THS4521 datasheet(26/48 Pages) TI

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V )

50k

OCM

S+

S-

S+

OCM

S-

100kW

EXT

Tointernal

circuit

OCM

THS452x

S-

OCM

IN+

Optional;

installedto

balance

impedanceseen

at V

IN+

OCM Control

PD Control

OUT-

OUT+

S+

0.22 F

THS4521

THS4522

THS4524

SBOS458D – DECEMBER 2008 – REVISED AUGUST 2010

www.ti.com

Figure 62 represents the VOCM input. The internal

Single-Supply Operation

VOCM circuit has typically 23 MHz of –3 dB bandwidth,

To facilitate testing with common lab equipment, the

which is required for best performance, but it is

THS4521EVM allows for split-supply operation; most

intended to be a dc bias input pin. A 0.22-mF bypass

of the characterization data presented in this data

capacitor is recommended on this pin to reduce

sheet is measured using split-supply power inputs.

noise. The external current required to overdrive the

The device can easily be used with a single-supply

internal resistor divider is given approximately by the

power input without degrading performance.

formula in Equation 2:

Figure 63 shows a dc-coupled single-supply circuit

with single-ended inputs. This circuit can also be

applied to differential input sources.

where:

•

VOCM is the voltage applied to the VOCM pin

(2)

Figure 62. VOCM Input Circuit

Typical Performance Variation with Supply

Figure 63. THS4521 DC-Coupled Single-Supply

Voltage

with Single-Ended Inputs

The THS4521, THS4522, and THS4524 family of

devices provide excellent performance across the

The input common-mode voltage range of the

specified power-supply range of 2.5 V to 5.5 V with

THS4521,

THS4522,

and

THS4524

family

only minor variations. The input and output voltage

designed to include the negative supply voltage. in

compliance ranges track with the power supply in

the circuit shown in Figure 63, the signal source is

nearly a 1:1 correlation. Other changes can be

referenced to ground. VOCM is set by an external

observed in slew rate, output current drive, open-loop

control source or, if left unconnected, the internal

gain, bandwidth, and distortion. Table 3 shows the

circuit defaults to midsupply. Together with the input

typical

variation

expected

these

key

impedance of the amplifier circuit, RIT provides input

performance parameters.

termination, which is also referenced to ground.

Note that RIT and optional matching components are

added

the

alternate

input

balance

the

impedance at signal input.

Table 3. Typical Performance Variation versus Power-Supply Voltage

PARAMETER

VS = 5 V

VS = 3.3 V

VS = 2.5 V

–3-dB Small-signal bandwidth

145 MHz

135 MHz

125 MHz

Slew rate (2-V step)

490 V/ms

420 V/ms

210 V/ms

Harmonic distortion at 1 MHz, 2 VPP, RL = 1 kΩ

xxxSecond harmonic

–85 dBc

–84 dBc

xxxThird harmonic

–91 dBc

–90 dBc

–88 dBc

Open-loop gain

119 dB

116 dB

115 dB

Linear output current drive

55 mA

35 mA

24 mA

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