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dc1639f
DEMO MANUAL DC1639
DESCRIPTION
LTC6360
High Speed Op Amp with
True Zero Output
Demonstration circuit 1639 allows quick setup of the
LTC6360 true zero op amp. The op amp is configured as
a unity gain buffer, with landing pads provided to make
other gains configurable. Ample bypass is provided for
both the input supply and for the –0.6V on-chip charge
pump. The recommended 10Ω 330pF output compensa-
tion is provided on board for unity-gain stability. If this
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OPERATING PRINCIPLES
compensation is removed, gain bandwidth increases but
the op amp is stable only in gains of four and higher.
Design files for this circuit board are available at
http://www.linear.com/demo
Most op amps which operate on single supplies have
outputs that cannot get all the way to ground. The satu-
ration of their output devices leave 10’s of millivolts of
output voltage error when the output tries to swing to
ground. The LTC6360 has an onboard charge pump that
creates a –0.6V internal supply for the output stage, so
it can swing all the way to ground and even a little below
ground.
QUICK START PROCEDURE
Demonstration circuit 1639 is simple to use, with only one
jumper provided to allow the shutdown option.
1. Set the power supply to 5V, then turn off the power
supply. As shown in Figure 1, connect the +5V lead
from the power supply to the V
+
terminal of the demo
circuit, and connect the COM side of the supply to the
GND terminal of the demo circuit.
2. Turn on the supply. Note that without input exciatation
the output is very near 0mV, much closer to ground
than most op amps can achieve.
3. You are now free to connect a source to the input and
exercise the LTC6360. The input range is 0V to about
4.25V. (Under high frequency large signal swing exciata-
tion, you may see some odd behavior as the negative
charge pump voltage begins to safely collapse.)
4. If you want to set the LTC6360 for some other positive
gain, turn off the supply and disconnect the board. Refer
to the schematic in Figure 2. Install appropriate resis-
tors at R7 and R6, and install appropriate impedances
at C7 and R5 (shorts and/or blocking capacitance). The
time domain and frequency responses can be adjusted
using a small capacitance at C8.
5. For inverting gain, install J2 and appropriate passives
in the path to the –input. For inverting gains, the
+input must be biased up at some voltage. Installing
R13 connects the +input to the “EXT_VCM” turret which
is biased nominally at 2V by R11 and R12, or the turret
can be driven with an external supply.
6.
Shutdown:
The LTC6360 can be shut down by moving
the shunt on JP1 from the “Enable” position to the “Dis-
able” position. It can also be shut down and reactivated
electrically via the
SHDN
turret, in which case the shunt
on JP1 should be removed entirely.
