LTC2488
8
2488fb
For more information www.linear.com/LTC2488
PIN FUNCTIONS
F
O
(Pin 1): Frequency Control Pin. Digital input that controls
the internal conversion clock rate. When F
O
is connected to
ground, the converter uses its internal oscillator running
at 307.2kHz. The conversion clock may also be overridden
by driving the F
O
pin with an external clock in order to
change the output rate and the digital filter rejection null.
SDI (Pin 2): Serial Data Input. This pin is used to select
the input channel. The serial data input is applied under
control of the serial clock (SCK) during the data output/
input operation. The first conversion following a new input
is valid.
SCK (Pin 3): Bidirectional, Digital I/O, Clock Pin. In Internal
Serial Clock Operation mode, SCK is generated internally
and is seen as an output on the SCK pin. In External Serial
Clock Operation mode, the digital I/O clock is externally
applied to the SCK pin. The Serial Clock operation mode
is determined by the logic level applied to the SCK pin at
power up and during the most recent falling edge of CS.
CS (Pin 4): Active LOW Chip Select. A LOW on this pin enables
the digital input/output and wakes up the
ADC. Following
each conversion, the ADC automatically enters the Sleep
mode and remains in this low power state as long as CS
is HIGH. A LOW-to-HIGH transition on CS during the data
output aborts the data transfer and starts a new conversion.
SDO (Pin 5): Three-State Digital Output. During the data
output period, this pin is used as the serial data output.
When the chip select pin is HIGH, the SDO pin is in a high
impedance state. During the conversion and sleep periods,
this pin is used as the conversion status output. When
the conversion is in progress this pin is HIGH; once the
conversion is complete SDO goes low. The conversion
status is monitored by pulling CS LOW.
GND (Pin 6): Ground. Connect this pin to a common ground
plane through a low impedance connection.
COM (Pin 7): The common negative input (IN
–
) for all
single ended multiplexer configurations. The voltage on
CH0 to CH3 and COM pins can have any value between
GND – 0.3V to V
CC
+ 0.3V. Within these limits, the two
selected inputs (IN
+
and IN
–
) provide a bipolar input range
(V
IN
= IN
+
– IN
–
) from –0.5 • V
REF
to 0.5 • V
REF
. Outside
this input range,
the converter produces unique over-range
and under-range output codes.
CH0 to CH3 (Pins 8-11): Analog Inputs. May be pro
-
grammed for single-ended or differential mode.
V
CC
(Pin 12): Positive Supply Voltage. Bypass to GND with
a 10µF tantalum capacitor in parallel with a 0.1µF ceramic
capacitor as close to the part as possible.
REF
+
(Pin 13), REF
–
(Pin 14): Differential Reference Input.
The voltage on these pins can have any value between
GND and V
CC
as long as the reference positive input, REF
+
,
remains more positive than the negative reference input,
REF
–
, by at least 0.1V. The differential voltage (V
REF
=
REF
+
– REF
–
) sets the fullscale range for all input channels.
Exposed Pad (Pin 15): Ground. This pin is ground and
must be soldered to the PCB ground plane. For prototyping
purposes, this pin may remain floating.
