TPS73233DBVR datasheet(13/26 Pages) TI

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dV dt +

OUT

80kW ø RLOAD

(4)

dV dt +

OUT

80kW ø (R1 ) R2) ø RLOAD

(5)

POWER DISSIPATION

REVERSE CURRENT

+ (VIN * VOUT)

OUT

(6)

THERMAL PROTECTION

Package Mounting

TPS732xx

SBVS037L – AUGUST 2003 – REVISED AUGUST 2007

The TPS732xx does not have active pull-down when

Any tendency to activate the thermal protection circuit

the output is over-voltage. This allows applications

indicates

excessive

power

dissipation

that

connect

higher

voltage

sources,

such

inadequate heatsink. For reliable operation, junction

alternate power supplies, to the output. This also

temperature should be limited to +125

°C maximum.

results in an output overshoot of several percent if the

To estimate the margin of safety in a complete design

load current quickly drops to zero when a capacitor is

(including

heatsink),

increase

the

ambient

connected to the output. The duration of overshoot

temperature until the thermal protection is triggered;

can be reduced by adding a load resistor. The

use worst-case loads and signal conditions. For good

overshoot decays at a rate determined by output

reliability, thermal protection should trigger at least

capacitor

COUT

and

the

internal/external

load

+35

°C above the maximum expected ambient

resistance. The rate of decay is given by:

condition

your

application.

This

produces

worst-case junction temperature of +125

°C at the

(Fixed voltage version)

highest

expected

ambient

temperature

and

worst-case load.

The internal protection circuitry of the TPS732xx has

been designed to protect against overload conditions.

(Adjustable voltage version)

It was not intended to replace proper heatsinking.

Continuously running the TPS732xx into thermal

shutdown will degrade device reliability.

The ability to remove heat from the die is different for

The NMOS pass element of the TPS732xx provides

each

package

type,

presenting

different

inherent protection against current flow from the

considerations in the PCB layout. The PCB area

output of the regulator to the input when the gate of

around the device that is free of other components

the pass device is pulled low. To ensure that all

moves the heat from the device to the ambient air.

charge is removed from the gate of the pass element,

Performance data for JEDEC low- and high-K boards

the enable pin must be driven low before the input

are shown in the Power Dissipation Ratings table.

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

Using heavier copper will increase the effectiveness

element may be left on due to stored charge on the

in removing heat from the device. The addition of

gate.

plated through-holes to heat-dissipating layers will

also improve the heat-sink effectiveness.

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

needed on any pin for reverse current blocking. Note

Power dissipation depends on input voltage and load

that reverse current is specified as the current flowing

conditions. Power dissipation (PD) is equal to the

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

product of the output current times the voltage drop

pin. There will be additional current flowing into the

across the output pass element (VIN to VOUT):

OUT pin due to the 80k

Ω internal resistor divider to

ground (see Figure 1 and Figure 2).

For the TPS73201, reverse current may flow when

Power dissipation can be minimized by using the

VFB is more than 1.0V above VIN.

lowest possible input voltage necessary to assure the

required output voltage.

Thermal protection disables the output when the

junction temperature rises to approximately +160

°C,

Solder

pad

footprint

recommendations

for

the

allowing the device to cool. When the junction

TPS732xx are presented in Application Bulletin

temperature cools to approximately +140

°C, the

Solder Pad Recommendations for Surface-Mount

output circuitry is again enabled. Depending on power

Devices

(SBFA015),

available

from

the

Texas

dissipation,

thermal

resistance,

and

ambient

Instruments web site at www.ti.com.

temperature, the thermal protection circuit may cycle

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

protecting it from damage due to overheating.

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