4
dc955af
DEMO MANUAL DC955A
parts List
ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER
1 2 C1, C2 CAP., X7R, 0.1µF, 16V, 20%, 0402 TDK, C1005X7R1C104M
2 1 C3 CAP., X5R, 4.7µF, 6.3V, 20%, 0603 TDK, C1608X5R0J475M
3 1 C4 CAP., X5R, 1µF, 6.3V, 20%, 0402 TDK, C1005X5R0J105M
4 1 C5 CAP., X7R, 0.01µF, 25V, 10%, 0402 AVX, 04023C103KAT1A
5 9 E1 to E9 TESTPOINT, TURRET, .064" MILL-MAX, 2308-2
6 4 JP1, JP2, JP3, JP4 JMP, 3-PIN, 1 ROW .079CC SAMTEC, TMM-103-02-L-S
7 4 SHUNTS FOR JP1 to JP4 PIN 1 & 2 SHUNT, .079" CENTER SAMTEC, 2SN-BK-G
8 1 J1 HEADER, 2 × 7 PIN, 0.079CC MOLEX, 87831-1420
9 3 R1, R2, R3 RES., CHIP 4.99k, 1/16W, 1%, 0402 VISHAY, CRCW04024991FM
10 1 U1 I.C., LTC2483CDD, DFN10DD LINEAR TECH., LTC2483CDD
11 1 U2 I.C., LT1790ACS6-5, SOT23-6 LINEAR TECH., LT1790ACS6-5
12 1 U3 I.C., 24LC025, TSSOP8 MICROCHIP, 24LC025-I/ST
experiments
Bipolar Symmetry
To demonstrate the symmetry of the ADCs transfer func
-
tion, connect a stable, low noise, floating voltage source
(with a voltage less than V
REF/2
) from IN
+
to IN
–
and note
the indicated voltage. Reverse the polarity; the indicated
voltage will typically be within one LSB of the first reading
multiplied by –1.
One convenient voltage source for this experiment is a
single alkaline battery. While a battery has fairly low noise,
it is sensitive to temperature drift. It is best to use a large
(D-size) battery that is insulated from air currents. A bet
-
ter source is a battery powered series reference such as
the LT1790. This part is available with output voltages of
1.25V, 2.048V, 2.5V, 3V, 3.3V, 4.096V and 5V.
Input Normal Mode Rejection
The LTC2483’s SINC4 digital filter is trimmed to reject
50Hz and 60Hz line noise when operated with the internal
conversion clock. To measure input normal mode rejection,
connect IN
–
to a 2.5V source such as an LT1790-2.5 refer-
ence or 1k – 1k divider from the onboard 5V reference to
ground. Apply a 10Hz, 2V peak-to-peak sine wave to IN
+
through a 1µF capacitor. No DC bias is required because
the 2M to 3M input impedance of the LTC2483 tends to
self-bias the input to mid-reference (see data sheet ap-
plications information for details.)
Start taking data. The input noise will be quite large, and
the graph of output vs. time should show large variations.
Next, slowly increase the frequency to 55Hz. The noise
should be
almost undetectable in the graph. Note that
the indicated noise in ppm may still be above that of the
data sheet specification because IN
+
is not connected to
a DC source.
