MAX4137 Datasheet, PDF (10/12 Pages) Maxim Integrated Products – 1-Input/4-Output Video Distribution Amplifiers

1-Input/4-Output
Video Distribution Amplifiers
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CL = 15pF
CL = 10pF
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CL = 5pF
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4
2
0
0.1M
1M
10M 100M
1G
FREQUENCY (Hz)
RISO
VOUT
VIN
CL
RL
MAX4137
MAX4138
Figure 3. Effect of CLOAD on Frequency Response (without
RISO)
To drive larger-capacitance loads or to reduce ringing,
add an isolation resistor between the amplifier’s output
and the load, as shown in Figure 4.
The value of RISO depends on the circuit’s gain and the
capacitive load. Figure 5 shows the optional isolation
resistor (RISO) vs. capacitive load (CL). At the higher
capacitor values, the bandwidth is dominated by the
RC network, formed by RISO and CL.
Power-Dissipation Considerations
The MAX4137/MAX4138 can drive up to four outputs
simultaneously. Quiescent power dissipation is typically
520mW and 650mW maximum, respectively, with all
channels enabled. The maximum package power dissi-
pation is rated at 1540mW.
In a typical application, four outputs drive a standard
video signal into a 150Ω load. The amount of power
added to the quiescent dissipation is minimal and no
special precautions are necessary.
However, each output driving the maximum 65mA into
30Ω will cause a power-dissipation increase of approxi-
mately 200mW. Therefore, you should not allow more
than three outputs to deliver that load simultaneously.
Similarly, one output shorted to ground will cause a
power-dissipation increase of 650mW. Only one output
can be shorted to ground without violating the package
power rating.
Figure 4. Capacitive-Load Driving Circuit
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10 40 70 100 130 160 190 220
CLOAD (pF)
Figure 5. Optimal Isolation Resistor (RISO) vs. CLOAD
In conclusion, during normal operation in a matched-
load environment, the total power dissipation is well
within the package’s dissipation rating. The maximum
power dissipation is violated only if multiple channels
are driving the maximum current into minimum loads at
the same time.
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