11
225916fa
LTC2259-16
PIN FUNCTIONS
PINS THAT ARE THE SAME FOR ALL DIGITAL OUTPUT
MODES
A
IN
+
(Pin 1): Positive Differential Analog Input.
A
IN
–
(Pin 2): Negative Differential Analog Input.
GND (Pin 3, Exposed Pad Pin 41): ADC Power Ground.
REFH (Pins 4, 5): ADC High Reference. Bypass to Pins
6, 7 with a 2.2µF ceramic capacitor and to ground with a
0.1µF ceramic capacitor.
REFL (Pins 6, 7): ADC Low Reference. Bypass to Pins
4, 5 with a 2.2µF ceramic capacitor and to ground with a
0.1µF ceramic capacitor.
PAR/SER (Pin 8): Programming Mode Selection Pin. Con-
nect to ground to enable the serial programming mode.
CS, SCK, SDI, SDO become a serial interface that control
the A/D operating modes. Connect to V
DD
to enable the
parallel programming mode where CS, SCK, SDI become
parallel logic inputs that control a reduced set of the A/D
operating modes. PAR/SER should be connected directly
to ground or the V
DD
of the part and not be driven by a
logic signal.
V
DD
(Pins 9, 10, 40): 1.8V Analog Power Supply. Bypass
to ground with 0.1µF ceramic capacitors. Pins 9 and 10
can share a bypass capacitor.
ENC
+
(Pin 11): Encode Input. Conversion starts on the
rising edge.
ENC
–
(Pin 12): Encode Complement Input. Conversion
starts on the falling edge.
CS (Pin 13): In serial programming mode, (PAR/SER =
0V), CS is the serial interface chip select input. When
CS is low, SCK is enabled for shifting data on SDI into
the mode control registers. In the parallel programming
mode (PAR/SER = V
DD
), CS controls the clock duty cycle
stabilizer. When CS is low, the clock duty cycle stabilizer is
turned off. When CS is high, the clock duty cycle stabilizer
is turned on. CS can be driven with 1.8V to 3.3V logic.
SCK (Pin 14): In serial programming mode, (PAR/SER =
0V), SCK is the serial interface clock input. In the parallel
programming mode (PAR/SER = V
DD
), SCK controls the
digital output mode. When SCK is low, the full-rate CMOS
output mode is enabled. When SCK is high, the double-
data rate LVDS output mode (with 3.5mA output current)
is enabled. SCK can be driven with 1.8V to 3.3V logic.
SDI (Pin 15): In serial programming mode, (PAR/SER =
0V), SDI is the serial interface data input. Data on SDI is
clocked into the mode control registers on the rising edge
of SCK. In the parallel programming mode (PAR/SER =
V
DD
), SDI can be used to power down the part. When SDI
is low, the part operates normally. When SDI is high, the
part enters sleep mode. SDI can be driven with 1.8V to
3.3V logic.
SDO (Pin 16): In serial programming mode, (PAR/SER
= 0V), SDO is the optional serial interface data output.
Data on SDO is read back from the mode control registers
and can be latched on the falling edge of SCK. SDO is an
open-drain NMOS output that requires an external 2k
pull-up resistor to 1.8V-3.3V. If read back from the mode
control registers is not needed, the pull-up resistor is not
necessary and SDO can be left unconnected. In the parallel
programming mode (PAR/SER = V
DD
), SDO is not used
and should not be connected.
OGND (Pin 25): Output Driver Ground.
OV
DD
(Pin 26): Output Driver Supply. Bypass to ground
with a 0.1µF ceramic capacitor.
V
CM
(Pin 37): Common Mode Bias Output, Nominally
Equal to V
DD
/2. V
CM
should be used to bias the common
mode of the analog inputs. Bypass to ground with a 0.1µF
ceramic capacitor.
V
REF
(Pin 38): Reference Voltage Output. Bypass to ground
with a 1µF ceramic capacitor, nominally 1.25V.
SENSE (Pin 39): Reference Programming Pin. Connecting
SENSE to V
DD
selects the internal reference and a ±1V input
range. Connecting SENSE to ground selects the internal
reference and a ±0.5V input range. An external reference
between 0.625V and 1.3V applied to SENSE selects an
input range of ±0.8 • V
SENSE
.
