Datasheet

A1
A2
Single-Pole Filter
Capacitor
+2.7 V to +18 V
5 kW5 kW
96 kW
R
L
PRE OUT BUF IN
GND
Output
IN–IN+ V+
Load
Supply
R
S
Second-Order, Sallen-Key Filter Connection
C
FILT
C
FILT
GND
R
S
a ) S i n g le - P o le F ilte r b ) S e c o n d - O r d e r, S a l le n - K e y F ilte r
IN A 27 0 INA27 0
5 kW5 kW
IN–IN+
+2.7 V to +18 V
PRE OUT BUF IN
V+
A1
A2
Output
96 kW
R
L
R
S
Load
Supply
INA270-Q1, INA271-Q1
www.ti.com SBOS401B –JULY 2007–REVISED FEBRUARY 2010
Use of MOVs or VDRs is not recommended except when they are used in addition to a semiconductor transient
absorber. Select the transient absorber such that it will never allow the INA270 and INA271 to be exposed to
transients greater than 80 V (that is, allow for transient absorber tolerance, as well as additional voltage because
of transient absorber dynamic impedance).
Despite the use of internal zener-type ESD protection, the INA270 and INA271 are not suited to using external
resistors in series with the inputs, since the internal gain resistors can vary up to ±30%, but the internal resistors
are tightly matched. If gain accuracy is not important, then resistors can be added in series with the INA270 and
INA271 inputs, with two equal resistors on each input.
Output Voltage Range
The output of the INA270 and INA271 is accurate within the output voltage swing range set by the power-supply
pin, V+.
The INA270 and INA271 readily enable the inclusion of filtering between the preamp output and buffer input.
Single-pole filtering can be accomplished with a single capacitor because of the 96-kΩ output impedance at
PRE OUT on pin 3 (see Figure 2a).
The INA270 and INA271 readily lend themselves to second-order Sallen-Key configurations (see Figure 2b).
When designing these configurations consider that the PRE OUT 96-kΩ output impedance exhibits an initial
variation of ±30% with the addition of a –2200-ppm/°C temperature coefficient.
A. The INA270 and INA271 can be easily connected for first-order or second-order filtering. Remember to use the
appropriate buffer gain (INA270 = 1.4, INA271 = 2) when designing Sallen-Key configurations.
Figure 2. First-Order or Second-Order Filtering
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Product Folder Link(s): INA270-Q1 INA271-Q1