EL8171IS-T7 [INTERSIL]

Micropower, Single Supply, Rail-to-Rail Input-Output Instrumentation Amplifiers; 微功耗,单电源,轨到轨输入输出仪表放大器
EL8171IS-T7
型号: EL8171IS-T7
厂家: Intersil    Intersil
描述:

Micropower, Single Supply, Rail-to-Rail Input-Output Instrumentation Amplifiers
微功耗,单电源,轨到轨输入输出仪表放大器

仪表放大器
文件: 总11页 (文件大小:825K)
中文:  中文翻译
下载:  下载PDF数据表文档文件
EL8171, EL8172  
®
Data Sheet  
October 26, 2005  
FN6293.0  
Micropower, Single Supply, Rail-to-Rail  
Input-Output Instrumentation Amplifiers  
Features  
• 78µA maximum supply current  
The EL8171 and EL8172 are micropower instrumentation  
amplifiers optimized for operation at 2.9V to 5V single  
supplies. Inputs and outputs can operate rail-to-rail. As with  
all instrumentation amplifiers, a pair of inputs provide very  
high common-mode rejection and are completely  
independent from a pair of feedback terminals. The  
feedback terminals allow zero input to be translated to any  
output offset, including ground. A feedback divider controls  
the overall gain of the amplifier.  
• Maximum input offset voltage  
- 300µV (EL8172)  
- 1000µV (EL8171)  
• 200pA maximum input bias current  
• 3µV/°C offset voltage drift  
• 450kHz -3dB bandwidth (G = 10)  
• 170kHz -3dB bandwidth (G = 100)  
• 0.5V/µs slew rate  
The EL8172 is compensated for a gain of 100 or more, and  
the EL8171 is compensated for a gain of 10 or more. The  
EL8171 and EL8172 have PMOS input devices that provide  
sub-nA input bias currents.  
• Single supply operation  
- Input voltage range is rail-to-rail  
- Output swings rail-to-rail  
The amplifiers can be operated from one lithium cell or two  
Ni-Cd batteries. The EL8171 and EL8172 input range goes  
from below ground to slightly above positive rail. The output  
stage swings completely to ground or positive supply - no  
pull-up or pull-down resistors are needed.  
• Output sources and sinks ±29mA load current  
• 0.2% gain accuracy  
• Pb-free plus anneal available (RoHS compliant)  
Applications  
• Battery- or solar-powered systems  
Pinout  
EL8171, EL8172  
(8 LD SO)  
• Strain gauges  
TOP VIEW  
• Current monitors  
+
-
ENABLE  
IN-  
1
2
3
4
8
7
6
5
FB+  
VS+  
OUT  
FB-  
• Thermocouple amplifiers  
-
Σ
+
IN+  
VS-  
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. 2005. All Rights Reserved.  
1
All other trademarks mentioned are the property of their respective owners.  
EL8171, EL8172  
Ordering Information  
PART  
TAPE &  
REEL  
PKG.  
PART  
PART NUMBER MARKING  
TAPE &  
REEL  
PKG.  
PART NUMBER MARKING  
PACKAGE  
8 Ld SO  
8 Ld SO  
8 Ld SO  
DWG. #  
MDP0027  
MDP0027  
MDP0027  
MDP0027  
PACKAGE  
8 Ld SO  
8 Ld SO  
8 Ld SO  
DWG. #  
EL8171IS  
8171IS  
8171IS  
8171IS  
8171ISZ  
-
7”  
13”  
-
EL8172IS  
8172IS  
8172IS  
8172IS  
8172ISZ  
-
7”  
13”  
-
MDP0027  
MDP0027  
MDP0027  
MDP0027  
EL8171IS-T7  
EL8171IS-T13  
EL8172IS-T7  
EL8172IS-T13  
EL8171ISZ  
(See Note)  
8 Ld SO  
(Pb-free)  
EL8172ISZ  
(See Note)  
8 Ld SO  
(Pb-free)  
EL8171ISZ-T7  
(See Note)  
8171ISZ  
8171ISZ  
7”  
8 Ld SO  
(Pb-free)  
MDP0027  
MDP0027  
EL8172ISZ-T7  
(See Note)  
8172ISZ  
8172ISZ  
7”  
8 Ld SO  
(Pb-free)  
MDP0027  
MDP0027  
EL8171ISZ-T13  
(See Note)  
13”  
8 Ld SO  
(Pb-free)  
EL8172ISZ-T13  
(See Note)  
13”  
8 Ld SO  
(Pb-free)  
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.  
Pin Description  
EL8171/EL8172  
PIN NAME  
PIN FUNCTION  
1
ENABLE  
Active Low. When pulled up above 2V, the in-amp conserves 3µA disabled supply current and the output is  
in a high impedance state. An internal pull down defines the ENABLE low when left floating.  
2
3
5
8
IN-  
IN+  
FB-  
FB+  
Inverting (IN-) and non-inverting (IN+) high impedance input terminals. The input terminals are equivalent to  
the gate of PMOS transistor.  
High impedance feedback terminals. The feedback terminals have a very similar equivalent circuit as the  
input terminals. The negative feedback (FB-) pin connects to an external resistive network to set the gain of  
the in-amp. The positive feedback (FB+) pin can be used to shift the DC level of the output or as an output  
offset.  
7
4
6
VS+  
VS-  
Positive supply terminal.  
Negative supply terminal.  
Output Voltage.  
VOUT  
FN6293.0  
2
October 26, 2005  
EL8171, EL8172  
Absolute Maximum Ratings (T = 25°C)  
A
Supply Voltage, V . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5V  
Output Short-Circuit Duration . . . . . . . . . . . . . . . . . . . . . . .Indefinite  
Ambient Operating Temperature . . . . . . . . . . . . . . . .-40°C to +85°C  
Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . .-65°C to +150°C  
S
Differential Input Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5mA  
Differential Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5V  
V
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .0.5V to V + + 0.5V  
S
EN  
ESD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3kV  
CAUTION: Stresses above those listed in “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress only rating and operation of the  
device at these or any other conditions above those indicated in the operational sections of this specification is not implied.  
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: T = T = T  
A
J
C
Electrical Specifications V + = +5V, V - = GND, VCM = 1/2V + T = 25°C, unless otherwise specified.  
S
S
S
A
PARAMETER  
DESCRIPTION  
CONDITIONS  
MIN  
TYP  
400  
150  
3
MAX  
1000  
300  
UNIT  
µV  
V
Input Offset Voltage  
EL8171  
EL8172  
OS  
µV  
TCV  
Input Offset Voltage Temperature  
Coefficient  
Temperature = -40°C to 85°C  
µV/°C  
OS  
I
I
Input Offset Current  
Input Bias Current  
Input Noise Voltage  
10  
10  
10  
4
200  
200  
pA  
pA  
OS  
B
e
EL8171  
EL8172  
f = 0.1Hz to 10Hz  
µV  
µV  
N
P-P  
P-P  
Input Noise Voltage Density  
Input Resistance  
f = 1kHz  
50  
25  
nV/Hz  
GΩ  
V
o
R
IN  
V
Input Voltage Range  
Guaranteed by CMRR test  
0
80  
80  
80  
70  
-1.5  
-0.8  
0
5
IN  
CMRR  
PSRR  
Common Mode Rejection Ratio  
EL8172, V  
EL8171, V  
= 0V to +5V  
= 0V to +5V  
108  
104  
104  
90  
dB  
CM  
CM  
dB  
Power Supply Rejection Ratio  
Gain Error  
EL8172, V = 2.4V to 5V  
dB  
S
EL8171, V = 2.4V to 5V  
dB  
S
E
V
EL8172, R = 100kto 2.5V  
+0.3  
+0.2  
4
+1.5  
+0.8  
10  
%
G
L
EL8171, R = 100kto 2.5V  
%
L
Maximum Voltage Swing  
Output low, 100kto 2.5V  
Output low, 1kto 2.5V  
Output high, 100kto 2.5V  
Output high, 1kto GND  
mV  
V
OUT  
0.13  
4.996  
4.88  
0.5  
450  
210  
66  
0.25  
4.990  
4.75  
0.3  
V
V
SR  
Slew Rate  
R = 1kto GND  
0.7  
V/µs  
kHz  
kHz  
kHz  
kHz  
kHz  
kHz  
kHz  
kHz  
µA  
L
-3dB BW  
-3dB Bandwidth  
EL8171  
Gain = 10V/V  
Gain = 20  
Gain = 50  
Gain = 100  
Gain = 100  
Gain = 200  
Gain = 500  
Gain = 1000  
33  
EL8172  
172  
70  
25  
12  
I
Supply Current, Enabled  
40  
60  
78  
S,EN  
FN6293.0  
3
October 26, 2005  
EL8171, EL8172  
Electrical Specifications V + = +5V, V - = GND, VCM = 1/2V + T = 25°C, unless otherwise specified. (Continued)  
S
S
S
A
PARAMETER  
DESCRIPTION  
CONDITIONS  
MIN  
1.5  
2
TYP  
MAX  
UNIT  
µA  
V
I
Supply Current, Disabled  
Enable Pin for Shut-down  
Enable Pin for Power-on  
Minimum Supply Voltage  
EN = V +  
2.9  
5
S,DIS  
S
V
V
V
ENH  
ENL  
S
0.8  
2.4  
V
2.2  
±29  
±7.5  
V
I
Output Current into 10to V /2  
V
V
= 5V  
±18  
±4  
mA  
mA  
O
S
S
= 2.9V  
S
Typical Performance Curves  
70  
60  
50  
40  
30  
G=2000  
G=100  
40  
G=1000  
G=500  
G=50  
30  
G=20  
G=200  
G=100  
G=10  
20  
G=5  
G=50  
10  
Vs=5V  
Vs=5V  
10  
20  
1
0
100  
1K  
10K  
100K  
1M  
1
10  
100  
1K  
10K  
100K  
1M  
FREQUENCY (Hz)  
FREQUENCY (Hz)  
FIGURE 1. EL8171 FREQUENCY RESPONSE vs CLOSED  
LOOP GAIN  
FIGURE 2. EL8172 FREQUENCY RESPONSE vs CLOSED  
LOOP GAIN  
25  
45  
V =±2.5V  
V =±2.5V  
S
S
40  
20  
35  
V =±1.25V  
S
V =±1V  
S
30  
25  
20  
15  
10  
5
15  
10  
5
V =±1V  
S
V =±1.25V  
S
A =10  
A =100  
V
V
L
R =10k  
R =10kΩ  
L
C =10pF  
C =10pF  
L
L
R /R =9.08Ω  
R /R =99.02Ω  
F G  
F
G
R =178kΩ  
R =221kΩ  
F
F
G
R
=19.6kΩ  
R
=2.23kΩ  
G
0
0
100  
1k  
10k  
100k  
1M  
100  
1k  
10k  
100k  
1M  
FREQUENCY (Hz)  
FREQUENCY (Hz)  
FIGURE 3. EL8171 FREQUENCY RESPONSE vs SUPPLY  
VOLTAGE  
FIGURE 4. EL8172 FREQUENCY RESPONSE vs SUPPLY  
VOLTAGE  
FN6293.0  
October 26, 2005  
4
EL8171, EL8172  
Typical Performance Curves (Continued)  
30  
50  
45  
40  
35  
30  
25  
25  
20  
15  
10  
5
C =100pF  
L
C =47pF  
L
C =2200pF  
L
C =1000pF  
L
C =27pF  
L
C =820pF  
L
A =10  
V
A =100  
V
C =390pF  
V =5V  
L
S
V =5V  
S
R =10kΩ  
L
R =10kΩ  
L
R /R =9.08Ω  
F
G
R /R =99.02Ω  
F
G
R =178kΩ  
F
G
R =221kΩ  
F
R
=19.6kΩ  
R =2.23kΩ  
G
0
100  
1k  
10k  
100k  
1M  
100  
1k  
10k  
FREQUENCY (Hz)  
FIGURE 6. EL8172 FREQUENCY RESPONSE vs C  
100k  
1M  
FREQUENCY (Hz)  
FIGURE 5. EL8171 FREQUENCY RESPONSE vs C  
LOAD  
LOAD  
4
4
25°C  
-45°C  
2
0
2
0
Vs=2.9V  
Vs=2.9V  
Vs=3.3V  
Vs=3.3V  
-2  
-2  
Vs=5V  
Vs=5V  
-4  
-0.5  
-4  
-0.5  
0
0.5  
1
1.5  
2
2.5  
3
3.5  
4
4.5  
5
5.5  
0
0.5  
1
1.5  
2
2.5  
3
3.5  
4
4.5  
5
5.5  
COMMON-MODE INPUT VOLTAGE (V)  
COMMON-MODE INPUT VOLTAGE (V)  
FIGURE 7. EL8171 AND EL8172 AVERAGE INPUT BIAS  
CURRENT vs COMMON-MODE INPUT VOLTAGE  
@ 25°C  
FIGURE 8. EL8171 AND EL8172 AVERAGE INPUT BIAS  
CURRENT vs COMMON-MODE INPUT VOLTAGE  
@ -45°C  
100  
10  
85°C  
Vs=5V  
50  
0
5
0
Vs=5V  
-5  
-50  
Vs=2.9V  
Vs=3.3V  
-10  
-0.5  
-100  
0
0.5  
1
1.5  
2
2.5  
3
3.5  
4
4.5  
5
5.5  
-0.5  
0
0.5  
1
1.5  
2
2.5  
3
3.5  
4
4.5  
5
5.5  
COMMON-MODE INPUT VOLTAGE (V)  
COMMON-MODE INPUT VOLTAGE (V)  
FIGURE 9. EL8171 AND EL8172 AVERAGE INPUT BIAS  
FIGURE 10. EL8171 AND EL8172 INPUT OFFSET CURRENT  
vs COMMON-MODE INPUT VOLTAGE  
CURRENT vs COMMON-MODE INPUT VOLTAGE  
@ 85°C  
FN6293.0  
October 26, 2005  
5
EL8171, EL8172  
Typical Performance Curves (Continued)  
200  
600  
25°C  
25°C  
500  
400  
300  
200  
100  
0
Vs=5V  
100  
0
Vs=5.0V  
Vs=2.9V  
Vs=2.9V  
Vs=3.3V  
Vs=3.3V  
-100  
-200  
-0.5  
0
0.5  
1
1.5  
2
2.5  
3
3.5  
4
4.5  
5
5.5  
-0.5  
0
0.5  
1
1.5  
2
2.5  
3
3.5  
4
4.5  
5
5.5  
COMMON-MODE INPUT VOLTAGE (V)  
COMMON-MODE INPUT VOLTAGE (V)  
FIGURE 11. EL8171 INPUT OFFSET VOLTAGE vs COMMON-  
MODE INPUT VOLTAGE @ 25°C  
FIGURE 12. EL8172 INPUT OFFSET VOLTAGE vs COMMON-  
MODE INPUT VOLTAGE @ 25°C  
600  
100  
-45°C  
-45°C  
500  
400  
300  
200  
100  
0
0
-100  
-200  
-300  
Vs=5V  
Vs=5.0V  
Vs=2.9V  
Vs=2.9V  
Vs=3.3V  
Vs=3.3V  
-0.5  
0
0.5  
1
1.5  
2
2.5  
3
3.5  
4
4.5  
5
5.5  
-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5  
COMMON-MODE INPUT VOLTAGE (V)  
COMMON-MODE INPUT VOLTAGE (V)  
FIGURE 13. EL8171 INPUT OFFSET VOLTAGE vs COMMON-  
MODE INPUT VOLTAGE @ -45°C  
FIGURE 14. EL8172 INPUT OFFSET VOLTAGE vs COMMON-  
MODE INPUT VOLTAGE @ -45°C  
800  
500  
85°C  
85°C  
700  
600  
500  
400  
300  
200  
400  
300  
200  
100  
Vs=5V  
Vs=2.9V  
Vs=5.0V  
Vs=3.3V  
Vs=2.9V  
Vs=3.3V  
-0.5  
0
0.5  
1
1.5  
2
2.5  
3
3.5  
4
4.5  
5
5.5  
-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5  
COMMON-MODE INPUT VOLTAGE (V)  
COMMON-MODE INPUT VOLTAGE (V)  
FIGURE 15. EL8171 INPUT OFFSET VOLTAGE vs COMMON-  
MODE INPUT VOLTAGE @ 85°C  
FIGURE 16. EL8172 INPUT OFFSET VOLTAGE vs COMMON-  
MODE INPUT VOLTAGE @ 85°C  
FN6293.0  
6
October 26, 2005  
EL8171, EL8172  
Typical Performance Curves (Continued)  
120  
110  
100  
90  
120  
110  
100  
GAIN=100  
90  
80  
80  
70  
60  
GAIN=1000  
GAIN=100  
70  
60  
50  
50  
GAIN=10  
40  
40  
1
10  
100  
1K  
10K  
100K  
1M  
1
10  
100  
1K  
10K  
100K  
1M  
FREQUENCY (Hz)  
FREQUENCY (Hz)  
FIGURE 17. EL8171 CMRR vs FREQUENCY  
FIGURE 18. EL8172 CMRR vs FREQUENCY  
100  
80  
120  
100  
80  
PSRR+  
PSRR+  
PSRR-  
PSRR-  
60  
60  
40  
40  
1
10  
100  
1K  
10K  
100K  
1M  
1
10  
100  
1K  
10K  
100K  
1M  
FREQUENCY (Hz)  
FREQUENCY (Hz)  
FIGURE 19. EL8171 PSRR vs FREQUENCY  
FIGURE 20. EL8172 PSRR vs FREQUENCY  
1s/DIV  
1s/DIV  
FIGURE 21. EL8171 0.1Hz to 10Hz INPUT VOLTAGE NOISE  
(GAIN = 10)  
FIGURE 22. EL8172 0.1Hz to 10Hz INPUT VOLTAGE NOISE  
(GAIN = 100)  
FN6293.0  
October 26, 2005  
7
EL8171, EL8172  
Typical Performance Curves (Continued)  
70  
60  
50  
40  
30  
20  
10  
0
2
2.5  
3
3.5  
SUPPLY VOLTAGE (V)  
FIGURE 23. EL8171 AND EL8172 SUPPLY CURRENT vs SUPPLY VOLTAGE  
4
4.5  
5
5.5  
JEDEC JESD51-7 HIGH EFFECTIVE THERMAL  
JEDEC JESD51-3 LOW EFFECTIVE THERMAL  
CONDUCTIVITY TEST BOARD  
CONDUCTIVITY TEST BOARD  
1.4  
1.2  
1
1
0.9  
0.8  
0.7  
0.6  
0.5  
0.4  
0.3  
0.2  
0.1  
0
909mW  
625mW  
0.8  
0.6  
0.4  
0.2  
0
0
25  
50  
75 85 100  
125  
150  
0
25  
50  
75 85 100  
125  
150  
AMBIENT TEMPERATURE (°C)  
AMBIENT TEMPERATURE (°C)  
FIGURE 24. PACKAGE POWER DISSIPATION vs AMBIENT  
TEMPERATURE  
FIGURE 25. PACKAGE POWER DISSIPATION vs AMBIENT  
TEMPERATURE  
FN6293.0  
October 26, 2005  
8
EL8171, EL8172  
obsession of the EL8171 and EL8172 in-amp is to maintain  
Description of Operation and Application  
Information  
Product Description  
The EL8171 and EL8172 are micropower instrumentation  
amplifiers (in-amps) which deliver rail-to-rail input  
the differential voltage across FB+ and FB- equal to IN+ and  
IN-; (FB+ - FB-) = (IN+ - IN-). Consequently, the transfer  
function can be derived. The gain of the EL8171 and EL8172  
is set by two external resistors, the feedback resistor RF, and  
the gain resistor RG.  
amplification and rail-to-rail output swing on a single 2.4V to  
5V supply. The EL8171 and EL8172 also deliver excellent  
DC and AC specifications while consuming only 60µA typical  
supply current. Because EL8171 and EL8172 provide an  
independent pair of feedback terminals to set the gain and to  
adjust the output level, these in-amps achieve high common-  
mode rejection ratio regardless of the tolerance of the gain  
setting resistors. The EL8171 is internally compensated for a  
minimum closed loop gain of 10 or greater, well suited for  
moderate to high gains. For higher gains, the EL8172 is  
internally compensated for a minimum gain of 100. An  
ENABLE pin is used to reduce power consumption, typically  
2.9µA, while the instrumentation amplifier is disabled.  
2.9V to 5V  
EN_BAR  
7
1
VIN/2  
VIN/2  
VS+  
EN  
2
3
8
5
IN+  
IN-  
+
-
6
VOUT  
EL8171/2  
FB+  
FB-  
+
-
VCM  
VS-  
4
RG  
RF  
Input Protection  
FIGURE 26. CIRCUIT 1 - GAIN IS BY EXTERNAL RESISTORS  
R
AND R  
All input and feedback terminals of the EL8171 and EL8172  
have internal ESD protection diodes to both positive and  
negative supply rails, limiting the input voltage to within one  
diode drop beyond the supply rails. If overdriving the inputs  
is necessary, the external input current must never exceed  
5mA. External series resistor may be used as a protection to  
limit excessive external voltage and current from damaging  
the inputs.  
F
G
R
F
VOUT = 1 + -------- VIN  
R
G
In Figure 26, the FB+ pin and one end of resistor RG are  
connected to GND. With this configuration, the above gain  
equation is only true for a positive swing in VIN; negative  
input swings will be ignored and the output will be at ground.  
Input Stage and Input Voltage Range  
Reference Connection  
The input terminals (IN+ and IN-) of the EL8171 and EL8172  
are single differential pair P-MOSFET devices aided by an  
Input Range Enhancement Circuit to increase the headroom  
of operation of the common-mode input voltage. The  
feedback terminals (FB+ and FB-) also have a similar  
topology. As a result, the input common-mode voltage range  
of both the EL8171 and EL8172 is rail-to-rail. These in-amps  
are able to handle input voltages that are at or slightly  
beyond the supply and ground making these in-amps well  
suited for single 5V or 3.3V low voltage supply systems.  
There is no need then to move the common-mode input of  
the in-amps to achieve symmetrical input voltage.  
Unlike a three-opamp instrumentation amplifier, a finite  
series resistance seen at the REF terminal does not degrade  
the EL8171 and EL8172's high CMRR performance  
eliminating the need for an additional external buffer  
amplifier. Circuit 2 (Figure 27) uses the FB+ pin to provide a  
high impedance REF terminal.  
2.9V to 5V  
EN_BAR  
7
1
VIN/2  
VIN/2  
VS+  
EN  
2
3
8
5
IN+  
IN-  
+
-
6
VOUT  
EL8171/2  
FB+  
FB-  
+
-
Output Stage and Output Voltage Range  
VCM  
2.9V to 5V  
A pair of complementary MOSFET devices drives the output  
VOUT to within a few mV of the supply rails. At a 100k  
load, the PMOS sources current and pulls the output up to  
4mV below the positive supply, while the NMOS sinks  
current and pulls the output down to 4mV above the negative  
supply, or ground in the case of a single supply operation.  
The current sinking and sourcing capability of the EL8171  
and EL8172 are internally limited to 29mA.  
VS-  
4
R1  
REF  
R2  
RG  
RF  
FIGURE 27. CIRCUIT 2 - GAIN SETTING AND REFERENCE  
CONNECTION  
Gain Setting  
R
R
F
R
G
F
VIN, the potential difference across IN+ and IN-, is replicated  
(less the input offset voltage) across FB+ and FB-. The  
VOUT = 1 + -------- (VIN) + 1 + -------- (VREF)  
R
G
FN6293.0  
9
October 26, 2005  
EL8171, EL8172  
The FB+ pin is used as a REF terminal to center or to adjust  
error due to the tolerance of the resistors used. The resulting  
non-ideal transfer function effectively becomes:  
the output. Because the FB+ pin is a high impedance input,  
an economical resistor divider can be used to set the voltage  
at the REF terminal without degrading or affecting the CMRR  
performance. Any voltage applied to the REF terminal will  
shift VOUT by VREF times the closed loop gain, which is set  
by resistors RF and RG. See Circuit 2 (Figure 27).  
R
F
VOUT = 1 + -------- × [1 (E  
+ E  
+ E )] × VIN  
RF G  
RG  
R
G
Where:  
ERG = Tolerance of RG  
ERF = Tolerance of RF  
The FB+ pin can also be connected to the other end of  
resistor, RG. See Circuit 3 (Figure 28). Keeping the basic  
concept that the EL8171 and EL8172 in-amps maintain  
constant differential voltage across the input terminals and  
feedback terminals (IN+ - IN- = FB+ - FB-), the transfer  
function of Circuit 3 can be derived.  
EG = Gain Error of the EL8171 or EL8172  
The term [1-(ERG +ERF +EG)] is the deviation from the  
theoretical gain. Thus, (ERG +ERF +EG) is the total gain  
error. For example, if 1% resistors are used for the EL8171,  
the total gain error would be:  
2.9V to 5V  
EN_BAR  
7
1
= ±(E  
+ E  
+ E (typical))  
RF G  
VIN/2  
VIN/2  
RG  
VS+  
EN  
2
3
8
5
IN+  
IN-  
+
= ±(0.01 + 0.01 + 0.003)  
= ±2.3%  
-
6
VOUT  
EL8171/2  
FB+  
FB-  
+
-
VCM  
VS-  
4
Disable/Power-Down  
The EL8171 and EL8172 can be powered down reducing  
the supply current to typically 2.9µA. When disabled, the  
output is in a high impedance state. The active low ENABLE  
bar pin has an internal pull down and hence can be left  
floating and the in-amp enabled by default. When the  
ENABLE bar is connected to an external logic, the in-amp  
will power down when ENABLE bar is pulled above 2V, and  
will power on when ENABLE bar is pulled below 0.8V.  
RG  
RF  
VREF  
FIGURE 28. CIRCUIT 3 - REFERENCE CONNECTION WITH AN  
AVAILABLE VREF  
R
F
VOUT = 1 + -------- (VIN) + (VREF)  
R
G
A finite resistance Rs in series with the VREF source, adds  
an output offset of VIN*(RS/RG). As the series resistance Rs  
approaches zero, the gain equation is simplified to the above  
equation for Circuit 3. VOUT is simply shifted by an amount  
VREF.  
External Resistor Mismatches  
Because of the independent pair of feedback terminals  
provided by the EL8171 and EL8172, the CMRR is not  
degraded by any resistor mismatches. Hence, unlike a three  
opamp and especially a two opamp in-amp, the EL8171 and  
EL8172 reduce the cost of external components by allowing  
the use of 1% or more tolerance resistors without sacrificing  
CMRR performance. The EL8171 and EL8172 CMRR will be  
108dB regardless of the tolerance of the resistors used.  
Gain Error and Accuracy  
The EL8172 has a Gain Error, EG, of 0.2% typical. The  
EL8171 has an EG of 0.3% typical. The gain error indicated  
in the electrical specifications table is the inherent gain error  
of the EL8171 and EL8172 and does not include the gain  
error contributed by the resistors. There is an additional gain  
FN6293.0  
10  
October 26, 2005  
EL8171, EL8172  
Package Outline Drawing  
NOTE: The package drawing shown here may not be the latest version. To check the latest revision, please refer to the Intersil website at  
http://www.intersil.com/design/packages/index.asp  
All Intersil U.S. products are manufactured, assembled and tested utilizing ISO9000 quality systems.  
Intersil Corporation’s quality certifications can be viewed at www.intersil.com/design/quality  
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  
notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and  
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  
from its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries.  
For information regarding Intersil Corporation and its products, see www.intersil.com  
FN6293.0  
11  
October 26, 2005  

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