LTC2444/LTC2445/
LTC2448/LTC2449
6
2444589fc
For more information www.linear.com/LTC2444
pin FuncTions
GND (Pins 1, 4, 5, 6, 31, 32, 33): Ground. Multiple ground
pins internally connected for optimum ground current flow
and V
CC
decoupling. Connect each one of these pins to
a common ground plane through a low impedance con-
nection. All seven pins must be connected to ground for
proper operation.
BUSY (Pin 2): Conversion in Progress Indicator. This pin
is HIGH while the conversion is in progress and goes LOW
indicating the conversion is complete and data is ready.
It remains LOW during the sleep and data output states.
At the conclusion of the data output state, it goes HIGH
indicating a new conversion has begun.
EXT (Pin 3): Internal/External SCK Selection Pin. This
pin is used to select internal or external SCK for output
-
ting/inputting data. If EXT is tied low, the device is in the
external SCK mode and data is shifted out of the device
under the control of a user applied serial clock. If EXT is
tied high, the internal serial clock mode is selected. The
device generates its own SCK signal and outputs this on
the SCK pin. A framing signal BUSY (Pin 2) goes low
indicating data is being output.
COM (Pin 7):
The common negative input (IN
–
) for all
single ended multiplexer configurations. The voltage on
CH0 to CH15 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 overrange
and underrange output codes.
CH0 to CH15 (Pins 8 to 23): LTC2448/LTC2449 Analog
Inputs. May be programmed for single-ended or differ
-
ential mode.
C
H0 to CH7
(Pins 9, 10, 13, 14, 17, 18, 21, 22): LTC2444/
LTC2445 Analog Inputs. May be programmed for single-
ended or differential mode.
NC (Pins 8, 11, 12, 15, 16, 19, 20, 23): LTC2444/LTC2445
No Connect/Channel Isolation Shield. May be left floating
or tied to any voltage 0 to V
CC
in order to provide isolation
for pairs of differential input channels.
NC (Pins 24, 25, 26, 27): LTC2444/LTC2448 No Connect.
These pins can either be tied to ground or left floating.
MUXOUTP (Pin 24): LTC2445/LTC2449 Positive Mul
-
tiplexer Output. Used to drive the input to an external
buffer/amplifier.
ADCINP (Pin 25): LTC2445/LTC2449 Positive ADC Input.
Tie to output of buffer/amplifier driven by MUXOUTP.
ADCINN (Pin 26): LTC2445/LTC2449 Negative ADC Input.
Tie to output of buffer/amplifier driven by MUXOUTN.
MUXOUTN (Pin 27): LTC2445/LTC2449 Negative Mul
-
tiplexer Output. Used to drive the input to an external
buffer/amplifier.
V
CC
(Pin 28): 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 29), REF
–
(Pin 30): 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
+
,
is maintained more positive than the negative reference
input, REF
+
, by at least 0.1V.
SDI (Pin 34): Serial Data Input. This pin is used to select
the speed, 1X or 2X mode, resolution, and input channel,
for the next conversion cycle. At initial power up, the
default mode of operation is CH0 to CH1, OSR of 256,
and 1X mode. The serial data input contains an enable
bit which determines if a new channel/speed is selected.
If this bit is low the following conversion remains at the
same speed and selected channel. The serial data input
is applied to the device under control of the serial clock
(SCK) during the data output cycle. The first conversion
following a new channel/speed is valid.
F
O
(Pin 35): Frequency Control Pin. Digital input that con-
trols the internal conversion clock. When F
O
is connected
to V
CC
or GND, the converter uses its internal oscillator.