ISL28470 Intersil Corporation, ISL28470 Datasheet - Page 13

• Manufacturer Part Number: ISL28470
• Description: (ISL28270 - ISL28470) Rail-to-Rail Input and Output (RRIO) Instrumentation Amplifier
• Manufacturer: Intersil Corporation

due to the tolerance of the resistors used. The resulting
non-ideal transfer function effectively becomes Equation 5:
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 as follows in Equation 6:
Disable/Power-Down
The ISL28270, ISL28273 and ISL28470 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
internal pull down and hence can be left floating and the
in-amp enabled by default. When the
external logic, the in-amp will shutdown when the
TotalGainError
TotalGainError
V
RG
RF
G
OUT
= Tolerance of RG
= Tolerance of RF
= Gain Error of the ISL28270
=
⎛
⎜
⎝
1
+
------- -
R
R
G
F
⎞
⎟
⎠
RG
=
=
×
±
±
[
+E
(
(
1
E
0.01
±
RG
RF
(
E
+
+
RG
RG
+E
0.01
E
RF
+
G
13
+E
E
)] is the deviation from the
+
+
RF
RF
0.005
E
G
+
+E
(
E
typical
G
EN
)
G
=
)
) is the total gain
]
±
is connected to an
×
2.5%
EN
)
V
)
ISL28270, ISL28273, ISL28470
IN
pin has an
EN
pin is
(EQ. 5)
(EQ. 6)
pulled above 2V, and will power up when the
below 0.8V.
Unused Channels
The ISL28270, ISL28273 and ISL28470 are Dual-channel
and Quad-channel op-amps. If the application only requires
one channel when using the ISL28270, ISL28273 or less
than 4-channels when using the ISL28470, 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 31).
FIGURE 31. PREVENTING OSCILLATIONS IN UNUSED
CHANNELS
R
G
FB+
FB-
IN+
IN-
+
+
-
-
R
F
1/2 ISL28270, ISL28273
1/4 ISL28470
EN
bar is pulled
April 13, 2007
FN6260.2