THS4271_16 Datasheet, PDF (32/50 Pages) Texas Instruments – LOW NOISE, HIGH SLEW RATE, UNITY GAIN STABLE VOLTAGE FEEDBACK AMPLIFIER

THS4271
THS4275
SLOS397F – JULY 2002 – REVISED OCTOBER 2009
The peaking in the frequency response is due to the
lead inductance in the feedback path. Each pad and
trace on a PCB has an inductance associated with it,
which in conjunction with the inductance associated
with the package may cause peaking in the frequency
response, causing the device to become unstable.
In order to achieve the maximum performance of the
device, PCB layout is very critical. Texas Instruments
has developed an EVM for the evaluation of the
THS4271 in a gain of 1. The EVM is shown in
Figure 101 through Figure 104. This EVM is designed
to minimize peaking in the unity gain configuration.
Minimizing the inductance in the feedback path is
critical for reducing the peaking of the frequency
response in unity gain. The recommended maximum
inductance allowed in the feedback path is 4 nH. This
can be calculated by using Equation 8.
ƪ ƫ L(nH) +
Kȏ
ln
2ȏ
W)
T
)
0.223
W
)
ȏ
T
)
0.5
where:
W = Width of trace in inches.
ȏ = Length of the trace in inches.
T = Thickness of the trace in inches.
K = 5.08 for dimensions in inches, and K = 2 for dimensions
in cm.
(8)
space
space
space
J1
Vin−
J2
Vin+
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J9
Power Down
Vs+
R8
R3
R2
C8
R5
R9
Vs+
7 8 _U1
2_{_}
6
R6
3₊
41
Vs −
J4
R7
Vout
Vs −
J8
Power Down Ref
C7
R1
R4
J7
VS−
FB1
C5
C6
J6
GND TP1
VS−
C1
+
VS+
C2 ⁺
J5
VS+
FB2
C3
C4
Figure 95. THS4271/THS4275 EVM
Circuit Configuration
32
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