THS4521 datasheet(31/71 Pages) TI2

31 / 71 page

THS452x

24.9 W

1kW

24.9 W

OCM

Open

From

Analyzer

OUT+

IN+

ToAP

Analyzer

S+

IN-

S-

0.22 F

OUT-

0.1

100

1000

Frequency (MHz)

FREQUENCY RESPONSE vs C

LOAD

R = 124

C = 10 pF

each output

R = 37.5

C = 100 pF each output

R = 7.15

C = 1000 pF each output

R = 150

C = 4.7 pF

each output

= 5.0 V, Gain = 1 V/V

S+

R = 1 k

differential

R = 1 k

= 100 mV

OUT

100

1000

(pF)

LOAD

RECOMMENDED R vs C

For Flat Frequency Response

LOAD

= 5.0 V

Gain = 1 V/V

S+

R = 1 k

Differential

= 100 mV

OUT

THS4521, THS4522, THS4524

www.ti.com

SBOS458H – DECEMBER 2008 – REVISED JUNE 2015

8.3.10 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 (RO) in

series with the output, placed as close to the device as possible. Without RO, 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

RO isolates the phase shift from the loop gain path and restores the phase margin, but it also limits bandwidth.

Figure 64 shows the recommended values of RO versus capacitive loads (CL), and Figure 65 shows an

illustration of the frequency response with various values.

Figure 64. Recommended Series Output Resistor Versus

Figure 65. Frequency Response for Various RO and CL

Capacitive Load for Flat Frequency Response, With RLOAD

Values, With RLOAD = 1 kΩ

= 1 k

8.3.11 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-VRMS output voltage. Performance is the same on

both 3.3-V and 5-V supplies. Figure 66 shows the test circuit used; see Figure 67 and Figure 68 for the

performance of the analyzer using internal loopback mode (generator) together with the THS4521.

Figure 66. THS4521 AP Analyzer Test Circuit

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Product Folder Links: THS4521 THS4522 THS4524

THS4521 Datasheet(PDF) 31 Page - Texas Instruments

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