THS4501CD datasheet(22/37 Pages) TI

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THS4500

THS4501

SLOS350D − APRIL 2002 − REVISED JANUARY 2004

www.ti.com

Figure 98

VOCM

+VS

Rg1

Rg2

Rf1

Rf2

−

−VS

Application Circuit for the THS4500 and THS4501,

Featuring Split-Supply Operation With an Input

Signal Referenced at the Midrail

Equations 1−5 allow for calculation of the required input

common-mode range for a given set of input conditions.

The equations allow calculation of the input common-

mode range requirements given information about the

input signal, the output voltage swing, the gain, and the

output common-mode voltage. Calculating the maximum

and minimum voltage required for VN and VP (the

amplifier’s input nodes) determines whether or not the

input common-mode range is violated or not. Four

equations are required. Two calculate the output voltages

and two calculate the node voltages at VN and VP (note

that only one of these needs calculation, as the amplifier

forces a virtual short between the two nodes).

OUT

) +

)(1–β)–VIN–(1–β) ) 2VOCMβ

OUT– +

–V

)(1–β) ) VIN–(1–β) ) 2VOCMβ

(1)

(2)

N + VIN–(1–β) ) V OUT

)β

Where:

β +

F ) RG

P + VIN

)(1–β) ) VOUT–β

(3)

(4)

(5)

NOTE:

The equations denote the device inputs as VN and

VP, and the circuit inputs as VIN+ and VIN−.

Figure 99

VOCM

−

VOUT−

VOUT+

VIN+

VIN−

Diagram For Input Common-Mode Range Equations

The two tables below depict the input common-mode

range requirements for two different input scenarios, an

input referenced around the negative rail and an input

referenced around midrail. The tables highlight the

differing requirements on input common-mode range, and

illustrate reasoning for choosing either the THS4500/1 or

the THS4502/3. For signals referenced around the

negative power supply, the THS4500/1 should be chosen

since its input common-mode range includes the negative

supply rail. For all other situations, the THS4502/3 offers

slightly improved distortion and noise performance for

applications with input signals centered between the

power supply rails.

Table 1. Negative-Rail Referenced

Gain

(V/V)

VIN+ (V)

VIN−

(V)

VIN

(VPP)

VOCM

(V)

VOD

(VPP)

VNMIN

(V)

VNMAX

(V)

−2.0 to

2.0

2.5

0.75

1.75

−1.0 to

1.0

2.5

0.5

1.167

−0.5 to

0.5

2.5

0.3

0.7

−0.25 to

0.25

0.5

2.5

0.167

0.389

NOTE: This table assumes a negative-rail referenced, single-ended

input signal on a single 5-V supply as shown in Figure 97.

VNMIN = VPMIN and VNMAX = VPMAX.

Table 2. Midrail Referenced

Gain

(V/V)

VIN+ (V)

VIN−

(V)

VIN

(VPP)

VOCM

(V)

VOD

(VPP)

VNMIN

(V)

VNMAX

(V)

0.5 to

4.5

2.5

1.5 to

3.5

2.5

2.16

2.83

2.0 to

3.0

2.5

2.3

2.7

2.25 to

2.75

2.5

0.5

2.5

2.389

2.61

NOTE: This table assumes a midrail referenced, single-ended input

signal on a single 5-V supply.

VNMIN = VPMIN and VNMAX = VPMAX.

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