Datasheet

22
22654312fb
LTC2265-12/
LTC2264-12/LTC2263-12
Reference
The LTC2265-12/LTC2264-12/LTC2263-12 has an internal
1.25V voltage reference. For a 2V input range using the
internal reference, connect SENSE to V
DD
. For a 1V input
range using the internal reference, connect SENSE to
ground. For a 2V input range with an external reference,
apply a 1.25V reference voltage to SENSE (Figure 9).
The input range can be adjusted by applying a voltage to
SENSE that is between 0.625V and 1.30V. The input range
will then be 1.6 • V
SENSE
.
The reference is shared by both ADC channels, so it is
not possible to independently adjust the input range of
individual channels.
The V
REF
, REFH and REFL pins should be bypassed, as
shown in Figure 8. The 0.1µF capacitor between REFH and
REFL should be as close to the pins as possible (not on
the backside of the circuit board).
APPLICATIONS INFORMATION
V
REF
REFH
SENSE
TIE TO V
DD
FOR 2V RANGE;
TIE TO GND FOR 1V RANGE;
RANGE = 1.6 • V
SENSE
FOR
0.625V < V
SENSE
< 1.300V
1.25V
REFL
0.1µF2.2µF
INTERNAL ADC
HIGH REFERENCE
BUFFER
5Ω
0.8x
DIFF AMP
INTERNAL ADC
LOW REFERENCE
1.25V BANDGAP
REFERENCE
0.625V
RANGE
DETECT
AND
CONTROL
1µF
0.1µF
0.1µF
LTC2265-12
226512 F08
Figure 8. Reference Circuit
SENSE
1.25V
EXTERNAL
REFERENCE
1µF
1µF
V
REF
226512 F09
LTC2265-12
Figure 9. Using an External 1.25V Reference
V
DD
LTC2265-12
226512 F10
ENC
–
ENC
+
15k
V
DD
DIFFERENTIAL
COMPARATOR
30k
Figure 10. Equivalent Encode Input Circuit
for Differential Encode Mode
Encode Input
The signal quality of the encode inputs strongly affects
the A/D noise performance. The encode inputs should
be treated as analog signals—do not route them next to
digital traces on the circuit board. There are two modes
of operation for the encode inputs: the differential encode
mode (Figure 10), and the single-ended encode mode
(Figure 11).
30k
ENC
+
ENC
–
226512 F11
0V
1.8V TO 3.3V
LTC2265-12
CMOS LOGIC
BUFFER
Figure 11. Equivalent Encode Input Circuit
for Single-Ended Encode Mode