Datasheet

LM7321, LM7322
www.ti.com SNOSAW8D –MAY 2008–REVISED MARCH 2013
Figure 73. V
COM
Driver Performance Scope Photo
OUTPUT SHORT CIRCUIT CURRENT AND DISSIPATION ISSUES
The LM7321/LM7321Q/LM7322/LM7322Q output stage is designed for maximum output current capability. Even
though momentary output shorts to ground and either supply can be tolerated at all operating voltages, longer
lasting short conditions can cause the junction temperature to rise beyond the absolute maximum rating of the
device, especially at higher supply voltage conditions. Below supply voltage of 6V, the output short circuit
condition can be tolerated indefinitely.
With the op amp tied to a load, the device power dissipation consists of the quiescent power due to the supply
current flow into the device, in addition to power dissipation due to the load current. The load portion of the
power itself could include an average value (due to a DC load current) and an AC component. DC load current
would flow if there is an output voltage offset, or the output AC average current is non-zero, or if the op amp
operates in a single supply application where the output is maintained somewhere in the range of linear
operation.
Therefore:
P
TOTAL
= P
Q
+ P
DC
+ P
AC
P
Q
= I
S
· V
S
Op Amp Quiescent Power Dissipation
P
DC
= I
O
· (V
r
- V
o
) DC Load Power
P
AC
= See Table 1 AC Load Power
where:
I
S
: Supply Current
V
S
: Total Supply Voltage (V
+
− V
−
)
V
O
: Average Output Voltage
V
r
: V
+
for sourcing and V
−
for sinking current
Table 1 shows the maximum AC component of the load power dissipated by the op amp for standard Sinusoidal,
Triangular, and Square Waveforms:
Table 1. Normalized AC Power Dissipated in the Output Stage for Standard Waveforms
P
AC
(W.Ω/V
2
)
Sinusoidal Triangular Square
50.7 x 10
−3
46.9 x 10
−3
62.5 x 10
−3
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