THS4521 datasheet(26/43 Pages) TI

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Setting the Output Common-Mode Voltage

Single-Supply Operation

EXT

V )

50k

OCM

S+

S-

(2)

THS452x

S-

OCM

IN+

Optional;

installedto

balance

impedanceseen

at V

IN+

OCM Control

PD Control

OUT-

OUT+

S+

0.22 F

S+

OCM

S-

100kW

EXT

Tointernal

circuit

OCM

Typical Performance Variation with Supply

THS4521

THS4522

THS4524

SBOS458B – DECEMBER 2008 – REVISED MAY 2009.................................................................................................................................................... www.ti.com

The output common-model voltage is set by the

To facilitate testing with common lab equipment, the

voltage at the VOCM pin. The internal common-mode

THS4521EVM allows for split-supply operation; most

control circuit maintains the output common-mode

of the characterization data presented in this data

voltage within 5-mV offset (typ) from the set voltage.

sheet is measured using split-supply power inputs.

If left unconnected, the common-mode set point is set

The device can easily be used with a single-supply

to midsupply by internal circuitry, which may be

power input without degrading performance.

overdriven from an external source. Figure 62

Figure 63 shows a dc-coupled single-supply circuit

represents the VOCM input. The internal VOCM circuit

with single-ended inputs. This circuit can also be

has typically 23 MHz of –3 dB bandwidth, which is

applied to differential input sources.

required for best performance, but it is intended to be

a dc bias input pin. A 0.22-

µF bypass capacitor is

recommended on this pin to reduce noise. The

external current required to overdrive the internal

resistor divider is given approximately by the formula

in Equation 2:

where:

• V

OCM is the voltage applied to the VOCM pin

Figure 63. THS4521 DC-Coupled Single-Supply

with Single-Ended Inputs

The input common-mode voltage range of the

THS4521,

THS4522,

and

THS4524

family

Figure 62. VOCM Input Circuit

designed to include the negative supply voltage. in

the circuit shown in Figure 63, the signal source is

referenced to ground. VOCM is set by an external

control source or, if left unconnected, the internal

Voltage

circuit defaults to midsupply. Together with the input

The THS4521, THS4522, and THS4524 family of

impedance of the amplifier circuit, RIT provides input

devices provide excellent performance across the

termination, which is also referenced to ground.

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

Note that RIT and optional matching components are

only minor variations. The input and output voltage

added

the

alternate

input

balance

the

compliance ranges track with the power supply in

impedance at signal input.

nearly a 1:1 correlation. Other changes can be

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

gain, bandwidth, and distortion. Table 3 shows the

typical

variation

expected

these

key

performance parameters.

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/

µs

420 V/

µs

210 V/

µs

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

xxx

Second harmonic

–85 dBc

–84 dBc

xxx

Third 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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Product Folder Link(s): THS4521 THS4522 THS4524

THS4521 Datasheet(PDF) 26 Page - Texas Instruments

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