LTC2410IGN datasheet(17/44 Pages) LINER

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LTC2410

APPLICATIO S I FOR ATIO

A similar situation may occur during the sleep state when

CS is pulsed HIGH-LOW-HIGH in order to test the conver-

sion status. If the device is in the sleep state (EOC = 0), SCK

will go LOW. Once CS goes HIGH (within the time period

defined above as tEOCtest), the internal pull-up is activated.

For a heavy capacitive load on the SCK pin, the internal

pull-up may not be adequate to return SCK to a HIGH level

before CS goes low again. This is not a concern under

normal conditions where CS remains LOW after detecting

EOC = 0. This situation is easily overcome by adding an

external 10k pull-up resistor to the SCK pin.

Internal Serial Clock, 2-Wire I/O,

Continuous Conversion

This timing mode uses a 2-wire, all output (SCK and SDO)

interface. The conversion result is shifted out of the device

by an internally generated serial clock (SCK) signal, see

Figure 10. CS may be permanently tied to ground, simpli-

fying the user interface or isolation barrier.

The internal serial clock mode is selected at the end of the

power-on reset (POR) cycle. The POR cycle is concluded

approximately 0.5ms after VCC exceeds 2.2V. An internal

weak pull-up is active during the POR cycle; therefore, the

internal serial clock timing mode is automatically selected

if SCK is not externally driven LOW (if SCK is loaded such

that the internal pull-up cannot pull the pin HIGH, the

external SCK mode will be selected).

During the conversion, the SCK and the serial data output

pin (SDO) are HIGH (EOC = 1). Once the conversion is

complete, SCK and SDO go LOW (EOC = 0) indicating the

conversion has finished and the device has entered the

low power sleep state. The part remains in the sleep state

a minimum amount of time (1/2 the internal SCK period)

then immediately begins outputting data. The data output

cycle begins on the first rising edge of SCK and ends after

the 32nd rising edge. Data is shifted out the SDO pin on

each falling edge of SCK. The internally generated serial

clock is output to the SCK pin. This signal may be used

to shift the conversion result into external circuitry. EOC

can be latched on the first rising edge of SCK and the last

bit of the conversion result can be latched on the 32nd

rising edge of SCK. After the 32nd rising edge, SDO goes

HIGH (EOC = 1) indicating a new conversion is in progress.

SCK remains HIGH during the conversion.

Figure 10. Internal Serial Clock, Continuous Operation

SDO

SCK

(INTERNAL)

LSB24

MSB

SIG

BIT 5

BIT 0

BIT 27

BIT 26

BIT 28

BIT 29

BIT 30

EOC

BIT 31

SLEEP

DATA OUTPUT

CONVERSION

2410 F10

= 50Hz REJECTION

= EXTERNAL OSCILLATOR

= 60Hz REJECTION

VCC

REF+

REF–

SCK

IN+

IN–

SDO

GND

214

1, 7, 8, 9, 10, 15, 16

REFERENCE

VOLTAGE

0.1V TO VCC

ANALOG INPUT RANGE

–0.5VREF TO 0.5VREF

3-WIRE

SPI INTERFACE

µF

2.7V TO 5.5V

LTC2410

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