Datasheet

LTC2258-12
LTC2257-12/LTC2256-12
18
225812fd
For more information www.linear.com/LTC2258-12
CONVERTER OPERATION
The LTC2258-12/LTC2257-12/LTC2256-12 are low power
12-bit 65Msps/40Msps/25Msps A/D converters that are
powered by a single 1.8V supply. The analog inputs should
be driven differentially. The encode input can be driven
differentially or single-ended for lower power consump
-
tion. The digital outputs can be CMOS, double data rate
CMOS (to halve the number of output lines), or double
data rate LVDS (to reduce digital noise in the system.)
Many additional features can be chosen by programming
the mode control registers through a serial SPI port. See
the Serial Programming Mode section.
ANALOG INPUT
The analog input is a differential CMOS sample-and-hold
circuit (Figure 2). The inputs should be driven differentially
around a common mode voltage set by the V
CM
output
pin, which is nominally V
DD
/2. For the 2V input range,
the inputs should swing from V
CM
– 0.5V to V
CM
+ 0.5V.
There should be 180° phase difference between the inputs.
C
SAMPLE
3.5pF
R
ON
25Ω
R
ON
25Ω
V
DD
V
DD
LTC2258-12
A
IN
+
225812 F02
C
SAMPLE
3.5pF
V
DD
A
IN
–
ENC
–
ENC
+
1.2V
10k
1.2V
10k
C
PARASITIC
1.8pF
C
PARASITIC
1.8pF
10Ω
10Ω
Figure 2. Equivalent Input Circuit
applicaTions inForMaTion