ISL59830 Datasheet, PDF (13/14 Pages) Intersil Corporation – True Single Supply Video Driver

ISL59830
amplifier from the cable and allow extensive capacitive drive.
However, other applications may have high capacitive loads
without a back-termination resistor. Again, a small series
resistor at the output can help to reduce peaking. The
ISL59830 is a triple amplifier designed to drive three
channels; simply deal with each channel separately as
described in this section.
DC-Restore
When the ISL59830 is AC-coupled it becomes necessary to
restore the DC reference for the signal. This is accomplished
with a DC-restore system applied between the capacitive
"AC" coupling and the input of the device. Refer to
Application Circuit for reference DC-restore solution.
Disable/Power-Down
The ISL59830 can be disabled and placed its output in a
high impedance state. The turn-off time is around 25ns and
the turn-on time is around 200ns. When disabled, the
amplifier's supply current is reduced to 30µA typically,
thereby effectively eliminating the power consumption. The
amplifier's power-down can be controlled by standard TTL or
CMOS signal levels at the ENABLE pin. The applied logic
signal is relative to V_S- pin. Letting the ENABLE pin float or
applying a signal that is less than 0.8V above V_S- will enable
the amplifier. The amplifier will be disabled when the signal
at ENABLE pin is 2V above V_S-.
Output Drive Capability
The ISL59830 does not have internal short-circuit protection
circuitry. A short-circuit current of 80mA sourcing and 150mA
sinking for the output is connected to half way between the
rails with a 10Ω resistor. If the output is shorted indefinitely,
the power dissipation could easily increase such that the part
will be destroyed. Maximum reliability is maintained if the
output current never exceeds ±40mA, after which the
electro-migration limit of the process will be exceeded and
the part will be damaged. This limit is set by the design of the
internal metal interconnections.
Power Dissipation
With the high output drive capability of the ISL59830, it is
possible to exceed the 150°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 and Printed Circuit
Board Layout
Strip line design techniques are recommended for the input
and output signal traces. As with any high frequency device,
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-internal supplies are to be used. In this case, the V_S-
pin becomes the negative supply rail.
For good AC performance, parasitic capacitance should be
kept to a 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 can result in
compromised performance. Minimizing parasitic capacitance
at the amplifier's inverting input pin is also very important.
13
FN7489.2
August 15, 2005