Datasheet
LTC2389-18
15
238918f
pin FuncTions
PD (Pin 33): Power-Down Input. When this pin is brought
high, the LTC2389-18 is powered down and subsequent
conversion requests are ignored. Before enabling power-
down, the result of the last conversion result should be
read. Logic levels are determined by OV
DD
.
CNVST (Pin 34): Conversion Start Input. A falling edge
on this pin puts the internal sample-and-hold into the
hold mode and starts a conversion. CNVST is independent
of CS. Logic levels are determined by V
DD
.
VCM (Pin 36): Common Mode Analog Output. Typically
the output voltage on this pin is 2.08V. Bypass to GND
with a 10μF capacitor.
REFOUT (Pin 37): Internal Reference Output. Connect
this pin to REFIN if using the internal reference, giving a
nominal reference voltage of 4.096V. If an external refer-
ence is used, connect REFOUT to ground to power down
the internal reference.
REFIN (Pin 38): Reference Input. Connect this pin to
REFOUT if using the internal reference, giving a nominal
reference voltage of 4.096V. An external reference can be
applied to REFIN if a more accurate reference is required.
If an external reference is used tie REFOUT to ground to
power down the internal reference. For increased filtering
of reference noise, bypass this pin to REFSENSE using a
1μF, or larger, ceramic capacitor.
REFSENSE (Pin 39): Reference Input Sense. Do not con-
nect REFSENSE to ground when using the internal reference.
If an external reference is used, connect REFSENSE to the
ground pin of the external reference.
IN
–
, IN
+
(Pin 42, Pin 43): Negative and Positive Analog
Inputs. The analog input range depends on the levels ap-
plied to Pin 30 (PD/FD) and Pin 6 (OB/2C), as described
in Table 2.
Table 2. Analog Input Range and Output Binary Format Configuration Table. Use Inputs PD/FD and OB/2C to Select Converter Analog
Input Range and Binary Format of Conversion Result.
PD/FD OB/2C ANALOG INPUT RANGE BINARY FORMAT OF CONVERSION RESULT
0 0 Fully-Differential Two’s Complement
0 1 Fully-Differential Offset Binary
1 0 Pseudo-Differential Bipolar Two’s Complement
1 1 Pseudo-Differential Unipolar Straight Binary