ISL28271FAZ Intersil, ISL28271FAZ Datasheet - Page 12

• Manufacturer Part Number: ISL28271FAZ
• Description: IC INSTR AMP RRIO SGL 16-QSOP
• Manufacturer: Intersil

Specifications of ISL28271FAZ

• Amplifier Type: Instrumentation
• Number Of Circuits: 2
• Output Type: Rail-to-Rail
• Slew Rate: 0.5 V/µs
• -3db Bandwidth: 180kHz
• Current - Input Bias: 10pA
• Voltage - Input Offset: 35µV
• Current - Supply: 120µA
• Current - Output / Channel: 31mA
• Voltage - Supply, Single/dual (±): 2.4 V ~ 5.5 V, ±1.2 V ~ 2.75 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-QSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Gain Bandwidth Product: -

.
The FB+ pin is used as a REF terminal to center or to adjust
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 R
The FB+ pin can also be connected to the other end of
resistor, R
the in-amp maintains constant differential voltage across the
input terminals and feedback terminals (FB- - FB+) =
(IN+ - IN-), the transfer function of Figure 39 can be derived.
VIN
VOUT
VOUT
VIN
FIGURE 38. GAIN SETTING AND REFERENCE CONNECTION
FIGURE 39. REFERENCE CONNECTION WITH AN AVAILABLE
VCM
VCM
VREF
=
=
RS
IN+ IN-
=
IN+ IN-
2.9V to 5.5V
=
REF
IN+
IN-
IN+
IN-
⎛
⎜
⎝
G
1
1
–
. See Figure 39. Keeping the basic concept that
–
+
+
------- -
R
VREF
R
--------------------- -
R
F
R1
R2
G
S
F
and R
R
⎞
⎟
⎠
RG
+
RG
G
(
VIN
R
F
G
)
+
. See Figure 38.
+
VREF
⎛
⎜
⎝
1
+
FB+
FB-
FB+
FB-
IN+
IN-
IN+
IN-
12
------- -
R
2.4V TO 5.5V
R
2.4V TO 5.5V
G
F
+
+
+
+
-
-
-
-
⎞
⎟
⎠
ISL28271
ISL28271
(
RF
RF
VREF
V+
V+
ISL28271
ISL28272
ISL28271
ISL28272
V-
V-
)
EN
EN
ISL28271, ISL28272
EN
EN
(EQ. 2)
(EQ. 3)
VOUT
VOUT
A finite resistance R
an output offset of VIN*(R
approaches zero, Equation 3 is simplified to Equation 4 for
Figure 39. VOUT is simply shifted by an amount VREF.
External Resistor Mismatches
Because of the independent pair of feedback terminals
provided by the in-amps, the CMRR is not degraded by any
resistor mismatches. Hence, unlike a three op amp and
especially a two op amp in-amp realization, the ISL28271
and ISL28272 reduce the cost of external components by
allowing the use of 1% or more tolerance resistors without
sacrificing CMRR performance. The CMRR will be typically
110dB regardless of the tolerance of the resistors used.
Instead, a resistor mismatch results in a higher deviation
from the theoretical gain - Gain Error.
Gain Error and Accuracy
The gain error indicated in the “Electrical Specifications”
table on page 2 is the inherent gain error alone. The gain
error specification listed does not include the gain error
contributed by the resistors. There is an additional gain error
due to the tolerance of the resistors used. The resulting non-
ideal transfer function effectively becomes:
Where:
E
E
E
The term [1 - (E
theoretical gain. Thus, (E
error. For example, if 1% resistors are used, the total gain
error would be:
Disable/Power-Down
The ISL28271 and ISL28272 have an enable/disable pin for
each channel. They can be powered down to reduce the
supply current to typically 4µA when all channels are off.
When disabled, the corresponding output is in a high
impedance state. The active low EN pin has an internal pull
down and hence can be left floating and the in-amp enabled
by default. When the EN is connected to an external logic,
the in-amp will shutdown when EN pin is pulled above 2V,
and will power up when EN bar is pulled below 0.8V.
VOUT
TotalGainError
TotalGainError
VOUT
RG
RF
G
= Tolerance of RG
= Tolerance of RF
= Gain Error of the ISL28271
=
=
⎛
⎜
⎝
⎛
⎜
⎝
1
1
+
+
------- -
R
------- -
R
R
R
G
G
F
F
RG
=
=
⎞
⎟
⎠
⎞
⎟
⎠
(
×
±
±
VIN
[
+E
(
(
S
1
E
0.01
RG
in series with the VREF source, adds
±
)
RF
+
(
E
+
+
(
RG
S
+E
RG
VREF
0.01
E
/R
RF
G
+E
G
+
)] is the deviation from the
). As the series resistance R
E
+
+
RF
)
RF
0.005
E
G
+E
+
(
typical
E
)
G
G
=
) is the total gain
)
]
±
×
2.5%
)
)
VIN
August 17, 2007
FN6390.2
(EQ. 4)
(EQ. 5)
S