AMS682EP

Advanced Monolithic Systems FEATURES • 99.9% Voltage Conversion Efficiency • 92% Power Conversion Efficiency • Wide Input Voltage Range +2.4V to 5.5V • 185µA Supply Current • Available in SO-8 and PDIP Packages • Only 3 external Capacitors Required AMS682 INVERTING VOLTAGE DOUBLER RoHS compliant APPLICATIONS • Portable Handheld Instrumentation • Cellular Phones • Panel Meters • -10V from +5V logic Supply • -6V from a Single 3V Lithium Cell • LCD Display Bias Generator • Operational Amplifiers Power Supplies GENERAL DESCRIPTION The AMS682 is a CMOS charge pump converter that provides an inverted doubled output from a single positive supply. Requiring only three external capacitors for full circuit implementation the device has an on -board 12kHz (typical) oscillator which provides the clock. Low output source impedance (typically 140Ω), provides output current up to 10mA. The AMS682 features low quiescent current and high efficiency, making it the ideal choice for a wide variety of applications that require a negative voltage derived from a single positive supply. The compact size and minimum external parts count of the AMS682 makes it useful in many medium current, dual voltage analog power supplies. The AMS682E is operational in the full industrial temperature range of -40°C to 85°C while AMS682C is operating over a 0°C to 70°C temperature range. The AMS682E/AMS682C are available in surface mount 8-Pin SOIC (SO-8) and 8-Pin Plastic DIP (PDIP) packages. ORDERING INFORMATION: PACKAGE TYPE 8 LEAD SOIC AMS682ES AMS682CS 8 LEAD PDIP AMS682EP AMS682CP OPERATING TEMPERATURE RANGE -40 to 85° C 0 to 70° C TYPICAL OPERATING CIRCUIT VIN +2.4V < V IN < +5.5V VIN ON/OFF PIN CONFIGURATIONS 8-LEAD DIP/ 8-LEAD SOIC C-2 1 8 7 ON/OFF C+1 VIN GND + C1 + C2 - C 1+ C 1C 2+ C 2- VOUT = -(2 X VIN) VOUT GND + COUT C+2 2 C-2 VOUT 3 4 AMS682 6 5 VOUT GND All Caps = 3.3µ F Advanced Monolithic Systems, Inc. www.advanced-monolithic.com Phone (925) 443-0722 Fax (925) 443-0723 AMS682 ABSOLUTE MAXIMUM RATINGS VIN VIN ∆V/∆T VOUT VOUT Short Circuit Duration Power Dissipation (TA ≤ 70°C) Plastic DIP SOIC +5.8V 1V/µsec -11.6V Continuous 730mW 470mW Operating Temperature Range AMS682E AMS682C Storage temperature Soldering information Lead Temperature (Soldering 25sec) -40°C to 85°C 0°C to 70°C -85°C to +150°C 265°C ELECTRICAL CHARACTERISTICS Electrical Characteristics at VIN =+5V and TA = +25°C test circuit figure 1, unless otherwise specified. Parameter Supply Voltage Range Supply Current Conditions VIN IIN RL=2kΩ RL = ∞ RL = ∞ 2.4 ⎯ ⎯ ⎯ ⎯ ⎯ ⎯ R L = 2k Ω VOUT RL= ∞ 90 99 Min AMS682 Typ Max ⎯ 185 ⎯ 140 170 5.5 300 400 180 230 320 12 92 99.9 ⎯ ⎯ ⎯ Units V µA VOUT Source Resistance Source Resistance ROUT I = 10mA I =10mA I = 5mA , VIN = 2.8V L L L Ω Oscillator Frequency Power Efficiency Voltage Conversion Efficiency FOSC PEFF VOUTEFF kHz % % PIN DESCRIPTION PIN NO 8-PIN DIP/SOIC 1 2 3 4 5 6 7 8 SYMBOL C1C2+ C2VOUT GND VIN C1+ ON/OFF DESCRIPTION Input. Capacitor C1 negative terminal. Input. Capacitor C2 positive terminal. Input. Capacitor C2 negative terminal Output. Negative output voltage (-2VIN) Input. Device ground. Input. Power supply voltage. Input. Capacitor C1 positive terminal. ON/OFF Oscilator. VIN (+5V) 7 + C1 + C2 3 1 2 6 VIN 8 C1+ ON/OFF C1C2+ C2V-OUT 4 GND 5 V-OUT + COUT RL GND All Caps = 3.3µ F Figure 1. AMS682 Test Circuit Advanced Monolithic Systems, Inc. www.advanced-monolithic.com Phone (925) 443-0722 Fax (925) 443-0723 AMS682 DETAILED DESCRIPTION Phase 1 EFFICIENCY CONSIDERATIONS Theoretically a charge pump voltage multiplier can approach 100% efficiency under the following conditions: • The charge pump switches have virtually no offset and are extremely low on resistance. • Minimal power is consumed by the drive circuitry. • The Impedances of the reservoir and pump capacitors are negligible. For the AMS682, efficiency is as shown below: VSS charge storage- before this phase of the clock cycle, capacitor C1 is already charged to +5V. C1+ is then switched to ground and the charge in C1- is transferred to C2-. Since C2+ is at +5V, the voltage potential across capacitor C2 is now -10V. VIN =+5V SW1 + C1 SW2 -5V + C2 SW3 VOUT SW4 C3 + Voltage Efficiency = VOUT / (-2VIN ) VOUT = -2VIN + VDROP VDROP = (IOUT) (R OUT) Power Loss = IOUT (VDROP) Figure 2. Charge Pump - Phase 1 Phase 2 There will be a substantial voltage difference between VOUT and 2VIN if the impedances of the pump capacitors C1 and C2 are high with respect to their respective output loads. If the values of the reservoir capacitor C3 are larger the output ripple will be reduced. The efficiency will be improved if both pump and reservoir capacitors have larger values. ( See “Capacitor Selection” in Application Section.) VSS transfer- phase two of the clock connects the negative terminal of C2 to the negative side of reservoir capacitor C3 and the positive terminal of C2 to the ground, transferring the generated -10V to C3. Simultaneously, the positive side of capacitor C1 is switched to +5V and the negative side is connected to ground. C2 is then switched to VCC and GND and Phase 1 begins again. VIN =+5V APPLICATIONS Negative Doubling Converter The AMS682 is most commonly used as a charge pump voltage converter which provides a negative output of two times a positive input voltage (Fig.4) VOUT SW1 + C1 SW2 + C2 SW4 SW3 - C3 + C1 + 22 µ F 1 2 -10V C2 + 22 µ F C1- ON/OFF C2+ C2C1+ VIN 8 7 6 5 + C3 22 µ F GND 3 4 VIN Figure 3. Charge Pump - Phase 2 V-OUT GND V-OUT MAXIMUM OPERATING LIMITS The AMS682 has on-chip zener diodes that clamp VIN to approximately 5.8V, and V-OUT to -11.6V. Exceeding the maximum supply voltage will potentially damage the chip. With an input voltage of 2V to 5.5V the AMS682 will operate over the entire operating temperature range. Figure 4. Inverting Voltage Doubler Advanced Monolithic Systems, Inc. www.advanced-monolithic.com Phone (925) 443-0722 Fax (925) 443-0723 AMS682 APPLICATIONS (Continued) Capacitor Selection Paralleling devices The output resistance of the AMS682 is determined in part by the ESR of the capacitors used. An expression for ROUT is derived as shown below: ROUT = 2( RSW1+RSW2+ESRC1+ RSW3+RSW4+ESRC2) +2(RSW1+RSW2+ESRC1+ RSW3+RSW4+ESRC2) +1/ (fPUMP X C1) +1/ (fPUMP X C2) + ESRC3 Assuming all switch resistances are approximately equal: ROUT = 16 RSW+ 4ESRC1+ 4ESRC2+ ESRC3 +1/ (fPUMP X C1) +1/ (fPUMP X C2) ROUT is typically 140Ω at +25°C with VIN =+5V and 3.3µF low ESR capacitors. The fixed term (16RSW) is about 8090Ω. Increasing or decreasing values of C1 and C2 will affect efficiency by changing ROUT. Table 1 shows ROUT for various values of C1 and C2 (assume 0.5Ω ESR). C1 must be rated at 6VDC or greater while C2 and C3 must be rated at 12VDC or greater. Output voltage ripple is affected by C3. Typically the larger the value of C3 the less the ripple for a given load current. The formula for p-p VRIPPLE is : VRIPPLE = [1/[2(fPUMP X C3)]+2(ESRC3)] (IOUT) For a 10µF (0.5Ω ESR), fPUMP = 10kHz and IOUT=10mA the peak -to-peak ripple voltage at the output will be less than 60mV. In most applications (IOUT ≤ 10mA) a 10-20µF capacitor and 1-5µF pump capacitors will be sufficient. Table 2 shows VRIPPLE for different values of C3 (assume 1Ω ESR). Paralleling multiple AMS682 reduces the output resistance of the converter. The effective output resistance is the output resistance of one device divided by the number of devices. Figure 5 illustrates how each device requires separate pump capacitors C1 and C2, but all can share a single reservoir capacitor. -5V Regulated Supply From A Single 3V Battery Figure 6 shows a -5V power supply using one 3V battery. The AMS682 provides -6V at V-OUT , which is regulated to -5V by the negative LDO. The AMS682 input can vary from 3V to 5.5V without affecting regulation significantly. A voltage detector is connected to the battery to detect undervoltage. This unit is set to detect at 2.7V. With higher input voltage, more current can be drawn from the outputs of the AMS682. With 5V at VIN , 10mA can be drawn from the regulated output. Assuming 150Ω source resistance for the converter, with IL=10mA, the charge pump will drop 1.5V. Table 1. ROUT vs. C1, C2 C1, C2 (µF) 0.05 0.10 0.47 1.00 3.30 5.00 10.00 22.00 100.00 ROUT (Ω) 4085 2084 510 285 145 125 105 94 87 Table 2. VRIPPLE Peak-to-Peak vs. C3 (IOUT =10mA) VRIPPLE (mV) C3(µF) 0.50 1020 1.00 520 3.30 172 5.00 120 10.00 70 22.00 43 100.00 25 Advanced Monolithic Systems, Inc. www.advanced-monolithic.com Phone (925) 443-0722 Fax (925) 443-0723 AMS682 APPLICATIONS (Continued) VIN + 10 µ F + VIN C1+ C1C2+ C2GND 10 µ F 10 µ F 10 µ F + + - VIN C1+ C1C2+ C2GND V-OUT V-OUT C-OUT 22 µ F NEGATIVE SUPPLY + GND Figure 5. Paralleling AMS682 for Lower Output Source Resistance 10µ F + 3V 10µ F + + - VIN C1+ C1C2+ C2- V-OUT GND VSS VIN VOUT + - GROUND 1µ F -5 SUPPLY + 22µ F C-OUT NEG. LDO VOLTAGE DETECT. VOUT VIN VSS LOW BATTERY Figure 6. Negative Supply Derived from 3V Battery Advanced Monolithic Systems, Inc. www.advanced-monolithic.com Phone (925) 443-0722 Fax (925) 443-0723 AMS682 TYPICAL PERFORMANCE CHARACTERISTICS (FOSC = 12kHz) VOUT vs. Load Current 240 Output Resistance vs. V OUTPUT RESISTANCE (Ω) -7.5 -8.0 -8.5 VIN = 5V IN C1-C3 = 3.3 µF 220 200 180 160 140 120 VOUT (V) -9.0 -9.5 -10.0 -10.5 0 5 10 15 1 2 3 4 5 6 LOAD CURRENT Output Source Resistance vs. Temperature OUTPUT SOURCE RESISTANCE ( Ω ) 200 180 160 140 120 100 80 -50 0 50 100 VIN = 5V IOUT = 10mA 300 NO LOAD VIN (V) Supply Current vs. VIN SUPPLY CURRENT ( µA) 250 200 150 100 50 1 2 3 VIN (V) 4 5 6 TEMPERATURE (°C) Output Ripple vs. Output Current 200 OUTPUT RIPPLE (mV PK-PK) 150 VIN = 5V C3 = 10 µF 100 50 C3 = 100 µF 0 0 5 10 15 20 OUTPUT CURRENT (mA) Advanced Monolithic Systems, Inc. www.advanced-monolithic.com Phone (925) 443-0722 Fax (925) 443-0723 AMS682 PACKAGE DIMENSIONS inches (millimeters) unless otherwise noted. 8 LEAD SOIC PLASTIC PACKAGE (S) 0.189-0.197* (4.801-5.004) 8 7 6 5 0.228-0.244 (5.791-6.197) 0.150-0.157** (3.810-3.988) 1 2 3 4 0.053-0.069 (1.346-1.752) 0.004-0.010 (0.101-0.254) 0.008-0.010 (0.203-0.254) 0.010-0.020 x 45° (0.254-0.508) 0°-8° TYP 0.014-0.019 (0.355-0.483) 0.050 (1.270) TYP 0.016-0.050 (0.406-1.270) S (SO-8 ) AMS DRW# 042293 *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE 8 LEAD PLASTIC DIP PACKAGE (P) 0.400* (10.160) MAX 8 7 6 5 0.255±0.015* (6.477±0.381) 1 2 3 4 0.045-0.065 (1.143-1.651) 0.130±0.005 (3.302±0.127) 0.300-0.325 (7.620-8.255) 0.065 (1.651) TYP 0.005 (0.127) MIN 0.100±0.010 (2.540±0.254) 0.125 (3.175) MIN 0.018±0.003 (0.457±0.076) 0.015 (0.380) MIN 0.009-0.015 (0.229-0.381) 0.325 +0.025 -0.015 (8.255 +0.635 ) -0.381 P (8L PDIP ) AMS DRW# 042294 *DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTUSIONS. MOLD FLASH OR PROTUSIONS SHALL NOT EXCEED 0.010" (0.254mm) Advanced Monolithic Systems, Inc. www.advanced-monolithic.com Phone (925) 443-0722 Fax (925) 443-0723