AD ADA4505

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