Datasheet

LTC2609/LTC2619/LTC2629
16
26091929fb
operation
loads a 16-bit data word from the 32-bit shift register
into the input register of the selected DAC, n. An update
operation copies the data word from the input register to
the DAC register. Once copied into the DAC register, the
data word becomes the active 16-, 14- or 12-bit input
code, and is converted to an analog voltage at the DAC
output. The update operation also powers up the selected
DAC if it had been in power-down mode. The data path
and registers are shown in the Block Diagram.
Power-Down Mode
For power-constrained applications, power-down mode can
be used to reduce the supply current whenever less than
four outputs are needed. When in power-down, the buffer
amplifiers, bias circuits and reference inputs are disabled,
and draw essentially zero current. The DAC outputs are
put into a high impedance state, and the output pins are
passively pulled to REFLO through individual 90k resis-
tors. Input- and DAC-register contents are not disturbed
during power down.
Any channel or combination of channels can be put into
power-down mode by using command 0100b in combi-
nation with the appropriate DAC address, (n). The 16-bit
data word is ignored. The supply current is reduced by
approximately 1/4 for each DAC powered down. The effec-
tive resistance at REFx (Pins 3, 6, 12 and 15) are at high
impedance (typically > 1GΩ) when the corresponding DACs
are powered down. Normal operation can be resumed by
executing any command which includes a DAC update,
as shown in Table 2.
The selected DAC is powered up as its voltage output is
updated. When a DAC which is in a powered-down state
is powered up and updated, normal settling is delayed. If
less than four DACs are in a powered-down state prior to
the update command, the power-up delay time is 5µs. If on
the other hand, all four DACs are powered down, then the
C3
1ST DATA BYTE
Input Word (LTC2609)
Write Word Protocol for LTC2609/LTC2619/LTC1629
C2
C1
C0
A3
D13D14D15
S
W A
SLAVE ADDRESS
1ST DATA BYTE
D12
D11 D10 D9 D8
D7
D6
D5 D4 D3 D2 D1
D0
A 2ND DATA BYTE A 3RD DATA BYTE A P
2609 F03
2ND DATA BYTE
INPUT WORD
3RD DATA BYTE
C3
1ST DATA BYTE
Input Word (LTC2619)
C2
C1
C0
A3
D11D12D13
D10
D9 D8 D7 D6
D5
D4
D3 D2 D1 D0 X
X
2ND DATA BYTE 3RD DATA BYTE
C3
1ST DATA BYTE
Input Word (LTC2629)
C2
C1
C0
A3
A2
A2
A2
A1
A1
A1
A0
A0
A0
D9D10D11
D8
D7 D6 D5 D4
D3
D2
D1 D0 X X X
X
2ND DATA BYTE 3RD DATA BYTE
Figure 3
Table 2
COMMAND*
C3 C2 C1 C0
0 0 0 0 Write to Input Register n
0 0 0 1 Update (Power Up) DAC Register n
0 0 1 0 Write to Input Register n, Update (Power Up) All n
0 0 1 1 Write to and Update (Power Up) n
0 1 0 0 Power Down n
1 1 1 1 No Operation
ADDRESS (n)*
A3 A2 A1 A0
0 0 0 0 DAC A
0 0 0 1 DAC B
0 0 1 0 DAC C
0 0 1 1 DAC D
1 1 1 1 All DACs
*Command and address codes not shown are reserved and should not be used.