TPS73619DBVT datasheet(13/23 Pages) TI

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Reverse Current

Power Dissipation

Thermal Protection

+ (VIN * VOUT)

OUT

(6)

Package Mounting

TPS736xx

SBVS038N – SEPTEMBER 2003 – REVISED JANUARY 2007

+35

°C above the maximum expected ambient

condition of your application. This produces a

The NMOS pass element of the TPS736xx provides

worst-case junction temperature of +125

°C at the

inherent protection against current flow from the

highest

expected

ambient

temperature

and

output of the regulator to the input when the gate of

worst-case load.

the pass device is pulled low. To ensure that all

charge is removed from the gate of the pass

The internal protection circuitry of the TPS736xx has

element, the enable pin must be driven low before

been

designed

protect

against

overload

the input voltage is removed. If this is not done, the

conditions. It was not intended to replace proper heat

pass element may be left on due to stored charge on

sinking. Continuously running the TPS736xx into

the gate.

thermal shutdown will degrade reliability.

After the enable pin is driven low, no bias voltage is

needed on any pin for reverse current blocking. Note

that reverse current is specified as the current

The ability to remove heat from the die is different for

flowing out of the IN pin due to voltage applied on

each

package

type,

presenting

different

the OUT pin. There will be additional current flowing

considerations in the PCB layout. The PCB area

into the OUT pin due to the 80k

Ω internal resistor

around the device that is free of other components

divider to ground (see Figure 1 and Figure 2).

moves the heat from the device to the ambient air.

Performance data for JEDEC low and high K boards

For the TPS73601, reverse current may flow when

are shown in the Power Dissipation Ratings table.

VFB is more than 1.0V above VIN.

Using heavier copper will increase the effectiveness

in removing heat from the device. The addition of

plated through-holes to heat-dissipating layers will

also improve the heat-sink effectiveness.

Thermal protection disables the output when the

junction temperature rises to approximately +160

°C,

Power dissipation depends on input voltage and load

allowing the device to cool. When the junction

conditions. Power dissipation (PD) is equal to the

temperature cools to approximately +140

°C, the

product of the output current times the voltage drop

output circuitry is again enabled. Depending on

across the output pass element (VIN to VOUT):

power dissipation, thermal resistance, and ambient

temperature, the thermal protection circuit may cycle

on and off. This limits the dissipation of the regulator,

Power dissipation can be minimized by using the

protecting it from damage due to overheating.

lowest possible input voltage necessary to assure

Any tendency to activate the thermal protection

the required output voltage.

circuit indicates excessive power dissipation or an

inadequate heat sink. For reliable operation, junction

temperature should be limited to +125

°C maximum.

To estimate the margin of safety in a complete

Solder

pad

footprint

recommendations

for

the

design (including heat sink), increase the ambient

TPS736xx are presented in Application Bulletin

temperature until the thermal protection is triggered;

Solder Pad Recommendations for Surface-Mount

use worst-case loads and signal conditions. For good

Devices

(SBFA015),

available

from

the

Texas

reliability, thermal protection should trigger at least

Instruments web site at www.ti.com.

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