TEA6810V データシートの表示（PDF） - Philips Electronics

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TEA6810V

Front-end and PLL synthesizers for car radios

Philips Electronics 

TPS72501

TPS72515, TPS72516

TPS72518, TPS72525

SLVS341D – MAY 2002 – REVISED MARCH 2004

www.ti.com

APPLICATION INFORMATION (continued)

Regulator Protection

The TPS725xx pass element has a built-in back diode that safely conducts reverse current when the input

voltage drops below the output voltage (e.g., during power down). Current is conducted from the output to the

input and is not internally limited. If extended reverse voltage is anticipated, external limiting might be

appropriate.

The TPS725xx also features internal current limiting and thermal protection. During normal operation, the

TPS725xx limits output current to approximately 1.6 A. When current limiting engages, the output voltage scales

back linearly until the overcurrent condition ends. While current limiting is designed to prevent gross device

failure, care should be taken not to exceed the power dissipation ratings of the package. If the temperature of the

device exceeds 165°C, thermal-protection circuitry shuts it down. Once the device has cooled down to below

145°C, regulator operation resumes.

THERMAL INFORMATION

The amount of heat that an LDO linear regulator generates is directly proportional to the amount of power it

dissipates during operation. All integrated circuits have a maximum allowable junction temperature (TJmax)

above which normal operation is not assured. A system designer must design the operating environment so that

the operating junction temperature (TJ) does not exceed the maximum junction temperature (TJmax). The two

main environmental variables that a designer can use to improve thermal performance are air flow and external

heatsinks. The purpose of this information is to aid the designer in determining the proper operating environment

for a linear regulator that is operating at a specific power level.

In general, the maximum expected power (PD(max)) consumed by a linear regulator is computed as:

ǒ Ǔ PDmax + VI(avg) * VO(avg) IO(avg) ) VI(avg) x I(Q)

(3)

Where:

• VI(avg) is the average input voltage.

• VO(avg) is the average output voltage.

• IO(avg) is the average output current.

• I(Q) is the quiescent current.

For most TI LDO regulators, the quiescent current is insignificant compared to the average output current;

therefore, the term VI(avg) x I(Q) can be neglected. The operating junction temperature is computed by adding the

ambient temperature (TA) and the increase in temperature due to the regulator's power dissipation. The

temperature rise is computed by multiplying the maximum expected power dissipation by the sum of the thermal

resistances between the junction and the case (RθJC), the case to heatsink (RθCS), and the heatsink to ambient

(RθSA). Thermal resistances are measures of how effectively an object dissipates heat. Typically, the larger the

device, the more surface area available for power dissipation and the lower the object's thermal resistance.

Figure 20 illustrates these thermal resistances for (a) a SOT223 package mounted in a JEDEC low-K board, and

(b) a DDPAK package mounted on a JEDEC high-K board.

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