OUT 1 IN 2 C1- 3 5 C1+ 4 GND MAX870 MAX871 GND SOT23-5 NEGATIVE VOLTAGE CONVERTER ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com. 1 MAX870/MAX871 General Description Switched-Capacitor Voltage Inverters MAX870/MAX871 ABSOLUTE MAXIMUM RATINGS Continuous Power Dissipation (TA = +70C) SOT23-5 (derate 7.1mW/C above +70C)...................571mW Operating Temperature Range MAX870EUK/MAX871EUK ...............................-40C to +85C Storage Temperature Range .............................-65C to +160C Lead Temperature (soldering, 10s) .................................+300C IN to GND ..............................................................+6.0V to -0.3V OUT to GND ..........................................................-6.0V to +0.3V C1+ ..............................................................(VIN + 0.3V) to -0.3V C1-............................................................(VOUT - 0.3V) to +0.3V OUT Output Current ...........................................................50mA OUT Short Circuit to GND .............................................Indefinite Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (VIN = +5V, C1 = C2 = 1F (MAX870), C1 = C2 = 0.33F (MAX871), TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER CONDITIONS Supply Current TA = +25C (Note 3) Minimum Supply Voltage RLOAD = 10k Maximum Supply Voltage RLOAD = 10k TYP MAX MAX870 0.7 1.0 MAX871 2.7 3.8 TA = +25C 1.4 TA = 0C to + 85C 1.5 TA = +25C Power Efficiency RLOAD = 500k, TA =+25C Voltage Conversion Efficiency RLOAD = , TA =+25C MAX870 81 125 169 MAX871 325 500 675 MAX870 90 MAX871 75 MAX870 98 99.3 MAX871 96 99 MAX870 Output Resistance (Note 1) 1.0 MAX871 C1 = C2 = 1F 20 C1 = C2 = 0.47F 25 C1 = C2 = 0.33F 20 C1 = C2 = 0.22F 25 C1 = C2 = 0.1F 35 TA = 0C to + 85C UNITS mA V 5.5 Oscillator Frequency IOUT = TA = +25C 5mA MIN V kHz % % 50 50 65 Note 1: Capacitor contribution is approximately 20% of the output impedance [ESR + 1 / (pump frequency x capacitance)]. ELECTRICAL CHARACTERISTICS (VIN = +5V, C1 = C2 = 1F (MAX870), C1 = C2 = 0.33F (MAX871), TA = -40C to +85C, unless otherwise noted.) (Note 2) PARAMETER CONDITIONS MIN TYP MAX UNITS Supply Current (Note 3) MAX870 1.3 MAX871 4.4 Minimum Supply-Voltage Range RLOAD = 10k Maximum Supply-Voltage Range RLOAD = 10k Oscillator Frequency 1.6 V 5.5 MAX870 56 194 MAX871 225 775 Output Resistance IOUT = 5mA Voltage Conversion Efficiency RLOAD = 65 MAX870 97 MAX871 95 mA V kHz % Note 2: All -40C to +85C specifications are guaranteed by design. Note 3: The MAX870/MAX871 may draw high supply current during startup, up to the minimum operating supply voltage. To guarantee proper startup, the input supply must be capable of delivering 90mA more than the maximum load current. 2 _______________________________________________________________________________________ Switched-Capacitor Voltage Inverters MAX871 1.0 MAX870 50 40 MAX871 30 MAX870 0.5 20 0 10 45 OUTPUT RESISTANCE () 2.0 50 MAX828/829-02 MAX870/71-TOC01 SUPPLY CURRENT (mA) 2.5 60 OUTPUT RESISTANCE () 3.0 1.5 MAX870 OUTPUT RESISTANCE vs. TEMPERATURE OUTPUT RESISTANCE vs. SUPPLY VOLTAGE MAX870/71 ROC3 SUPPLY CURRENT vs. SUPPLY VOLTAGE 40 VIN = 1.5V 35 30 VIN = 3.3V 25 20 15 VIN = 5.0V 10 5 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 2.0 2.5 3.5 4.0 4.5 5.0 -40 5.5 85 VIN = 1.9V, VOUT = -1.5V 15 350 300 250 200 150 60 1.0 1.5 2.0 2.5 3.0 -40 VIN = 3.15V, VOUT = -2.5V 20 15 VIN = 1.9V, VOUT = -1.5V 5 0 450 400 VIN = 4.75V, VOUT = -4.0V 350 300 VIN = 3.15V, VOUT = -2.5V 250 200 VIN = 1.9V, VOUT = -1.5V 150 CAPACITANCE (F) 2.0 2.5 60 85 0 -0.5 VIN = 2.0V -1.0 -1.5 VIN = 3.3V -2.0 -2.5 -3.0 -3.5 100 -4.0 50 -4.5 VIN = 5.0V -5.0 0 1.5 35 MAX870 OUTPUT VOLTAGE vs. OUTPUT CURRENT MAX870/71 TOC08 500 OUTPUT VOLTAGE RIPPLE (mVp-p) 30 10 TEMPERATURE (C) MAX871 OUTPUT VOLTAGE RIPPLE vs. CAPACITANCE MAX870/871-07 VIN = 4.75V, VOUT = -4.0V 1.0 -15 CAPACITANCE (F) MAX871 OUTPUT CURRENT vs. CAPACITANCE 0.5 VIN = 5.0V 20 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 CAPACITANCE (F) 25 VIN = 3.3V 30 0 0 3.5 OUTPUT VOLTAGE (V) 0.5 40 10 0 0 VIN = 1.5V 50 100 50 5 MAX870/71-TOC06 400 70 MAX870/871-TOC9 20 VIN = 4.75V, VOUT = -4.0V VIN = 3.15V, VOUT = -2.5V VIN = 1.9V, VOUT = -1.5V MAX870/871-05 MAX870/871-04 25 450 OUTPUT RESISTANCE () 30 0 60 MAX871 OUTPUT RESISTANCE vs. TEMPERATURE VIN = 3.15V, VOUT = -2.5V 10 35 MAX870 OUTPUT VOLTAGE RIPPLE vs. CAPACITANCE 35 35 10 MAX870 OUTPUT CURRENT vs. CAPACITANCE VIN = 4.75V, VOUT = -4.0V 0 -15 TEMPERATURE (C) 10 OUTPUT CURRENT (mA) 3.0 SUPPLY VOLTAGE (V) OUTPUT VOLTAGE RIPPLE (mVp-p) OUTPUT CURRENT (mA) 1.5 SUPPLY VOLTAGE (V) 45 40 0 5.5 0 0.5 1.0 1.5 CAPACITANCE (F) 2.0 2.5 0 5 10 15 20 25 30 35 40 45 OUTPUT CURRENT (mA) _______________________________________________________________________________________ 3 MAX870/MAX871 __________________________________________Typical Operating Characteristics (Circuit of Figure 1, VIN = +5V, C1 = C2 = C3, TA = +25C, unless otherwise noted.) ____________________________Typical Operating Characteristics (continued) (Circuit of Figure 1, VIN = +5V, C1 = C2 = C3, TA = +25C, unless otherwise noted.) VIN = 5.0V VIN = 2.0V 60 70 EFFICIENCY (%) VIN = 3.3V 70 50 40 500 60 VIN = 3.3V VIN = 2.0V 50 40 450 350 300 30 20 20 200 10 10 150 0 0 5 10 15 20 25 30 35 40 45 50 VIN = 1.5V, MAX871 400 30 0 VIN = 3.3V OR 5.0V, MAX871 550 PUMP FREQUENCY (kHz) 80 VIN = 5.0V 80 PUMP FREQUENCY vs. TEMPERATURE 600 MAX870/71 TOC11 90 90 MAX870/71-TOC10 100 MAX871 EFFICIENCY vs. OUTPUT CURRENT VIN = 1.5V, MAX870 250 VIN = 3.3V OR 5.0V, MAX870 100 0 5 10 OUTPUT CURRENT (mA) 15 20 25 30 35 -40 40 -15 10 35 60 TEMPERATURE (C) OUTPUT CURRENT (mA) MAX870 OUTPUT NOISE AND RIPPLE MAX870/71-TCC14 MAX870/71-TCC13 MAX871 OUTPUT NOISE AND RIPPLE 2s/div 1s/div VIN = 3.3V, VOUT = -3.18V, IOUT = 5mA, 20mV/div, AC COUPLED VIN = 3.3V, VOUT = -3.14V, IOUT = 5mA, 20mV/div, AC COUPLED _____________________Pin Description PIN NAME 1 OUT 2 IN 3 C1- 4 GND Ground 5 C1+ Flying Capacitor's Positive Terminal VIN C3 0.33F* FUNCTION RL VOUT Inverting Charge-Pump Output 1 Positive Power-Supply Input 2 Flying Capacitor's Negative Terminal C1+ OUT 5 C2 0.33F* IN MAX870 MAX871 3 C1- GND 4 *1F (MAX870) VOLTAGE INVERTER Figure 1. Test Circuit 4 MAX870/71-TOC12 MAX870 EFFICIENCY vs. OUTPUT CURRENT EFFICIENCY (%) MAX870/MAX871 Switched-Capacitor Voltage Inverters _______________________________________________________________________________________ C1 0.33F* 85 Switched-Capacitor Voltage Inverters The MAX870/MAX871 capacitive charge pumps invert the voltage applied to their input. For highest performance, use low equivalent series resistance (ESR) capacitors (e.g., ceramic). During the first half-cycle, switches S2 and S4 open, switches S1 and S3 close, and capacitor C1 charges to the voltage at IN (Figure 2). During the second halfcycle, S1 and S3 open, S2 and S4 close, and C1 is level shifted downward by VIN volts. This connects C1 in parallel with the reservoir capacitor C2. If the voltage across C2 is smaller than the voltage across C1, then charge flows from C1 to C2 until the voltage across C2 reaches -VIN. The actual voltage at the output is more positive than -VIN, since switches S1-S4 have resistance and the load drains charge from C2. Charge-Pump Output The MAX870/MAX871 are not voltage regulators: the charge pump's output source resistance is approximately 20 at room temperature (with VIN = +5V), and VOUT approaches -5V when lightly loaded. VOUT will droop toward GND as load current increases. The droop of the negative supply (VDROOP-) equals the current draw from OUT (IOUT) times the negative converter's source resistance (RS-): VDROOP- = IOUT x RSThe negative output voltage will be: VOUT = -(VIN - VDROOP-) Efficiency Considerations The efficiency of the MAX870/MAX871 is dominated by its quiescent supply current (IQ) at low output current and by its output impedance (ROUT) at higher output current; it is given by: x ROUT IOUT I 1 - OUT IOUT + IQ VIN S1 S2 IN C1 S3 C2 S4 VOUT = -(VIN) Figure 2. Ideal Voltage Inverter where the output impedance is roughly approximated by: ROUT 1 (fOSC ) x C1 + 2RSW + 4ESRC1 + ESRC2 The first term is the effective resistance of an ideal switched-capacitor circuit (Figures 3a and 3b), and RSW is the sum of the charge pump's internal switch resistances (typically 8 to 9 at VIN = +5V). The typical output impedance is more accurately determined from the Typical Operating Characteristics. __________Applications Information Capacitor Selection To maintain the lowest output resistance, use capacitors with low ESR (Table 1). The charge-pump output resistance is a function of C1's and C2's ESR. Therefore, minimizing the charge-pump capacitor's ESR minimizes the total output resistance. f REQUIV V+ VOUT C1 MAX870/MAX871 _______________Detailed Description C2 Figure 3a. Switched-Capacitor Model RL V+ VOUT 1 REQUIV = f x C1 C2 RL Figure 3b. Equivalent Circuit _______________________________________________________________________________________ 5 MAX870/MAX871 Switched-Capacitor Voltage Inverters Flying Capacitor (C1) Increasing the flying capacitor's size reduces the output resistance. Small C1 values increase the output resistance. Above a certain point, increasing C1's capacitance has a negligible effect, because the output resistance becomes dominated by the internal switch resistance and capacitor ESR. Output Capacitor (C2) Increasing the output capacitor's size reduces the output ripple voltage. Decreasing its ESR reduces both output resistance and ripple. Smaller capacitance values can be used with light loads if higher output ripple can be tolerated. Use the following equation to calculate the peak-to-peak ripple: VRIPPLE = IOUT + 2 x IOUT x ESRC2 fOSC x C2 Input Bypass Capacitor Bypass the incoming supply to reduce its AC impedance and the impact of the MAX870/MAX871's switching noise. The recommended bypassing depends on the circuit configuration and on where the load is connected. When the inverter is loaded from OUT to GND, current from the supply switches between 2 x IOUT and zero. Therefore, use a large bypass capacitor (e.g., equal to the value of C1) if the supply has a high AC impedance. When the inverter is loaded from IN to OUT, the circuit draws 2 x IOUT constantly, except for short switching spikes. A 0.1F bypass capacitor is sufficient. Voltage Inverter The most common application for these devices is a charge-pump voltage inverter (Figure 1). This application requires only two external components--capacitors C1 and C2--plus a bypass capacitor, if necessary. Refer to the Capacitor Selection section for suggested capacitor types. Cascading Devices Two devices can be cascaded to produce an even larger negative voltage (Figure 4). The unloaded output voltage is normally -2 x VIN, but this is reduced slightly by the output resistance of the first device multiplied by the quiescent current of the second. When cascading more than two devices, the output resistance rises dramatically. For applications requiring larger negative voltages, see the MAX864 and MAX865 data sheets. The maximum load current and startup current of the nth cascaded circuit must not exceed the maximum output current capability of the (n-1)th circuit to ensure proper stability. Table 1. Low-ESR Capacitor Manufacturers PRODUCTION METHOD Surface-Mount Tantalum Surface-Mount Ceramic MANUFACTURER SERIES PHONE FAX AVX TPS series (803) 946-0690 (803) 626-3123 Matsuo 267 series (714) 969-2491 (714) 960-6492 Sprague 593D, 595D series (603) 224-1961 (603) 224-1430 AVX X7R (803) 946-0690 (803) 626-3123 Matsuo X7R (714) 969-2491 (714) 960-6492 Table 2. Capacitor Selection for Minimum Output Resistance or Capacitor Size 6 CAPACITORS TO MINIMIZE OUTPUT RESISTANCE (RO = 23, TYP) C1 = C2 CAPACITORS TO MINIMIZE SIZE (RO = 40, TYP) C1 = C2 PART fOSC MAX870 125kHz 1F 0.33F MAX871 500kHz 0.33F 0.1F _______________________________________________________________________________________ Switched-Capacitor Voltage Inverters MAX870/MAX871 ... ... 2 4 5 2 2 3 C1 +VIN +VIN 3 MAX870 MAX871 "1" 4 C1 1 5 2 3 3 MAX870 MAX871 "n" C1 1 ... 4 5 VOUT MAX870 MAX871 "1" 1 5 C2 1 VOUT ... C2 ROUT OF SINGLE DEVICE ROUT = NUMBER OF DEVICES VOUT = -nVIN Figure 4. Cascading MAX870s or MAX871s to Increase Output Voltage MAX870 MAX871 "n" 4 C1 VOUT = -VIN C2 Figure 5. Paralleling MAX870s or MAX871s to Reduce Output Resistance Paralleling Devices Paralleling multiple MAX870s or MAX871s reduces the output resistance. Each device requires its own pump capacitor (C1), but the reservoir capacitor (C2) serves all devices (Figure 5). Increase C2's value by a factor of n, where n is the number of parallel devices. Figure 5 shows the equation for calculating output resistance. +VIN 3 C1 D1, D2 = 1N4148 2 4 MAX870 MAX871 5 D1 1 VOUT = -VIN Combined Doubler/Inverter In the circuit of Figure 6, capacitors C1 and C2 form the inverter, while C3 and C4 form the doubler. C1 and C3 are the pump capacitors; C2 and C4 are the reservoir capacitors. Because both the inverter and doubler use part of the charge-pump circuit, loading either output causes both outputs to decline toward GND. Make sure the sum of the currents drawn from the two outputs does not exceed 40mA. C2 D2 C3 C4 VOUT = (2VIN) (VFD1) - (VFD2) Figure 6. Combined Doubler and Inverter Heavy Output Current Loads Under heavy loads, where higher supply is sourcing current into OUT, the OUT supply must not be pulled above ground. Applications that sink heavy current into OUT require a Schottky diode (1N5817) between GND and OUT, with the anode connected to OUT (Figure 7). GND MAX870 MAX871 Layout and Grounding Good layout is important, primarily for good noise performance. To ensure good layout, mount all components as close together as possible, keep traces short to minimize parasitic inductance and capacitance, and use a ground plane. 4 OUT 1 Figure 7. High V- Load Current _______________________________________________________________________________________ 7 Shutdown Control For a similar device with logic-controlled shutdown, please refer to the MAX1720/MAX1721. To add manual shutdown control to the MAX870/MAX871, use the circuit in Figure 8. The output resistance of the MAX870/ MAX871 will typically be 20 plus two times the output resistance of the buffer driving IN. The 0.1F capacitor at the IN pin absorbs the transient input currents of the MAX870/MAX871. The output resistance of the buffer driving the IN pin can be reduced by connecting multiple buffers in parallel. The polarity of the shutdown signal can also be changed by using a noninverting buffer to drive IN. INPUT 3 C1 5 4 IN C1- CIN 0.1F MAX870 C1+ MAX871 GND SHUTDOWN LOGIC SIGNAL 2 OFF ON OUT 1 OUTPUT C2 Figure 8. Shutdown Control ___________________Chip Information TRANSISTOR COUNT: 58 Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.) SOT-23 5L .EPS MAX870/MAX871 Switched-Capacitor Voltage Inverters PACKAGE OUTLINE, SOT-23, 5L 21-0057 E 1 1 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. 8 ___________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600 (c) 2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.