ADV3201ASWZ datasheet(32/36 Pages) AD

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ADV3200/ADV3201

Rev. 0 | Page 32 of 3

QNPN

QPNP

VNEG

VPOS

VOUTPUT

IOUTPUT

IOUTPUT, QUIESCENT

Figure 105. Simplified Output Stage

Example

For the ADV3200, in an ambient temperature of 85°C, with all

32 outputs driving 1 V rms into 150 Ω loads and power supplies

at ±2.5 V, follow these steps:

Calculate the power dissipation of the ADV3200 using data

sheet quiescent currents. Disregard VDD current, which is

insignificant.

PD,QUIESCENT = (VPOS × IVPOS) + (VNEG × IVNEG)

PD,QUIESCENT = (2.5 V × 250 mA) + (2.5 V × 250 mA) = 1.25 W

Calculate the power dissipation from the loads.

PD,OUTPUT = (VPOS – VOUTPUT,RMS) × IOUTPUT,RMS

PD,OUTPUT = (2.5 V – 1 V) × (1 V/150 Ω) = 10 mW

There are 32 outputs, therefore, 32 output currents.

nPD,OUTPUT = 32 × 10 mW = 0.32 W

Subtract the quiescent output stage current for the number

of loads (32 in this example). The output stage is either

standing or driving a load, but the current needs to be

counted only once (valid for output voltages > 0.5 V).

PDQ,OUTPUT = (VPOS – VNEG) × IOUTPUT,QUIESCENT

PDQ,OUTPUT = (2.5 V – (–2.5 V)) × (0.95 mA) = 4.75 mW

There are 32 outputs, therefore, 32 output currents.

nPDQ,OUTPUT = 32 × 4.75 mW = 0.15 W

Verify that the power dissipation does not exceed the

maximum allowed value.

PD,ON-CHIP = PD,QUIESCENT + nPD,OUTPUT − nPDQ,OUTPUT

PD,ON-CHIP = 1.25 W + 0.32 W − 0.15 W= 1.42 W

As shown in Figure 104 or Equation 1, this power dissipation is

below the maximum allowed dissipation for all ambient temper-

atures up to and including 85°C.

CROSSTALK

Many systems, such as broadcast video and KVM switches, that

handle numerous analog signal channels have strict require-

ments for keeping the various signals from influencing any of

the others in the system. Crosstalk is the term used to describe

the coupling of the signals of other nearby channels to a given

channel.

When there are many signals in close proximity in a system, as

is undoubtedly the case in a system that uses the ADV3200/

ADV3201, the crosstalk issues can be quite complex. A good

understanding of the nature of crosstalk and some definition of

terms is required in order to specify a system that uses one or

more crosspoint devices.

Types of Crosstalk

Crosstalk can be propagated by any of three means: electric

field, magnetic field, and sharing of common impedances. This

section explains these effects.

Every conductor can be both a radiator of electric fields and a

receiver of electric fields. The electric field crosstalk mechanism

occurs when the electric field created by the transmitter

propagates across a stray capacitance (for example, free space),

couples with the receiver, and induces a voltage. This voltage is

an unwanted crosstalk signal in any channel that receives it.

Currents flowing in conductors create magnetic fields that

circulate around the currents. These magnetic fields then

generate voltages in any other conductors whose paths they

link. The undesired induced voltages in these other channels are

crosstalk signals. The channels with crosstalk can be said to

have a mutual inductance that couples signals from one channel

to another.

The power supplies, grounds, and other signal return paths

of a multichannel system are generally shared by the various

channels. When a current from one channel flows in one of

these paths, a voltage that is developed across the impedance

becomes an input crosstalk signal for other channels that share

the common impedance.

All these sources of crosstalk are vector quantities, so the mag-

nitudes cannot simply be added together to obtain the total

crosstalk. In fact, there are conditions where driving additional

circuits in parallel in a given configuration can actually reduce

the crosstalk.

Areas of Crosstalk

A practical ADV3200/ADV3201 circuit must be mounted to

some sort of circuit board in order to connect it to power

supplies and measurement equipment. Great care has been

taken to create an evaluation board that adds minimum cross-

talk to the intrinsic device. This, however, raises the issue that

the crosstalk of a system is the combination of the intrinsic

crosstalk of the devices and the crosstalk of the circuit board to

which the devices are mounted. It is important to separate these

two areas when attempting to minimize the effect of crosstalk.

In addition, crosstalk can occur among the inputs to a cross-

point switch and among the outputs. It can also occur from

input to output. Techniques are discussed in the following

sections for diagnosing which part of a system is contributing

to crosstalk.

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