MAX4214/MAX4215/MAX4217/MAX4219/MAX4222
As the load resistance decreases, the useful input range
is effectively limited by the output drive capability, since
the buffers have a fixed voltage gain of 2V/V or -1V/V.
For example, a 50Ω load can typically be driven from
40mV above V
EE
to 1.6V below V
CC
, or 40mV to 3.4V
when operating from a single 5V supply. If the buffer is
operated in the noninverting, gain of 2V/V configuration
with the inverting input grounded, the useful input volt-
age range becomes 20mV to 1.7V instead of the
-100mV to 2.75V indicated by the Electrical Character-
istics. Beyond the useful input range, the buffer output
is a nonlinear function of the input, but it will not under-
go phase reversal or latchup.
Enable
The MAX4215/MAX4219 have an enable feature (EN_)
that allows the buffer to be placed in a low-power state.
When the buffers are disabled, the supply current is
reduced to 400µA per buffer.
As the voltage at the EN_ pin approaches the negative
supply rail, the EN_ input current rises. Figure 2 shows
a graph of EN_ input current versus EN_ pin voltage.
Figure 3 shows the addition of an optional resistor in
series with the EN pin, to limit the magnitude of the cur-
rent increase. Figure 4 displays the resulting EN pin
input current to voltage relationship.
Disabled Output Resistance
The MAX4214/MAX4215/MAX4217/MAX4219/MAX4222
include internal protection circuitry that prevents dam-
age to the precision input stage from large differential
input voltages (Figure 5). This protection circuitry con-
sists of five back-to-back Schottky diodes between
IN_+ and IN_-. These diodes reduce the disabled out-
put resistance from 1kΩ to 500Ω when the output volt-
age is 3V greater or less than the voltage at IN_+.
Under these conditions, the input protection diodes will
be forward biased, lowering the disabled output resis-
tance to 500Ω.
Output Capacitive Loading and Stability
The MAX4214 family provides maximum AC perfor-
mance with no load capacitance. This is the case when
the load is a properly terminated transmission line.
These devices are designed to drive up to 20pF of load
capacitance without oscillating, but AC performance
will be reduced under these conditions.
High-Speed, Single-Supply, Gain of 2,
Closed-Loop, Rail-to-Rail Buffers with Enable
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