OPA690IDBVT datasheet(25/37 Pages) TI1

25 / 37 page

OPA690

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SBOS223F – DECEMBER 2001 – REVISED FEBRUARY 2010

THERMAL ANALYSIS

As a worst-case example, compute the maximum TJ

using an OPA690IDBV (SOT23-6 package) in the

Due to the high output power capability of the

circuit of Figure 36 operating at the maximum

OPA690, heatsinking or forced airflow may be

specified ambient temperature of +85°C and driving a

required

under

extreme

operating

conditions.

grounded 20

Ω load.

Maximum desired junction temperature will set the

maximum allowed internal power dissipation as

PD = 10V × 6.2mA + 5

2/(4 × (20Ω || 804Ω)) = 382mW

described below. In no case should the maximum

Maximum TJ = +85°C + (0.38W × 150°C/W) = 142°C.

junction temperature be allowed to exceed 175°C.

Although

this

still

well

below

the

specified

Operating junction temperature (TJ) is given by TA +

maximum junction temperature, system reliability

PD × qJA. The total internal power dissipation (PD) is

considerations may require lower tested junction

the sum of quiescent power (PDQ) and additional

temperatures.

The

highest

possible

internal

power dissipated in the output stage (PDL) to deliver

dissipation will occur if the load requires current to be

load power. Quiescent power is simply the specified

forced into the output for positive output voltages or

no-load supply current times the total supply voltage

sourced from the output for negative output voltages.

across the part. PDL depends on the required output

This puts a high current through a large internal

signal and load but, for a grounded resistive load, be

voltage drop in the output transistors. Figure 19, the

at a maximum when the output is fixed at a voltage

output

V-I

plot

shown

the

±5V

Typical

equal to 1/2 of either supply voltage (for equal bipolar

Characteristics, include a boundary for 1W maximum

supplies). Under this condition, PDL = VS2/(4 × RL)

internal power dissipation under these conditions.

where RL includes feedback network loading.

Note that it is the power in the output stage and not

into

the

load

that

determines

internal

power

dissipation.

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