LTC2995 datasheet(72/90 Pages) AD

72 / 90 page

LTM2985

Rev. 0

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Voltage Output Mode

For standard (non table mode) voltage output mode, the

channel assignment word is 0xF000 0000 for differential

readingsand0xF4000000forsingle-ended(seeTable 75).

The data is represented as a 32-bit word (see Table 74)

where the eight most significant bits are fault bits and

the bottom 24 are the ADC reading in volts. For direct

APPLICATIONS INFORMATION

ADC readings hard fault errors do not clamp the digital

output. Readings beyond ±1.125 • VREF/2 exceed the

normal accuracy range of the LTM2985 and flag a soft

error;theseresultsshouldbediscarded.Readingsbeyond

±1.75 • VREF/2 exceed the usable range of the LTM2985;

these result in a hard fault and should be discarded.

Table 74. Direct ADC Voltage Output Result Format

START ADDRESS

START ADDRESS + 1

START ADDRESS + 2

START ADDRESS + 3

(END ADDRESS)

D31

D30 D29 D28 D27

D26

D25

D24

D23 D22 D21 D20 D19 D18 D17 D16 D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0

Fault Data

SIGN MSB

LSB

Volts

Sensor

Hard

Fault

Range

Hard

Fault

NA NA Soft

Above

Soft

Below

Soft

Range

Valid

Always

± 2V 1V

0.5V 0.25V ...

Integer

Fraction

>VREF

CLAMPED to Factory Programmed Value

of VREF

1.75 • VREF/2

1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

1.125 • VREF/2

1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

VREF/2

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

2–21V

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

–2–21V

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

–VREF/2

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

–1.125 • VREF

0 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

–1.75 • VREF

0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

< –VREF

CLAMPED to Factory Programmed Value

of –VREF

Table 75. Direct ADC Channel Assignment Data

CONFIGURATION

FIELD

DESCRIPTION # BITS

BINARY

DATA

MEMORY

ADDRESS 0x200

MEMORY

ADDRESS 0x201

MEMORY

ADDRESS 0x202

MEMORY

ADDRESS 0x203

(1) Direct ADC

Directly Measure

ADC

11110 1 1 1 1 0

(2) SE/Diff

Single-Ended or

Differential

(3) TBL

Table Lookup

(4) Not Used

Set to 0

0000000000000

0 0 0 0 0 0 0 0 0 0 0 0 0

(4) Direct ADC Table

Data Pointer

Start Address = 0

000000

0 0 0 0 0 0

(5) Direct ADC Table

Data Length-1

Data Length-1 = 0

000000

0 0 0 0 0 0

Example: Direct ADC with Differential Input

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