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LTC6363 Family

Rev. C

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APPLICATIONS INFORMATION

even-order harmonics and maximizes the rejection of

common mode signals and noise.

The VOCMpinshouldbebypassedtothegroundplanewith

a high quality 0.1µF ceramic capacitor. This will prevent

common mode signals and noise on this pin from being

inadvertently converted to differential signals and noise

by impedance mismatches both externally and internally

to the IC.

Power Dissipation

Due to the wide supply voltage range, it is possible for

the LTC6363 family to exceed the maximum junction

temperature under certain conditions. Maximum junction

temperature (TJ) is calculated from the ambient tempera-

ture (TA) and power dissipation (PD) as follows: TJ= TA+

(PD • θJA). The power dissipation in the IC is a function of

the supply voltage, output voltage and the load, input and

feedbackresistances.Foragivensupplyvoltage,theworst-

case power dissipation, PD(MAX), occurs at the maximum

quiescent supply current and at an output voltage which is

half of either supply voltage (or the maximum swing if it

is less than half the supply voltage). In this condition, the

LTC6363 will supply current to the load resistors and the

inputandfeedbackresistors,RIandRF.PD(MAX)isgivenby:

PD(MAX) = V+ −V–

(

) IS(MAX)

(

)+2•

V+

⎛

⎝

⎜⎜

⎞

⎠

⎟⎟

+2 •

V +

⎛

⎝

⎜

⎞

⎠

⎟

⎛

⎝

⎜⎜

⎞

⎠

⎟⎟

RI+RF

Example: An LTC6363HMS8 in the 8-Lead MSOP package

has a thermal resistance of θJA = 273°C/W. Operating on

±5V supplies, with RI = RF = 500Ω, and driving a 500Ω

load to ground at each output, the worst-case power dis-

sipation is given by:

PD(MAX) = 10V

(

) 2.2mA

(

)+2 •

2.5V

(

)

500Ω

+ 2 •

( )

1000Ω

= 97mW

In this example, the maximum ambient temperature that

the part is allowed to operate is:

TA = TJ – (PD(MAX) • 273°C/W)

TA = 150°C – (97mW)(273°C/W) = 123.5°C

To operate the device at a higher ambient temperature

for the same conditions, use the LTC6363 in the 8-Lead

DFN package.

Interfacing to ADCs

WhendrivinganADC,anadditionalpassivefiltershouldbe

used between the outputs of the LTC6363 family and the

inputs of the ADC. Depending on the application, a single-

pole RC filter will often be sufficient. The sampling process

of ADCs creates a charge transient due to the switching in

of the ADC sampling capacitor. This momentarily creates

highfrequencycurrentpulsesattheoutputoftheamplifier

as charge is transferred between amplifier and sampling

capacitor. The amplifier must recover and settle from this

load transient before the acquisition period has ended for

a valid representation of the input signal. The RC network

between the outputs of the driver and the inputs of the

ADC decouples this sampling transient (see Figure 5).

The capacitance serves to provide the bulk of the charge

during the sampling process, and the two resistors at the

outputs of the LTC6363 family are used to dampen and

attenuate any charge injected by the ADC. Additionally, the

RC filter band limits broadband output noise.

The selection of an appropriate filter depends on the spe-

cific ADC, and the following procedure is suggested for

choosing filter component values. Begin by selecting an

appropriate RC time constant for the input signal. Gener-

ally, longer time constants improve SNR at the expense of

settling time. Output transient settling to 20-bit accuracy

will require nearly 14 RC time constants to completely

settle. To select the resistor value, remember the resistors

in the decoupling network should be at least 10Ω. Keep

in mind that these resistors also serve to decouple the

LTC6363 family outputs from load capacitance. Too large

of a resistor will leave insufficient settling time. Too small

of a resistor will not properly dampen the load transient

of the sampling process, prolonging the time required for

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