THS4521 datasheet(28/48 Pages) TI

28 / 48 page

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

THS452x

24.9 W

1kW

24.9 W

OCM

Open

From

Analyzer

OUT+

IN+

ToAP

Analyzer

S+

IN-

S-

0.22 F

OUT-

THS4521

THS4522

THS4524

SBOS458D – DECEMBER 2008 – REVISED AUGUST 2010

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 (RO) in series with the output, placed as

the

device

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 66 shows the recommended

Figure 67. Frequency Response for Various RO

values of RO versus capacitive loads (CL), and

and CL Values, with RLOAD = 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

1-VRMS

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 RLOAD = 1 kΩ

Figure 68. THS4521 AP Analyzer Test Circuit

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Product Folder Link(s): THS4521 THS4522 THS4524

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