LTC2415-1CGN Linear Technology, LTC2415-1CGN Datasheet - Page 33

• Manufacturer Part Number: LTC2415-1CGN
• Description: IC ADC 24BIT DIFFINPUT/REF16SSOP
• Manufacturer: Linear Technology

Specifications of LTC2415-1CGN

• Number Of Bits: 24
• Sampling Rate (per Second): 13.75
• Data Interface: MICROWIRE™, Serial, SPI™
• Number Of Converters: 2
• Power Dissipation (max): 1mW
• Voltage Supply Source: Single Supply
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 16-SSOP (0.150", 3.90mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

APPLICATIO S I FOR ATIO
Sample Driver for LTC2415/LTC2415-1 SPI Interface
Figure 35 shows the use of an LTC2415/LTC2415-1 with
a differential multiplexer. This is an inexpensive multi-
plexer that will contribute some error due to leakage if
used directly with the output from the bridge, or if
resistors are inserted as a protection mechanism from
overvoltage. Although the bridge output may be within the
input range of the A/D and multiplexer in normal opera-
tion, some thought should be given to fault conditions
that could result in full excitation voltage at the inputs to
the multiplexer or ADC. The use of amplification prior to
the multiplexer will largely eliminate errors associated
with channel leakage developing error voltages in the
source impedance.
The LTC2415/LTC2415-1 have a very simple serial inter-
face that makes interfacing to microprocessors and
microcontrollers very easy.
The listing in Figure 38 is a simple assembler routine for
the 68HC11 microcontroller. It uses PORT D, configuring
it for SPI data transfer between the controller and the
LTC2415/LTC2415-1. Figure 36 shows the simple 3-wire
SPI connection.
Figure 36. Connecting the LTC2415/LTC2415-1 to a 68HC11 MCU Using the SPI Serial Interface
U
U
Figure 35. Use a Differential Multiplexer to Expand Channel Capability
W
TO OTHER
DEVICES
5V
U
LTC2415-1
LTC2415/
12
14
15
11
1
5
2
4
74HC4052
SDO
SCK
8
CS
16
9
13
12
11
10
The code begins by declaring variables and allocating four
memory locations to store the 32-bit conversion result.
This is followed by initializing PORT D’s SPI configuration.
The program then enters the main sequence. It activates
the LTC2415/LTC2415-1 serial interface by setting the SS
output low, sending a logic low to CS. It next waits in a loop
for a logic low on the data line, signifying end-of-conver-
sion. After the loop is satisfied, four SPI transfers are
completed, retrieving the conversion. The main sequence
ends by setting SS high. This places the LTC2415/
LTC2415-1 serial interface in a high impedance state and
initiates another conversion.
The performance of the LTC2415/LTC2415-1 can be
verified using the demonstration board DC291A, see
Figure 40 for the schematic. This circuit uses the
computer’s serial port to generate power and the SPI
digital signals necessary for starting a conversion and
reading the result. It includes a Labview application
software program (see Figure 39) which graphically cap-
tures the conversion results. It can be used to determine
noise performance, stability and with an external source,
linearity. As exemplified in the schematic, the LTC2415/
LTC2415-1 are extremely easy to use. This demonstra-
tion board and associated software is available by con-
tacting Linear Technology.
13
3
6
+
SCK (PD4)
MISO (PD2)
SS (PD5)
47 F
68HC11
3
4
5
6
2415 F36
REF
REF
IN
IN
LTC2415-1
+
–
LTC2415/
+
–
GND
V
5V
CC
LTC2415/LTC2415-1
2
1, 7, 8, 9,
10, 15, 16
2415 F35
A0
A1
sn2415 24151fs
33