OPA3690ID Datasheet, PDF (27/39 Pages) Texas Instruments – Triple, Wideband, Voltage-Feedback OPERATIONAL AMPLIFIER with Disable

OPA3690
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THERMAL ANALYSIS
Due to the high output power capability of the
OPA3690, heatsinking or forced airflow may be
required under extreme operating conditions.
Maximum desired junction temperature will set the
maximum allowed internal power dissipation as
described below. In no case should the maximum
junction temperature be allowed to exceed 175°C.
Operating junction temperature (T_J) is given by:
T_A + P_D × q_JA
The total internal power dissipation (P_D) is the sum of
quiescent power (P_DQ) and additional power
dissipated in the output stage (P_DL) to deliver load
power. Quiescent power is simply the specified
no-load supply current times the total supply voltage
across the part. P_DL depends on the required output
signal and load but, for a grounded resistive load, is
at a maximum when the output is fixed at a voltage
equal to 1/2 of either supply voltage (for equal bipolar
supplies). Under this condition, P_DL = V_S2/(4 × R_L)
where R_L includes feedback network loading.
SBOS237G – MARCH 2002 – REVISED MARCH 2010
Note that it is the power in the output stage and not
into the load that determines internal power
dissipation.
As a worst-case example, compute the maximum T_J
using an OPA3690IDBQ in the circuit of Figure 36
operating at the maximum specified ambient
temperature of +85°C and driving a grounded 100Ω.
P_D = 10V × 18.6mA + 3 [5²/(4 × (100Ω || 804Ω))
P_D = 397mW
Maximum T_J = +85°C + (0.40W × 100°C/W)
T_J = 125°C
This worst-case condition is still well within rated
maximum T_J for this 100Ω load. Heavier loads may,
however, exceed the 150°C maximum junction
temperature rating. Careful attention to internal power
dissipation is required and perhaps airflow considered
under extreme conditions.
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