LTC2268-14/
LTC2267-14/LTC2266-14
16
22687614fa
pin FuncTions
AIN1+ (Pin 1): Channel 1 Positive Differential Analog Input.
AIN1–(Pin2):Channel1NegativeDifferentialAnalogInput.
VCM1(Pin3):CommonModeBiasOutput,NominallyEqual
to VDD/2. VCM should be used to bias the common mode
of the analog inputs of channel 1. Bypass to ground with
a 0.1F ceramic capacitor.
REFH (Pins 4,5): ADC High Reference. Bypass to pins 6, 7
with a 2.2F ceramic capacitor and to ground with a 0.1F
ceramic capacitor.
REFL (Pins 6,7): ADC Low Reference. Bypass to pins 4, 5
with a 2.2F ceramic capacitor and to ground with a 0.1F
ceramic capacitor.
VCM2(Pin8):CommonModeBiasOutput,NominallyEqual
to VDD/2. VCM should be used to bias the common mode
of the analog inputs of channel 2. Bypass to ground with
a 0.1F ceramic capacitor.
AIN2+ (Pin 9): Channel 2 Positive Differential Analog
Input.
AIN2– (Pin 10): Channel 2 Negative Differential Analog
Input.
VDD (Pins 11, 12, 39, 40): 1.8V Analog Power Supply.
Bypass to ground with 0.1F ceramic capacitors. Adjacent
pins can share a bypass capacitor.
ENC+ (Pin 13): Encode Input. Conversion starts on the
rising edge.
ENC– (Pin 14): Encode Complement Input. Conversion
starts on the falling edge.
CS(Pin15):Inserialprogrammingmode,(PAR/SER=0V),
CS is the serial interface chip select input. When CS is low,
SCKisenabledforshiftingdataonSDIintothemodecontrol
registers. In the parallel programming mode (PAR/SER =
VDD), CS selects 2-lane or 1-lane output mode. CS can
be driven with 1.8V to 3.3V logic.
SCK (Pin 16): In serial programming mode, (PAR/SER =
0V), SCK is the serial interface clock input. In the parallel
programming mode (PAR/SER= VDD), SCK selects 3.5mA
or 1.75mA LVDS output currents. SCK can be driven with
1.8V to 3.3V logic.
SDI (Pin 17): 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 =
VDD), SDI can be used to power down the part. SDI can
be driven with 1.8V to 3.3V logic.
GND (Pins 18, 33, 37, Exposed Pad Pin 41): ADC Power
Ground. The exposed pad must be soldered to the PCB
ground.
OGND (Pin 25): Output Driver Ground. Must be shorted
to the ground plane by a very low inductance path. Use
multiple vias close to the pin.
OVDD (Pin 26): Output Driver Supply. Bypass to ground
with a 0.1F ceramic capacitor.
SDO (Pin 34): 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
programmingmode(PAR/SER=VDD),SDOisaninputthat
enables internal 100Ω termination resistors on the digital
outputs. When used as an input, SDO can be driven with
1.8V to 3.3V logic through a 1k series resistor.
PAR/SER (Pin 35): Programming Mode Selection Pin.
Connecttogroundtoenabletheserialprogrammingmode.
CS, SCK, SDI, SDO become a serial interface that control
the A/D operating modes. Connect to VDD to enable the
parallel programming mode where CS, SCK, SDI, SDO