OPA378
OPA2378
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SBOS417D – JANUARY 2008 – REVISED OCTOBER 2009
Low-Noise, 900kHz, RRIO,
Precision OPERATIONAL AMPLIFIER
Zerø-Drift Series
Check for Samples: OPA378 OPA2378
FEATURES
DESCRIPTION
•
The OPA378 and OPA2378 represent a new
generation of Zerø-Drift, microPOWER™ operational
amplifiers that use a proprietary auto-calibration
technique to provide minimal input offset voltage
(20μV) and offset voltage drift (0.1μV/°C). The
combination of low input voltage noise, high gain
bandwidth (900kHz), and low power (150μA max)
enable these devices to achieve optimum
performance for low-power precision applications. In
addition, the excellent PSRR performance, coupled
with a wide input supply range of 2.2V to 5.5V and
rail-to-rail input and output, makes it an outstanding
choice for single-supply applications that run directly
from batteries without regulation.
1
23
•
•
•
•
•
•
•
LOW NOISE
– 0.4μVPP, 0.1Hz to 10Hz
– 20nV/√Hz at 1kHz
ZERØ-DRIFT SERIES
– LOW OFFSET VOLTAGE: 20μV
– LOW OFFSET DRIFT: 0.1μV/°C
QUIESCENT CURRENT: 125μA
GAIN BANDWIDTH: 900kHz
RAIL-TO-RAIL INPUT/OUTPUT
EMI FILTERING
SUPPLY VOLTAGE: 2.2V to 5.5V
microSIZE PACKAGES: SC70 and SOT23
APPLICATIONS
•
•
•
•
•
•
PORTABLE MEDICAL DEVICES
– GLUCOSE METERS
– OXYGEN METERING
– HEART RATE MONITORS
WEIGH SCALES
BATTERY-POWERED INSTRUMENTS
THERMOPILE MODULES
HANDHELD TEST EQUIPMENT
SENSOR SIGNAL CONDITIONING
The OPA378 (single version) is available in both a
microSIZE SC70-5 and a SOT23-5 package. The
OPA2378 (dual version) is offered in a SOT23-8
package. All versions are specified for operation from
–40°C to +125°C.
NOISE SPECTRAL DENSITY vs FREQUENCY
0.1Hz TO 10Hz NOISE
1k
100nV/div
Voltage Noise Density (nV/ÖHz)
Current Noise (fA/ÖHz)
Continues with No 1/f (flicker) Noise
Current Noise
100
Voltage Noise
10
1
Time (1s/div)
1
10
100
1k
10k
Frequency (Hz)
1
2
3
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas
Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
microPOWER is a trademark of Texas Instruments Incorporated.
All other trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2008–2009, Texas Instruments Incorporated
OPA378
OPA2378
SBOS417D – JANUARY 2008 – REVISED OCTOBER 2009
www.ti.com
This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more
susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.
PACKAGE INFORMATION (1)
(1)
PRODUCT
PACKAGE-LEAD
PACKAGE DESIGNATOR
PACKAGE MARKING
OPA378
SOT23-5
DBV
OAZI
OPA378
SC70-5
DCK
BTS
OPA2378
SOT23-8
DCN
OCAI
For the most current package and ordering information, see the Package Option Addendum at the end of this document, or see the TI
web site at www.ti.com.
ABSOLUTE MAXIMUM RATINGS (1)
Over operating free-air temperature range (unless otherwise noted).
OPA378, OPA2378
UNIT
+7
V
Supply Voltage, VS = (V+) – (V–)
Signal Input Terminals
Voltage (2)
(V–) – 0.3 ≤ VIN ≤ (V+) + 0.3
V
Current (2)
±10
mA
Output Short-Circuit (3)
Continuous
Operating Temperature, TA
–55 to +150
°C
Storage Temperature, TA
–65 to +150
°C
Junction Temperature, TJ
+150
°C
Human Body Model (HBM)
4000
V
Charged Device Model (CDM)
1000
V
Machine Model (MM)
200
V
ESD Ratings
(1)
(2)
(3)
Stresses above these ratings may cause permanent damage. Exposure to absolute maximum conditions for extended periods may
degrade device reliability. These are stress ratings only, and functional operation of the device at these or any other conditions beyond
those specified is not supported.
Input terminals are diode-clamped to the power-supply rails. Input signals that can swing more than 0.3V beyond the supply rails should
be current limited to 10mA or less.
Short-circuit to ground, one amplifier per package.
PIN CONFIGURATIONS
OPA378
SC70-5
(TOP VIEW)
+In
V-In
2
1
5
V+
2
3
OPA2378
SOT23-8
(TOP VIEW)
OPA378
SOT23-5
(TOP VIEW)
Out
V4
Out
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+In
1
5
Out A
V+
-In A
2
3
4
-In
1
2
+In A
3
V-
4
A
B
8
V+
7
Out B
6
-In B
5
+In B
Copyright © 2008–2009, Texas Instruments Incorporated
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OPA2378
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SBOS417D – JANUARY 2008 – REVISED OCTOBER 2009
ELECTRICAL CHARACTERISTICS: VS = +2.2V to +5.5V
Boldface limits apply over the specified temperature range, TA = –40°C to +125°C.
At TA = +25°C, RL = 10kΩ connected to VS/2, VCM = VS/2, and VOUT = VS/2, unless otherwise noted.
OPA378, OPA2378
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
20
50
μV
0.1
0.25
μV/°C
20
70
µV
-40°C to +125°C
0.25
0.4
µV/°C
µV/°C
OFFSET VOLTAGE
Input Offset Voltage, OPA378
vs Temperature
VOS
VCM = V–
dVOS/dT
Input Offset Voltage, OPA2378
vs Temperature
vs Power Supply, OPA378
dVOS/dT
PSRR
over Temperature
vs Power Supply, OPA2378
–40°C to +85°C
0.15
0.25
VCM = 0V, VS = +2.2V to +5.5V
1.5
5
μV/V
VCM = 0V, VS = +2.2V to +5.5V
3
8
μV/V
VCM = 0V, VS = +2.2V to +5.5V
over Temperature
Channel Separation (Dual Version)
VCM = 0V, VS = +2.2V to +5.5V
3
At dc
135
10
μV/V
13
μV/V
dB
INPUT BIAS CURRENT
Input Bias Current, OPA378
IB
Input Bias Current, OPA2378
±150
±550
±150
±670
pA
±2
nA
±0.3
±1.1
nA
±0.3
±1.34
nA
over Temperature, OPA378 and OPA2378
Input Offset Current, OPA378
IOS
Input Offset Current, OPA2378
pA
NOISE
Input Voltage Noise
en
f = 0.1Hz to 10Hz, VS = +5.5V
0.4
μVPP
Input Voltage Noise Density
en
f = 1kHz
20
nV/√Hz
in
f = 10Hz
200
fA/√Hz
Input Current Noise
INPUT VOLTAGE RANGE
Common-Mode Voltage Range
VCM
Common-Mode Rejection Ratio
CMRR
over Temperature
(V–) – 0.05
(V+) + 0.05
V
(V–) – 0.05V < VCM < (V+) + 0.05V, VS = 5.5V
100
112
dB
(V–) – 0.05V < VCM < (V+) + 0.05V, VS = 2.2V
94
106
(V–) – 0.05V < VCM < (V+) + 0.05V, VS = 5.5V
96
dB
(V–) – 0.05V < VCM < (V+) + 0.05V, VS = 2.2V
90
dB
dB
INPUT CAPACITANCE
Differential
CIN
Common-Mode
4
pF
5
pF
dB
OPEN-LOOP GAIN
Open-Loop Voltage Gain
AOL
over Temperature
50mV < VO < (V+) – 50mV, RL = 100kΩ
110
134
100mV < VO < (V+) – 100mV, RL = 10kΩ
110
130
100mV < VO < (V+) – 100mV, RL = 10kΩ
106
dB
dB
FREQUENCY RESPONSE
Gain-Bandwidth Product
Slew Rate
GBW
SR
900
kHz
G = +1
0.4
V/μs
Settling Time 0.1%
tS
VS = 5.5V, 2V Step, G = +1
7
μs
Settling Time 0.01%
tS
VS = 5.5V, 2V Step, G = +1
9
μs
VIN × Gain > VS
4
μs
VS = 5V, VO = 3VPP, G = +1, f = 1kHz
0.003
%
Overload Recovery Time
THD + Noise
THD + N
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OPA2378
SBOS417D – JANUARY 2008 – REVISED OCTOBER 2009
www.ti.com
ELECTRICAL CHARACTERISTICS: VS = +2.2V to +5.5V (continued)
Boldface limits apply over the specified temperature range, TA = –40°C to +125°C.
At TA = +25°C, RL = 10kΩ connected to VS/2, VCM = VS/2, and VOUT = VS/2, unless otherwise noted.
OPA378, OPA2378
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
RL = 10kΩ
6
8
mV
RL = 10kΩ
8
13
mV
RL = 10kΩ
6
10
mV
RL = 10kΩ
8
15
mV
RL = 100kΩ
0.7
2
mV
3
mV
OUTPUT
Voltage Output Swing from Rail,
OPA378
VO
over Temperature
Voltage Output Swing from Rail,
OPA2378
VO
over Temperature
Voltage Output Swing from Rail
over Temperature
RL = 100kΩ
Short-Circuit Current
Capacitive Load Drive
±30
mA
CLOAD
ISC
See Figure 18
pF
ZO
See Figure 23
Ω
Open-Loop Output Impedance
POWER SUPPLY
Specified Voltage Range
Quiescent Current (per Amplifier)
VS
IQ
2.2
IO = 0mA, VS = +5.5V
125
over Temperature
5.5
V
150
μA
165
μA
°C
TEMPERATURE RANGE
Specified Range
–40
+125
Operating Range
–55
+150
Thermal Resistance
4
θJA
°C
°C/W
SOT23-5
200
°C/W
SC70-5
250
°C/W
SOT23-8
100
°C/W
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OPA2378
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SBOS417D – JANUARY 2008 – REVISED OCTOBER 2009
TYPICAL CHARACTERISTICS
At TA = +25°C, RL = 10kΩ, VS = +5.5V and VOUT = VS/2, unless otherwise noted.
INPUT CURRENT AND VOLTAGE NOISE
SPECTRAL DENSITY vs FREQUENCY
0.1Hz TO 10Hz NOISE
1k
100nV/div
Voltage Noise Density (nV/ÖHz)
Current Noise (fA/ÖHz)
Continues with No 1/f (flicker) Noise
Current Noise
100
Voltage Noise
10
1
Time (1s/div)
1
10
100
1k
10k
Frequency (Hz)
Figure 1.
Figure 2.
OFFSET VOLTAGE
PRODUCTION DISTRIBUTION
OFFSET VOLTAGE DRIFT DISTRIBUTION
VS = 5.5V
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.10
0.11
0.12
0.13
0.14
0.15
0.16
0.17
0.18
0.19
0.20
0.21
0.22
0.23
0.24
0.25
-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
5
10
15
20
25
30
35
40
45
50
Population
Population
VS = 5.5V
Offset Voltage (mV)
|Offset Voltage Drift| (mV/°C)
Figure 3.
Figure 4.
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OPA378
OPA2378
SBOS417D – JANUARY 2008 – REVISED OCTOBER 2009
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TYPICAL CHARACTERISTICS (continued)
At TA = +25°C, RL = 10kΩ, VS = +5.5V and VOUT = VS/2, unless otherwise noted.
POWER-SUPPLY REJECTION RATIO
vs FREQUENCY
OFFSET VOLTAGE vs TEMPERATURE
80
120
60
100
Offset Voltage (mV)
40
+PSRR
80
PSRR (dB)
20
0
-20
60
-PSRR
40
-40
20
-60
-80
0
-75
-50
-25
25
0
75
50
100
125
150
10
1
100
Temperature (°C)
Figure 5.
Figure 6.
OPEN-LOOP GAIN AND PHASE
vs FREQUENCY
OPEN-LOOP GAIN
vs TEMPERATURE
140
120
Phase
140
150
120
145
140
100
100
60
60
40
40
Gain
AOL (dB)
80
Phase (°)
80
20
100k
1M
RL = 100kW
135
Gain (dB)
10k
1k
Frequency (Hz)
RL = 10kW
130
RL = 5kW
125
120
115
20
110
0
0
-20
1
0.1
10
100
1k
10k
100k
1M
105
-20
10M
100
-75
-50
-25
0
Frequency (Hz)
75
100
125
150
Figure 8.
COMMON-MODE REJECTION RATIO
vs FREQUENCY
COMMON-MODE REJECTION RATIO AND
POWER-SUPPLY REJECTION RATIO vs TEMPERATURE
120
140
100
130
PSRR, CMRR (dB)
CMRR (dB)
50
Figure 7.
80
60
40
VSCMRR
= 5.5V
VS = 5.5V
120
PSRR
110
CMRR
VS = 2.2V
100
90
20
80
0
10
100
1k
10k
100k
1M
-75
-25
-50
Figure 9.
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0
25
50
75
100
125
150
Temperature (°C)
Frequency (Hz)
6
25
Temperature (°C)
Figure 10.
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OPA2378
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SBOS417D – JANUARY 2008 – REVISED OCTOBER 2009
TYPICAL CHARACTERISTICS (continued)
At TA = +25°C, RL = 10kΩ, VS = +5.5V and VOUT = VS/2, unless otherwise noted.
INPUT BIAS CURRENT
vs INPUT COMMON-MODE VOLTAGE
INPUT BIAS CURRENT
vs TEMPERATURE
2000
400
1500
-IB
200
Input Bias Current (pA)
Input Bias Current (pA)
300
100
0
-100
-200
+IB
500
0
-500
-1000
-1500
-300
-400
-0.5 0
1000
-2000
-75
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
-50
-25
0
75
Figure 12.
QUIESCENT CURRENT
vs SUPPLY VOLTAGE
QUIESCENT CURRENT
vs TEMPERATURE
200
200
175
175
Quiescent Current (mA)
Quiescent Current (mA)
50
Figure 11.
150
125
100
75
100
125
150
150
125
100
75
2.5
2.0
3.0
3.5
4.0
4.5
5.0
5.5
-75
-50
-25
VS (V)
0
25
50
75
100
125
150
Temperature (°C)
Figure 13.
Figure 14.
OUTPUT VOLTAGE SWING
vs OUTPUT CURRENT
MAXIMUM OUTPUT VOLTAGE
vs FREQUENCY
6
3
V+ = +2.75
+125°C
+25°C -40°C
1
0
+125°C
VS = ±1.1
+25°C
-40°C
-1
+125°C
-2
VS = 5.5V
5
Output Voltage (V)
2
Output Swing (V)
25
Temperature (°C)
Input Common-Mode Voltage (V)
4
3
2
VS = 2.2V
+25°C -40°C
1
V- = -2.75
-3
0
0
2
4
6
8
10
12
14
16
18
20
1k
10k
100k
1M
10M
Frequency (Hz)
Output Current (mA)
Figure 15.
Figure 16.
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OPA2378
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TYPICAL CHARACTERISTICS (continued)
At TA = +25°C, RL = 10kΩ, VS = +5.5V and VOUT = VS/2, unless otherwise noted.
TOTAL HARMONIC DISTORTION + NOISE
vs FREQUENCY
SMALL-SIGNAL OVERSHOOT
vs LOAD CAPACITANCE
1
60
50
40
Overshoot (%)
THD+N (%)
0.1
0.01
30
Gain = +1V/V, -1V/V
R = 10kW
20
0.001
Gain = -1V/V
R = 5kW
10
0.0001
0
10
100
10k
1k
1
10
Frequency (Hz)
100
1k
Load Capacitance (pF)
Figure 17.
Figure 18.
POSITIVE OVER-VOLTAGE RECOVERY
NEGATIVE OVER-VOLTAGE RECOVERY
10kW
+2.5V
2V/div
Output
0
+2.5V
1kW
2V/div
10kW
1kW
0
OPA378
Output
RL
OPA378
-2.5V
RL
1V/div
1V/div
-2.5V
0
Input
Input
0
Time (4ms/div)
Time (10ms/div)
Figure 19.
Figure 20.
SMALL-SIGNAL STEP RESPONSE
LARGE-SIGNAL STEP RESPONSE
VS = ±2.75V
Voltage (1V/div)
Output Voltage (10mV/div)
G = +1
VIN
Time (5ms/div)
Time (20ms/div)
Figure 21.
8
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VOUT
Figure 22.
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OPA2378
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SBOS417D – JANUARY 2008 – REVISED OCTOBER 2009
TYPICAL CHARACTERISTICS (continued)
At TA = +25°C, RL = 10kΩ, VS = +5.5V and VOUT = VS/2, unless otherwise noted.
INPUT BIAS CURRENT vs
INPUT DIFFERENTIAL VOLTAGE
OPEN-LOOP OUTPUT IMPEDANCE vs FREQUENCY
50
10k
Normal Operating Range
(see the Input Differential
Voltage section in the
Applications Information)
40
Input Bias Current (mA)
Output Impedance (W)
1k
IO = 0A
100
10
IO = 400mA
1
1
10
100
1k
20
10
0
-10
-20
-30
Over-Driven Condition
Over-Driven Condition
-40
IO = 2mA
0.1
30
-50
10k
100k
-1V -800 -600 -400 -200
1M
0
200 400 600 800
1V
Input Differential Voltage (mV)
Frequency (Hz)
Figure 23.
Figure 24.
OPA2378 CHANNEL SEPARATION
-160
-140
Overshoot (%)
-120
-100
-80
-60
-40
-20
0
1k
10k
100k
1M
10M
100M
1G
Frequency (Hz)
Figure 25.
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OPA2378
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APPLICATIONS INFORMATION
OPERATING VOLTAGE
The OPA378 and OPA2378 can be used with single
or dual supplies from an operating range of VS =
+2.2V (±1.1V) and up to VS = +5.5V (±2.75V). This
device does not require symmetrical supplies, only a
differential supply voltage of 2.2V to 5.5V. A
power-supply rejection ratio of 1.5μV/V (typical)
ensures that the device functions with an unregulated
battery source. Supply voltages higher than +7V can
permanently damage the device; see the Absolute
Maximum Ratings table. Key parameters are assured
over the specified temperature range, TA = –40°C to
+125°C. Parameters that vary over the supply voltage
or temperature range are shown in the Typical
Characteristics section of this data sheet.
INPUT VOLTAGE
50
40
VS = ±2.75V
10 Typical Units Shown
30
20
VOS (mV)
The OPA378 and OPA2378 are unity-gain stable,
precision operational amplifiers that are free from
phase reversal. The use of proprietary Zerø-Drift
circuitry gives the benefit of low input offset voltage
over time and temperature as well as lowering the 1/f
noise component. This design provides the
optimization of gain, noise, and power, making the
OPA378 series one of the best performers in this
bandwidth range. As a result of the high PSRR, this
device works well in applications that run directly from
battery power without regulation. They are optimized
for low-voltage, single-supply operation. These
miniature, high-precision, low quiescent current
amplifiers offer high-impedance inputs that have a
common-mode range 100mV beyond the supplies,
excellent CMRR, and a rail-to-rail output that swings
within 10mV of the supplies. This design results in
superior performance for driving analog-to-digital
converters (ADCs) without degradation of differential
linearity.
10
0
-10
-20
-30
-40
-50
-3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0
0.5 1.0 1.5 2.0 2.5 3.0
VCM (V)
Figure 26. Offset Voltage versus Common-Mode
Voltage
Normally, input bias current is about 150pA; however,
input voltages exceeding the power supplies can
cause excessive current to flow into or out of the
input pins. Momentary voltages greater than the
power supply can be tolerated if the input current is
limited to 10mA. This limitation is easily accomplished
with an input resistor, as Figure 27 shows.
Current-limiting resistor
required if input voltage
exceeds supply rails by
³ 0.5V.
+5V
IOVERLOAD
10mA max
OPA378
VOUT
VIN
5kW
Figure 27. Input Current Protection
The OPA378 and OPA2378 input common-mode
voltage range extends 0.05V beyond the supply rails.
The OPA378 achieves a common-mode rejection
ratio of 112dB (typical) over the common-mode
voltage range. Figure 26 shows the variation of offset
voltage over the entire specified common-mode
range for 10 typical units.
10
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The typical input bias current of the OPA378 during
normal operation is approximately 150pA. In
over-driven conditions, the bias current can increase
significantly (see Figure 24). The most common
cause of an over-driven condition occurs when the op
amp is outside of the linear range of operation. When
the output of the op amp is driven to one of the
supply rails the feedback loop requirements cannot
be satisfied and a differential input voltage develops
across the input pins. This differential input voltage
results in activation of parasitic diodes inside the front
end input chopping switches that combine with 1.5kΩ
EMI filter resistors to create the equivalent circuit
shown in Figure 28.
1.5kW
Clamp
OPA378 operational amplifier family incorporates an
internal input low-pass filter that reduces the amplifier
response to EMI. Both common-mode and
differential-mode filtering are provided by the input
filter. The filter is designed for a cutoff frequency of
approximately 25MHz (–3dB), with a roll-off of 20dB
per decade. Figure 29 shows the EMI filter.
0
Filter Response (dB)
INPUT DIFFERENTIAL VOLTAGE
-10
-20
-30
fC = 25MHz with Parasitics
Over Temperature
-29dB at 800MHz
+In
CORE
-In
-40
1k
1.5kW
10k
100k
1M
10M
100M
1G
Frequency (Hz)
Figure 28. Equivalent Input Circuit
Figure 29. EMI Filter
INTERNAL OFFSET CORRECTION
The OPA378 and OPA2378 family of op amps use an
auto-calibration technique with a time-continuous
350kHz op amp in the signal path. This amplifier is
zero-corrected every 3μs using a proprietary
technique. Upon power-up, the amplifier requires
approximately 100μs to achieve specified VOS
accuracy. This architecture has no aliasing or flicker
noise.
NOISE
The OPA378 series of op amps have excellent
distortion characteristics. Total harmonic distortion +
noise is below 0.003% (G = +1, VO = 3VRMS, and f =
1kHz, with a 10kΩ load). Design of low-noise op amp
circuits requires careful consideration of a variety of
possible noise contributors: noise from the signal
source, noise generated in the op amp, and noise
from the feedback network resistors. The total noise
of the circuit is the root-sum-square combination of all
the noise components.
EMI SUSCEPTIBILITY AND INPUT FILTERING
Operational amplifiers vary in their susceptibility to
electromagnetic interference (EMI). If conducted EMI
enters the operational amplifier, the dc offset
observed at the amplifier output may shift from its
nominal value while the EMI is present. This shift is a
result of signal rectification associated with the
internal semiconductor junctions. While all operational
amplifier pin functions can be affected by EMI, the
input pins are likely to be the most susceptible. The
GENERAL LAYOUT GUIDELINES
Attention to good layout practices is always
recommended. Keep traces short and, when
possible, use a printed circuit board (PCB) ground
plane with surface-mount components placed as
close to the device pins as possible. Place a 0.1μF
capacitor closely across the supply pins. These
guidelines should be applied throughout the analog
circuit to improve performance.
For lowest offset voltage and precision performance,
circuit layout and mechanical conditions should be
optimized. Avoid temperature gradients that create
thermoelectric (Seebeck) effects in the thermocouple
junctions formed from connecting dissimilar
conductors. These thermally-generated potentials can
be made to cancel by assuring they are equal on
both input terminals. Other layout and design
considerations include:
• Use low thermoelectric-coefficient conditions
(avoid dissimilar metals).
• Thermally isolate components from power
supplies or other heat sources.
• Shield op amp and input circuitry from air
currents, such as cooling fans.
Following these guidelines reduces the likelihood of
junctions being at different temperatures, which can
cause thermoelectric voltages of 0.1μV/°C or higher,
depending on materials used.
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Product Folder Link(s): OPA378 OPA2378
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OPA378
OPA2378
SBOS417D – JANUARY 2008 – REVISED OCTOBER 2009
www.ti.com
ELECTRICAL OVERSTRESS
Designers often ask questions about the capability of
an operational amplifier to withstand electrical
overstress. These questions tend to focus on the
device inputs, but may involve the supply voltage pins
or even the output pin. Each of these different pin
functions have electrical stress limits determined by
the voltage breakdown characteristics of the
particular semiconductor fabrication process and
specific circuits connected to the pin. Additionally,
internal electrostatic discharge (ESD) protection is
built into these circuits to protect them from
accidental ESD events both before and during
product assembly.
It is helpful to have a good understanding of this
basic ESD circuitry and its relevance to an electrical
overstress event. Figure 30 shows the ESD circuits
contained in the OPA378 (indicated by the dashed
line area). The ESD protection circuitry involves
several current-steering diodes connected from the
input and output pins and routed back to the internal
power-supply lines, where they meet at an absorption
device internal to the operational amplifier. This
protection circuitry is intended to remain inactive
during normal circuit operation.
RF
+V
+VS
ESD
OPA378
V-
ESD
RI
ESD CurrentSteering Diodes
-In
Op-Amp
Core
+In
Edge-Triggered ESD
Absorption Circuit
ID
Out
RL
ESD
VIN
(1)
ESD
V+
-V
-VS
(1) VIN = +VS + 500mV.
Figure 30. Equivalent Internal ESD Circuitry and Its Relation to a Typical Circuit Application
12
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OPA378
OPA2378
www.ti.com
SBOS417D – JANUARY 2008 – REVISED OCTOBER 2009
An ESD event produces a short duration,
high-voltage pulse that is transformed into a short
duration, high-current pulse as it discharges through
a semiconductor device. The ESD protection circuits
are designed to provide a current path around the
operational amplifier core to prevent it from being
damaged. The energy absorbed by the protection
circuitry is then dissipated as heat.
When an ESD voltage develops across two or more
of the amplifier device pins, current flows through one
or more of the steering diodes. Depending on the
path that the current takes, the absorption device
may activate. The absorption device has a trigger, or
threshold voltage, that is above the normal operating
voltage of the OPA378 but below the device
breakdown voltage level. Once this threshold is
exceeded, the absorption device quickly activates
and clamps the voltage across the supply rails to a
safe level.
When the operational amplifier connects into a circuit
such as that illustrated in Figure 30, the ESD
protection components are intended to remain
inactive and not become involved in the application
circuit operation. However, circumstances may arise
where an applied voltage exceeds the operating
voltage range of a given pin. Should this condition
occur, there is a risk that some of the internal ESD
protection circuits may be biased on, and conduct
current. Any such current flow occurs through
steering diode paths and rarely involves the
absorption device.
Figure 30 depicts a specific example where the input
voltage, VIN, exceeds the positive supply voltage
(+VS) by 300mV or more. Much of what happens in
the circuit depends on the supply characteristics. If
+VS can sink the current, one of the upper input
steering diodes conducts and directs current to +VS.
Excessively high current levels can flow with
increasingly higher VIN. As a result, the datasheet
specifications recommend that applications limit the
input current to 10mA.
If the supply is not capable of sinking the current, VIN
may begin sourcing current to the operational
amplifier, and then take over as the source of positive
supply voltage. The danger in this case is that the
voltage can rise to levels that exceed the operational
amplifier absolute maximum ratings. In extreme but
rare cases, the absorption device triggers on while
+VS and –VS are applied. If this event happens, a
direct current path is established between the +VS
and –VS supplies. The power dissipation of the
absorption device is quickly exceeded, and the
extreme internal heating destroys the operational
amplifier.
Another common question involves what happens to
the amplifier if an input signal is applied to the input
while the power supplies +VS and/or –VS are at 0V.
Again, it depends on the supply characteristic while at
0V, or at a level below the input signal amplitude. If
the supplies appear as high impedance, then the
operational amplifier supply current may be supplied
by the input source via the current steering diodes.
This state is not a normal bias condition; the amplifier
most likely will not operate normally. If the supplies
are low impedance, then the current through the
steering diodes can become quite high. The current
level depends on the ability of the input source to
deliver current, and any resistance in the input path.
APPLICATION IDEAS
Figure 31 shows the basic configuration for a bridge
amplifier.
A low-side current shunt monitor is shown in
Figure 32. RN are optional resistors used to isolate
the ADS8325 from the noise of the digital two-wire
bus. Because the ADS8325 is a 16-bit converter, a
precise reference is essential for maximum accuracy.
If absolute accuracy is not required, and the 5V
power supply is sufficiently stable, the REF3330 may
be omitted.
Figure 33 shows a high-side current monitor. The
load current develops a voltage drop across RSHUNT.
The noninverting input monitors this voltage and is
duplicated on the inverting input. RG then has the
same voltage drop as RSHUNT. RG can be sized to
provide whatever current is most convenient to the
designer based on design constraints. The current
from RG then flows through the MOSFET and to
resistor RL, creating a voltage that can be read. Note
that RL and RG set the voltage gain of the circuit.
The supply voltage for the op amp is derived from the
zener diode. For the OPA378 VS must be between
2.2V and 5.5V. Two possible methods to bias the
zener are shown in the circuit of Figure 33: the
customary resistor bias and the current monitor. The
current monitor biasing achieves the lowest possible
voltage. Resistor R1 and the diode on the
noninverting input provide short-circuit protection.
VEX
R1
+5V
R R
R R
OPA378
VOUT
R1
VREF
Figure 31. Single Op Amp Bridge Amplifier
Copyright © 2008–2009, Texas Instruments Incorporated
Product Folder Link(s): OPA378 OPA2378
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OPA378
OPA2378
SBOS417D – JANUARY 2008 – REVISED OCTOBER 2009
www.ti.com
REF3330
+5V
3V
Load
R1
4.99kW
R2
49.9kW
ILOAD
R6
71.5kW
RS
600W
V
RSHUNT
1W
OPA378
C1
1.2nF
R4
48.7kW
R3
4.99kW
ADS1100
R7
1.18kW
Stray Ground-Loop Resistance
RN
56W
RN
56W
2
IC
(PGA Gain = 4)
FS = 3.0V
NOTE: 1% resistors provide adequate common-mode rejection at small ground-loop errors.
Figure 32. Low-Side Current Monitor
RG
RSHUNT
zener
(1)
V+
(2)
R1
10kW
CBYPASS
MOSFET rated to
stand-off supply voltage
such as BSS84 for
up to 50V.
OPA378
+5V
V+
Two zener
biasing methods
(3)
are shown.
Output
Load
RBIAS
RL
(1) Zener rated for op amp supply capability (that is, 5.1V for the OPA378).
(2) Current-limiting resistor.
(3) Choose zener biasing resistor or dual NMOSFETs (2N7002, NTZD511ON, SM6K2T110).
Figure 33. High-Side Current Monitor
14
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Product Folder Link(s): OPA378 OPA2378
OPA378
OPA2378
www.ti.com
SBOS417D – JANUARY 2008 – REVISED OCTOBER 2009
REF3333
+5V
0.1mF
3.3V
+
R1
6.04kW
D1
-
R2
2.94kW
-
+ +
R8
150kW
R5
31.6kW
+5V
10mF
0.1mF
R7
549W
R4
6.04kW
R3
60.4W
VO
OPA378
R6
200W
K-Type
Thermocouple
40.7mV/°C
Zero Adj.
Figure 34. Temperature Measurement
1MW
60kW
100kW
V1
-In
INA152
OPA378
3V
1MW
NTC
Thermistor
R2
OPA378
R1
2
5
6
R2
3
Figure 35. Thermistor Measurement
VO
1
OPA378
V2
+In
VO = (1 + 2R2/R1) (V2 - V1)
Figure 36. Precision Instrumentation Amplifier
Copyright © 2008–2009, Texas Instruments Incorporated
Product Folder Link(s): OPA378 OPA2378
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OPA378
OPA2378
SBOS417D – JANUARY 2008 – REVISED OCTOBER 2009
www.ti.com
+VS
R1
100kW
fLPF = 150Hz
C4
1.06nF
1/2
OPA2378
RA
+VS
R2
100kW
R6
100kW
1/2
OPA2378
+VS
3
2
LL
7
INA321
(1)
4
5
R8
100kW
+VS
dc
R3
100kW
1/2
OPA2378
Wilson
LA
R14
1MW
GTOT = 1kV/V
R7
100kW
ac
GINA = 5
R12
5kW
6
+VS
1
C3
1mF
VOUT
OPA378
R13
318kW
GOPA = 200
+VS
1/2
OPA2378
VCENTRAL
C1
47pF
(RA + LA + LL)/3
fHPF = 0.5Hz
(provides ac signal coupling)
1/2 VS
R5
390kW
R9
20kW
+VS
R4
100kW
1/2
OPA2378
RL
Inverted
VCM
+VS
VS = +2.7V to +5.5V
1/2
OPA2378
BW = 0.5Hz to 150Hz
+VS
R10
1MW
1/2 VS
C2
0.64mF
R11
1MW
fO = 0.5Hz
(1) Other instrumentation amplifiers can be used, such as the INA326, which has lower noise but higher quiescent current.
Figure 37. Single-Supply, Very Low Power ECG Circuit
16
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OPA378
OPA2378
www.ti.com
SBOS417D – JANUARY 2008 – REVISED OCTOBER 2009
C7
110pF
C4
600pF
Digital Stethoscope
Microphone Output
R5
100kW
R3
100kW
C2
10mF
Electret
Microphone
Element
with
Internal FET
+5V
R2
10kW
Out
OPA378
C6
470nF
C3
1 mF
2.2kW
Mic
Bias
Mic
Output
+5V
R4
10kW
OPA378
C1
33pF
Gnd
C5
10mF
VBIAS1
VBIAS2
Figure 38. Digital Stethoscope Circuit
Copyright © 2008–2009, Texas Instruments Incorporated
Product Folder Link(s): OPA378 OPA2378
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OPA378
OPA2378
SBOS417D – JANUARY 2008 – REVISED OCTOBER 2009
www.ti.com
REVISION HISTORY
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision C (June 2009) to Revision D
Page
•
Changed OPA2378 orderable status to production data; updated references throughout document ................................. 1
•
Changed first sentence of Description section ..................................................................................................................... 1
•
Deleted footnote 2 from Package Information table ............................................................................................................. 2
•
Added OPA2378 parameters to the Offset Voltage section of the Electrical Characteristics table ...................................... 3
•
Deleted footnote 1 from Electrical Characteristics table ....................................................................................................... 3
•
Added OPA378 to the Offset Voltage, Input Offset Voltage and vs Power Supply parameters of the Electrical
Characteristics table ............................................................................................................................................................. 3
•
Added typical specification to the OPA378 Offset Voltage, Over Temperature parameter of the Electrical
Characteristics table ............................................................................................................................................................. 3
•
Added Offset Voltage, Channel Separation parameter to the Electrical Characteristics table ............................................. 3
•
Added OPA2378 parameters to the Input Bias Current section of the Electrical Characteristics table ............................... 3
•
Added OPA378 to the Input Bias Current, Input Bias Current and Input Offset Current parameters of the Electrical
Characteristics table ............................................................................................................................................................. 3
•
Added typical specification to the Input Bias Current, Input Offset Current, OPA378 parameter of the Electrical
Characteristics table ............................................................................................................................................................. 3
•
Added OPA378 to the Output, Voltage Output Swing from Rail parameter of the Electrical Characteristics ...................... 4
•
Added typical specification to the OPA378 Output, Over Temperature parameter of the Electrical Characteristics
table ...................................................................................................................................................................................... 4
•
Added the OPA2378 Output, Voltage Output Swing from Rail and Over Temperature parameters to the Electrical
Characteristics table ............................................................................................................................................................. 4
•
Updated Figure 18 ................................................................................................................................................................ 8
•
Added Figure 25 ................................................................................................................................................................... 9
•
Updated Figure 32 .............................................................................................................................................................. 14
•
Updated Figure 33 and changed footnote 3 ....................................................................................................................... 14
18
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Product Folder Link(s): OPA378 OPA2378
PACKAGE OPTION ADDENDUM
www.ti.com
10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
OPA2378AIDCNR
ACTIVE
SOT-23
DCN
8
3000
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 125
OCAI
OPA2378AIDCNT
ACTIVE
SOT-23
DCN
8
250
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 125
OCAI
OPA378AIDBVR
ACTIVE
SOT-23
DBV
5
3000
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 125
OAZI
OPA378AIDBVT
ACTIVE
SOT-23
DBV
5
250
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 125
OAZI
OPA378AIDCKR
ACTIVE
SC70
DCK
5
3000
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 125
BTS
OPA378AIDCKT
ACTIVE
SC70
DCK
5
250
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 125
BTS
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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