LTC2637-HMI10 LINER [Linear Technology], LTC2637-HMI10 Datasheet - Page 22

• Manufacturer Part Number: LTC2637-HMI10
• Manufacturer: LINER [Linear Technology]

LTC2637
OPERATION
The LTC2637-LMI/ LTC2637-LMX/ LTC2637-LZ provides
a full-scale output of 2.5V. The LTC2637-HMI/ LTC2637-
HMX/ LTC2637-HZ provides 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 0110b, and is
the power-on default for LTC2637-HZ/ LTC2637-LZ, as
well as for LTC2637-HMI/ LTC2637-LMI.
The 10ppm/°C, 1.25V (LTC2637-LMI/ LTC2637-LMX/
LTC2637-LZ) or 2.048V (LTC2637-HMI/ LTC2637-HMX/
LTC2637-HZ) internal reference is available at the REF pin.
Adding bypass capacitance to the REF pin will improve
noise performance; and up to 10μF can be driven without
oscillation. The REF output must be buffered when driving
an external DC load current.
Alternatively, the DAC can operate in External Reference
mode using command 0111b. In this mode, an input voltage
supplied externally to the REF pin provides the reference
(1V ≤ V
external reference voltage supplied sets the full-scale DAC
output voltage. External Reference mode is the power-on
default for LTC2637-HMX/ LTC2637-LMX.
22
REF
≤ V
CC
) and the supply current is reduced. The
Write Word Protocol for LTC2637
Input Word (LTC2637-12)
Input Word (LTC2637-10)
Input Word (LTC2637-8)
C3
C3
C3
S
C2
C2
C2
SLAVE ADDRESS
C1 C0
C1 C0
C1 C0
1ST DATA BYTE
1ST DATA BYTE
1ST DATA BYTE
A3 A2
A3 A2
A3 A2
W ACK
A1 A1
A1 A0
A1 A0
Figure 3. Command and Data Input Format
1ST DATA BYTE
D11
D9
D7
D10
D8
D6
ACK 2ND DATA BYTE ACK 3RD DATA BYTE ACK
D9
D7
D5
2ND DATA BYTE
2ND DATA BYTE
2ND DATA BYTE
D8
D6
D4
INPUT WORD
D7 D6
D5 D4
D3 D2
The reference mode of LTC2637-HZ/ LTC2637-LZ/ LTC2637-
HMI/ LTC2637-LMI (internal reference power-on default),
can be changed by software command after power up. The
same is true for LTC2637-HMX/ LTC2637-LMX (external
reference power-on default).
Power-Down Mode
For power-constrained applications, power-down mode can
be used to reduce the supply current whenever less than
eight DAC outputs are needed. When in power-down, the
buffer amplifi ers, bias circuits, and integrated reference
circuits 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 ground through in-
dividual 200kΩ resistors. Input and DAC register contents
are not disturbed during power down.
Any DAC channel or combination of channels can be put
into power-down mode by using command 0100b in
combination with the appropriate DAC address, (n). The
supply current is reduced approximately 10% for each DAC
powered down. The integrated reference is automatically
powered down when external reference is selected using
D5 D4 D3 D2 D1 D0
D3 D2 D1 D0
D1 D0
X
X
X
X
3RD DATA BYTE
3RD DATA BYTE
3RD DATA BYTE
X
X
P
X
X
X
X
X
X
X
X
X
2637 F03
X
X
X
2637fb