LTC2415-1IGN datasheet(19/40 Pages) LINER

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LTC2415/LTC2415-1

sn2415 24151fs

APPLICATIO S I FOR ATIO

Figure 8. External Serial Clock, Single Cycle Operation

EOC

BIT 31

SDO

SCK

(EXTERNAL)

TEST EOC

SUB LSB

MSB

SIG

BIT 0

LSB

BIT 5

BIT 27

BIT 26

BIT 28

BIT 29

BIT 30

SLEEP

DATA OUTPUT

CONVERSION

2415 F08

CONVERSION

= 50Hz REJECTION (LTC2415)

= EXTERNAL OSCILLATOR

= 60Hz REJECTION (LTC2415)

= 50Hz/60Hz REJECTION (LTC2415-1)

Hi-Z

VCC

TEST EOC

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

µF

2.7V TO 5.5V

LTC2415/

LTC2415-1

3-WIRE

SPI INTERFACE

The serial clock mode is selected on the falling edge of CS.

To select the external serial clock mode, the serial clock pin

(SCK) must be LOW during each CS falling edge.

The serial data output pin (SDO) is Hi-Z as long as CS is

HIGH. At any time during the conversion cycle, CS may be

pulled LOW in order to monitor the state of the converter.

While CS is pulled LOW, EOC is output to the SDO pin.

EOC = 1 while a conversion is in progress and EOC = 0 if

the device is in the sleep state. Independent of CS, the

device automatically enters the sleep state once the con-

version is complete. While in the sleep state, if CS is high,

the LTC2415/LTC2415-1 power consumption is reduced

by an order of magnitude

When the device is in the sleep state (EOC = 0), its

conversion result is held in an internal static shift regis-

ter. The device remains in the sleep state until the first

rising edge of SCK is seen while CS is LOW. Data is shifted

out the SDO pin on each falling edge of SCK. This enables

external circuitry to latch the output on the rising edge of

SCK. 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. On the 32nd falling edge of

SCK, the device begins a new conversion. SDO goes HIGH

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

At the conclusion of the data cycle, CS may remain LOW

and EOC monitored as an end-of-conversion interrupt.

Alternatively, CS may be driven HIGH setting SDO to Hi-Z.

As described above, CS may be pulled LOW at any time in

order to monitor the conversion status.

Typically, CS remains LOW during the data output state.

However, the data output state may be aborted by pulling

CS HIGH anytime between the first rising edge and the

32nd falling edge of SCK, see Figure 9. On the rising edge

of CS, the device aborts the data output state and imme-

diately initiates a new conversion. This is useful for sys-

tems not requiring all 32 bits of output data, aborting an

invalid conversion cycle or synchronizing the start of a

conversion.

External Serial Clock, 2-Wire I/O

This timing mode utilizes a 2-wire serial I/O interface. The

conversion result is shifted out of the device by an exter-

nally generated serial clock (SCK) signal, see Figure 10. CS

may be permanently tied to ground, simplifying the user

interface or isolation barrier.

The external 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. The level

applied to SCK at this time determines if SCK is internal or

external. SCK must be driven LOW prior to the end of POR

in order to enter the external serial clock timing mode.

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