LTC2420I LINER [Linear Technology], LTC2420I Datasheet - Page 5

• Manufacturer Part Number: LTC2420I
• Description: 20-Bit uPower No Latency ADC in SO-8
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
PIN
V
(Pin 4) with a 10 F tantalum capacitor in parallel with
0.1 F ceramic capacitor as close to the part as possible.
V
is 0.1V to V
V
– 0.125 • V
voltage range may be limited by the pin absolute maxi-
mum rating of – 0.3V to V
GND (Pin 4): Ground. Shared pin for analog ground,
digital ground, reference ground and signal ground. Should
be connected directly to a ground plane through a mini-
mum length trace or it should be the single-point-ground
in a single point grounding system.
CS (Pin 5): Active LOW Digital Input. A LOW on this pin
enables the SDO digital 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 on CS wakes up the ADC. A
LOW-to-HIGH transition on this pin disables the SDO
digital output. A LOW-to-HIGH transition on CS during the
Data Output transfer aborts the data transfer and starts a
new conversion.
The LTC2420 is pin compatible with the LTC2400. The two
devices are designed to allow the user to incorporate
either device in the same design with no modifications.
While the LTC2420 output word length is 24 bits (as
opposed to the 32-bit output of the LTC2400), its output
clock timing can be identical to the LTC2400. As shown in
Figure 1, the LTC2420 data output is concluded on the
falling edge of the 24th serial clock (SCK). In order to
maintain drop-in compatibility with the LTC2400, it is
possible to clock the LTC2420 with an additional 8 serial
clock pulses. This results in 8 additional output bits which
are always logic HIGH.
CC
REF
IN
U
(Pin 3): Analog Input. The input voltage range is
(Pin 1): Positive Supply Voltage. Bypass to GND
(Pin 2): Reference Input. The reference voltage range
FUNCTIONS
U
REF
CC
.
to 1.125 • V
U
U
U
CC
REF
+ 0.3V.
. For V
W
REF
> 2.5V the input
U
SDO (Pin 6): Three-State Digital Output. During the data
output period this pin is used for serial data output. When
the chip select CS is HIGH (CS = V
high impedance state. During the Conversion and Sleep
periods, this pin can be used as a conversion status out-
put. The conversion status can be observed by pulling CS
LOW.
SCK (Pin 7): Bidirectional Digital Clock Pin. In Internal
Serial Clock Operation mode, SCK is used as digital output
for the internal serial interface clock during the data output
period. In External Serial Clock Operation mode, SCK is
used as digital input for the external serial interface. A
weak internal pull-up is automatically activated in Internal
Serial Clock Operation mode. The Serial Clock mode is
determined by the level applied to SCK at power up and the
falling edge of CS.
F
controls the ADC’s notch frequencies and conversion
time. When the F
converter uses its internal oscillator and the digital filter’s
first null is located at 50Hz. When the F
to GND (F
and the digital filter first null is located at 60Hz. When F
is driven by an external clock signal with a frequency f
the converter uses this signal as its clock and the digital
filter first null is located at a frequency f
Output Data Format
The LTC2420 serial output data stream is 24 bits long. The
first 4 bits represent status information indicating the
sign, input range and conversion state. The next 20 bits are
the conversion result, MSB first.
Bit 23 (first output bit) is the end of conversion (EOC)
indicator. This bit is available at the SDO pin during the
conversion and sleep states whenever the CS pin is LOW.
This bit is HIGH during the conversion and goes LOW
when the conversion is complete.
Bit 22 (second output bit) is a dummy bit (DMY) and is
always LOW.
O
(Pin 8): Frequency Control Pin. Digital input that
O
= OV) the converter uses its internal oscillator
O
pin is connected to V
CC
), the SDO pin is in a
O
CC
EOSC
pin is connected
LTC2420
(F
O
/2560.
= V
CC
), the
EOSC
5
O
,