Datasheet

OPA690
www.ti.com SBOS223F –DECEMBER 2001–REVISED FEBRUARY 2010
THERMAL ANALYSIS As a worst-case example, compute the maximum T
J
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 20Ω load.
Maximum desired junction temperature will set the
maximum allowed internal power dissipation as P
D
= 10V × 6.2mA + 5
2
/(4 × (20Ω || 804Ω)) = 382mW
described below. In no case should the maximum
Maximum T
J
= +85°C + (0.38W × 150°C/W) = 142°C.
junction temperature be allowed to exceed 175°C.
Although this is still well below the specified
Operating junction temperature (T
J
) is given by T
A
+
maximum junction temperature, system reliability
P
D
× q
JA
. The total internal power dissipation (P
D
) is
considerations may require lower tested junction
the sum of quiescent power (P
DQ
) and additional
temperatures. The highest possible internal
power dissipated in the output stage (P
DL
) 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. P
DL
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 in 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, P
DL
= V
S2
/(4 × R
L
)
internal power dissipation under these conditions.
where R
L
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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