the output high can cause damage to internal low current

paths in a manner similar to that just described in the “Short-

ing the Regulator Input” section.

Regulator Floating Ground (

Figure 2): When the ground

pin alone becomes disconnected, the output approaches the

unregulated input, causing possible damage to other circuits

connected to V

“ON”, damage may also occur to the regulator. This fault is

most likely to occur when plugging in regulators or modules

with on card regulators into powered up sockets. Power

should be turned off first, thermal limit ceases operating, or

ground should be connected first if power must be left on.

Transient Voltages: If transients exceed the maximum

rated input voltage of the device, or reach more than 0.8V

below ground and have sufficient energy, they will damage

the regulator. The solution is to use a large input capacitor, a

series input breakdown diode, a choke, a transient suppres-

sor or a combination of these.

When a value for

θ

a heatsink must be selected that has

a value that is less than

or equal to this number.

θ

in this catalog, or shown in a curve that plots temperature

rise vs power dissipation for the heatsink.

HEATSINKING TO-263 AND SOT-223 PACKAGE PARTS

Both the TO-263 (“S”) and SOT-223 (“MP”) packages use a

copper plane on the PCB and the PCB itself as a heatsink.

To optimize the heat sinking ability of the plane and PCB,

solder the tab of the plane.

shows for the TO-263 the measured values of

θ

ferent copper area sizes using a typical PCB with 1 ounce

copper

and no solder mask over the copper area used for

heatsinking.

As shown in the figure, increasing the copper area beyond 1

square inch produces very little improvement. It should also

be observed that the minimum value of

θ

package mounted to a PCB is 32˚C/W.

As a design aid,

Figure 5 shows the maximum allowable

power dissipation compared to ambient temperature for the

TO-263 device (assuming

θ

mum junction temperature is 125˚C).

DS007781-8

FIGURE 1. Input Short

DS007781-9

FIGURE 2. Regulator Floating Ground

DS007781-10

FIGURE 3. Transients

DS007781-39

FIGURE 4.

θ

Area for the TO-263 Package

DS007781-40

FIGURE 5. Maximum Power Dissipation vs

T

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