LMP8350

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SNOSB80C – FEBRUARY 2011 – REVISED OCTOBER 2015

10.3 Power Dissipation

The LMP8350 is optimized for maximum performance in the small form factor of the standard SOIC package,

and is essentially a dual-channel amplifier. To ensure maximum output drive and highest performance, thermal

shutdown is not provided. Therefore, it is of utmost importance to make sure that the TJMAX of 150°C is never

exceeded due to the overall power dissipation.

Follow these steps to determine the Maximum power dissipation for the LMP8350:

1. Calculate the quiescent (no-load) power using Equation 5 (Be sure to include any current through the

feedback network if VOCM is not mid-rail.):

PAMP = ICC× (VS)

where

•

VS = V

+ – V−.

(5)

2. Calculate the RMS power dissipated in each of the output stages using Equation 6:

PD (rms) = rms ((VS – V

+

OUT) × I

+

OUT) + rms ((VS − V

−

OUT) × I

−

OUT)

where

•

VOUT and IOUT are the voltage and the current measured at the output pins of the differential amplifier as if they

were single ended amplifiers and VS is the total supply voltage.

(6)

3. Calculate the total RMS power: PT = PAMP + PD.

The maximum power that the LMP8350 package can dissipate at a given temperature can be derived from

Equation 7:

PMAX = (150° – TAMB)/ θJA

where

•

TAMB = Ambient temperature (°C)

•

and

θJA = Thermal resistance, from junction to ambient, for a given package (°C/W). For the SOIC package θJA

is 150°C/W.

(7)

NOTE

If VOCM is not 0 V then there will be quiescent current flowing in the feedback network.

This current should be included in the thermal calculations and added into the quiescent

power dissipation of the amplifier.

10.4 Evaluation Board

Generally, a good high-frequency layout will keep power supply and ground traces away from the inverting input

and output pins. Parasitic capacitances on these nodes to ground will cause frequency response peaking and

possible circuit oscillations (see Application Note OA-15 (SNOA367) for more information). Texas Instruments

suggests the following evaluation boards in Table 4 as a guide for high-frequency layout and as an aid in device

testing and characterization:

Table 4. Evaluation Board Guide

EVALUATION BOARD

DEVICE

PACKAGE

PART NUMBER

LMP8350MA

SOIC

LMH730154

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