LT6210/LT6211
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62101fc
applicaTions inForMaTion
Capacitive Loads
The LT6210/LT6211 are stable with any capacitive load.
Although peaking and overshoot may result in the AC
transient response, the amplifier’s compensation decreases
bandwidth with increasing output capacitive load to ensure
stability. To maintain a response with minimal peaking, the
feedback resistor can be increased at the cost of bandwidth
as shown in the Typical Performance Characteristics.
Alternatively, a small resistor (5Ω to 35Ω) can be put in
series with the output to isolate the capacitive load from
the amplifier output. This has the advantage that the ampli-
fier bandwidth is only reduced when the capacitive load
is present. The disadvantage of this technique is that the
gain is a function of the load resistance.
Power Supplies
The LT6210/LT6211 will operate on single supplies from
3V to 12V and on split supplies from ±1.5V to ±6V. If split
supplies of unequal absolute value are used, input offset
voltage and inverting input current will shift from the values
specified in the Electrical Characteristics table. Input offset
voltage will shift 2mV and inverting input current will shift
0.5µA for each volt of supply mismatch.
Slew Rate
Unlike a traditional voltage feedback op amp, the slew rate
of a current feedback amplifier is not independent of the
amplifier gain configuration. In a current feedback ampli-
fier, both the input stage and the output stage have slew
rate limitations. In the inverting mode, and for gains of 2
or more in the noninverting mode, the signal amplitude
between the input pins is small and the overall slew rate
is that of the output stage. For gains less than 2 in the
noninverting mode, the overall slew rate is limited by the
input stage. The input slew rate of the LT6210/LT6211 on
±5V supplies with an R
SET
resistor of 20k (I
S
= 6mA) is
approximately 600V/µs and is set by internal currents and
capacitances. The output slew rate is additionally con-
strained by the value of the feedback resistor and internal
capacitance. At a gain of 2 with 887Ω feedback and gain
resistors, ±5V supplies and the same biasing as above,
the output slew rate is typically 700V/µs. Larger feedback
resistors, lower supply voltages and lower supply current
levels will all reduce slew rate. Input slew rates significantly
exceeding the output slew capability can actually decrease
slew performance in a positive gain configuration; the
cleanest transient response will be obtained from input
signals with slew rates slower than 1000V/µs.
Output Swing and Drive
The output stage of the LT6210/LT6211 consists of a pair
of class-AB biased common emitters that enable the output
to swing rail-to-rail. Since the amplifiers can potentially
deliver output currents well beyond the specified minimum
short-circuit current, care should be taken not to short the
output of the device indefinitely. Attention must be paid to
keep the junction temperature of the IC below the absolute
maximum rating of 150°C if the output is used to drive
low impedance loads. See Note 5 for details. Additionally,
the output of the amplifier has reverse-biased ESD diodes
connected to each supply. If the output is forced beyond
either supply, large currents will flow through these diodes.
If the current is limited to 80mA or less, no damage to
the part will occur.
