Datasheet

0.1 1 10 100 1000
Frequency (MHz)
5
0
5
10
15
20
25
-
-
-
-
-
Normalized Gain (dB)
FREQUENCY RESPONSE vs C
LOAD
R = 124
C = 10 pF
each output
W
O
L
R = 37.5
C = 100 pF each output
W
O
L
R = 7.15
C = 1000 pF each output
W
O
L
R = 150
C = 4.7 pF
each output
W
O
L
V = 5.0 V, Gain = 1 V/V
S+
PP
R = 1 k differential
R = 1 k
V = 100 mV
F
L
OUT
W
W
1k
100
10
1
10 100 1000
C (pF)
LOAD
Series Output Resistor ( )W
RECOMMENDED R vs C
For Flat Frequency Response
O LOAD
V = 5.0 V
Gain = 1 V/V
S+
PP
R = 1 k
R = 1 k Differential
V = 100 mV
F
L
OUT
W
W
THS452x
24.9 W
1kW
1kW
1kW
1kW
24.9 W
V
OCM
PD
Open
Open
From
AP
Analyzer
V
OUT+
V
IN+
ToAP
Analyzer
V
S+
V
IN-
V
S-
0.22 Fm
0.22 Fm
V
OUT-
THS4521
THS4522
THS4524
SBOS458F –DECEMBER 2008–REVISED SEPTEMBER 2011 www.ti.com
Driving Capacitive Loads
The THS4521, THS4522, and THS4524 family is
designed for a nominal capacitive load of 1 pF on
each output to ground. When driving capacitive loads
greater than 1 pF, it is recommended to use small
resistors (R
O
) in series with the output, placed as
close to the device as possible. Without R
O
,
capacitance on the output interacts with the output
impedance of the amplifier and causes phase shift in
the loop gain of the amplifier that reduces the phase
margin. This reduction in phase margin results in
frequency response peaking; overshoot, undershoot,
and/or ringing when a step or square-wave signal is
applied; and may lead to instability or oscillation.
Inserting R
O
isolates the phase shift from the loop
gain path and restores the phase margin, but it also
limits bandwidth. Figure 66 shows the recommended
Figure 67. Frequency Response for Various R
O
values of R
O
versus capacitive loads (C
L
), and
and C
L
Values, with R
LOAD
= 1 kΩ
Figure 67 shows an illustration of the frequency
response with various values.
Audio Performance
The THS4521, THS4522, and THS4524 family
provide excellent audio performance with very low
quiescent power. To show performance in the audio
band, the device was tested with a SYS-2722 audio
analyzer from Audio Precision. THD+N and FFT tests
were performed at 1-V
RMS
output voltage.
Performance is the same on both 3.3-V and 5-V
supplies. Figure 68 shows the test circuit used; see
Figure 69 and Figure 70 for the performance of the
analyzer using internal loopback mode (generator)
together with the THS4521.
Figure 66. Recommended Series Output Resistor
versus Capacitive Load for Flat Frequency
Response, with R
LOAD
= 1 kΩ
Figure 68. THS4521 AP Analyzer Test Circuit
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Product Folder Link(s): THS4521 THS4522 THS4524