Analog Devices DC2837A-A, Demo Manual

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The DC2837A board provides multiple empty mostly-0805
component footprints for users to configure the LTC2063/
LTC2066 as desired. Common configurations and func-
tions are illustrated below.
In the following schematics, components not mentioned
should be left unstuffed, and jumpers not mentioned
are not relevant.
SINGLE SUPPLY VS SPLIT RAILS
By default, the board is set up is for split supplies (V
+
, V
–
).
To switch to a single supply, V
+
and GND:
1. Remove any negative supplies from the V
–
turret. This
is important to prevent shorting the power supply out.
2. Disconnect and change offset voltage of input signal
source(s), then reconnect.
3. Move jumper JP4 to connect V
–
and GND. All con-
nections formerly tied to V
–
are now at GND.
The supplies are reverse-protected by Schottky diodes
and bypassed with 10µF. Additional 1210 capacitors may
be added in parallel as needed.
INPUT FILTER
As shown in Figure 3, the 10k R4 and C11 create an
input lowpass filter at +IN. C11’s value is 33nF for a
480Hz cutoff for LTC2063, 6.8nF for a 2.4kHz cutoff for
LTC2066. These pass bands should be sufficient for most
input signals.
If an input filter at –IN is desired, the resistors at R1
and R2 may be swapped (R1 = 10k, R2 = 0Ω) and the
capacitor C1 populated with either 33nF (for LTC2063)
or 6.8nF (LTC2066). Jumper JP2 must be installed for
C1 to be connected.
In general, to minimize the effect of chopper clock
feedthrough, signal bandwidths should be limited to at
least a decade below the internal chopping frequency,
which is 5kHz for LTC2063 and 25kHz for LTC2066.
DEFAULT: UNITY GAIN WITH INPUT FILTER
The default configuration of the board is for unity gain
with split supplies, as shown in Figure 3. R4 is 10k for
input protection, and R7 is 49.9Ω for 50Ω instrument
termination. R5 = 0Ω sets gain at unity. JP6 ties SHDN
to V
+
to enable the op amp.
Figure 3. Unity Gain with +IN Lowpass Filter
OUT
1
3
JP6
C10
0.1µF
+IN
R3
0Ω
R4
10k
R5
0Ω
R6
0Ω
R7
49.9Ω
R8
1k
V
+ 2
V
–
ENABLED
DC2837A-B F03
S
C11
33nF/
6.8nF
V
+
V
–
INVERTING GAIN
A
V
=
– R
FB
R
G
To set the board up for inverting gain with split supplies
(see Figure 4):
1. Populate R5 with the desired R
FB
2. Populate R2 with the desired R
G
3. Tie +IN turret to GND (or populate Z4 with 0Ω)
4. Connect the input signal to the –IN turret
Figure 4. Inverting Gain
OUT
1 3
–IN
+IN
J1
C10
0.1µF
R5
R
FB
R2
R
G
R1
0Ω
R3
0Ω
R4*
R
G
||R
FB
R8
1k
R6
0Ω
R7
49.9Ω
V
+
2
V
–
ENABLED
*OPTIONAL
V
+
V
–
DC2837A-B F04
S
4
DEMO MANUAL
DC2837A-A/DC2837A-B
Rev. 0
OPERATING PRINCIPLES