LTC2486IDE datasheet(18/36 Pages) LINER

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LTC2486

2486f

APPLICATIONS INFORMATION

The ﬁrst three bits shifted into the device consist of two

preamble bits and an enable bit. These bits are used to

enable the device conﬁguration and input channel selec-

tion. Valid settings for these three bits are 000, 100 and

101. Other combinations should be avoided. If the ﬁrst

three bits are 000 or 100, the following data is ignored

(don’t care) and the previously selected input channel and

conﬁguration remain valid for the next conversion.

If the ﬁrst three bits shifted into the device are 101, then

the next ﬁve bits select the input channel for the next

conversion cycle (see Table 3).

The ﬁrst input bit (SGL) following the 101 sequence

determines if the input selection is differential (SGL =

0) or single-ended (SGL = 1). For SGL = 0, two adjacent

channels can be selected to form a differential input. For

SGL = 1, one of four channels is selected as the positive

input. The negative input is COM for all single ended

operations. The remaining four bits (ODD, A2, A1, A0)

determine which channel(s) is/are selected and the polarity

(for a differential input).

The next serial input bit immediately following the input

channel selection is the enable bit for the conversion

conﬁguration (EN2). If this bit is set to 0, then the next

conversion is performed using the previously selected

converter conﬁguration.

The second set of conﬁguration data can be loaded into

the device by setting EN2 = 1 (see Table 4). The ﬁrst bit

(IM) is used to select the internal temperature sensor. If

IM = 1, the following conversion will be performed on

the internal temperature sensor rather than the selected

input channel. The next two bits (FA and FB) are used to

set the rejection frequency. The next bit (SPD) is used to

select either the 1x output rate if SPD = 0 (auto-calibration

is enabled and the offset is continuously calibrated and

removed from the ﬁnal conversion result) or the 2x output

rate if SPD = 1 (offset calibration disabled, multiplexing

output rates up to 15Hz with no latency). When IM = 1

(temperature measurement) SPD, GS2, GS1 and GS0 will

be ignored and the device will operate in 1x mode. The

ﬁnal 3 bits (GS2, GS1, GS0) are used to set the gain. The

conﬁguration remains valid until a new input word with

EN = 1 (the ﬁrst three bits are 101) and EN2 = 1 is shifted

into the device.

Table 3 Channel Selection

MUX ADDRESS

CHANNEL SELECTION

SGL

ODD/

SIGN

COM

IN+

IN–

00001

IN+

IN–

01000

IN–

IN+

01001

IN–

IN+

10000

IN+

IN–

10001

IN+

IN–

11000

IN+

IN–

11001

IN+

IN–

*Default at power up

Table 2. LTC2486 Output Data Format

DIFFERENTIAL INPUT VOLTAGE

VIN*

BIT 23

EOC

BIT 22

DMY

BIT 21

SIG

BIT 20

MSB

BIT 19

BIT 18

BIT 17

…

BIT 4

BITS 3 TO 0

VIN* ≥ FS**

0011000

…

0000

FS** – 1LSB

0010111

…

0000

0.5 • FS**

0010100

…

0000

0.5 • FS** – 1LSB

0010011

…

0000

0010000

…

0000

–1LSB

0001111

…

0000

–0.5 • FS**

0001100

…

0000

–0.5 • FS** – 1LSB

0001011

…

0000

–FS**

0001000

…

0000

VIN* < –FS**

0000111

…

0000

*The differential input voltage VIN = IN

+ – IN–. **The full-scale voltage FS = 0.5 • VREF/Gain.

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