TPS73233DBVT datasheet(14/18 Pages) TI

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dV dt

OUT

80kW ø (R1 ) R2)

(5)

REVERSE CURRENT

POWER DISSIPATION

THERMAL PROTECTION

+ (VIN * VOUT)

OUT

(6)

Package Mounting

TPS73201, TPS73215, TPS73216

TPS73218, TPS73225, TPS73230

TPS73233, TPS73250

SBVS037F – AUGUST 2003 – REVISED SEPTEMBER 2004

(Adjustable voltage version)

reliability, thermal protection should trigger at least

°C above the maximum expected ambient con-

dition of your application. This produces a worst-case

junction temperature of 125

°C at the highest ex-

pected ambient temperature and worst-case load.

The internal protection circuitry of the TPS732xx has

The NMOS pass element of the TPS732xx provides

been designed to protect against overload conditions.

inherent protection against current flow from the

It was not intended to replace proper heatsinking.

output of the regulator to the input when the gate of

Continuously running the TPS732xx into thermal

the pass device is pulled low. To ensure that all

shutdown will degrade device reliability.

charge is removed from the gate of the pass element,

the enable pin must be driven low before the input

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

The ability to remove heat from the die is different for

element may be left on due to stored charge on the

each package type, presenting different consider-

gate.

ations in the PCB layout. The PCB area around the

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

device that is free of other components moves the

needed on any pin for reverse current blocking. Note

heat from the device to the ambient air. Performance

that reverse current is specified as the current flowing

data for JEDEC low- and high-K boards are shown in

out of the IN pin due to voltage applied on the OUT

the Power Dissipation Ratings table. Using heavier

pin. There will be additional current flowing into the

copper will increase the effectiveness in removing

OUT pin due to the 80k

Ω internal resistor divider to

heat

from

the

device.

The

addition

plated

ground (see Figure 1 and Figure 2).

through-holes to heat-dissipating layers will also im-

prove the heat-sink effectiveness.

For the TPS73201, reverse current may flow when

VFB is more than 1.0V above VIN.

Power dissipation depends on input voltage and load

conditions. Power dissipation is equal to the product

of the output current times the voltage drop across

the output pass element (VIN to VOUT):

Thermal protection disables the output when the

junction temperature rises to approximately 160

°C,

allowing the device to cool. When the junction tem-

Power dissipation can be minimized by using the

perature cools to approximately 140

°C, the output

lowest possible input voltage necessary to assure the

circuitry is again enabled. Depending on power dissi-

required output voltage.

pation, thermal resistance, and ambient temperature,

the thermal protection circuit may cycle on and off.

This limits the dissipation of the regulator, protecting

it from damage due to overheating.

Solder

pad

footprint

recommendations

for

the

TPS732xx are presented in Application Bulletin

Any tendency to activate the thermal protection circuit

Solder Pad Recommendations for Surface-Mount De-

indicates excessive power dissipation or an inad-

vices (AB-132), available from the Texas Instruments

equate heatsink. For reliable operation, junction tem-

web site at www.ti.com.

perature should be limited to 125

°C maximum. To

estimate the margin of safety in a complete design

(including heatsink), increase the ambient tempera-

ture until the thermal protection is triggered; use

worst-case loads and signal conditions. For good

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