LM2941CSXSLASHNOPB datasheet(16/30 Pages) TI1

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GND

CIN

COUT

LM2941, LM2941C

SNVS770I – JUNE 1999 – REVISED JANUARY 2015

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Layout Example (continued)

Figure 23. LM2941 TO-263 Package Typical Layout

10.3 Power Dissipation

Consideration should be given to the maximum power dissipation (PD(MAX)) which is limited by the maximum

operating junction temperature (TJ(MAX)) of 125°C, the maximum operating ambient temperature (TA(MAX)) of the

application, and the thermal resistance (RθJA) of the package. Under all possible conditions, the junction

temperature (TJ) must be within the range specified in the Operating Ratings. The total power dissipation of the

device is given by:

PD = ( (VIN − VOUT) x IOUT) + (VIN x IGND)

(3)

where IGND is the operating ground pin current of the device (specified under Electrical Characteristics: LM2941T,

LM2941S, LM2941LD and Electrical Characteristics: LM2941CT, LM2941CS).

The maximum allowable junction temperature rise (

ΔTJ) depends on the maximum expected ambient

temperature (TA(MAX)) of the application, and the maximum allowable junction temperature (TJ(MAX)):

ΔTJ = TJ(MAX) − TA(MAX)

(4)

The maximum allowable value for junction to ambient Thermal Resistance, RθJA, required to keep the junction

temperature, TJ, from exceeding maximum allowed can be calculated using the formula:

RθJA = ΔTJ / PD(MAX)

(5)

The maximum allowable power dissipation, PD(MAX), required allowed for a specific ambient temperature can be

calculated using the formula:

PD(MAX) = ΔTJ / RθJA

(6)

Additional information for thermal performance of surface mount packages can be found in AN-1520: A Guide to

Board Layout for Best Thermal Resistance for Exposed Packages (SNVA183), AN-1187: Leadless Leadframe

Package (LLP) (SNOA401), and AN-2020: Thermal Design By Insight, Not Hindsight (SNVA419).

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