8

LTC1663

Slave Address (SOT-23 Package)

The slave address for the SOT-23 package has been

factory programmed to be “0100 000.” If another address

is required, please consult the factory.

Command Byte

765

43

2

1

0

XXX

XX

BG

SD

SY

SY

1

Allows update on Acknowledge of SYNC Address only

0

Update on Stop condition only (Power-On Default)

SD

1

Puts the device in power-down mode

0

Puts the device in standard operating mode

(Power-On Default)

BG

1

Selects the internal bandgap reference

0

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. This allows for simultaneous update

of more than one DAC or other devices on the bus. This can

be overridden by setting the “SY” bit of the command byte.

Setting this bit sets the device to update the DAC output

latches at the reception of a SYNC address quick com-

mand. 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 com-

mand 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.

Data Bytes

Least Significant Data Byte

765

4

3

2

1

0

D7

D6

D5

D4

D3

D2

D1

D0

Most Significant Data Byte

76

5

4

3

2

10

X

X

X

X

X

X

D9

D8

X = Don’t care

Send Byte Protocol

The Send Byte protocol used on the LTC1663 is actually a

subset of the Write Word protocol described previously.

The Send Byte protocol can only be used to send the

command byte information to the LTC1663.

Command Byte

A

Slave Address

A

Wr

P

S

81

1

71

1

1663 TA04

1

S = Start Condition, Wr = Write Bit, A = Acknowledge, P = Stop Condition

The Send Byte protocol is also used whenever the Write

Word protocol is interrupted for any reason. Reception of

a START or STOP condition after the Acknowledge of the

command byte, but before the Acknowledge of the last

data byte, will cause both data bytes to be ignored and the

command byte to be accepted.

Reception of a START or STOP condition before the

Acknowledge of the command byte will cause the inter-

rupted command byte to be ignored.