ISL59111 Datasheet, PDF (8/10 Pages) Intersil Corporation – 8MHz Rail-to-Rail Composite Video Driver

ISL59111
surrounding resistance network provide a band pass
function with a low pass band low enough to exclude very
low frequencies down to DC, and with a high pass band pass
sufficiently high to include frequencies at the higher end of
the video spectrum.
SAG AC COUPLING
NETWORK CAPACITOR
C₅
R_OUT
R₆
R₇
C₄
R_L
R₅
R₄
FIGURE 23. SAG NETWORK AND AC COUPLING
CAPACITORS
Typically this is accomplished with 220µF coupling capacitor,
a large and somewhat costly solution providing a low
frequency pole around 5Hz. If the size of this capacitor is
even slightly reduced we have found that the accompanying
phase shift in the 50Hz to 100Hz frequency range results in
field tilt resulting in a degraded video image.
The internal SAG network of the ISL59111 replaces the
220µF AC coupling capacitor with a network of two smaller
capacitors as shown in Figure 23. Additionally, the network is
designed to place a zero in the ~30Hz range, providing a
small amount of peaking to compensate the phase response
associated with field tilt.
DC Output Coupling
The ISL59111 internal sync clamp makes it possible to DC
couple the output to a video load, eliminating the need for
any AC coupling capacitors, saving board space and
additional expense for capacitors making the ISL59111 is
designed to be extremely attractive for portable video
applications Additionally, this solution completely eliminates
the issue of field tilt in the lower frequency. The trade off is
greater demand of supply current. Typical load current for
AC coupled is around 3mA compared to typical 6mA used
when DC coupling.
ENABLE
+
-
R_OUT
Output Drive Capability
The ISL59111 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 ISL59111, 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-_Θ----–-_J---_A-^T----^A---^M-----^A----^X--
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_OUT)
×
-^V----^O----^U----^T--
R_L
for sinking:
PD_MAX = V_S × I_SMAX + (V_OUT – V_S) × I_LOAD
TELEVISION
OR VCR
FIGURE 24. DC COUPLE
8
FN6172.3
August 29, 2006