10 μA, Rail-to-Rail I/O, Zero Input Crossover Distortion Amplifiers ADA4505-2/ADA4505-4 PIN CONFIGURATIONS OUT A 1 8 V+ –IN A 2 ADA4505-2 7 OUT B +IN A 3 TOP VIEW (Not to Scale) 6 –IN B 5 +IN B V– 4 07416-004 PSRR: 100 dB minimum CMRR: 105 dB typical Very low supply current: 10 μA per amplifier maximum 1.8 V to 5 V single-supply or ±0.9 V to ±2.5 V dual-supply operation Rail-to-rail input and output 3 mV offset voltage maximum Very low input bias current: 0.5 pA typical Figure 1. 8-Lead MSOP (RM-8) BALL A1 CORNER APPLICATIONS OUT B V+ A1 A2 –IN B Pressure and position sensors Remote security Medical monitors Battery-powered consumer equipment Hazard detectors OUT A A3 –IN A B1 B3 +IN B V– +IN A C1 C2 C3 ADA4505-2 TOP VIEW (BALL SIDE DOWN) 07416-003 FEATURES 14 OUT D 13 –IN D 12 +IN D 11 V– +IN B 5 10 +IN C –IN B 6 9 –IN C OUT B 7 8 OUT C OUT A 1 –IN A 2 +IN A 3 V+ 4 ADA4505-4 TOP VIEW (Not to Scale) 07416-005 Figure 2. 8-Ball WLCSP (CB-8-2) Figure 3. 14-Lead TSSOP (RU-14) GENERAL DESCRIPTION The ADA4505-2/ADA4505-4 are dual and quad micropower amplifiers featuring rail-to-rail input and output swings while operating from a single 1.8 V to 5 V power supply or from dual ±0.9 V to ±2.5 V power supplies. Employing a new circuit technology, these low cost amplifiers offer zero input crossover distortion (excellent PSRR and CMRR performance) and very low bias current, while operating with a supply current of less than 10 μA per amplifier. This combination of features makes the ADA4505-2/ADA4505-4 amplifiers ideal choices for battery-powered applications because they minimize errors due to power supply voltage variations over the lifetime of the battery, and maintain high CMRR even for a rail-to-rail op amp. Remote battery-powered sensors, handheld instrumentation and consumer equipment, hazard detectors (for example, smoke, fire, and gas), and patient monitors can benefit from the features of the ADA4505-2/ADA4505-4 amplifiers. The ADA4505-2/ADA4505-4 are specified for both the industrial temperature range (−40°C to +85°C) and the extended industrial temperature range (−40°C to +125°C). The ADA4505-2 dual amplifier is available in standard 8-lead MSOP and 8-ball WLCSP packages. The ADA4505-4 quad amplifier is available in a 14-lead TSSOP package. The ADA4505-2/ADA4505-4 are members of a growing series of zero crossover op amps offered by Analog Devices, Inc., including the AD8506/AD8508, which also operate from a single 1.8 V to 5 V power supply or from dual ±0.9 V to ±2.5 V power supplies. Rev. A Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 ©2008 Analog Devices, Inc. All rights reserved. ADA4505-2/ADA4505-4 TABLE OF CONTENTS Features .............................................................................................. 1 ESD Caution...................................................................................5 Applications ....................................................................................... 1 Typical Performance Characteristics ..............................................6 Pin Configurations ........................................................................... 1 Theory of Operation ...................................................................... 14 General Description ......................................................................... 1 Applications Information .............................................................. 16 Revision History ............................................................................... 2 Pulse Oximeter Current Source ............................................... 16 Specifications..................................................................................... 3 Electrical Characteristics—5 V Operation................................ 3 Four-Pole Low-Pass Butterworth Filter for Glucose Monitor ................................................................... 17 Electrical Characteristics—1.8 V Operation ............................ 4 Outline Dimensions ....................................................................... 18 Absolute Maximum Ratings............................................................ 5 Ordering Guide .......................................................................... 19 Thermal Resistance ...................................................................... 5 REVISION HISTORY 10/08—Rev. 0 to Rev. A Added ADA4505-4, 8-Ball WLCSP, and 14-Lead TSSOP .............................................................. Throughout Change to Features Section ............................................................. 1 Added Figure 2 and Figure 3; Renumbered Sequentially ........... 1 Changes to Table 1 ............................................................................ 3 Changes to Table 2 ............................................................................ 4 Changes to Thermal Resistance Section........................................ 5 Changes to Figure 22 and Figure 25 ............................................... 9 Changes to Figure 40 and Figure 43 ............................................. 12 Deleted Figure 46 and Figure 48 ................................................... 13 Change to Theory of Operation Section ..................................... 14 Changes to Figure 52 ...................................................................... 16 Change to Four-Pole Low-Pass Butterworth Filter for Glucose Monitor Section ......................................................... 17 Updated Outline Dimensions ....................................................... 18 Changes to Ordering Guide .......................................................... 19 7/08—Revision 0: Initial Version Rev. A | Page 2 of 20 ADA4505-2/ADA4505-4 SPECIFICATIONS ELECTRICAL CHARACTERISTICS—5 V OPERATION VSY = 5 V, VCM = VSY/2, TA = 25°C, RL = 100 kΩ to GND, unless otherwise specified. Table 1. Parameter INPUT CHARACTERISTICS Offset Voltage Input Bias Current Symbol Test Conditions/Comments VOS 0 V ≤ VCM ≤ 5 V −40°C ≤ TA ≤ +125°C Min IB Typ Max Unit 0.5 3 4 2 50 375 1 25 130 5 mV mV pA pA pA pA pA pA V dB dB dB dB dB μV/°C GΩ pF pF 0.5 −40°C ≤ TA ≤ +85°C −40°C ≤ TA ≤ +125°C Input Offset Current IOS Input Voltage Range Common-Mode Rejection Ratio CMRR Large Signal Voltage Gain AVO Offset Voltage Drift Input Resistance Input Capacitance Differential Mode Input Capacitance Common Mode OUTPUT CHARACTERISTICS Output Voltage High Output Voltage Low ΔVOS/ΔT RIN CINDM CINCM VOH VOL Short-Circuit Limit POWER SUPPLY Power Supply Rejection Ratio ISC Supply Current per Amplifier ISY DYNAMIC PERFORMANCE Slew Rate Gain Bandwidth Product Phase Margin NOISE PERFORMANCE Voltage Noise Voltage Noise Density Current Noise Density PSRR 0.05 −40°C ≤ TA ≤ +85°C −40°C ≤ TA ≤ +125°C −40°C ≤ TA ≤ +125°C 0 V ≤ VCM ≤ 5 V −40°C ≤ TA ≤ +85°C −40°C ≤ TA ≤ +125°C 0.05 V ≤ VOUT ≤ 4.95 V −40°C ≤ TA ≤ +125°C −40°C ≤ TA ≤ +125°C 0 90 90 85 105 100 105 120 2 220 2.5 4.7 RL = 100 kΩ to GND −40°C ≤ TA ≤ +125°C RL = 10 kΩ to GND −40°C ≤ TA ≤ +125°C RL = 100 kΩ to VSY −40°C ≤ TA ≤ +125°C RL = 10 kΩ to VSY −40°C ≤ TA ≤ +125°C VOUT = VSY or GND 4.98 4.98 4.9 4.9 VSY = 1.8 V to 5 V −40°C ≤ TA ≤ +85°C −40°C ≤ TA ≤ +125°C VOUT = VSY/2 −40°C ≤ TA ≤ +125°C 100 100 95 4.99 4.95 2 10 5 5 25 25 ±40 110 7 10 15 V V V V mV mV mV mV mA dB dB dB μA μA SR GBP ΦM RL = 100 kΩ, CL = 20 pF, G = 1 RL = 1 MΩ, CL = 20 pF, G = 1 RL = 1 MΩ, CL = 20 pF, G = 1 6 50 52 mV/μs kHz Degrees en p-p en in f = 0.1 Hz to 10 Hz f = 1 kHz f = 1 kHz 2.95 65 20 μV p-p nV/√Hz fA/√Hz Rev. A | Page 3 of 20 ADA4505-2/ADA4505-4 ELECTRICAL CHARACTERISTICS—1.8 V OPERATION VSY = 1.8 V, VCM = VSY/2, TA = 25°C, RL = 100 kΩ to GND, unless otherwise specified. Table 2. Parameter INPUT CHARACTERISTICS Offset Voltage Input Bias Current Symbol Test Conditions/Comments VOS 0 V ≤ VCM ≤ 1.8 V −40°C ≤ TA ≤ +125°C Min IB Typ Max Unit 0.5 3 4 2 50 375 1 25 130 1.8 mV mV pA pA pA pA pA pA V dB dB dB dB dB μV/°C GΩ pF pF 0.5 −40°C ≤ TA ≤ +85°C −40°C ≤ TA ≤ +125°C Input Offset Current IOS Input Voltage Range Common-Mode Rejection Ratio CMRR Large Signal Voltage Gain AVO Offset Voltage Drift Input Resistance Input Capacitance Differential Mode Input Capacitance Common Mode OUTPUT CHARACTERISTICS Output Voltage High Output Voltage Low ΔVOS/ΔT RIN CINDM CINCM VOH VOL Short-Circuit Limit POWER SUPPLY Power Supply Rejection Ratio ISC Supply Current per Amplifier ISY DYNAMIC PERFORMANCE Slew Rate Gain Bandwidth Product Phase Margin NOISE PERFORMANCE Voltage Noise Voltage Noise Density Current Noise Density PSRR 0.05 −40°C ≤ TA ≤ +85°C −40°C ≤ TA ≤ +125°C −40°C ≤ TA ≤ +125°C 0 V ≤ VCM ≤ 1.8 V −40°C ≤ TA ≤ +85°C −40°C ≤ TA ≤ +125°C 0.05 V ≤ VOUT ≤ 1.75 V −40°C ≤ TA ≤ +125°C −40°C ≤ TA ≤ +125°C 0 85 85 80 95 95 100 115 2.5 220 2.5 4.7 RL = 100 kΩ to GND −40°C ≤ TA ≤ +125°C RL = 10 kΩ to GND −40°C ≤ TA ≤ +125°C RL = 100 kΩ to VSY −40°C ≤ TA ≤ +125°C RL = 10 kΩ to VSY −40°C ≤ TA ≤ +125°C VOUT = VSY or GND 1.78 1.78 1.65 1.65 VSY = 1.8 V to 5 V −40°C ≤ TA ≤ +85°C −40°C ≤ TA ≤ +125°C VOUT = VSY/2 −40°C ≤ TA ≤ +125°C 100 100 95 1.79 1.75 2 12 5 5 25 25 ±3.8 110 7 10 15 V V V V mV mV mV mV mA dB dB dB μA μA SR GBP ΦM RL = 100 kΩ, CL = 20 pF, G = 1 RL = 1 MΩ, CL = 20 pF, G = 1 RL = 1 MΩ, CL = 20 pF, G = 1 6.5 50 52 mV/μs kHz Degrees en p-p en in f = 0.1 Hz to 10 Hz f = 1 kHz f = 1 kHz 2.95 65 20 μV p-p nV/√Hz fA/√Hz Rev. A | Page 4 of 20 ADA4505-2/ADA4505-4 ABSOLUTE MAXIMUM RATINGS THERMAL RESISTANCE Table 3. Parameter Supply Voltage Input Voltage Input Current1 Differential Input Voltage2 Output Short-Circuit Duration to GND Storage Temperature Range Operating Temperature Range Junction Temperature Range Lead Temperature (Soldering, 60 sec) θJA is specified for the worst-case conditions, that is, a device soldered in a circuit board for surface-mount packages. This was measured using a standard 2-layer board, unless otherwise specified. Rating 5.5 V ±VSY ± 0.1 V ±10 mA ±VSY Indefinite −65°C to +150°C −40°C to +125°C −65°C to +150°C 300°C Table 4. Thermal Resistance 1 Input pins have clamp diodes to the supply pins. Input current should be limited to 10 mA or less whenever the input signal exceeds the power supply rail by 0.5 V. 2 Differential input voltage is limited to 5 V or the supply voltage, whichever is less. Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Package Type 8-Lead MSOP (RM-8) 8-Ball WLCSP (CB-8-2) 2-Layer PCB (1SOP) 4-Layer PCB (2SOP) 14-Lead TSSOP (RU-14) 1 Junction-to-board thermal resistance. ESD CAUTION Rev. A | Page 5 of 20 θJA 206 θJB1 N/A θJC 44 Unit °C/W 178 82 180 42 23 N/A N/A N/A 35 °C/W °C/W °C/W ADA4505-2/ADA4505-4 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted. 140 VSY = 5V VCM = VSY/2 120 NUMBER OF AMPLIFIERS 120 100 80 60 40 20 100 80 60 40 1.0 1.5 2.0 2.5 3.0 0 –3.0 –2.5 –2.0 –1.5 –1.0 –0.5 0 0.5 VOS (mV) 07416-007 0 –3.0 –2.5 –2.0 –1.5 –1.0 –0.5 0 0.5 VOS (mV) Figure 4. Input Offset Voltage Distribution 14 10 8 6 4 2.5 3.0 10 8 6 4 2 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 TCVOS (µV/°C) 4.5 5.0 5.5 6.0 0 07416-009 0 0 Figure 5. Input Offset Voltage Drift Distribution 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 TCVOS (µV/°C) 4.5 5.0 5.5 6.0 Figure 8. Input Offset Voltage Drift Distribution 1500 1500 VSY = 5V VSY = 1.8V 1000 DEVICE 1 DEVICE 2 DEVICE 3 DEVICE 4 500 DEVICE 5 DEVICE 6 DEVICE 7 DEVICE 8 DEVICE 9 DEVICE 10 0 –500 DEVICE 1 DEVICE 2 DEVICE 3 500 VOS (µV) 1000 DEVICE 4 DEVICE 5 0 DEVICE 6 DEVICE 7 DEVICE 8 DEVICE 9 –500 DEVICE 10 –1000 0 0.2 0.4 0.6 0.8 1.0 VCM (V) 1.2 1.4 1.6 1.8 07416-011 –1000 –1500 0 1 2 3 VCM (V) Figure 6. Input Offset Voltage vs. Common-Mode Voltage 4 5 07416-012 VOS (µV) 2.0 VSY = 5V –40°C ≤ TA ≤ 125°C 12 NUMBER OF AMPLIFIERS NUMBER OF AMPLIFIERS 14 2 –1500 1.5 Figure 7. Input Offset Voltage Distribution VSY = 1.8V –40°C ≤ TA ≤ 125°C 12 1.0 07416-008 20 07416-010 NUMBER OF AMPLIFIERS 140 VSY = 1.8V VCM = VSY/2 Figure 9. Input Offset Voltage vs. Common-Mode Voltage Rev. A | Page 6 of 20 ADA4505-2/ADA4505-4 TA = 25°C, unless otherwise noted. 1000 1000 VSY = 1.8V 10 10 1 25 50 75 TEMPERATURE (°C) 100 125 0.1 07416-013 0 0 25 1000 1000 100 105°C 10 105°C IB (pA) 85°C 10 85°C 1 1 25°C 0.4 0.6 0.8 1.0 VCM (V) 1.2 1.4 1.6 1.8 0.1 VSY = 1.8V 1k 100 10 1 0.1 1 LOAD CURRENT (mA) 10 100 07416-017 –40°C +25°C +85°C +125°C 0.01 2 3 4 5 Figure 14. Input Bias Current vs. Common-Mode Voltage and Temperature OUTPUT VOLTAGE (VOH) TO SUPPLY RAIL (mV) 10k 0.01 0.001 1 VCM (V) Figure 11. Input Bias Current vs. Common-Mode Voltage and Temperature 0.1 0 07416-016 0.2 07416-014 0 25°C Figure 12. Output Voltage (VOH) to Supply Rail vs. Load Current and Temperature 10k VSY = 5V 1k 100 10 1 –40°C +25°C +85°C +125°C 0.1 0.01 0.001 0.01 0.1 1 LOAD CURRENT (mA) 10 100 Figure 15. Output Voltage (VOH) to Supply Rail vs. Load Current and Temperature Rev. A | Page 7 of 20 07416-018 IB (pA) 125 VSY = 5V IB+ AND IB– 125°C 100 OUTPUT VOLTAGE (VOH) TO SUPPLY RAIL (mV) 100 Figure 13. Input Bias Current vs. Temperature VSY = 1.8V IB+ AND IB– 125°C 50 75 TEMPERATURE (°C) 07416-015 1 Figure 10. Input Bias Current vs. Temperature 0.1 IB+ IB– 100 IB (pA) IB (pA) 100 0.1 VSY = 5V IB+ IB– ADA4505-2/ADA4505-4 TA = 25°C, unless otherwise noted. 10 1 0.01 0.1 1 LOAD CURRENT (mA) 10 10 1 100 –40°C +25°C +85°C +125°C 0.1 0.01 0.001 0.01 0.1 1 LOAD CURRENT (mA) 10 100 Figure 19. Output Voltage (VOL) to Supply Rail vs. Load Current and Temperature 1.800 5.000 OUTPUT VOLTAGE (VOH) TO SUPPLY RAIL (V) Figure 16. Output Voltage (VOL) to Supply Rail vs. Load Current and Temperature RL = 100kΩ 1.795 1.790 1.785 RL = 10kΩ 1.780 VSY = 1.8V 1.775 –40 –25 –10 5 20 35 50 65 TEMPERATURE (°C) 80 95 110 125 4.990 4.980 4.975 VSY = 5V 4.970 –40 OUTPUT VOLTAGE (VOL) TO SUPPLY RAIL (mV) 20 RL = 10kΩ 10 5 RL = 100kΩ –10 5 20 35 50 65 TEMPERATURE (°C) 80 95 110 125 07416-023 OUTPUT VOLTAGE (VOL) TO SUPPLY RAIL (mV) VSY = 1.8V –25 –25 –10 5 20 35 50 65 TEMPERATURE (°C) 80 95 110 125 Figure 20. Output Voltage (VOH) to Supply Rail vs. Temperature 25 0 –40 RL = 10kΩ 4.985 Figure 17. Output Voltage (VOH) to Supply Rail vs. Temperature 15 RL = 100kΩ 4.995 Figure 18. Output Voltage (VOL) to Supply Rail vs. Temperature 25 VSY = 5V 20 RL = 10kΩ 15 10 5 RL = 100kΩ 0 –40 –25 –10 5 20 35 50 65 TEMPERATURE (°C) 80 95 110 125 Figure 21. Output Voltage (VOL) to Supply Rail vs. Temperature Rev. A | Page 8 of 20 07416-024 0.01 0.001 100 07416-019 –40°C +25°C +85°C +125°C 1k 07416-020 100 VSY = 5V 07416-022 1k 0.1 10k OUTPUT VOLTAGE (VOL) TO SUPPLY RAIL (mV) VSY = 1.8V 07416-021 OUTPUT VOLTAGE (VOH) TO SUPPLY RAIL (V) OUTPUT VOLTAGE (VOL) TO SUPPLY RAIL (mV) 10k ADA4505-2/ADA4505-4 TA = 25°C, unless otherwise noted. 180 80 135 60 PHASE 45 GAIN 0 0 PHASE (Degrees) 20 90 –20 –45 –40 –90 –60 –135 –80 –180 –100 100 1k 10k FREQUENCY (Hz) –225 1M 100k 07416-025 40 VSY = 5V 135 PHASE 45 GAIN 0 –45 –40 –90 –60 –135 –80 –180 –100 100 1k 10k FREQUENCY (Hz) –225 1M 100k Figure 25. Open-Loop Gain and Phase vs. Frequency 60 40 40 CLOSED-LOOP GAIN (dB) 30 G = –10 20 10 G = –1 0 –10 –20 –30 30 20 10 0 –50 1M –60 100 07416-027 100k Figure 23. Closed-Loop Gain vs. Frequency VSY = 1.8V 1k 10k FREQUENCY (Hz) 100k 1M Figure 26. Closed-Loop Gain vs. Frequency 10k VSY = 5V G = –10 G = –10 1k 1k G = –100 G = –100 G = –1 ZOUT (Ω) 100 10 100 G = –1 10 100 1k 10k FREQUENCY (Hz) 100k 1M 0.1 10 Figure 24. Output Impedance vs. Frequency 100 1k 10k FREQUENCY (Hz) 100k Figure 27. Output Impedance vs. Frequency Rev. A | Page 9 of 20 1M 07416-030 1 1 0.1 10 G = –1 –30 –40 10k FREQUENCY (Hz) G = –10 –20 –50 1k G = –100 –10 –40 –60 100 VSY = 5V 50 G = –100 07416-028 VSY = 1.8V 50 CLOSED-LOOP GAIN (dB) 0 –20 60 ZOUT (Ω) 90 20 Figure 22. Open-Loop Gain and Phase vs. Frequency 10k 225 180 40 07416-029 OPEN-LOOP GAIN (dB) 60 100 PHASE (Degrees) 80 225 07416-026 VSY = 1.8V OPEN-LOOP GAIN (dB) 100 ADA4505-2/ADA4505-4 TA = 25°C, unless otherwise noted. 120 120 VSY = 5V 100 80 80 60 60 40 40 20 20 0 100 1k 10k FREQUENCY (Hz) 100k 1M 0 100 1k Figure 28. CMRR vs. Frequency 1M Figure 31. CMRR vs. Frequency VSY = 5V VSY = 1.8V 100 100 80 80 PSRR (dB) 60 60 40 40 20 PSRR+ PSRR– 100 1k 10k FREQUENCY (Hz) 100k 1M 0 10 07416-033 0 10 PSRR+ PSRR– 100 1k 10k FREQUENCY (Hz) 100k 1M 07416-034 PSRR (dB) 100k 120 120 20 10k FREQUENCY (Hz) 07416-032 CMRR (dB) 100 07416-031 CMRR (dB) VSY = 1.8V Figure 32. PSRR vs. Frequency Figure 29. PSRR vs. Frequency 1k 140 1.8V ≤ VSY ≤ 5V 130 VSY = 5V en (nV/√Hz) 110 100 VSY = 1.8V 100 80 –40 –25 –10 5 20 35 50 65 TEMPERATURE (°C) 80 95 110 125 10 1 10 100 FREQUENCY (Hz) Figure 30. PSRR vs. Temperature Figure 33. Voltage Noise Density vs. Frequency Rev. A | Page 10 of 20 1000 07416-050 90 07416-035 PSRR (dB) 120 ADA4505-2/ADA4505-4 TA = 25°C, unless otherwise noted. 80 80 60 60 VSY = 5V VIN = 10mV p-p 70 R = 100kΩ L OVERSHOOT (%) 50 40 30 OS+ OS– 20 50 40 30 20 OS+ OS– 10 10 100 CAPACITANCE (pF) 1000 0 10 07416-036 0 10 Figure 34. Small Signal Overshoot vs. Load Capacitance T 100 CAPACITANCE (pF) 1000 Figure 37. Small Signal Overshoot vs. Load Capacitance T LOAD = 100kΩ || 100pF VSY = 1.8V LOAD = 100kΩ || 100pF VSY = 5V TIME (200µs/DIV) 07416-038 VOLTAGE (1V/DIV) 1.490V p-p TIME (200µs/DIV) Figure 35. Large Signal Transient Response Figure 38. Large Signal Transient Response T LOAD = 100kΩ || 100pF VSY = 1.8V LOAD = 100kΩ || 100pF VSY = 5V TIME (200µs/DIV) Figure 36. Small Signal Transient Response Figure 39. Small Signal Transient Response Rev. A | Page 11 of 20 07416-041 TIME (200µs/DIV) 07416-040 VOLTAGE (2mV/DIV) VOLTAGE (2mV/DIV) T 07416-039 VOLTAGE (500mV/DIV) 3.959V p-p 07416-037 OVERSHOOT (%) VSY = 1.8V VIN = 10mV p-p 70 R = 100kΩ L ADA4505-2/ADA4505-4 TA = 25°C, unless otherwise noted. 35 40 30 35 ADA4505-4 25 ADA4505-4, V SY = 1.8V 30 ADA4505-4, V SY = 5V 20 ISY (µA) ISY (µA) 25 ADA4505-2 15 20 ADA4505-2, V SY = 1.8V 15 ADA4505-2, V SY = 5V 10 10 5 0.5 1.0 1.5 2.0 2.5 3.0 VSY (V) 3.5 4.0 4.5 5.0 0 –40 –25 Figure 40. Supply Current vs. Supply Voltage VSY = 1.8V –10 20 35 50 65 TEMPERATURE (°C) 80 95 110 125 Figure 43. Total Supply Current vs. Temperature VSY = 5V 2.95µV p-p TIME (s) TIME (s) Figure 44. 0.1 Hz to 10 Hz Noise 0 VSY = 1.8V RL = 100kΩ –20 G = –100 0 VSY = 5V RL = 100kΩ –20 G = –100 VIN = 0.5V p-p VIN = 1V p-p VIN = 1.7V p-p CHANNEL SEPARATION (dB) 100kΩ 1kΩ –60 –80 –100 –120 100kΩ 1kΩ –60 –80 –100 –120 1k 10k FREQUENCY (Hz) 100k 07416-057 –140 100 –40 VIN = 1V p-p VIN = 2V p-p VIN = 3V p-p VIN = 4V p-p VIN = 4.99V p-p –140 100 1k 10k FREQUENCY (Hz) Figure 45. Channel Separation vs. Frequency Figure 42. Channel Separation vs. Frequency Rev. A | Page 12 of 20 100k 07416-058 –40 07416-053 07416-052 INPUT NOISE VOLTAGE (0.5µV/DIV) INPUT NOISE VOLTAGE (0.5µV/DIV) 2.95µV p-p Figure 41. 0.1 Hz to 10 Hz Noise CHANNEL SEPARATION (dB) 5 07416-055 0 07416-054 0 5 ADA4505-2/ADA4505-4 TA = 25°C, unless otherwise noted. 1.8 1.5 OUTPUT SWING (V) 1.2 0.9 0.6 0.3 4 3 2 1 100 1k FREQUENCY (Hz) 10k 100k 0 10 Figure 46. Output Swing vs. Frequency 100 1k FREQUENCY (Hz) 10k Figure 47. Output Swing vs. Frequency Rev. A | Page 13 of 20 100k 07416-060 0 10 VSY = 5V VIN = 4.9V G=1 RL = 100kΩ 5 07416-059 OUTPUT SWING (V) 6 VSY = 1.8V VIN = 1.7V G=1 RL = 100kΩ ADA4505-2/ADA4505-4 THEORY OF OPERATION VDD The ADA4505-2/ADA4505-4 are unity-gain stable CMOS railto-rail input/output operational amplifiers designed to optimize performance in current consumption, PSRR, CMRR, and zero crossover distortion, all embedded in a small package. The typical offset voltage is 500 μV, with a low peak-to-peak voltage noise of 2.95 μV from 0.1 Hz to 10 Hz and a voltage noise density of 65 nV/√Hz at 1 kHz. VBIAS VIN+ The ADA4505-2/ADA4505-4 are designed to solve two key problems in low voltage battery-powered applications: battery voltage decrease over time and rail-to-rail input stage distortion. One differential pair amplifies the input signal when the commonmode voltage is on the high end, whereas the other pair amplifies the input signal when the common-mode voltage is on the low end. This method also requires control circuitry to operate the two differential pairs appropriately. Unfortunately, this topology leads to a very noticeable and undesirable problem: if the signal level moves through the range where one input stage turns off and the other one turns on, noticeable distortion occurs (see Figure 49). Q2 Q4 VIN– IB 07416-043 VSS Figure 48. Typical Dual Differential Pair Input Stage Op Amp (Dual PMOS Q1 and Q2 Transistors Form the Lower End of the Input Voltage Range; Dual NMOS Q3 and Q4 Transistors Form the Upper End) 300 VSY = 5V TA = 25°C 250 200 150 100 50 0 –50 –100 –150 –200 –250 –300 0 0.5 1.0 1.5 2.0 2.5 3.0 VCM (V) 3.5 4.0 4.5 5.0 07416-044 The second problem with battery-powered applications is the distortion caused by the standard rail-to-rail input stage. Using a CMOS non-rail-to-rail input stage (that is, a single differential pair) limits the input voltage to approximately one VGS (gatesource voltage) away from one of the supply lines. Because VGS for normal operation is commonly over 1 V, a single differential pair input stage op amp greatly restricts the allowable input voltage range when using a low supply voltage. This limitation restricts the number of applications where the non-rail-to-rail input op amp was originally intended to be used. To solve this problem, a dual differential pair input stage is usually implemented (see Figure 48); however, this technique has its own drawbacks. Q1 IB VOS (µV) In battery-powered applications, the supply voltage available to the IC is the voltage of the battery. Unfortunately, the voltage of a battery decreases as it discharges itself through the load. This voltage drop over the lifetime of the battery causes an error in the output of the op amps. Some applications requiring precision measurements during the entire lifetime of the battery use voltage regulators to power up the op amps as a solution. If a design uses standard battery cells, the op amps experience a supply voltage change from roughly 3.2 V to 1.8 V during the lifetime of the battery. This means that for a PSRR of 70 dB minimum in a typical op amp, the input-referred offset error is approximately 440 μV. If the same application uses the ADA4505-2/ADA4505-4 with a 100 dB minimum PSRR, the error is only 14 μV. It is possible to calibrate this error out or to use an external voltage regulator to power the op amp, but these solutions can increase system cost and complexity. The ADA4505-2/ADA4505-4 solve the impasse with no additional cost or error-nullifying circuitry. Q3 Figure 49. Typical Input Offset Voltage vs. Common-Mode Voltage Response in a Dual Differential Pair Input Stage Op Amp (Powered by 5 V Supply; Results of Approximately 100 Units per Graph Are Displayed) This distortion forces the designer to devise impractical ways to avoid the crossover distortion areas, therefore narrowing the common-mode dynamic range of the operational amplifier. The ADA4505-2/ADA4505-4 solve this crossover distortion problem by using an on-chip charge pump to power the input differential pair. The charge pump creates a supply voltage higher than the voltage of the battery, allowing the input stage to handle a wide range of input signal voltages without using a second differential pair. With this solution, the input voltage can vary from one supply extreme to the other with no distortion, thereby restoring the full common-mode dynamic range of the op amp. Rev. A | Page 14 of 20 ADA4505-2/ADA4505-4 The charge pump has been carefully designed so that switching noise components at any frequency, both within and beyond the amplifier bandwidth, are much lower than the thermal noise floor. Therefore, the spurious-free dynamic range (SFDR) is limited only by the input signal and the thermal or flicker noise. There is no intermodulation between input signal and switching noise. Figure 51 shows the typical response of two devices from Figure 9, which shows the input offset voltage vs. input common-mode voltage for 10 devices. Figure 51 is expanded to make it easier to compare with Figure 49, which shows the typical input offset voltage vs. common-mode voltage response in a dual differential pair input stage op amp. 300 Figure 50 displays a typical front-end section of an operational amplifier with an on-chip charge pump. 200 VPP = POSITIVE PUMPED VOLTAGE = VDD + 1.8V VPP 150 VDD 100 VBIAS Q1 Q2 –IN CASCODE STAGE AND RAIL-TO-RAIL OUTPUT STAGE VOS (µV) 50 0 –50 –100 OUT –150 –200 VSS Figure 50. Typical Front-End Section of an Op Amp with Embedded Charge Pump –300 0 0.5 1.0 1.5 2.0 2.5 3.0 VCM (V) 3.5 4.0 4.5 5.0 07416-046 –250 07416-045 +IN VSY = 5V TA = 25°C 250 Figure 51. Input Offset Voltage vs. Input Common-Mode Voltage Response (Powered by a 5 V Supply; Results of Two Units Are Displayed) This solution improves the CMRR performance tremendously. For example, if the input varies from rail to rail on a 2.5 V supply rail, using a part with a CMRR of 70 dB minimum, an input-referred error of 790 μV is introduced. Another part with a CMRR of 52 dB minimum generates a 6.3 mV error. The ADA4505-2/ADA4505-4 CMRR of 90 dB minimum causes only a 79 μV error. As with the PSRR error, there are complex ways to minimize this error, but the ADA4505-2/ADA4505-4 solve this problem without incurring unnecessary circuitry complexity or increased cost. Rev. A | Page 15 of 20 ADA4505-2/ADA4505-4 APPLICATIONS INFORMATION +5V PULSE OXIMETER CURRENT SOURCE C2 0.1µF CONNECT TO RED LED A pulse oximeter is a noninvasive medical device used for measuring continuously the percentage of hemoglobin (Hb) saturated with oxygen and the pulse rate of a patient. Hemoglobin that is carrying oxygen (oxyhemoglobin) absorbs light in the infrared (IR) region of the spectrum; hemoglobin that is not carrying oxygen (deoxyhemoglobin) absorbs visible red (R) light. In pulse oximetry, a clip containing two LEDs (sometimes more, depending on the complexity of the measurement algorithm) and the light sensor (photodiode) is placed on the finger or earlobe of the patient. One LED emits red light (600 nm to 700 nm) and the other emits light in the near IR (800 nm to 900 nm) region. The clip is connected by a cable to a processor unit. The LEDs are rapidly and sequentially excited by two current sources (one for each LED), whose dc levels depend on the LED being driven, based on manufacturer requirements; the detector is synchronized to capture the light from each LED as it is transmitted through the tissue. U1 1/2 ADA4505-2 62.5mA 8 R2 V 22Ω OUT1 V+ 7 Q1 IRLMS2002 16 VDD V– 4 +5V S1A 12 14 D1 5 U2 ADG733 S1B 13 6 S2A 2 15 D2 S2B 1 C3 22pF R3 1kΩ R4 53.6kΩ VREF = 1.25V U3 ADR1581 S3A 5 4 D3 S3B 3 R1 20Ω 0.1% 1/4 W MIN RED CURRENT SOURCE 8 9 A2 10 A1 11 A0 6 EN GND VSS CONNECT TO INFRARED LED 101mA U1 1/2 7 +5V ADA4505-2 R6 22Ω VOUT2 Q2 IRLMS2002 8 1 V+ V– 4 3 2 I_BIT2 I_BIT1 I_BIT0 I_ENA C4 22pF R7 1kΩ R5 INFRARED CURRENT 12.4Ω SOURCE 0.1% 1/2 W MIN 07416-047 An example design of a dc current source driving the red and infrared LEDs is shown in Figure 52. These dc current sources allow 62.5 mA and 101 mA to flow through the red and infrared LEDs, respectively. First, to prolong battery life, the LEDs are driven only when needed. One third of the ADG733 SPDT analog switch is used to disconnect/connect the 1.25 V voltage reference from/to each current circuit. When driving the LEDs, the ADR1581 1.25 V voltage reference is buffered by one half of the ADA4505-2; the presence of this voltage on the noninverting input forces the output of the op amp (due to the negative feedback) to maintain a level that causes its inverting input to track the noninverting pin. Therefore, the 1.25 V appears in parallel with the 20 Ω R1 or 12.4 Ω R5 current source resistor, creating the flow of the 62.5 mA or 101 mA current through the red or infrared LED as the output of the op amp turns on the Q1 or Q2 N-MOSFET IRLMS2002. +5V C1 0.1µF Figure 52. Pulse Oximeter Red and Infrared Current Sources Using the ADA4505-2 as a Buffer to the Voltage Reference Device The maximum total quiescent currents for one half of the ADA4505-2, the ADR1581, and the ADG733 are 15 μA, 70 μA, and 1 μA, respectively, for a total of 86 μA current consumption (430 μW power consumption) per circuit, which is good for a system powered by a battery. If the accuracy and temperature drift of the total design need to be improved, a more accurate and low temperature coefficient drift voltage reference and current source resistor should be used. C3 and C4 are used to improve stabilization of U1; R3 and R7 are used to provide some current limit into the U1 inverting pin; and R2 and R6 are used to slow the rise time of the N-MOSFET when it turns on. These elements may not be needed, or some bench adjustments may be required. Rev. A | Page 16 of 20 ADA4505-2/ADA4505-4 Another consideration is operation from a 3.3 V battery. Glucose signal currents are usually less than 3 μA full scale, so the I-to-V converter requires low input bias current. The ADA4505-2/ ADA4505-4 family is an excellent choice because it provides 0.5 pA typical and 2 pA maximum of input bias current at ambient temperature. FOUR-POLE LOW-PASS BUTTERWORTH FILTER FOR GLUCOSE MONITOR There are several methods of glucose monitoring: spectroscopic absorption of infrared light in the 2 μm to 2.5 μm range, reflectance spectrophotometry, and the amperometric type using electrochemical strips with glucose oxidase enzymes. The amperometric type generally uses three electrodes: a reference electrode, a control electrode, and a working electrode. Although this is a very old and widely used technique, signal-to-noise ratio and repeatability can be improved using the ADA4505-2/ ADA4505-4 family, with its low peak-to-peak voltage noise of 2.95 μV from 0.1 Hz to 10 Hz and voltage noise density of 65 nV/√Hz at 1 kHz. A low-pass filter with a cutoff frequency of 80 Hz to 100 Hz is desirable in a glucose meter device to remove extraneous noise; this can be a simple two-pole or four-pole Butterworth filter. Low power op amps with bandwidths of 50 kHz to 500 kHz should be adequate. The ADA4505-2/ADA4505-4 family, with its 50 kHz GBP and 7 μA typical current consumption, meets these requirements. A circuit design of a four-pole Butterworth filter (preceded by a one-pole low-pass filter) is shown in Figure 53. With a 3.3 V battery, the total power consumption of this design is 198 μW typical at ambient temperature. C1 1000pF R1 5MΩ +3.3V WORKING CONTROL +3.3V 3 8 V+ 1 V– 2 4 U1 1/2 R3 22.6kΩ 5 C3 0.047µF 8 V+ 7 V– ADA4505-2 U1 1/2 ADA4505-2 6 4 R4 22.6kΩ +3.3V R5 22.6kΩ ADA4505-2 3 C5 0.047µF 8 V+ 1 V– C2 0.1µF U2 1/2 2 VOUT 4 C4 0.1µF DUPLICATE OF CIRCUIT ABOVE 07416-048 REFERENCE R2 22.6kΩ Figure 53. Four-Pole Butterworth Filter That Can Be Used in a Glucose Meter Rev. A | Page 17 of 20 ADA4505-2/ADA4505-4 OUTLINE DIMENSIONS 3.20 3.00 2.80 8 3.20 3.00 2.80 5.15 4.90 4.65 5 1 4 PIN 1 0.65 BSC 0.95 0.85 0.75 1.10 MAX 0.15 0.00 0.38 0.22 COPLANARITY 0.10 0.80 0.60 0.40 8° 0° 0.23 0.08 SEATING PLANE COMPLIANT TO JEDEC STANDARDS MO-187-AA Figure 54. 8-Lead Mini Small Outline Package [MSOP] (RM-8) Dimensions shown in millimeters 0.650 0.595 0.540 1.460 1.420 SQ 1.380 SEATING PLANE 3 2 1 0.340 0.320 0.300 BALL 1 IDENTIFIER A B 0.50 BALL PITCH 0.380 0.355 0.330 COPLANARITY 0.075 C BOTTOM VIEW 0.270 0.240 0.210 Figure 55. 8-Ball Wafer Level Chip Scale Package [WLCSP] (CB-8-2) Dimensions shown in millimeters Rev. A | Page 18 of 20 (BALL SIDE UP) 011008-B TOP VIEW ADA4505-2/ADA4505-4 5.10 5.00 4.90 14 8 4.50 4.40 4.30 6.40 BSC 1 7 PIN 1 0.65 BSC 1.20 MAX 0.15 0.05 COPLANARITY 0.10 0.30 0.19 0.20 0.09 SEATING PLANE 8° 0° COMPLIANT TO JEDEC STANDARDS MO-153-AB-1 0.75 0.60 0.45 061908-A 1.05 1.00 0.80 Figure 56. 14-Lead Thin Shrink Small Outline Package [TSSOP] (RU-14) Dimensions shown in millimeters ORDERING GUIDE Model ADA4505-2ACBZ-RL 1 ADA4505-2ACBZ-R71 ADA4505-2ARMZ-R21 ADA4505-2ARMZ-RL1 ADA4505-4ARUZ1 ADA4505-4ARUZ-RL1 1 Temperature Range −40°C to +125°C −40°C to +125°C −40°C to +125°C −40°C to +125°C −40°C to +125°C −40°C to +125°C Package Description 8-Ball WLCSP 8-Ball WLCSP 8-Lead MSOP 8-Lead MSOP 14-Lead TSSOP 14-Lead TSSOP Z = RoHS Compliant Part. Rev. A | Page 19 of 20 Package Option CB-8-2 CB-8-2 RM-8 RM-8 RU-14 RU-14 Branding A21 A21 A21 A21 ADA4505-2/ADA4505-4 NOTES ©2008 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D07416-0-10/08(A) Rev. A | Page 20 of 20