EL2157CS datasheet(16/19 Pages) INTERSIL

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Video Sync Pulse Remover Application

All CMOS Analog to Digital Converters (A/Ds) have a

parasitic latch-up problem when subjected to negative input

voltage levels. Since the sync tip contains no useful video

information and it is a negative going pulse, we can chop it

off. Figure 7 shows a unity gain connected EL2150 and

EL2157. Figure 8 shows the complete input video signal

applied at the input, as well as the output signal with the

negative going sync pulse removed.

Multiplexing with the EL2157

The ENABLE pin on the EL2157 allows for multiplexing

applications. Figure 9 shows two EL2157s with their outputs

tied together, driving a back terminated 75

Ω video load. A

2VP-P 10MHz sinewave is applied at one input, and a 1VP-P

5MHz sinewave to the other. Figure 10 shows the CLOCK

signal which is applied, and the resulting output waveform at

VOUT. Switching is complete in about 50ns. Notice the

outputs are tied directly together. Decoupling resistors at

each output are not necessary. In fact, adding them

approximately doubles the switching time to 100ns.

Short Circuit Current Limit

The EL2150 and EL2157 have internal short circuit

protection circuitry that protect it in the event of its output

being shorted to either supply rail. This limit is set to around

100mA nominally and reduces with increasing junction

temperature. It is intended to handle temporary shorts. If an

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 ±90mA. A heat sink may be required to keep the

junction temperature below absolute maximum when an

output is shorted indefinitely.

Power Dissipation

With the high output drive capability of the EL2150 and

EL2157, 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 the application to

determine if power-supply voltages, load conditions, or

FIGURE 6.

Propagation Delay vs Overdrive

EL2157 as a Comparator

FIGURE 7.

FIGURE 8.

FIGURE 9.

FIGURE 10.

EL2150, EL2157

EL2157CS Datasheet(PDF) 16 Page - Intersil Corporation

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