Linear Technology DC1009A-C - LTC2486 16-bit 2-ch ADC with Temp Sensor, PGA, req DC590 DC1009A-C DC1009A-C Scheda Tecnica

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DEMO MANUAL DC1009A

JP1, JP2: Select the source for REF+ and REF–, respectively. 
REF+ can be 5.00V from the onboard LT1236 reference 
(default) or supplied externally. REF– can be ground (0V, 
default) or supplied externally.

J2 is the power and digital interface connector. Connect to 
a DC590 serial controller with the supplied 14-conductor 
ribbon cable. Digital signals are also connected to through-
hole test points on the circuit board.

Analog signal connections are made via the row of turret 
posts along the edge of the board.

GND: Ground turrets are connected directly to the internal 
analog ground plane.

: This is the supply for the ADC. Do not draw any 

power from this point. External power may be applied to 
this point after disabling the V

CC

 supply on DC590. See 

the DC590 quick start guide for details.

REF+, REF–: These turrets are connected to the LTC2486/
LTC2488/LTC2492 REF+ and REF– pins. If the onboard 
reference is being used, the reference voltage may be 
monitored from this point. An external reference may be 
connected to these terminals if JP1 and JP2 are configured 
for external reference.

CH0-CH3: These are the differential inputs to the LTC2492/
LTC2488/LTC2486. They may be configured as single–
ended inputs with respect to the COM pin, or as differential 
inputs (CH0-CH1, CH2-CH3) with the polarity software 
selected.

Solder a short wire between the CH0 and CH1 turrets. 
Connect the inputs to ground through a short wire and 
start taking data. LTC2492 Noise should be approximately 
0.12ppm of 5V (600nV

RMS

.) The electrical noise of the 

LTC2488 is also 600nV

RMS

, however this is masked by 

the 76.3μV quantization level. If the input is well between 
code transitions, the noise level will read zero. If the input 
is exactly between two codes such that the two adjacent 
output codes have equal probability, the noise level will be 
approximately 7.9ppm. The input noise of the LTC2486 is 
apparent at very high gain settings (128 or 256.) Note that 
with a 5V reference and gain set to 256, 1LSB is equal to 
298nV which is lower than the 600nV

RMS

 electrical noise 

of the input stage.

Tie the two inputs (still connected together from previous 
experiment) to ground through a short wire and note the 
indicated voltage. Tie the inputs to REF+; the difference 

should be less than 0.5μV due to the 140dB+ CMRR of 
the LTC2492. The LTC2488 will produce less than 1LSB 
difference.

The LTC2492 and LTC2486 SINC4 digital filter can be 
software selected to reject 50Hz, 60Hz by 110dB, or both 
50Hz and 60Hz by 87dB. The LTC2488’s SINC4 filter is fixed 
at 50Hz/60Hz. To measure input normal mode rejection, 
connect COM to a 2.5V source such as an LT1790-2.5 
reference or a power supply. Connect any other input 
(CH0-CH3) to the same supply through a 10k resistor. 
Apply a 10Hz, 2V peak-to-peak sine wave to the input 
through a 1μF capacitor. 

Set the rejection frequency to 55Hz (LTC2492 only) and 
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.