ISL59112 Datasheet, PDF (5/6 Pages) Intersil Corporation – 40MHz Rail-to-Rail Video Buffer

ISL59112
Output Drive Capability
The ISL59112 does not have internal short-circuit protection
circuitry. If the output is shorted indefinitely, the power
dissipation could easily overheat the die or the current could
eventually compromise metal integrity. Maximum reliability is
maintained if the output current never exceeds ±40mA. This
limit is set by the design of the internal metal interconnect.
Note that in transient applications, the part is robust.
Short-circuit protection can be provided externally with a
back match resistor in series with the output placed close as
possible to the output pin. In video applications this would be
a 75Ω resistor and will provide adequate short-circuit
protection to the device. Care should still be taken not to
stress the device with a short at the output.
Power Dissipation
With the high output drive capability of the ISL59112, it is
possible to exceed the 125°C absolute maximum junction
temperature under certain load current conditions.
Therefore, it is important to calculate the maximum junction
temperature for an application to determine if load conditions
or package types need to be modified to assure operation of
the amplifier in a safe operating area.
The maximum power dissipation allowed in a package is
determined according to:
PD_MAX
=
T_{----J---M-----A----X-----–-----}T_{----A---M-----A----X--}
Θ_JA
Where:
T_JMAX = Maximum junction temperature
T_AMAX = Maximum ambient temperature
Θ_JA = Thermal resistance of the package
The maximum power dissipation actually produced by an IC
is the total quiescent supply current times the total power
supply voltage, plus the power in the IC due to the load, or
for sourcing:
PD_MAX
=
V_S
×
I_SMAX
+
(V_S
–
V_OUTi)
×
-^V----^O----^U----^T----ⁱ
R_Li
for sinking:
PD_MAX = V_S × I_SMAX + (V_OUTi – V_S) × I_LOADi
Where:
V_S = Supply voltage
I_SMAX = Maximum quiescent supply current
V_OUT = Maximum output voltage of the application
R_LOAD = Load resistance tied to ground
I_LOAD = Load current
By setting the two P_DMAX equations equal to each other, we
can solve the output current and R_LOAD to avoid the device
overheat.
Power Supply Bypassing Printed Circuit Board
Layout
As with any modern operational amplifier, a good printed
circuit board layout is necessary for optimum performance.
Lead lengths should be as short as possible. The power
supply pin must be well bypassed to reduce the risk of
oscillation. For normal single supply operation, where the
V_S- pin is connected to the ground plane, a single 4.7µF
tantalum capacitor in parallel with a 0.1µF ceramic capacitor
from V_S+ to GND will suffice. This same capacitor
combination should be placed at each supply pin to ground if
split supplies are to be used. In this case, the V_S- pin
becomes the negative supply rail.
Printed Circuit Board Layout
For good AC performance, parasitic capacitance should be
kept to minimum. Use of wire wound resistors should be
avoided because of their additional series inductance. Use
of sockets should also be avoided if possible. Sockets add
parasitic inductance and capacitance that can result in
compromised performance. Minimizing parasitic capacitance
at the amplifier's inverting input pin is very important. The
feedback resistor should be placed very close to the
inverting input pin. Strip line design techniques are
recommended for the signal traces.
5
FN6142.1
August 15, 2005