ltc2631-z Linear Technology Corporation, ltc2631-z Datasheet - Page 23

• Manufacturer Part Number: ltc2631-z
• Description: Single 12-/10-/8-bit I 2c Vout Dacs With Bidirectional Reference
• Manufacturer: Linear Technology Corporation

OPERATION
Table 3. Command Codes
Reference Modes
For applications where an accurate external reference is
not available, the LTC2631 has a user selectable, inte-
grated reference. The LTC2631-LM/LTC2631-LZ provide
a full-scale output of 2.5V. The LTC2631-HM/LTC2631-HZ
provide a full-scale output of 4.096V. The internal reference
can be useful in applications where the supply voltage is
poorly regulated. Internal Reference mode can be selected
by using command 0110, and is the power-on default for
LTC2631-HZ/LTC2631-LZ, as well as for LTC2631-HM/
LTC2631-LM when REF_SEL is tied high.
The 10ppm/°C, 1.25V (LTC2631-LM/LTC2631-LZ) or
2.048V (LTC2631-HM/LTC2631-HZ) internal reference
is available at the REF pin. Adding bypass capacitance
COMMAND*
*Command codes not shown are reserved and should not be used.
C3
0
0
0
0
0
0
C2
0
0
0
1
1
1
C1
0
0
1
0
1
1
C0
0
1
1
0
0
1
Write Word Protocol for LTC2631
Input Word (LTC2631-12)
Input Word (LTC2631-10)
Input Word (LTC2631-8)
C3
C3
C3
S
Write to Input Register
Update (Power Up) DAC Register
Write to and Update (Power Up) DAC Register
Power Down
Select Internal Reference
Select External Reference
C2
C2
C2
SLAVE ADDRESS
C1 C0
C1 C0
C1 C0
1ST DATA BYTE
1ST DATA BYTE
1ST DATA BYTE
X
X
X
W
X
X
X
A
X
X
X
Figure 3. Command and Data Input Format
1ST DATA BYTE
X
X
X
D11
D9
D7
D10
D8
D6
D9
D7
D5
A
2ND DATA BYTE
2ND DATA BYTE
2ND DATA BYTE
D8
D6
D4
2ND DATA BYTE
INPUT WORD
D7 D6
D5 D4
D3 D2
to the REF pin will improve noise performance; 0.33μF
is recommended, and up to 10μF can be driven without
oscillation. This output must be buffered when driving
external DC load current.
Alternatively, the DAC can operate in External Reference
mode using command 0111. In this mode, an input voltage
supplied externally to the REF pin provides the reference
(0V ≤ V
External Reference mode is the power-on default for
LTC2631-HM/LTC2631-LM when REF_SEL is tied low.
The reference mode of LTC2631-HZ/LTC2631-LZ can be
changed only by software command. The same is true for
LTC2631-HM/LTC2631-LM after power-on, after which the
logic state on REF_SEL is ignored.
Power-Down Mode
For power-constrained applications, the LTC2631’s power-
down mode can be used to reduce the supply current
whenever the DAC output is not needed. When in power-
down, the buffer amplifi er, bias circuit, and reference circuit
are disabled and draw essentially zero current. The DAC
output is put into a high-impedance state, and the output
pin is passively pulled to ground through a 200kΩ resistor.
Input and DAC register contents are not disturbed during
power-down.
D5 D4 D3 D2 D1 D0
D3 D2 D1 D0
D1 D0
A
REF
3RD DATA BYTE
≤ V
X
X
CC
) and the supply current is reduced.
X
X
3RD DATA BYTE
3RD DATA BYTE
3RD DATA BYTE
A
X
X
P
X
X
X
X
X
X
X
X
X
2631 F03
X
X
X
LTC2631
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