ltc2435-1 Linear Technology Corporation, ltc2435-1 Datasheet - Page 35

• Manufacturer Part Number: ltc2435-1
• Description: 20-bit No Latency Delta Sigma Adcs With Differential Input And Differential Reference
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
Sample Driver for LTC2435/LTC2435-1 SPI Interface
Figure 41 shows the use of an LTC2435/LTC2435-1 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 LTC2435/LTC2435-1 have a very simple serial inter-
face that makes interfacing to microprocessors and
microcontrollers very easy.
Figure 42. Connecting the LTC2435/LTC2435-1 to a PIC16F73 MCU Using the SPI Serial Interface
U
LTC2435-1
LTC2435/
U
Figure 41. Use a Differential Multiplexer to Expand Channel Capability
SDO
SCK
CS
TO OTHER
DEVICES
13
12
11
W
5V
13
14
15
RC2
RC3
RC4
PIC16F73
8
U
V
CC
20
12
14
15
11
1
5
2
4
RC6
RC7
19
74HC4052
17
18
C1
C2
8
V
CC
16
9
10
12
11
13
10
18
The listing in Figure 43 is a data collection program for the
LTC2435/LTC2435-1 using the PIC16F73 microcontroller.
The microcontroller is configured to transfer data through
the SPI serial interface. Figure 42 shows the connection.
The LT1180A is a dual RS232 driver/receiver pair with
integral charge pump that generates RS232 voltage levels
from a single 5V supply.
The program begins by declaring variables and allocating
memory locations to store the 24-bit conversion result.
The main sequence starts with pulling CS LOW. It then
waits for SDO to go LOW to start reading data. Three bytes
are read to the MCU and the LTC2435/LTC2435-1 will
automatically start a new conversion. CS is also raised to
HIGH to ensure that a new conversion is started. The
collected data are sent out through the serial port at 57600
baud. This can be captured with a terminal program and
analyzed with a spreadsheet using the HEX2DEC function.
2
4
5
6
13
3
6
T1IN
T2IN
R1OUT
R2OUT
SHDN
C1
C1
C2
C2
+
–
+
–
+
LT1180A
47μF
T1OUT
T2OUT
R1IN
R2IN
GND
V
V
V
CC
+
–
3
4
5
6
15
8
14
9
17
3
7
16
REF
REF
IN
IN
C3
LTC2435/LTC2435-1
LTC2435-1
+
–
LTC2435/
C4
+
–
GND
V
5V
CC
2
1, 7, 8, 9,
10, 15, 16
2435 F41
C5
A0
A1
V
CC
1
2
3
4
5
X1
2435 F42
6
7
8
9
35
24351fb