Datasheet

27
LTC2400
TYPICAL APPLICATIONS
U
CS1
CS2
CS3
2400 F28
CS4
SCK
31 OR LESS
CLOCK PULSES
SDO
LTC2400
#1
V
CC
V
REF
V
IN
GND
F
O
SCK
SDO
CS
SCK
SDO
CS1
CS2
CS3
CS4
LTC2400
#2
V
CC
V
REF
V
IN
GND
F
O
SCK
SDO
CS
LTC2400
#3
V
CC
V
REF
V
IN
GND
F
O
SCK
SDO
CS
LTC2400
#4
V
CC
V
REF
V
IN
GND
F
O
SCK
SDO
CS
µCONTROLLER
EXTERNAL OSCILLATOR
(153,600HZ)
V
REF
(0.1V TO V
CC
)
Figure 28. 4× Output Rate LTC2400 System
Differential to Single-Ended
Analog Conditioning
The circuits in Figures 29 and 30 use the LTC1043 dual
precision, switched capacitor building block. Each circuit
uses one-half of an LTC1043 to perform a differential to
single-ended conversion over an input common mode
range that includes the power supplies. The LTC1043
samples a differential input voltage, holds it on C
S
and
transfers it to a ground-referenced capacitor C
H
. The
voltage on C
H
is applied to the LTC2400’s input and
converted to a digital value.
The LTC1043 achieves its best differential to single-ended
conversion when its internal switching frequency oper-
ates at a nominal 300Hz, as set by the 0.01µF capacitor C1,
and when 1µF capacitors are used for C
S
and C
H
. C
S
and
C
H
should be a film-type capacitor such as mylar or
polypropylene.
Simple Differential Front-End
for the LTC2400
The circuit in Figure 29 is ideal for wide dynamic range
differential signals in applications where absolute accu-
racy is secondary to high resolution, have large signal
swings, source impedances under 500Ω and use a 5V or
±5V supply.
The circuit achieves a nonlinearity of ±35ppm (a linearity
accuracy of 14.5 bits), noise of 1.5µV
RMS
and 21-bit
resolution. The circuit exhibits a typical 2.75mV zero
offset. However, this is not an offset that simply shifts the
output code by a constant value. It is a gain error that alters
the transfer function’s slope. The gain error revolves
around midscale (V
REF
/2). This gain error can be corrected
in software by measuring the error at 0V input and using
the result to create a correction factor.