EL4390CN 데이터 시트보기 (PDF) - Elantec -> Intersil

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EL4390CN

Triple 80 MHz Video Amplifier with DC Restore

Elantec -> Intersil 

EL4390C

Triple 80 MHz Video Amplifier with DC Restore

Applications Information Contd

In Figure 3 one of the three channels is used

together with a low-offset op-amp to automati-

cally trim the bias current of the other two chan-

nels The two remaining channels are shown in

the non-inverting configuration but could equal-

ly well be set to provide inverting gains Two

DC-restored channels are typically needed in fad-

er applications See the EL4094 and EL4095 for

suitable monolithic video faders

Layout and Dissipation Considerations

As with all high frequency circuits the supplies

should be bypassed with a 0 1mF ceramic capaci-

tor very close to the supply pins and a 4 7mF

tantalum capacitor fairly close to handle the

high current surges While a ground plane is rec-

ommended the amplifier will work well with a

‘‘star’’ grounding scheme The pin 3 ground is

only used for the internal bias generator and the

reference for the TTL compatible ‘‘HOLD’’ in-

put

As with all current feedback capacitors all stray

capacitance to the inverting inputs should be

kept as low as possible to avoid unwanted peak-

ing at the output This is especially true if the

value of Rf has already been reduced to raise the

bandwidth of the part while tolerating some

peaking In this situation additional capacitance

on the inverting input can lead to an unstable

amplifier

Since there are three amplifiers all in one pack-

age and each amplifier can sink or source typi-

cally more than 70mA some care is needed to

avoid excessive die temperatures Sustained DC

currents of over 30mA are not recommended

due to the limited current handling capability of

the metal traces inside the IC Also the short cir-

cuit protection can be tripped with currents as

low as 45mA which is seen as excessive distor-

tion in the output waveform As a quick rule of

thumb both the SOL and DIP 16 pin packages

can dissipate about 1 4 watts at 25 C and with

g15V supplies and a worst case quiescent current

of 32mA yields 0 96 watts before any load is

driven

Dissipation of the EL4390 can be reduced by low-

ering the supply voltage Although some per-

formance is degraded at lower supplies as seen in

the characteristic curves it is often found to be a

useful compromise The bandwidth can be recov-

ered by reducing the value of RF and RG as ap-

propriate

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