LT1461 LINER [Linear Technology], LT1461 Datasheet - Page 11

• Manufacturer Part Number: LT1461
• Description: Easy-to-Use, Ultra-Tiny, Differential, 16-Bit ADC With I2C Interface
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
fi rst to the decoupling capacitors described above, the
second to the ground return for the input signal source,
and the third to the ground return for the power supply
voltage source.
Driving REF
A simplifi ed equivalent circuit for REF
in Figure 8. Like all other A/D converters, the LTC2453 is
only as accurate as the reference it is using. Therefore, it
is important to keep the reference line quiet by careful low
and high frequency power supply decoupling.
The LT6660 reference is an ideal match for driving the
LTC2453’s REF
2mm DFN package with 2.5V, 3V, 3.3V and 5V options.
A 0.1μF, high quality, ceramic capacitor in parallel with
a 10μF ceramic capacitor should be connected between
the REF
Figure 8. LTC2453 Analog Input/Reference Equivalent Circuit
+
REF
REF
IN –
IN
/REF
+
+
–
+
–
and REF
I
I
I
I
I
I
I
I
+
and GND pins, as close as possible to the
LEAK
LEAK
LEAK
LEAK
LEAK
LEAK
LEAK
LEAK
pin. The LTC6660 is available in a 2mm ×
V
V
V
V
CC
CC
CC
CC
–
(TYP)
(TYP)
(TYP)
(TYP)
R
R
R
R
15k
15k
15k
15k
SW
SW
SW
SW
+
and REF
2453 F08
–
C
0.35pF
(TYP)
EQ
is shown
package. The 0.1μF capacitor should be placed closest
to the ADC.
Driving V
The input drive requirements can best be analyzed using
the equivalent circuit of Figure 9. The input signal V
connected to the ADC input pins (IN
equivalent source resistance R
the actual generator source resistance and any additional
optional resistors connected to the input pins. Optional
input capacitors C
pins. This capacitor is placed in parallel with the ADC
input parasitic capacitance C
layout, C
addition, the equivalent circuit of Figure 9 includes the
converter equivalent internal resistor R
capacitor C
There are some immediate trade-offs in R
needing a full circuit analysis. Increasing R
give the following benefi ts:
1) Due to the LTC2453’s input sampling algorithm, the
SIG
SIG
input current drawn by either V
version cycle is 50nA. A high R
high frequency components of the input current, and
R
+
–
S
values up to 1k result in <1LSB error.
+
–
+
–
Figure 9. LTC2453 Input Drive Equivalent Circuit
PAR
R
R
IN
S
S
EQ
+
has typical values between 2pF and 15pF. In
and V
.
C
C
IN
IN
IN
IN
C
C
are also connected to the ADC input
–
PAR
PAR
IN
IN
+
–
I
I
I
I
LEAK
LEAK
LEAK
LEAK
PAR
S
. This resistor includes both
V
V
CC
CC
. Depending on the PCB
IN
S
+
+
(TYP)
(TYP)
R
R
15k
15k
• C
and IN
0.35pF
0.35pF
SW
SW
or V
(TYP)
(TYP)
C
C
LTC2453
SW
IN
EQ
EQ
S
and C
IN
attenuates the
and sampling
S
–
–
) through an
and C
over a con-
IN
without
11
2453 F09
IN
I
I
SIG
CONV
CONV
can
2453f
is