INTERSIL ISL28478FAZ

ISL28278, ISL28478
®
Data Sheet
July 11, 2007
Dual and Quad Micropower Single Supply
Rail-to-Rail Input and Output (RRIO)
Op-Amp
The ISL28278 and ISL28478 are dual and quad channel
micropower operational amplifiers optimized for single
supply operation over the 2.4V to 5V range. They can be
operated from one lithium cell or two Ni-Cd batteries. For
equivalent performance in a single channel op-amp
reference EL8178.
These devices feature an Input Range Enhancement Circuit
(IREC) which enables them to maintain CMRR performance
for input voltages 10% above the positive supply rail and to
100mV below the negative supply. The output operation is
rail to rail.
The ISL28278 and ISL28478 draw minimal supply current
while meeting excellent DC-accuracy, AC-performance,
noise and output drive specifications. The ISL28278
contains a power down enable pin that reduces the power
supply current to typically 4µA in the disabled state.
Pinouts
FN6145.2
Features
• Low power 120µA typical supply current (ISL28278)
• 225μV max offset voltage
• 30pA max input bias current
• 300kHz typical gain-bandwidth product
• 105dB typical PSRR
• 100dB typical CMRR
• Single supply operation down to 2.4V
• Input is capable of swinging above V+ and below V(ground sensing)
• Rail-to-rail input and output (RRIO)
• Enable Pin (ISL28278 only)
• Pb-free plus anneal available (RoHS compliant)
Applications
• Battery- or solar-powered systems
• 4mA to 25mA current loops
ISL28278 (16 LD QSOP)
TOP VIEW
NC 1
16 NC
NC 2
15 V+
14 OUT_B
+
+
OUT_A 3
IN-_A 4
13 IN-_B
IN+_A 5
12 IN+_B
EN_A 6
11 EN_B
V- 7
10 NC
NC 8
9 NC
ISL28478 (16 LD QSOP)
TOP VIEW
OUT_A 1
16 OUT_D
15 IN-_D
IN-_A 2
+
+
IN+_A 3
14 IN+_D
V+ 4
13 V-
IN+_B 5
• Medical devices
• Thermocouple amplifiers
• Photodiode pre-amps
• pH probe amplifiers
Ordering Information
PART NUMBER
(Note)
PART
MARKING
PACKAGE
(Pb-Free)
PKG.
DWG. #
ISL28278FAZ*
28278FAZ
16 Ld QSOP
MDP0040
ISL28478FAZ*
28478FAZ
16 Ld QSOP
MDP0040
*“-T7” suffix is for tape and reel. Please refer to TB347 for details on
reel specifications.
NOTE: Intersil Pb-free plus anneal products employ special Pb-free
material sets; molding compounds/die attach materials and 100%
matte tin plate termination finish, which are RoHS compliant and
compatible with both SnPb and Pb-free soldering operations.
Intersil Pb-free products are MSL classified at Pb-free peak reflow
temperatures that meet or exceed the Pb-free requirements of
IPC/JEDEC J STD-020.
12 IN+_C
+
-
+
-
IN-_B 6
• Handheld consumer products
11 IN-_C
10 OUT_C
OUT_B 7
NC 8
9 NC
1
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a registered trademark of Intersil Americas Inc.
Copyright Intersil Americas Inc. 2006, 2007. All Rights Reserved
All other trademarks mentioned are the property of their respective owners.
ISL28278, ISL28478
Absolute Maximum Ratings (TA = +25°C)
Thermal Information
Supply Voltage, V- to V+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5V
Supply Turn On Voltage Slew Rate . . . . . . . . . . . . . . . . . . . . . 1V/μs
Differential Input Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5mA
Differential Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.5V
Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . V- - 0.5V to V+ + 0.5V
ESD Tolerance
Human Body Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3kV
Machine Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .300V
Thermal Resistance
θJA (°C/W)
16 Ld QSOP Package . . . . . . . . . . . . . . . . . . . . . . .
112
Output Short-Circuit Duration . . . . . . . . . . . . . . . . . . . . . . .Indefinite
Ambient Operating Temperature Range . . . . . . . . .-40°C to +125°C
Storage Temperature Range . . . . . . . . . . . . . . . . . .-65°C to +150°C
Operating Junction Temperature . . . . . . . . . . . . . . . . . . . . . +125°C
Pb-free reflow profile . . . . . . . . . . . . . . . . . . . . . . . . . .see link below
http://www.intersil.com/pbfree/Pb-FreeReflow.asp
CAUTION: Do not operate at or near the maximum ratings listed for extended periods of time. Exposure to such conditions may adversely impact product reliability and
result in failures not covered by warranty.
IMPORTANT NOTE: All parameters having Min/Max specifications are guaranteed. Typical values are for information purposes only. Unless otherwise noted, all tests
are at the specified temperature and are pulsed tests, therefore: TJ = TC = TA
Operating Junction
Electrical Specifications
PARAMETER
V+ = 5V, V- = 0V, VCM = 2.5V, RL = Open, TA = +25°C unless otherwise specified.
Boldface limits apply over the operating temperature range, -40°C to +125°C, temperature data
established by characterization
DESCRIPTION
CONDITIONS
MIN
(Note 1)
TYP
MAX
(Note 1)
UNIT
DC SPECIFICATIONS
VOS
Input Offset Voltage
ΔV OS
--------------ΔT
Input Offset Voltage vs Temperature
IOS
Input Offset Current
IB
-225
-450
±0.20
225
450
1.0
µV
µV/°C
-30
-80
±5
30
80
pA
-40°C to +85°C
-30
-80
±10
30
80
pA
-40°C to +85°C
5
V
Input Bias Current
CMIR
Common-Mode Voltage Range
Guaranteed by CMRR
0
CMRR
Common-Mode Rejection Ratio
VCM = 0V to 5V
80
75
100
dB
PSRR
Power Supply Rejection Ratio
V+ = 2.4V to 5V
85
80
105
dB
AVOL
Large Signal Voltage Gain
VO = 0.5V to 4.5V, RL = 100kΩ
200
190
300
V/mV
VO = 0.5V to 4.5V, RL = 1kΩ
60
V/mV
Output low, RL = 100kΩ
3
6
30
mV
130
175
225
mV
VOUT
Maximum Output Voltage Swing
Output low, RL = 1kΩ
IS,ON
IS,OFF
Quiescent Supply Current, Enabled
Quiescent Supply Current, Disabled
2
Output high, RL = 100kΩ
4.990
4.97
4.996
V
Output high, RL = 1kΩ
4.800
4.750
4.880
V
ISL28278, All channels enabled.
120
156
175
µA
ISL28478, All channels enabled.
240
315
350
µA
4
7
9
µA
All channels disabled.
ISL28278
FN6145.2
July 11, 2007
ISL28278, ISL28478
Electrical Specifications
PARAMETER
V+ = 5V, V- = 0V, VCM = 2.5V, RL = Open, TA = +25°C unless otherwise specified.
Boldface limits apply over the operating temperature range, -40°C to +125°C, temperature data
established by characterization (Continued)
DESCRIPTION
CONDITIONS
MIN
(Note 1)
TYP
MAX
(Note 1)
UNIT
IO+
Short Circuit Sourcing Capability
RL = 10Ω
29
24
31
mA
IO-
Short Circuit Sinking Capability
RL = 10Ω
24
20
26
mA
VSUPPLY
Supply Operating Range
V- to V+
2.4
VENH
EN Pin High Level
ISL28278
VENL
EN Pin Low Level
ISL28278
IENH
EN Pin Input High Current
VEN = V+
ISL28278
IENL
EN Pin Input Low Current
VEN = VISL28278
5.0
2
V
V
0.8
V
0.8
1
1.5
µA
0
0.1
µA
AC SPECIFICATIONS
GBW
Gain Bandwidth Product
AV = 100, RF = 100kΩ, RG = 1kΩ,
RL = 10kΩ to VCM
300
kHz
en
Input Noise Voltage Peak-to-Peak
f = 0.1Hz to 10Hz
4.5
µVP-P
Input Noise Voltage Density
fO = 1kHz
45
nV/√Hz
in
Input Noise Current Density
fO = 1kHz
0.04
pA/√Hz
CMRR @ 60Hz
Input Common Mode Rejection Ratio
VCM = 1VP-P, RL = 10kΩ to VCM
-70
dB
PSRR+ @
120Hz
Power Supply Rejection Ratio, +V
V+,V- = ±1.2V and ±2.5V,
VSOURCE = 1VP-P, RL = 10kΩ to VCM
-80
dB
PSRR- @
120Hz
Power Supply Rejection Ratio, -V
V+,V- = ±1.2V and ±2.5V
VSOURCE = 1VP-P, RL = 10kΩ to VCM
-60
dB
TRANSIENT RESPONSE
±0.12
±0.09
±0.14
±0.16
±0.21
V/µs
SR
Slew Rate
tEN
Enable to Output Turn-on Delay Time,
10% EN to 10% Vout
VEN = 5V to 0V, AV = -1,
RG = RF = RL = 1k to VCM, ISL28278
2
µs
Enable to Output Turn-off Delay Time,
10% EN to 10% Vout
VEN = 0V to 5V, AV = -1,
RG = RF = RL = 1k to VCM, ISL28278
0.1
µs
NOTE:
1. Parts are 100% tested at +25°C. Over temperature limits established by characterization and are not production tested.
3
FN6145.2
July 11, 2007
ISL28278, ISL28478
Typical Performance Curves V+ = 5V, V- = 0V, VCM = 2.5V, RL = Open, unless otherwise specified.
+1
45
35
V+,V-= ±1.2V
RL = 10k
30
GAIN (dB)
-2
GAIN (dB)
40
V+,V-= ±1.2V
RL = 1k
V+,V-= ±2.5V
RL = 1k
-1
V+,V-= ±2.5V
RL = 10k
-3
-4
20
15
-5
VOUT = 50mVP-P
AV = 1
CL = 3pF
RF = 0, RG = INF
-6
-7
8
1k
10
5
10k
100k
1M
V+,V-= ±2.5V
25
V+,V-= ±1.2V
AV = 100
RL = 10kΩ
CL = 3pF
RF = 100kΩ
RG = 1kΩ
0
100
5M
V+,V-= ±1.0V
1k
10k
FIGURE 1. FREQUENCY RESPONSE vs SUPPLY VOLTAGE
FIGURE 2. FREQUENCY RESPONSE vs SUPPLY VOLTAGE
80
120
200
100
150
80
40
80
PHASE
PHASE
GAIN (dB)
-40
0
PHASE (°)
0
40
-80
100
10k
1k
100k
1M
-120
10M
100
60
50
40
0
20
-80
-40
GAIN
-50
0
-100
-20
10
100
10k
1k
100k
-150
1M
FREQUENCY (Hz)
FREQUENCY (Hz)
FIGURE 3. AVOL vs FREQUENCY @ 100kΩ LOAD
FIGURE 4. AVOL vs FREQUENCY @ 1kΩ LOAD
10
0
-10
-20
10
V+,V- = ±2.5VDC
0
VSOURCE = 1VP-P
RL = 10kΩ
AV = +1
-10
-20
-30
CMRR (dB)
PSRR (dB)
GAIN (dB)
GAIN
10
1M
FREQUENCY (Hz)
FREQUENCY (Hz)
1
100k
PHASE (°)
0
PSRR -
-40
-50
-60
PSRR +
V+,V- = ±2.5VDC
VSOURCE = 1VP-P
RL = 10kΩ
-30
-40
-50
-60
-70
-70
-80
-80
-90
-90
-100
10
100
1k
10k
100k
FREQUENCY (Hz)
FIGURE 5. PSRR vs FREQUENCY
4
1M
-100
10
100
1k
10k
100k
1M
FREQUENCY (Hz)
FIGURE 6. CMRR vs FREQUENCY
FN6145.2
July 11, 2007
ISL28278, ISL28478
Typical Performance Curves V+ = 5V, V- = 0V, VCM = 2.5V, RL = Open, unless otherwise specified.
1k
CURRENT NOISE (fA/√Hz)
VOLTAGE NOISE (nV/√Hz)
1k
100
100
10
10
1
10
100
FREQUENCY (Hz)
1k
10k
1
FIGURE 7. VOLTAGE NOISE vs FREQUENCY
10
100
FREQUENCY (Hz)
1k
10k
FIGURE 8. CURRENT NOISE vs FREQUENCY
2.56
VIN
2.54
2.0
2.52
1.5
1.0
VOUT
VOLTS (V)
VOLTAGE NOISE (0.5µV/DIV)
2.5
0.5
0
2.50
2.48
-0.5
V+ = 5VDC
VOUT = 0.1VP-P
2.46
-1.0
-1.5
RL = 1kΩ
2.44
AV = +1
-2.0
-2.5
2.42
0
1
2
3
4
5
6
7
8
9
0
10
2
4
6
8
10
FIGURE 9. 0.1Hz TO 10Hz INPUT VOLTAGE NOISE
V+ = 5VDC
VOUT = 4VP-P
RL = 1kΩ
AV = -2
16
18
20
AV = -1
VIN = 200mVP-P
V+ = 5V
EN
INPUT
1V/DIV
VOUT
3
2
0
VIN
1
VOUT
0.1V/DIV
VOLTS (V)
14
FIGURE 10. SMALL SIGNAL TRANSIENT RESPONSE
5
4
12
TIME (µs)
TIME (1s/DIV)
0
0
0
50
100
150
200
250
10µs/DIV
TIME (µs)
FIGURE 11. LARGE SIGNAL TRANSIENT RESPONSE
5
FIGURE 12. ISL28278 ENABLE TO OUTPUT DELAY TIME
FN6145.2
July 11, 2007
ISL28278, ISL28478
1000
100
800
80
600
60
400
40
IBIAS (pA)
VOS (µV)
Typical Performance Curves V+ = 5V, V- = 0V, VCM = 2.5V, RL = Open, unless otherwise specified.
200
0
-200
-400
-800
-1000
-1
0
1
2
3
VCM (V)
4
0
-20
-60
-80
5
-100
6
FIGURE 13. INPUT OFFSET VOLTAGE vs COMMON MODE
INPUT VOLTAGE
280
20
-40
V+ = 5V
RL = OPEN
RF = 100k, RG = 100
AV = +1000
-600
2
3
VCM (V)
4
5
6
n = 12
4.6
MAX
4.4
CURRENT (µA)
CURRENT (µA)
1
4.8
250
MEDIAN
240
230
MIN
220
MAX
4.2
MEDIAN
4.0
3.8
3.6
210
MIN
3.4
200
-20
0
20
40
60
80
TEMPERATURE (°C)
100
3.2
-40
120
FIGURE 15. ISL28478 SUPPLY CURRENT vs TEMPERATURE,
V+,V- = ±2.5V, RL = INF
-20
0
100
120
500
N = 1000
400
400
300
N = 1000
300
MAX
MAX
200
20
40
60
80
TEMPERATURE (°C)
FIGURE 16. ISL28278 DISABLED SUPPLY CURRENT vs
TEMPERATURE, V+,V- = ±2.5V RL = INF
500
VOS (µV)
200
100
MEDIAN
0
-100
100
-100
MIN
-200
-300
-300
-20
0
20
40
60
80
TEMPERATURE (°C)
100
120
FIGURE 17. VOS vs TEMPERATURE, VIN = 0V, V+,V- = ±2.5V
6
MEDIAN
0
-200
-400
-40
0
FIGURE 14. INPUT BIAS CURRENT vs COMMON-MODE
INPUT VOLTAGE
260
VOS (µV)
-1
N = 1000
270
190
-40
V+ = 5V
RL = OPEN
RF= 100k, RG = 100
AV = +1000
-400
-40
MIN
-20
0
20
40
60
80
TEMPERATURE (°C)
100
120
FIGURE 18. VOS vs TEMPERATURE, VIN = 0V, V+,V- = ±1.2V
FN6145.2
July 11, 2007
ISL28278, ISL28478
Typical Performance Curves V+ = 5V, V- = 0V, VCM = 2.5V, RL = Open, unless otherwise specified.
200
500
n = 1000
n = 1000
0
0
IBIAS- (pA)
IBIAS+ (pA)
-200
-500
MAX
-1000
-1500
0
20
40
60
80
-800
MEDIAN
-1200
MIN
-20
MAX
-600
-1000
MEDIAN
-2000
-2500
-40
-400
100
-1400
120
MIN
-40
-20
0
TEMPERATURE (°C)
20
40
60
80
100
120
TEMPERATURE (°C)
FIGURE 19. IBIAS+ vs TEMPERATURE, V+,V- = ±2.5V
FIGURE 20. IBIAS- vs TEMPERATURE, V+,V- = ±2.5V
200
500
n = 1000
n = 1000
0
0
IBIAS- (pA)
IBIAS+ (pA)
-200
-500
MAX
-1000
-1500
MAX
-400
-600
-800
MEDIAN
-2000
MEDIAN
-1000
MIN
MIN
-2500
-1200
-40
-20
0
20
40
60
80
100
120
-40
-20
0
40
60
80
100
120
FIGURE 22. IBIAS- vs TEMPERATURE, V+,V- = ±1.2V
FIGURE 21. IBIAS+ vs TEMPERATURE, V+,V- = ±1.2V
200
550
n = 1000
N = 1000
0
500
-200
450
-400
AVOL (V/mV)
IOS (pA)
20
TEMPERATURE (°C)
TEMPERATURE (°C)
MAX
-600
-800
MAX
400
350
MEDIAN
300
MEDIAN
-1000
250
MIN
-1200
-1400
-40
200
MIN
-20
0
20
40
60
80
100
TEMPERATURE (°C)
FIGURE 23. IOS vs TEMPERATURE, V+,V- = ±2.5V
7
120
150
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
100
120
FIGURE 24. AVOL vs TEMPERATURE, V+,V- = ±2.5V, RL = 100k
FN6145.2
July 11, 2007
ISL28278, ISL28478
Typical Performance Curves V+ = 5V, V- = 0V, VCM = 2.5V, RL = Open, unless otherwise specified.
135
90
N = 1000
N = 1000
MAX
125
80
70
60
CMRR (dB)
AVOL (V/mV)
MAX
MEDIAN
50
MIN
40
30
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
100
MIN
-20
0
20
40
60
80
TEMPERATURE (°C)
100
120
FIGURE 26. CMRR vs TEMPERATURE, VCM = +2.5V TO -2.5V
V+,V- = ±2.5V
4.91
N = 1000
N = 1000
MAX
130
4.90
120
4.89
VOUT (V)
MAX
110
MEDIAN
4.88
MEDIAN
4.87
100
MIN
MIN
90
80
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
4.86
100
4.85
-40
120
FIGURE 27. PSRR vs TEMPERATURE, V+,V- = ±1.2V TO ±2.5V
20
40
60
80
TEMPERATURE (°C)
100
120
N = 1000
MAX
4.9980
0
160
n = 12
4.9982
-20
FIGURE 28. VOUT HIGH vs TEMPERATURE, V+,V- = ±2.5V,
RL= 1k
4.9984
150
4.9978
140
VOUT (mV)
4.9976
4.9974
MEDIAN
95
75
-40
120
140
PSRR (dB)
105
85
FIGURE 25. AVOL vs TEMPERATURE, V+,V- = ±2.5V, RL = 1k
VOUT (V)
115
MEDIAN
4.9972
MIN
4.9970
MEDIAN
120
MIN
110
4.9968
100
4.9966
4.9964
-40
MAX
130
-20
0
20
40
60
80
TEMPERATURE (°C)
100
120
FIGURE 29. VOUT HIGH vs TEMPERATURE, V+,V- = ±2.5V,
RL= 100k
8
90
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
100
120
FIGURE 30. VOUT LOW vs TEMPERATURE, V+,V- = ±2.5V,
RL= 1k
FN6145.2
July 11, 2007
ISL28278, ISL28478
4.3
+ OUTPUT SHORT CIRCUIT CURRENT
(mA)
Typical Performance Curves V+ = 5V, V- = 0V, VCM = 2.5V, RL = Open, unless otherwise specified.
n = 12
4.2
VOUT (mV)
4.1
4.0
3.9
MAX
MEDIAN
3.8
3.7
MIN
3.6
3.5
3.4
-40
-20
0
20
40
60
80
100
120
41
N = 1000
39
MAX
37
35
33
MEDIAN
31
MIN
29
27
25
-40
-20
0
TEMPERATURE (°C)
40
60
80
100
120
FIGURE 32. + OUTPUT SHORT CIRCUIT CURRENT vs
TEMPERATURE, VIN = -2.55V, RL = 10,
V+,V- = ±2.5V
FIGURE 31. VOUT LOW vs TEMPERATURE, V+,V- = ±2.5V,
RL= 100k
0.19
-21
N = 1000
-23
-25
MAX
-27
MEDIAN
-29
MIN
-31
N = 1000
0.18
+ SLEW RATE (V/µs)
- OUTPUT SHORT CIRCUIT CURRENT
(mA)
20
TEMPERATURE (°C)
0.17
0.16
MAX
0.15
0.14
MEDIAN
0.13
0.12
MIN
0.11
0.10
-33
-40
-20
0
20
40
60
80
100
0.09
-40
120
-20
0
20
40
60
80
100
120
TEMPERATURE (°C)
TEMPERATURE (°C)
FIGURE 34. + SLEW RATE vs TEMPERATURE, VOUT = ±1.5V,
AV = +2
FIGURE 33. - OUTPUT SHORT CIRCUIT CURRENT vs
TEMPERATURE, VIN = +2.55V, RL = 10,
V+,V- = ±2.5V
0.20
0.19
N = 1000
- SLEW RATE (V/µs)
0.18
0.17
MAX
0.16
0.15
MEDIAN
0.14
0.13
MIN
0.12
0.11
0.10
-40
-20
0
20
40
60
80
100
120
TEMPERATURE (°C)
FIGURE 35. - SLEW RATE vs TEMPERATURE, VOUT = ±1.5V, AV = +2
9
FN6145.2
July 11, 2007
ISL28278, ISL28478
Pin Descriptions
ISL28278
(16 LD QSOP)
ISL28478
(16 LD QSOP)
PIN NAME
EQUIVALENT
CIRCUIT
3
1
OUT_A
Circuit 3
Amplifier A output
4
2
IN-_A
Circuit 1
Amplifier A inverting input
5
3
IN+_A
Circuit 1
Amplifier A non-inverting input
15
4
V+
Circuit 4
Positive power supply
12
5
IN+_B
Circuit 1
Amplifier B non-inverting input
13
6
IN-_B
Circuit 1
Amplifier B inverting input
14
7
OUT_B
Circuit 3
Amplifier B output
1, 2, 8, 9, 10, 16
8, 9
NC
10
OUT_C
Circuit 3
Amplifier C output
11
IN-_C
Circuit 1
Amplifier C inverting input
12
IN+_C
Circuit 1
Amplifier B non-inverting input
7
DESCRIPTION
No internal connection
13
V-
Circuit 4
Negative power supply
14
IN+_D
Circuit 1
Amplifier D non-inverting input
15
IN-_D
Circuit 1
Amplifier D inverting input
16
OUT_D
Circuit 3
Amplifier D output
6
EN_A
Circuit 2
Amplifier A enable pin internal pull-down; Logic “1” selects the disabled state;
Logic “0” selects the enabled state.
11
EN_B
Circuit 2
Amplifier B enable pin with internal pull-down; Logic “1” selects the disabled
state; Logic “0” selects the enabled state.
V+
V+
IN-
IN+
LOGIC
PIN
V+
CAPACITIVELY
COUPLED
ESD CLAMP
OUT
V-
CIRCUIT 1
V+
V-
VCIRCUIT 2
Applications Information
Introduction
The ISL28278 and ISL28478 are dual and quad CMOS
rail-to-rail input, output (RRIO) micropower operational
amplifiers. These devices are designed to operate from a
single supply (2.4V to 5.0V) or dual supplies (±1.2V to
±2.5V) while drawing only 120μA (ISL28278) of supply
current. This combination of low power and precision
performance makes these devices suitable for solar and
battery power applications.
VCIRCUIT 3
CIRCUIT 4
undesired change in magnitude and polarity of input offset
current.
The ISL28278 achieves input rail-to-rail without sacrificing
important precision specifications and degrading distortion
performance. The devices’ input offset voltage exhibits a
smooth behavior throughout the entire common-mode input
range. The input bias current versus the common-mode
voltage range gives us an undistorted behavior from typically
100mV below the negative rail and 10% higher than the V+
rail (0.5V higher than V+ when V+ equals 5V).
Input Protection
Rail-to-Rail Input
Many rail-to-rail input stages use two differential input pairs,
a long-tail PNP (or PFET) and an NPN (or NFET). Severe
penalties have to be paid for this circuit topology. As the
input signal moves from one supply rail to another, the
operational amplifier switches from one input pair to the
other causing drastic changes in input offset voltage and an
10
All input terminals have internal ESD protection diodes to the
positive and negative supply rails, limiting the input voltage to
within one diode beyond the supply rails. There is an
additional pair of back-to-back diodes across the input
terminals. For applications where the input differential voltage
is expected to exceed 0.5V, external series resistors must be
used to ensure the input currents never exceed 5mA.
FN6145.2
July 11, 2007
ISL28278, ISL28478
Rail-to-Rail Output
A pair of complementary MOSFET devices are used to achieve
the rail-to-rail output swing. The NMOS sinks current to swing
the output in the negative direction. The PMOS sources current
to swing the output in the positive direction. Both parts, with a
100kΩ load, will typically swing to within 4mV of the positive
supply rail and within 3mV of the negative supply rail.
form a continuous loop around both inputs. For further
reduction of leakage currents, components can be mounted
to the PC board using Teflon standoff insulators.
V+
HIGH IMPEDANCE INPUT
IN
Enable/Disable Feature
The ISL28278 offers two EN pins (EN_A and EN_B) which
disable the op amp when pulled up to at least 2.0V. In the
disabled state (output in a high impedance state), the part
consumes typically 4µA. By disabling the part, multiple parts
can be connected together as a MUX. The outputs are tied
together in parallel and a channel can be selected by the EN
pins. The loading effects of the feedback resistors of the
disabled amplifier must be considered when multiple
amplifier outputs are connected together. The EN pin also
has an internal pull-down. If left open, the EN pin will pull to
the negative rail and the device will be enabled by default.
Using Only One Channel
The ISL28278 and ISL28478 are dual and quad channel
op amps. If the application only requires one channel when
using the ISL28278 or less than 4 channels when using the
ISL28478, the user must configure the unused channel(s) to
prevent them from oscillating. The unused channel(s) will
oscillate if the input and output pins are floating. This will
result in higher than expected supply currents and possible
noise injection into the channel being used. The proper way
to prevent this oscillation is to short the output to the
negative input and ground the positive input (as shown in
Figure 36).
FIGURE 37. GUARD RING EXAMPLE FOR UNITY GAIN
AMPLIFIER
Example Application
Thermocouples are the most popular temperature-sensing
device because of their low cost, interchangeability, and
ability to measure a wide range of temperatures. The
ISL28X78 (Figure 38) is used to convert the differential
thermocouple voltage into single-ended signal with 10X gain.
The ISL28X78's rail-to-rail input characteristic allows the
thermocouple to be biased at ground and the amplifier to run
from a single 5V supply.
.
R4
100kΩ
R3
10kΩ
R2
K TYPE
THERMOCOUPLE
10kΩ
V+
+
ISL28X78
V-
410µV/°C
+
5V
R1
100kΩ
-
FIGURE 38. THERMOCOUPLE AMPLIFIER
1/2 ISL28278
1/4 ISL28478
+
FIGURE 36. PREVENTING OSCILLATIONS IN UNUSED
CHANNELS
Proper Layout Maximizes Performance
To achieve the maximum performance of the high input
impedance and low offset voltage of the ISL28278 and
ISL28478, care should be taken in the circuit board layout.
The PC board surface must remain clean and free of
moisture to avoid leakage currents between adjacent traces.
Surface coating of the circuit board will reduce surface
moisture and provide a humidity barrier, reducing parasitic
resistance on the board. When input leakage current is a
concern, the use of guard rings around the amplifier inputs
will further reduce leakage currents. Figure 37 shows a
guard ring example for a unity gain amplifier that uses the
low impedance amplifier output at the same voltage as the
high impedance input to eliminate surface leakage. The
guard ring does not need to be a specific width, but it should
11
Current Limiting
The ISL28278 and ISL28478 have no internal currentlimiting circuitry. If the output is shorted, it is possible to
exceed the Absolute Maximum Rating for output current or
power dissipation, potentially resulting in the destruction of
the device.
Power Dissipation
It is possible to exceed the +150°C maximum junction
temperatures under certain load and power-supply
conditions. It is therefore important to calculate the
maximum junction temperature (TJMAX) for all applications
to determine if power supply voltages, load conditions, or
package type need to be modified to remain in the safe
operating area. These parameters are related in Equation 1:
T JMAX = T MAX + ( θ JA xPD MAXTOTAL )
(EQ. 1)
FN6145.2
July 11, 2007
ISL28278, ISL28478
where:
• PDMAXTOTAL is the sum of the maximum power
dissipation of each amplifier in the package (PDMAX)
• PDMAX for each amplifier is calculated in Equation 2:
V OUTMAX
PD MAX = 2*V S × I SMAX + ( V S - V OUTMAX ) × ---------------------------RL
(EQ. 2)
where:
• TMAX = Maximum ambient temperature
• θJA = Thermal resistance of the package
• PDMAX = Maximum power dissipation of 1 amplifier
• VS = Supply voltage (Magnitude of V+ and V-)
• IMAX = Maximum supply current of 1 amplifier
• VOUTMAX = Maximum output voltage swing of the
application
• RL = Load resistance
12
FN6145.2
July 11, 2007
ISL28278, ISL28478
Quarter Size Outline Plastic Packages Family (QSOP)
MDP0040
A
QUARTER SIZE OUTLINE PLASTIC PACKAGES FAMILY
D
(N/2)+1
N
INCHES
SYMBOL QSOP16 QSOP24 QSOP28 TOLERANCE NOTES
E
PIN #1
I.D. MARK
E1
1
(N/2)
A
0.068
0.068
0.068
Max.
-
A1
0.006
0.006
0.006
±0.002
-
A2
0.056
0.056
0.056
±0.004
-
b
0.010
0.010
0.010
±0.002
-
c
0.008
0.008
0.008
±0.001
-
D
0.193
0.341
0.390
±0.004
1, 3
E
0.236
0.236
0.236
±0.008
-
E1
0.154
0.154
0.154
±0.004
2, 3
e
0.025
0.025
0.025
Basic
-
L
0.025
0.025
0.025
±0.009
-
L1
0.041
0.041
0.041
Basic
-
N
16
24
28
Reference
-
B
0.010
C A B
e
H
C
SEATING
PLANE
0.007
0.004 C
b
C A B
Rev. F 2/07
NOTES:
L1
A
1. Plastic or metal protrusions of 0.006” maximum per side are not
included.
2. Plastic interlead protrusions of 0.010” maximum per side are not
included.
c
SEE DETAIL "X"
3. Dimensions “D” and “E1” are measured at Datum Plane “H”.
4. Dimensioning and tolerancing per ASME Y14.5M-1994.
0.010
A2
GAUGE
PLANE
L
A1
4°±4°
DETAIL X
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Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without
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reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result
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13
FN6145.2
July 11, 2007