LTC2401CMS datasheet(12/32 Pages) LINER

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LTC2401/LTC2402

APPLICATIO S I FOR ATIO

Figure 3. Output Data Timing

Bit 29 (third output bit) is the conversion result sign indi-

cator (SIG). If VIN is >0, this bit is HIGH. If VIN is <0, this

bit is LOW. The sign bit changes state during the zero code.

Bit 28 (forth output bit) is the extended input range (EXR)

indicator. If the input is within the normal input range

≤ VIN ≤ VREF, this bit is LOW. If the input is outside the

normal input range, VIN > VREF or VIN < 0, this bit is HIGH.

The function of these bits is summarized in Table 1.

Table 1. LTC2401/LTC2402 Status Bits

Bit 31

Bit 30

Bit 29

Bit 28

Input Range

EOC

CH0/CH1

SIG

EXR

VIN > VREF

0/1

0 < VIN ≤ VREF

0/1

VIN = 0

+/0–

0/1

1/0

VIN < 0

0/1

Bit 27 (fifth output bit) is the most significant bit (MSB).

Bits 27-4 are the 24-bit conversion result MSB first.

Bit 4 is the least significant bit (LSB).

Bits 3-0 are sub LSBs below the 24-bit level. Bits 3-0 may

be included in averaging or discarded without loss of

resolution.

Data is shifted out of the SDO pin under control of the serial

clock (SCK), see Figure 3. Whenever CS is HIGH, SDO

remains high impedance and any SCK clock pulses are

ignored by the internal data out shift register.

In order to shift the conversion result out of the device, CS

must first be driven LOW. EOC is seen at the SDO pin of the

device once CS is pulled LOW. EOC changes real time from

HIGH to LOW at the completion of a conversion. This

signal may be used as an interrupt for an external micro-

controller. Bit 31 (EOC) can be captured on the first rising

edge of SCK. Bit 30 is shifted out of the device on the first

falling edge of SCK. The final data bit (Bit 0) is shifted out

on the falling edge of the 31st SCK and may be latched on

the rising edge of the 32nd SCK pulse. On the falling edge

of the 32nd SCK pulse, SDO goes HIGH indicating a new

conversion cycle has been initiated. This bit serves as EOC

(Bit 31) for the next conversion cycle. Table 2 summarizes

the output data format.

As long as the voltage on the VIN pin is maintained within

the – 0.3V to (VCC + 0.3V) absolute maximum operating

range, a conversion result is generated for any input value

from – 0.125 • VREF to 1.125 • VREF. For input voltages

greater than 1.125 • VREF, the conversion result is clamped

to the value corresponding to 1.125 • VREF. For input

voltages below – 0.125 • VREF, the conversion result is

clamped to the value corresponding to – 0.125 • VREF.

Frequency Rejection Selection (FO Pin Connection)

The LTC2401/LTC2402 internal oscillator provides better

than 110dB normal mode rejection at the line frequency

and all its harmonics for 50Hz

±2% or 60Hz ±2%. For

60Hz rejection, FO (Pin 10) should be connected to GND

(Pin 6) while for 50Hz rejection the FO pin should be

connected to VCC (Pin 1).

The selection of 50Hz or 60Hz rejection can also be made

by driving FO to an appropriate logic level. A selection

change during the sleep or data output states will not

MSB

EXT

SIG

CH0/CH1

272832

BIT 0

BIT 27

BIT 4

LSB24

BIT 28

BIT 29

BIT 30

SDO

SCK

EOC

BIT 31

SLEEP

DATA OUTPUT

CONVERSION

24012 F03

Hi-Z

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