LMV321 datasheet(13/15 Pages) CADEKA

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Data Sheet

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the supplies.

PD = Psupply - Pload

Supply power is calculated by the standard power

equation.

Psupply = Vsupply × IRMS supply

Vsupply = VS+ - VS-

Power delivered to a purely resistive load is:

Pload = ((VLOAD)RMS2)/Rloadeff

The effective load resistor (Rloadeff) will need to include

the effect of the feedback network. For instance,

Rloadeff in Figure 3 would be calculated as:

RL || (Rf + Rg)

These measurements are basic and are relatively easy to

perform with standard lab equipment. For design purposes

however, prior knowledge of actual signal levels and load

impedance is needed to determine the dissipated power.

Here, PD can be found from

PD = PQuiescent + PDynamic - PLoad

Quiescent power can be derived from the speciﬁed IS

values along with known supply voltage, VSupply. Load

power can be calculated as above with the desired signal

amplitudes using:

(VLOAD)RMS = VPEAK / √2

( ILOAD)RMS = ( VLOAD)RMS / Rloadeff

The dynamic power is focused primarily within the output

stage driving the load. This value can be calculated as:

PDYNAMIC = (VS+ - VLOAD)RMS × ( ILOAD)RMS

Assuming the load is referenced in the middle of the

power rails or Vsupply/2.

The LMV321 is short circuit protected. However, this may

not guarantee that the maximum junction temperature

(+150°C) is not exceeded under all conditions.

Driving Capacitive Loads

Increased phase delay at the output due to capacitive

loading can cause ringing, peaking in the frequency

response, and possible unstable behavior. Use a series

resistance, RS, between the ampliﬁer and the load to

help improve stability and settling performance. Refer to

Figure 5.

Figure 5. Addition of RS for Driving Capacitive Loads

For a given load capacitance, adjust RS to optimize the

tradeoff between settling time and bandwidth. In general,

reducing RS will increase bandwidth at the expense of

additional overshoot and ringing.

Overdrive Recovery

An overdrive condition is deﬁned as the point when either

one of the inputs or the output exceed their speciﬁed

voltage range. Overdrive recovery is the time needed for

the ampliﬁer to return to its normal or linear operating

point. The recovery time varies, based on whether the

input or output is overdriven and by how much the range

is exceeded. The LMV321 and will typically recover in less

than 5us from an overdrive condition. Figure 6 shows the

LMV321 in an overdriven condition.

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Figure 6. Overdrive Recovery

Layout Considerations

General layout and supply bypassing play major roles

in high frequency performance. CADEKA has evaluation

boards to use as a guide for high frequency layout and as

an aid in device testing and characterization. Follow the

steps below as a basis for high frequency layout:

Include 6.8µF and 0.1µF ceramic capacitors for power

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