TS2938CS datasheet(4/5 Pages) TSC

4 / 5 page

TS2938/A

4-5

2004/09 rev. A

Application Information (continued)

The next parameter which must be calculated the

maximum allowable temperature rise.

TR(max) is calculated by the using to formula:

TR(max) = TJ(max) – TA(max)

Where: TJ(max) is the maximum allowable junction

temperature, which is 125

oC for commercial

grade parts.TA(max) is the maximum ambient

temperature which will be encountered in the

application.

Using the calculated values for TR(max) and PD, the

maximum allowable value for the junction to ambient

thermal resistance,

θja, can now be found:

θja = TR(max) / PD

Inhibit Input

TS2938/A feature an active-low (Inhibit) input that

allows ON/OFF control of the regulator. The Inhibit

input has TTL/CMOS compatible thresholds for simple

interfacing with logic interfacing. Inhibit should be

directly tied to Ground or keep open (not connected).

IMPORTANT:

if the maximum allowable value for is found to be ≥ 60

oC/W for the TO-220 package, ≥80 oC/W for the

TO-263 package, ≥150

oC/W for the TO-252 package,

or ≥170

oC/W for the SOT-223 package, no heatsink is

needed since the package alone will dissipate enough

heat to satisfy these requirements. If the calculated

value for

θja falls below these limits, a heatsink is

required.

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