LTC2984 datasheet(17/78 Pages) AD

17 / 78 page

LTC2984

2984fb

For more information www.linear.com/LTC2984

The LTC2984 combines high accuracy with ease of use.

The basic operation is simple and is composed of five

states (see Figure 3).

APPLICATIONS INFORMATION

Figure 3. Basic Operation

2984 F03

POWER-UP,

SLEEP

OR RESET

(OPTIONAL)

≈ 200ms(MAX)

YES

START-UP

CHANNEL ASSIGNMENT

INITIATE CONVERSION

CONVERSION

READ RESULTS

STATUS CHECK

COMPLETE?

Conversion States Overview

1. Start-Up. After power is applied to the LTC2984

(VDD > 2.6V), there is a 200ms wake up period. During

this time, the LDO, charge pump, ADCs, and reference

are powered up and the internal RAM is initialized. Once

start-up is complete, the INTERRUPT pin goes HIGH

and the command status register will return a value of

0x40 (Start bit = 0, Done bit = 1) when read.

2. Channel Assignment. The device automatically enters

thechannelassignmentstateafterstart-upiscomplete.

While in this state, the user writes sensor specific data

for each input channel into RAM or loads it from the

EEPROM (see the EEPROM section for more details).

The assignment data contains information about the

sensor type, pointers to cold junction sensors or sense

resistors, and sensor specific parameters.

3. InitiateConversion.Aconversionisinitiatedbywriting

a measurement command into RAM memory location

0x000. This command is a pointer to the channel in

which the conversion will be performed.

4. Conversion. A new conversion begins automatically

following an Initiate Conversion command. In this

state, the ADC is running a conversion on the specified

channelandassociatedcoldjunctionorRSENSEchannel

(if applicable). The user is locked out of RAM access

while in the state (except for reading status location

0x000). The end of conversion is indicated by both

the INTERRUPT pin going HIGH and a status register

START bit going LOW and DONE bit going HIGH.

5. Read Results. In this state, the user has access to

RAM and can read the completed conversion results

and fault status bits. It is also possible for the user to

modify/append the channel assignment data during the

read results state.

Conversion State Details

State 1: Start-Up

The start-up state automatically occurs when power is ap-

plied to the LTC2984. If the power drops below a threshold

of ≈2.6V and then returns to the normal operating voltage

(2.85Vto5.25V),theLTC2984resetsandentersthepower-

up state. Note that the LTC2984 also enters the start-up

state at the conclusion of the sleep state. The start-up state

can also be entered at any time during normal operation

by pulsing the RESET pin low.

In the first phase of the start-up state all critical analog

circuits are powered up. This includes the LDO, reference,

charge pump and ADCs. During this first phase, the com-

mand status register will be inaccessible to the user. This

phase takes a maximum of 100mS to complete. Once this

phase completes, the command status register will be

accessible and return a value of 0x80 until the LTC2984

is completely initialized. Once the LTC2984 is initialized

and ready to use, the interrupt pin will go high and the

command status register will return a read value of 0x40

(Start bit = 0, Done bit = 1). At this point the LTC2984

is fully initialized and is ready to perform a conversion.

State 2: Channel Assignment

The LTC2984 RAM can be programmed with up to 20 sets

of 32-bit (4-byte) channel assignment data. These reside

sequentially in RAM with a one-to-one correspondence

to each of the 20 analog input channels (see Table 3).

Channels that are not used should have their channel

assignment data set to all zeros (default at START-UP).

LTC2984 Datasheet(PDF) 17 Page - Analog Devices

LTC2984 Datasheet(HTML) 17 Page - Analog Devices

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