LM97600CIUTSLASHNOPB datasheet(41/58 Pages) TI1

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Cross Section Line

IC Die

Not to Scale

Mold Compound

Copper Heat Slug

Substrate

4JC_2

4JC_1

LM97600

www.ti.com

SNAS600A – JULY 2012 – REVISED MARCH 2013

Thermal Management

The LM97600 is capable of impressive speeds and performance at very low power levels for its speed. However,

the power consumption is still high enough to require attention to thermal management. The Thermally Enhanced

BGA package has 2 primary heat transfer paths. The copper heat slug mounted to the top of the substrate, and

exposed in the center top of the package is the first path. The thermal resistance of this path is referred to as

θJC_1. The other main heat path is via the center group of ground balls on the bottom of the package. The

thermal resistance of this path is provided as

θJC_2. In most applications, the center ground balls will form the

primary thermal path.

Figure 45. HSBGA Conceptual Drawing

For reliability reasons, the die temperature should be kept to a maximum of 130°C. That is, TA (ambient

temperature) plus ADC power consumption times the net

θJA (junction to ambient thermal resistance) should not

exceed 130°C. This is not a problem if the ambient temperature is kept to a maximum of +85°C as specified in

the Operating Ratings section and the center ground balls on the bottom of the package are thermally connected

to a large enough copper area of the PC board.

Please note that the following are general recommendations for mounting Thermally Enhanced BGA devices

onto a PCB. This should be considered the starting point in PCB and assembly process development. It is

recommended that the process be developed based upon past experience in package mounting.

The package of the LM97600 has a central group of ground balls that provide the primary heat removal path as

well as excellent electrical grounding to the printed circuit board. The land pattern design for attachment to the

PCB should be as recommended for the conventional BGA package (per AN-1126), but the center balls should

be connected to internal ground planes to remove the maximum amount of heat from the package, as well as to

ensure best product parametric performance.

To minimize junction temperature, it is recommended that a simple heat sink be built into the PCB. This is done

by including a copper area of about 2 square inches (6.5 square cm) on the opposite side of the PCB. This

copper area may be plated or solder coated to prevent corrosion, but should not have a conformal coating, which

could provide some thermal insulation. Thermal vias should be used to connect these top and bottom copper

areas. These thermal vias act as "heat pipes" to carry the thermal energy from the device side of the board to the

opposite side of the board where it can be more effectively dissipated. The use of 9 to 16 thermal vias is

recommended.

LAYOUT AND GROUNDING

Proper grounding and proper routing of all signals are essential to ensure accurate conversion. A single ground

plane should be used, instead of splitting the ground plane into analog and digital areas.

Since digital switching transients are composed largely of high frequency components, the skin effect tells us that

total ground plane copper weight will have little effect upon the logic-generated noise. Total surface area is more

important than is total ground plane volume. Coupling between the typically noisy digital circuitry and the

sensitive analog circuitry can lead to poor performance that may seem impossible to isolate and remedy. The

solution is to keep the analog circuitry well separated from the digital circuitry.

High power digital components should not be located on or near any linear component or power supply trace or

plane that services analog or mixed signal components as the resulting common return current path could cause

fluctuation in the analog input “ground” return of the ADC, causing excessive noise in the conversion result.

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