OPA569 datasheet(16/28 Pages) TI1

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OPA569

SBOS264A

www.ti.com

Any tendency to activate the thermal protection circuit indi-

cates excessive power dissipation or an inadequate heat

sink. For reliable, long term, continuous operation, the junc-

tion temperature should be limited to 125

°C maximum. To

estimate the margin of safety in a complete design (including

heat sink), increase the ambient temperature until the ther-

mal protection is triggered. Use worst-case loading and

signal conditions. For good, long-term reliability, thermal

protection should trigger more than 25

°C above the maxi-

mum expected ambient conditions of your application. This

produces a junction temperature of 125

°C at the maximum

expected ambient condition.

Fast transients of large output current swings (for example

switching quickly from sourcing 2A to sinking 2A) may cause

a glitch on the Thermal Flag pin. When switching large

currents is expected, the use of extra bypass between the

supplies or a low-pass filter on the Thermal Flag pin is

recommended.

POWER DISSIPATION AND

SAFE OPERATING AREA

Power dissipation depends on power supply, signal and load

conditions. It is dominated by the power dissipation of the

output transistors. For DC signals, power dissipation is equal

to the product of output current, IOUT and the output voltage

across the conducting output transistor (VS-VOUT). Dissipa-

tion with AC signals is lower. Application Bulletin AB-039

(SBOA022) explains how to calculate or measure power

dissipation with unusual signals and loads and can be found

at the TI web site (www.ti.com).

Output short-circuits are particularly demanding for the am-

plifier because the full supply voltage is seen across the

conducting transistor. It is very important to note that the

temperature protection will not shut the part down in over-

temperature conditions, unless the Thermal Flag pin is con-

nected to the Enable pin; see the section on Thermal Flag.

Figure 8 shows the safe operating area at room temperature

with various heatsinking efforts. Note that the safe output

current decreases as (VS – VOUT) increases. Figure 9 shows

the safe operating area at various temperatures with the

PowerPAD being soldered to a 2 oz copper pad.

The power that can be safely dissipated in the package is

related to the ambient temperature and the heatsink design.

The PowerPAD package was specifically designed to pro-

vide excellent power dissipation, but board layout greatly

influences the heat dissipation of the package. Refer to

the “PowerPAD Thermally Enhanced Package” section for

further details.

The OPA569 has a junction-to-ambient thermal resistance

(

JA) value of 21.6°C/W when soldered to 2oz copper plane.

This value can be further decreased to 12

°C/W by the

addition of forced air. Figure 10 shows the junction-to-

ambient thermal resistance of the DWP-20 package.

FIGURE 10. Junction-to-Ambient Thermal Resistance with

Various Heatsinking Efforts.

FIGURE 8. Safe Operating Area at Room Temperature.

FIGURE 9. Safe Operating Area at Various Ambient Tempera-

tures. PowerPAD soldered to a 2oz copper pad.

0.1

V

S – VOUT (V)

SAFE OPERATING AREA AT ROOM TEMPERATURE

Copper—soldered,

without forced air.

Copper—soldered,

with 150lfm airflow.

Copper—soldered,

with 500lfm airflow.

Current is limited by the

maximum output current.

Copper—soldered,

with 250lfm airflow.

0.1

V

S – VOUT (V)

SAFE OPERATING AREA AT VARIOUS

AMBIENT TEMPERATURES

A = +125°C

A = +85°C

A = +25°C

A = –40°C

A = 0°C

Current is limited by

the maximum output

current.

HEATSINKING METHOD

The part is soldered to a 2 oz copper pad under the

21.6

exposed pad.

Soldered to copper pad with forced airflow (150lfm).

15.1

Soldered to copper pad with forced airflow (250lfm).

13.2

Soldered to copper pad with forced airflow (500lfm).

12.0

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