LTC2411IMS#PBF Linear Technology, LTC2411IMS#PBF Datasheet - Page 22

• Manufacturer Part Number: LTC2411IMS#PBF
• Description: IC A/D CONV 24BIT MICRPWR 10MSOP
• Manufacturer: Linear Technology

Specifications of LTC2411IMS#PBF

• Number Of Bits: 24
• Sampling Rate (per Second): 7.5
• Data Interface: MICROWIRE™, Serial, SPI™
• Number Of Converters: 2
• Power Dissipation (max): 1mW
• Voltage Supply Source: Single Supply
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 10-TFSOP, 10-MSOP (0.118", 3.00mm Width)
• Number Of Elements: 1
• Resolution: 24Bit
• Architecture: Delta-Sigma
• Sample Rate: 0.008KSPS
• Input Polarity: Bipolar
• Input Type: Voltage
• Rated Input Volt: ±2.75V
• Differential Input: Yes
• Power Supply Requirement: Single
• Single Supply Voltage (typ): 3.3/5V
• Single Supply Voltage (min): 2.7V
• Single Supply Voltage (max): 5.5V
• Dual Supply Voltage (typ): Not RequiredV
• Dual Supply Voltage (min): Not RequiredV
• Dual Supply Voltage (max): Not RequiredV
• Integral Nonlinearity Error: 14ppm of Vref
• Operating Temp Range: -40C to 85C
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 10
• Package Type: MSOP
• Input Signal Type: Differential
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIO S I FOR ATIO
LTC2411/LTC2411-1
Particular attention must be given to the connection of the
F
external conversion clock. This clock is active during the
conversion time and the normal mode rejection provided
by the internal digital filter is not very high at this fre-
quency. A normal mode signal of this frequency at the
converter reference terminals may result into DC gain and
INL errors. A normal mode signal of this frequency at the
converter input terminals may result into a DC offset error.
Such perturbations may occur due to asymmetric capaci-
tive coupling between the F
input and/or reference connection traces. An immediate
solution is to maintain maximum possible separation
between the F
nals. When the F
converter, substantial AC current is flowing in the loop
formed by the F
ground return path. Thus, perturbation signals may be
inductively coupled into the converter input and/or refer-
ence. In this situation, the user must reduce to a minimum
the loop area for the F
the differential input and reference connections.
22
O
signal when the LTC2411/LTC2411-1 are used with an
SWITCHING FREQUENCY
f
f
SW
SW
V
V
I
V
V
I
REF
REF
I
I
REF
REF
IN
IN
IN
IN
= 76800Hz INTERNAL OSCILLATOR (F
= 0.5 • f
+
+
–
–
+
+
–
–
O
O
signal trace and the input/reference sig-
V
V
connection trace, the termination and the
EOSC
CC
CC
O
signal is parallel terminated near the
U
V
V
EXTERNAL OSCILLATOR
I
I
I
I
LEAK
LEAK
LEAK
LEAK
CC
CC
O
signal as well as the loop area for
I
I
I
I
LEAK
LEAK
LEAK
LEAK
U
O
signal trace and the converter
R
R
R
R
SW
SW
SW
SW
Figure 11. LTC2411/LTC2411-1 Equivalent Analog Input Circuit
20k
20k
20k
20k
(TYP)
(TYP)
(TYP)
(TYP)
W
O
= LOW OR HIGH)
2411 F11
U
C
6pF
(TYP)
EQ
I IN
I IN
I REF
I REF
where
V
V
V
V
R
R
R
R
IN
INCM
REF
REFCM
EQ
EQ
EQ
EQ
Driving the Input and Reference
The input and reference pins of the LTC2411/LTC2411-1
converter are directly connected to a network of sampling
capacitors. Depending upon the relation between the dif-
ferential input voltage and the differential reference volt-
age, these capacitors are switching between these four
pins transfering small amounts of charge in the process.
A simplified equivalent circuit is shown in Figure 11.
For a simple approximation, the source impedance R
driving an analog input pin (IN
considered to form, together with R
Figure 11), a first order passive network with a time
constant = (R
sample the input signal with better than 1ppm accuracy if
the sampling period is at least 14 times greater than the
input circuit time constant . The sampling process on the
four input analog pins is quasi-independent so each time
constant should be considered by itself and, under worst-
case circumstances, the errors may add.
When using the internal oscillator (F
LTC2411 (LTC2411-1)’s front-end switched-capacitor net-
work is clocked at 76800Hz (69900Hz) corresponding to
IN
AVG
AVG
: :
10 8
13 0
11 9
REF
1 67 10
AVG
AVG
.
.
.
.
IN
M
M
M
REF
IN
V
IN
V
1 5
2
IN
REF
.
INTERNAL OSCILLATOR
INTERNAL OSCILLATOR
INTERNAL OSCILLATOR F
IN
1 5
12
.
2
V
0 5
INCM
V
REF
.
0 5
V
/
REF
INCM
.
V
f
EOSC
REF
R
0 5
R
EQ
0 5
.
V
EQ
.
V
EXTERNAL OSCILLATOR
REFCM
INCM
V
S
V
R
REFCM
INCM
R
EQ
+ R
EQ
V
REFCM
SW
V
REFCM
) • C
60
50
O
Hz Notch F
Hz Notch F
V
REF
V
LOW LTC
EQ
REF
+
V
IN
2
, IN
V
. The converter is able to
R
IN
2
EQ
R
EQ
–
O
O
, REF
O
2411
2411 1
= LOW or HIGH), the
LOW LTC
HIGH LTC
SW
+
or REF
and C
2411
2411
–
) can be
EQ
(see
S