LTC2480 datasheet(21/42 Pages) LINER

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LTC2480

2480fc

Input signals applied to IN+ and IN– pins may extend by

300mV below ground and above VCC. In order to limit any

fault current, resistors of up to 5k may be added in series

with the IN+ and IN– pins without affecting the performance

of the devices. The effect of the series resistance on the

converter accuracy can be evaluated from the curves

presented in the Input Current/Reference Current sections.

In addition, series resistors will introduce a temperature

dependent offset error due to the input leakage current.

A 1nA input leakage current will develop a 1ppm offset

error on a 5k resistor if VREF = 5V. This error has a very

strong temperature dependency.

Serial Interface Timing Modes

The LTC2480’s 4-wire interface is SPI and MICROWIRE

compatible. This interface offers several ﬂexible modes of

operation. These include internal/external serial clock,

3- or 4-wire I/O, single cycle or continuous conversion. The

following sections describe each of these serial interface

timing modes in detail. In all these cases, the converter

can use the internal oscillator (fO = LOW or fO = HIGH)

or an external oscillator connected to the fO pin. Refer to

Table 6 for a summary.

External Serial Clock, Single Cycle Operation

(SPI/MICROWIRE Compatible)

This timing mode uses an external serial clock to shift

out the conversion result and a CS signal to monitor and

control the state of the conversion cycle, see Figure 5.

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.

APPLICATIONS INFORMATION

Table 6. LTC2480 Interface Timing Modes

CONFIGURATION

SCK SOURCE

CONVERSION

CYCLE CONTROL

DATA OUTPUT

CONTROL

CONNECTION

AND WAVEFORMS

External SCK, Single Cycle Conversion

External

CS and SCK

Figures 5, 6

External SCK, 3-Wire I/O

External

SCK

Figure 7

Internal SCK, Single Cycle Conversion

Internal

CS↓

Figures 8, 9

Internal SCK, 3-Wire I/O, Continuous Conversion

Internal

Continuous

Internal

Figure 10

EOC

BIT 23

SDO

SCK

(EXTERNAL)

GS2

GS1

GS0

SPD

SDI*

DON’T CARE

TEST EOC

MSB

SIG

BIT 0

LSB

BIT 4

BIT 19

BIT 18

BIT 17

BIT 16

BIT 20

BIT 21

BIT 22

SLEEP

DATA OUTPUT

CONVERSION

2480 F05

CONVERSION

Hi-Z

TEST EOC

VCC

VREF

IN+

IN–

SCK

SDI

SDO

GND

210

INT/EXT CLOCK

REFERENCE

VOLTAGE

0.1V TO VCC

ANALOG

INPUT

1μF

2.7V TO 5.5V

LTC2480

4-WIRE

SPI INTERFACE

DON’T CARE

TEST EOC

(OPTIONAL)

Figure 5. External Serial Clock, Single Cycle Operation

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