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ISL59111 Datasheet(PDF) 8 Page - Intersil Corporation |
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ISL59111 Datasheet(HTML) 8 Page - Intersil Corporation |
8 / 10 page 8 FN6172.3 August 29, 2006 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. 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. 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 75 Ω 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: Where: TJMAX = Maximum junction temperature TAMAX = Maximum ambient temperature ΘJA = 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: for sinking: R6 R5 R4 R7 C5 C4 ROUT RL SAG NETWORK AC COUPLING CAPACITOR FIGURE 23. SAG NETWORK AND AC COUPLING CAPACITORS - + TELEVISION OR VCR ROUT ENABLE FIGURE 24. DC COUPLE PD MAX T JMAX T AMAX – Θ JA --------------------------------------------- = PD MAX V S I SMAX V S V OUT – () + × V OUT R L ---------------- × = PD MAX V S I SMAX V OUT V S – () + × I LOAD × = ISL59111 |
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