AD8644 Analog Devices, AD8644 Datasheet - Page 10

• Manufacturer Part Number: AD8644
• Description: 18 V Operational Amplifier (Quad)
• Manufacturer: Analog Devices

Specifications of AD8644

• -3db Bandwidth: 5.5MHz
• Slew Rate: 7.5V/µs
• Vos: 1mV
• Ib: 80nA
• # Opamps Per Pkg: 4
• Input Noise (nv/rthz): 12nV/rtHz
• Vcc-vee: 5V to 18V
• Isy Per Amplifier: 1.1mA
• Packages: SOIC,SOP

AD8614/AD8644
INPUT OVERVOLTAGE PROTECTION
As with any semiconductor device, whenever the condition
exists for the input to exceed either supply voltage, attention
needs to be paid to the input overvoltage characteristic. As an
overvoltage occurs, the amplifier can be damaged, depending
on the voltage level and the magnitude of the fault current.
When the input voltage exceeds either supply by more than
0.6 V, internal pin junctions energize, allowing current to flow
from the input to the supplies. Observing Figure 26, the
AD8614/AD8644 have 1.5 kΩ resistors in series with each
input, which helps to limit the current. This input current is not
inherently damaging to the device as long as it is limited to
5 mA or less. If the voltage is large enough to cause more than
5 mA of current to flow, an external series resistor should be
added. The size of this resistor is calculated by dividing the
maximum overvoltage by 5 mA and subtracting the internal
1.5 kΩ resistor. For example, if the input voltage could reach 100 V,
the external resistor should be (100 V ÷ 5 mA) – 1.5 kΩ = 18.5 kΩ.
This resistance should be placed in series with either or both
inputs if they are subjected to the overvoltages.
OUTPUT PHASE REVERSAL
The AD8614/AD8644 are immune to phase reversal as long as
the input voltage is limited to within the supply rails. Although
the device’s output does not change phase, large currents due to
input overvoltage can result, damaging the device. In applica-
tions where the possibility of an input voltage exceeding the
supply voltage exists, overvoltage protection should be used, as
described in the previous section.
POWER DISSIPATION
The maximum power that can be safely dissipated by the
AD8614/AD8644 is limited by the associated rise in junction
temperature. The maximum safe junction temperature is 150°C,
and should not be exceeded or device performance could suffer.
If this maximum is momentarily exceeded, proper circuit
operation is restored as soon as the die temperature is reduced.
Leaving the device in an overheated condition for an extended
period can result in permanent damage to the device.
Rev. B | Page 10 of 16
To calculate the internal junction temperature of the
AD8614/AD8644, the following formula can be used:
where:
T
P
θ
resistance.
T
The power dissipated by the device can be calculated as:
where:
I
V
V
Figure 27 provides a convenient way to determine if the device
is being overheated. The maximum safe power dissipation can
be found graphically, based on the package type and the ambient
temperature around the package. By using the previous equation, it
is a simple matter to see if P
curve. To ensure proper operation, it is important to observe the
recommended derating curves shown in Figure 27.
UNUSED AMPLIFIERS
It is recommended that any unused amplifiers in the quad
package be configured as a unity-gain follower with a 1 kΩ
feedback resistor connected from the inverting input to the
output, and the noninverting input tied to the ground plane.
LOAD
JA
DISS
J
A
S
OUT
is the AD8614/AD8644 junction temperature.
is the AD8614/AD8644 junction-to-ambient package thermal
is the ambient temperature of the circuit.
is the AD8614/AD8644 supply voltage.
T
P
is the AD8614/AD8644 power dissipation.
is the AD8614/AD8644 output load current.
is the AD8614/AD8644 output voltage.
DISS
J
= P
1.5
1.0
0.5
Figure 27. Maximum Power Dissipation vs. Temperature
0
= I
–35
DISS
LOAD
14-LEAD SOIC PACKAGE
θ
14-LEAD TSSOP PACKAGE
θ
5-LEAD SOT-23 PACKAGE
θ
JA
JA
JA
× θ
= 120°C/W
= 180°C/W
= 230°C/W
(5-Lead and 14-Lead Package Types)
× (V
JA
–15
+ T
S
AMBIENT TEMPERATURE (°C)
– V
A
5
OUT
DISS
)
exceeds the device’s power derating
25
45
65
85