OP450GRU AD [Analog Devices], OP450GRU Datasheet - Page 11

• Manufacturer Part Number: OP450GRU
• Description: CMOS Single-Supply Rail-to-Rail Input/Output Operational Amplifiers
• Manufacturer: AD [Analog Devices]

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Power Dissipation
Although the OPx50 family of amplifiers are able to provide
load currents of up to 250 mA, proper attention should be given
to not exceed the maximum junction temperature for the device.
The equation for finding the junction temperature is given as:
Where
In any application, the absolute maximum junction temperature
must be limited to +150 C. If this junction temperature is ex-
ceeded, the device could suffer premature failure. If the output
voltage and output current are in phase, for example, with a
purely resistive load, the power dissipated by the OPx50 can be
found as:
Where
By calculating the power dissipation of the device and using the
thermal resistance value for a given package type, the maximum
allowable ambient temperature for an application can be found
using Equation 3.
Overdrive Recovery
The overdrive, or overload, recovery time of an amplifier is the
time required for the output voltage to return to a rated output
voltage from a saturated condition. This recovery time can be
important in applications where the amplifier must recover
quickly after a large transient event. The circuit in Figure 29
was used to evaluate the recovery time for the OPx50. Figures
30 and 31 show the overload recovery of the OP250 from the
positive and negative rails. It takes approximately 0.5 ms for the
amplifier to recover from output overload.
Figure 29. Overload Recovery Time Test Circuit
Figure 28. Output Short-Circuit Protection
T
P
the package; and
T
I
V
V
LOAD
JA
DISS
J
A
SY
OUT
= OPx50 junction temperature
V
= The ambient temperature of the circuit
= OPx50 junction-to-ambient thermal resistance of
IN
= OPx50 supply voltage; and
= OPx50 power dissipation
= The output voltage
= OPx50 output load current
V
IN
1V
1k
P–P
T
P
J
DISS
OP250
=
+5V
P
DISS
OP250
I
9k
LOAD
20
R
X
JA
+
V
T
SY
A
10k
V
V
OUT
OUT
V
OUT
(3)
(4)
–11–
Capacitive Loading
The OPx50 family of amplifiers is well suited to driving capaci-
tive loads. The device will remain stable at unity gain even un-
der heavy capacitive load conditions. However, a capacitive load
does not come without a penalty in bandwidth. Figure 32 shows
a graph of the OPx50 unity-gain bandwidth under various ca-
pacitive loads.
As with any amplifier, an increase in capacitive load will also re-
sult in an increase in overshoot and ringing. To improve the
output response, a series R-C network, known as a snubber, can
Figure 31. Saturation Recovery from the Negative Rail
Figure 30. Saturation Recovery from the Positive Rail
Figure 32. Unity-Gain Bandwidth vs. Capacitive Load
1.0
0.8
0.6
0.4
0.2
0
0
500mV
500mV
1
CAPACITIVE LOAD – nF
10
OP250/OP450
1µs
1µs
100
V
R
T
S
A
L
=
= 10k
= +25 C
2.5V
1k