19-0495; Rev 2; 4/97 Switched-Capacitor Voltage Inverters ________________________Applications Small LCD Panels Cell Phones Medical Instruments Handy-Terminals, PDAs ____________________________Features ♦ 5-Pin SOT23-5 Package ♦ 95% Voltage Conversion Efficiency ♦ Inverts Input Supply Voltage ♦ 60µA Quiescent Current (MAX828) ♦ +1.5V to +5.5V Input Voltage Range ♦ Requires Only Two Capacitors ♦ 25mA Output Current ______________Ordering Information PART TEMP. RANGE MAX828C/D 0°C to +70°C MAX828EUK -40°C to +85°C MAX829C/D 0°C to +70°C MAX829EUK -40°C to +85°C PINPACKAGE SOT TOP MARK — Dice* 5 SOT23-5 Dice* AABI — 5 SOT23-5 AABJ * Dice are tested at TA = +25°C. Battery-Operated Equipment __________Typical Operating Circuit __________________Pin Configuration TOP VIEW 5 IN C1+ 2 INPUT SUPPLY VOLTAGE MAX828 MAX829 3 1 IN 2 C1- 3 5 C1+ 4 GND MAX828 MAX829 C1OUT 4 OUT 1 GND NEGATIVE OUTPUT VOLTAGE SOT23-5 NEGATIVE VOLTAGE CONVERTER ________________________________________________________________ Maxim Integrated Products 1 For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800. For small orders, phone 408-737-7600 ext. 3468. MAX828/MAX829 _______________General Description The ultra-small MAX828/MAX829 monolithic, CMOS charge-pump inverters accept input voltages ranging from +1.5V to +5.5V. The MAX828 operates at 12kHz, and the MAX829 operates at 35kHz. Their high efficiency (greater than 90% over most of the load-current range) and low operating current (60µA for the MAX828) make these devices ideal for both battery-powered and boardlevel voltage-conversion applications. The MAX828/MAX829 combine low quiescent current and high efficiency. Oscillator control circuitry and four power MOSFET switches are included on-chip. Applications include 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. For applications requiring more power, the MAX860 delivers up to 50mA with a voltage drop of 600mV, in a space-saving µMAX package. MAX828/MAX829 Switched-Capacitor Voltage Inverters ABSOLUTE MAXIMUM RATINGS IN to GND .................................................................+6.0V, -0.3V OUT to GND .............................................................-6.0V, +0.3V OUT Output Current ...........................................................50mA OUT Short-Circuit to GND ............................................Indefinite Continuous Power Dissipation (TA = +70°C) SOT23-5 (derate 7.1mW/°C above +70°C)...................571mW Operating Temperature Range MAX828EUK/MAX829EUK ...............................-40°C to +85°C Storage Temperature Range .............................-65°C to +160°C Lead Temperature (soldering, 10sec) .............................+300°C 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 = 10µF (MAX828), C1 = C2 = 3.3µF (MAX829), TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS Supply Current TA = +25°C Minimum Supply Voltage RLOAD = 10kΩ Maximum Supply Voltage RLOAD = 10kΩ Oscillator Frequency TA = +25°C Power Efficiency RLOAD = 10kΩ, TA = +25°C Voltage Conversion Efficiency RLOAD = ∞ Output Resistance IOUT = 5mA TYP MAX MAX828 MIN 60 90 MAX829 150 260 TA = +25°C 1.25 TA = 0°C to + 85°C 1.5 1.0 MAX828 8.4 12 15.6 MAX829 24.5 35 45.5 98 95 TA = 0°C to + 85°C V kHz % 99.9 20 µA V 5.5 TA = +25°C UNITS % 50 65 Ω Note 1: Capacitor contribution is approximately 20% of the output impedance [ESR + 1 / (pump frequency x capacitance)]. ELECTRICAL CHARACTERISTICS (VIN = +5V, C1 = C2 = 10µF (MAX828), C1 = C2 = 3.3µF (MAX829), TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 2) PARAMETER Supply Current Supply Voltage Range Oscillator Frequency Output Resistance CONDITIONS MIN TYP 115 MAX829 325 RLOAD = 10kΩ 1.5 5.5 MAX828 6 20 MAX829 19 54.3 IOUT = 5mA Note 2: All -40°C to +85°C specifications above are guaranteed by design. 2 MAX MAX828 _______________________________________________________________________________________ 65 UNITS µA V kHz Ω Switched-Capacitor Voltage Inverters 20 MAX828 15 10 MAX828/829-02 35 30 25 VIN = 3.3V 20 VIN = 5.0V 1.5 2.5 3.5 4.5 VIN = 3.15V, VOUT = -2.5V 30 25 20 15 VIN = 1.9V, VOUT = -1.5V 10 0 -40 5.5 35 5 10 0 -20 0 20 40 60 80 0 5 10 15 20 25 30 35 40 45 50 TEMPERATURE (°C) CAPACITANCE (µF) MAX829 OUTPUT CURRENT vs. CAPACITANCE MAX828 OUTPUT VOLTAGE RIPPLE vs. CAPACITANCE MAX829 OUTPUT VOLTAGE RIPPLE vs. CAPACITANCE 35 VIN = 3.15V, V- = -2.5V 25 20 VIN = 1.9V, V- = -1.5V 15 10 5 400 350 300 250 200 150 100 50 450 0 0 5 10 15 20 25 300 250 200 150 100 50 5 10 15 20 25 30 0 5 10 15 20 25 30 CAPACITANCE (µF) CAPACITANCE (µF) CAPACITANCE (µF) SUPPLY CURRENT vs. SUPPLY VOLTAGE MAX828 PUMP FREQUENCY vs. TEMPERATURE MAX829 PUMP FREQUENCY vs. TEMPERATURE 60 MAX828/829-07 PUMP FREQUENCY (kHz) 175 150 125 55 MAX829 100 75 MAX828 50 45 40 VIN = 1.5V 35 30 25 VIN = 3.3V 20 25 55 PUMP FREQUENCY (kHz) 200 50 350 0 0 30 MAX828/829-08 0 VIN = 4.75V, VOUT = -4.0V VIN = 3.15V, VOUT = -2.5V VIN = 1.9V, VOUT = -1.5V 400 MAX828/829-9 30 VIN = 4.75V, VOUT = -4.0V VIN = 3.15V, VOUT = -2.5V VIN = 1.9V, VOUT = -1.5V 450 OUTPUT VOLTAGE RIPPLE (mVp-p) 40 500 MAX828/829-05 VIN = 4.75V, V- = -4.0V OUTPUT VOLTAGE RIPPLE (mVp-p) MAX828/829-04 SUPPLY VOLTAGE (V) 45 OUTPUT CURRENT (mA) VIN = 1.5V 15 5 SUPPLY CURRENT (µA) 40 VIN = 4.75V, VOUT = -4.0V 40 MAX828/829-06 MAX829 45 OUTPUT CURRENT (mA) 30 25 45 OUTPUT RESISTANCE (Ω) 35 OUTPUT RESISTANCE (Ω) 50 MAX828/829-01 40 MAX828 OUTPUT CURRENT vs. CAPACITANCE MAX828/829-03 OUTPUT RESISTANCE vs. TEMPERATURE OUTPUT RESISTANCE vs. SUPPLY VOLTAGE 50 VIN = 1.5V 45 40 VIN = 3.3V 35 VIN = 5.0V 15 0 2.5 3.5 4.5 SUPPLY VOLTAGE (V) 5.5 VIN = 5.0V 30 10 1.5 -40 -20 0 20 40 TEMPERATURE (°C) 60 80 -40 -20 0 20 40 60 80 TEMPERATURE (°C) _______________________________________________________________________________________ 3 MAX828/MAX829 __________________________________________Typical Operating Characteristics (Circuit of Figure 1, VIN = +5V, C1 = C2 = C3, TA = +25°C, unless otherwise noted.) ____________________________Typical Operating Characteristics (continued) (Circuit of Figure 1, VIN = +5V, C1 = C2 = C3, TA = +25°C, unless otherwise noted.) OUTPUT VOLTAGE vs. OUTPUT CURRENT -0.5 VIN = 3.3V -2.5 -3.5 80 EFFICIENCY (%) VIN = 2.0V -1.5 VIN = 5.0V 90 VIN = 3.3V VIN = 2.0V 70 MAX828/829-11 EFFICIENCY vs. OUTPUT CURRENT 100 MAX828/829-10 0.5 OUTPUT VOLTAGE (V) 60 50 40 30 VIN = 5.0V 20 -4.5 10 0 -5.5 5 0 10 15 20 25 30 35 40 45 50 5 10 15 20 25 30 35 40 45 50 OUTPUT CURRENT (mA) OUTPUT CURRENT (mA) MAX828 OUTPUT NOISE AND RIPPLE MAX829 OUTPUT NOISE AND RIPPLE MAX828/829-13 0 MAX828/829-12 MAX828/MAX829 Switched-Capacitor Voltage Inverters VOUT 20mV/div VOUT 20mV/div 10µs/div 20µs/div VIN = 3.3V, VOUT = -3.2V, IOUT = 5mA, AC COUPLED VIN = 3.3V, VOUT = -3.2V, IOUT = 5mA, AC COUPLED _____________________Pin Description PIN NAME 1 OUT 2 IN 3 C1- 4 GND Ground 5 C1+ Flying Capacitor’s Positive Terminal VIN C3 3.3µF* FUNCTION RL VOUT Inverting Charge-Pump Output 1 Positive Power-Supply Input 2 Flying Capacitor’s Negative Terminal C1+ OUT 5 C2 3.3µF* IN MAX828 MAX829 3 C1- GND 4 *10µF (MAX828) VOLTAGE INVERTER Figure 1. Test Circuit 4 _______________________________________________________________________________________ C1 3.3µF* Switched-Capacitor Voltage Inverters S1 Charge-Pump Output VDROOP- = IOUT x RSThe negative output voltage will be: VOUT = -(VIN - VDROOP-) C1 C2 S3 ΣPLOSS = PINTERNAL LOSSES + PSWITCH LOSSES + PPUMP CAPACITOR LOSSES + PCONVERSION LOSSES S4 VOUT = -(VIN) Figure 2. Ideal Voltage Inverter The internal losses are associated with the IC’s internal functions, such as driving the switches, oscillator, etc. These losses are affected by operating conditions such as input voltage, temperature, and frequency. The next two losses are associated with the voltage converter circuit’s output resistance. Switch losses occur because of the on-resistance of the MOSFET switches in the IC. Charge-pump capacitor losses occur because of their ESR. The relationship between these losses and the output resistance is as follows: Efficiency Considerations The power efficiency of a switched-capacitor voltage converter is affected by three factors: the internal losses in the converter IC, the resistive losses of the pump capacitors, and the conversion losses during charge transfer between the capacitors. The total power loss is: S2 IN 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. The MAX828/MAX829 are not voltage regulators: the charge pump’s output source resistance is approximately 20Ω 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-): P PUMP CAPACITOR LOSSES 2 = I xR OUT OUT R OUT ≅ 1 (fOSC ) x C1 ( + 4 2R + P CONVERSION LOSSES SWITCHES + ESR C1 ) + ESRC2 where fOSC is the oscillator frequency. The first term is the effective resistance from an ideal switchedcapacitor circuit. See Figures 3a and 3b. f REQUIV V+ VOUT V+ VOUT 1 REQUIV = f × C1 C1 MAX828/MAX829 _______________Detailed Description The MAX828/MAX829 capacitive charge pumps invert the voltage applied to their input. For highest performance, use low equivalent series resistance (ESR) capacitors. C2 Figure 3a. Switched-Capacitor Model RL C2 RL Figure 3b. Equivalent Circuit _______________________________________________________________________________________ 5 MAX828/MAX829 Switched-Capacitor Voltage Inverters Conversion losses occur during the charge transfer between C1 and C2 when there is a voltage difference between them. The power loss is: 2 2 PCONV.LOSS = [1/ 2 C1 VIN − VOUT + 2 1/ 2 C2 VRIPPLE − 2VOUT VRIPPLE ] x fOSC __________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. 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: V RIPPLE = IOUT fOSC x C2 + 2 x I OUT x ESR C2 Input Bypass Capacitor Bypass the incoming supply to reduce its AC impedance and the impact of the MAX828/MAX829’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 0.1µF 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 and values. 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. Paralleling Devices Paralleling multiple MAX828s or MAX829s 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. The equation for calculating output resistance is also shown in Figure 5. Table 1. Low-ESR Capacitor Manufacturers MANUFACTURER AVX Matsuo Sanyo Sprague 6 PHONE FAX DEVICE TYPE (803) 946-0690 (800) 282-4975 (803) 626-3123 Surface-mount, TPS series Surface-mount, 267 series (714) 969-2491 (714) 960-6492 USA (619) 661-6835 (619) 661-1055 Japan 81-7-2070-6306 81-7-2070-1174 (603) 224-1961 (603) 224-1430 Through-hole, OS-CON series Surface-mount, 595D series _______________________________________________________________________________________ Switched-Capacitor Voltage Inverters 2 3 +VIN 3 4 C1 … +VIN 2 MAX828 MAX829 “1” 5 1 2 2 4 C1 MAX828/MAX829 ROUT OF SINGLE DEVICE ROUT = NUMBER OF DEVICES … MAX828 MAX829 “n” 5 3 3 1 … VOUT C2 C1 4 5 MAX870 MAX871 “1” 4 C1 1 5 MAX870 MAX871 “n” 1 VOUT C2 … VOUT = -nVIN VOUT = -VIN Figure 4. Cascading MAX828s or MAX829s to Increase Output Voltage C2 Figure 5. Paralleling MAX828s or MAX829s to Reduce Output Resistance +VIN 3 C1 D1, D2 = 1N4148 2 GND 4 4 MAX828 MAX829 5 D1 1 VOUT = -VIN MAX870 MAX871 C2 D2 C3 C4 OUT VOUT = (2VIN) (VFD1) - (VFD2) Figure 6. Combined Doubler and Inverter 1 Figure 7. High V- Load Current Combined Doubler/Inverter Heavy Output Current Loads 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. When 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). 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. _______________________________________________________________________________________ 7 MAX828/MAX829 Switched-Capacitor Voltage Inverters Shutting Down the MAX828/MAX829 If shutdown is necessary, use the circuit in Figure 8. The output resistance of the MAX828/MAX829 will typically be 20Ω plus two times the output resistance of the buffer driving IN. The 0.1µF capacitor at the IN pin absorbs the transient input currents of the MAX828/MAX829. 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 C1- IN CIN 0.1µF MAX828 C1+ MAX829 GND SHUTDOWN LOGIC SIGNAL 2 OFF ON OUT 1 OUTPUT C2 Figure 8. Shutdown Control ___________________Chip Topography C1+ IN OUT 0.057" (1.45mm) GND C1- 0.038" (0.965mm) TRANSISTOR COUNT: 58 SUBSTRATE CONNECTED TO IN 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 © 1997 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.