Datasheet

Testing conditions TSH7x
24/36 DocID7502 Rev 4
4.4 Precautions when operating on an asymmetrical supply
The TSH7X can be used with either a dual or a single supply. If a single supply is used, the
inputs are biased to the mid-supply voltage (+V
CC
/2). This bias network must be carefully
designed, in order to reject any noise present on the supply rail.
As the bias current is 15 µA, you must carefully choose the resistance R1 so as not to
introduce an offset mismatch at the amplifier inputs.
Figure 49. Schematic of asymmetrical (single) supply
R1 = 10 kΩ is a typical and convenient value. C1, C2, C3 are bypass capacitors that filter
perturbations on V
CC
, as well as for the input and output signals. We choose C1 = 100 nF
and C2
= C3 = 100 µF.
R2, R3 are such that the current through them must be greater than 100 times the bias
current.
Therefore, we set R2 = R3 = 4.7 kΩ.
C
in
, as C
out
, is chosen to filter the DC signal by the low-pass filters (R1,C
in
and R
out
, C
out
).
By taking R1
= 10 kΩ, R
L
= 150 Ω, and C
in
= 2 µF, C
out
= 220 µF we provide a cut-off
frequency below 10 Hz.
Figure 50. Use of the TSH7x in gain = -1 configuration
Some precautions must be taken, especially for low-power supply applications.
IN
R1
Vcc+
OUT
R2
R3
C1
C3
C2
C
in
C
out
+
-
Cf
R5
R4
R
L
IN
R1
Vcc+
OUT
R2
R3
C1
C3
C2
C
in
C
out
+
-
1k
C
f
1k
R
L