LTC1663

8

1663fd

APPLICATIONS INFORMATION

Bit (Wr) = 0. The LTC1663 acknowledges and the master

delivers the command byte. The LTC1663 acknowledges

and latches the command byte into the command byte

input register. The master then delivers the least significant

data byte. Again the LTC1663 acknowledges and the data

is latched into the least significant data byte input register.

The master then delivers the most significant data byte.

The LTC1663 acknowledges once more and latches the

data into the most significant data byte input register.

Lastly, the master terminates the communication with a

STOP condition. On the reception of the STOP condition,

the LTC1663 transfers the input register information to

output registers and the DAC output is updated.

Slave Address (MSOP Package Only)

The LTC1663 can respond to one of eight 7-bit addresses.

The first 4 bits (MSBs) have been factory programmed to

0100. The first 4 bits of the LTC1663-8 have been factory

programmed to 0011. The three address bits, AD2, AD1

and AD0 are programmed by the user and determine the

LSBs of the slave address, as shown in the table below:

LTC1663

LTC1663-8

AD2

AD1

AD0

0100 xxx

0011 xxx

L

L

L

0100 000

0011 000

L

L

H

0100 001

0011 001

L

H

L

0100 010

0011 010

L

H

H

0100 011

0011 011

H

L

L

0100 100

0011 100

H

L

H

0100 101

0011 101

H

H

L

0100 110

0011 110

H

H

H

0100 111

0011 111

Slave Address (SOT-23 Package)

The slave address for the SOT-23 package has been

factory programmed to be “0100 000” (LTC1663),

“0100 001” (LTC1663-1) and “0100 010” (LTC1663-2) If

another address is required, please consult the factory.

Command Byte

7

6543

2

1

0

X

XXXX

BG

SD

SY

SY

1

0

Allows update on Acknowledge of SYNC Address only

Update on Stop condition only (Power-On Default)

SD

1

0

Puts the device in power-down mode

Puts the device in standard operating mode

(Power-On Default)

BG

1

0

Selects the internal bandgap reference

Selects the supply as the reference (Power-On Default)

X

X

Don’t Care

The stop condition normally initiates the update of the

DAC’s output latches. Simultaneous update of more than

one DAC or other devices on the bus can be achieved by

reissuing new start bit, address, command and data bytes

before issuing a final stop condition (which will update

all the devices). An alternate way to achieve simultaneous

LTC1663 updates is to override the stop condition update

by setting the “SY” bit of the command byte. Setting this

bit sets the device to update the DAC output latches only

at the reception of a SYNC address quick command. The

actual update occurs on the rising edge of SCL during the

Acknowledge. In this way, all devices can update on the

reception of the SYNC address quick command instead

of the STOP condition.

A Shutdown (SD) bit = HIGH will put the device in a low

power state but retain all data latch information. Shutdown

will occur at the reception of a STOP condition. This way

shutdown could be synchronized to other devices. The

output impedance of the DAC will go to a high impedance

state (≈ 500kΩ to GND).

The Bandgap (BG) bit when set to “0” selects the DAC

supply voltage as its voltage reference. The full-scale

output of the DAC with this setting is equal to the supply

voltage. When the BG bit is set to “1,” the internal bandgap

reference (≈1.25V) is selected as the DAC’s reference. The

full-scale output voltage for this setting is 2.5V.