LTC2489CDEPBF datasheet(12/24 Pages) LINER

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LTC2489

2489f

result in binary two’s complement format. The remaining

six bits are always 0.

As long as the voltage on the selected input channels (IN+

and IN–) remains between –0.3V and VCC + 0.3V (absolute

maximum operating range) a conversion result is gener-

ated for any differential input voltage VIN from –FS = –0.5

• VREF to +FS = 0.5 • VREF. For differential input voltages

greater than +FS, the conversion result is clamped to the

value corresponding to +FS. For differential input voltages

below –FS, the conversion result is clamped to the value

–FS – 1LSB.

Table 2. LTC2489 Status Bits

Input Range

Bit 23

SIG

Bit 22

MSB

VIN ≥ FS

0V ≤ VIN < FS

–FS ≤ VIN < 0V

VIN < –FS

INPUT DATA FORMAT

The LTC2489 serial input is 8 bits long and is written into

the device in one 8-bit word. SGL, ODD, A2, A1, A0 are

used to select the input channel.

After power-up, the device initiates an internal reset cycle

which sets the input channel to CH0-CH1 (IN+ = CH0,

IN– = CH1). The ﬁrst conversion automatically begins

at power-up using this default input channel. Once the

Table 1. Output Data Format

Differential Input Voltage

VIN*

Bit 23

SIG

Bit 22

MSB

Bit 21

Bit 20

Bit 19

…

Bit 6

LSB

Bits 5-0

Always 0

VIN* ≥ FS**

…

000000

FS** – 1LSB

…

000000

0.5 • FS**

…

000000

0.5 • FS** – 1LSB

…

000000

…

000000

–1LSB

…

000000

–0.5 • FS**

…

000000

–0.5 • FS** – 1LSB

…

000000

–FS**

…

000000

VIN* < –FS**

…

000000

*The differential input voltage VIN = IN+ – IN–. **The full-scale voltage FS = 0.5 • VREF.

conversion is complete, a new channel may be written

into the device.

The ﬁrst three bits of the input word consist of two pre-

amble bits and one enable bit. These three bits are used

to enable the input channel selection. 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 remains 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).

APPLICATIONS INFORMATION

Table 3 Channel Selection

MUX ADDRESS

CHANNEL SELECTION

SGL

ODD/

SIGN

COM

0000

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

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