LTC2668CUJ-12PBF View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
LTC2668CUJ-12PBF
Linear Technology
'LTC2668CUJ-12PBF' PDF : 28 Pages View PDF
LTC2668
Operation
The LTC2668 supports three types of toggle operations:
a first in which all selected channels are toggled together
using the SPI port; a second in which all selected channels
are toggled together using an external clock or logic signal;
and a third in which any combination of channels can be
instructed to update from either input register A or B.
The internal toggle-update circuit is edge triggered, so
only transitions (of TGB or TGP) trigger an update from
the respective input register.
To toggle all selected channels together using the SPI port,
ensure the TGP pin is high and that the bits in the toggle
select register corresponding to the desired channels are
also high. Use the global toggle command (1101b) to
alternate codes, sequentially changing the global toggle
bit TGB (see Figure 7). Changing TGB from 1 to 0 updates
the DAC registers from their respective input registers
A. Changing TGB from 0 to 1 updates the DAC registers
from their respective input registers B. Note that in this
way up to 16 channels may be toggled with just one se-
rial command.
To toggle all selected channels using an external logic
signal, ensure that the TGB bit in the global toggle register
is high and that in the toggle select register, the bits cor-
responding to the desired channels are also high. Apply
a clock or logic signal to the TGP pin to alternate codes.
TGP falling edges update the DAC registers from their
associated input registers A. TGP rising edges update
the DAC registers from their associated input registers B.
Note that once the input registers are set up, all toggling
is triggered by the signal applied to the TGP pin, with no
further SPI instructions needed.
To cause any combination of channels to update from
either input register A or B, ensure the TGP pin is high
and that the TGB bit in the global toggle register is also
high. Using the toggle select command, set the toggle
select bits as needed to select the input register (A or B)
with which each channel is to be updated. Then update all
channels, either by using the serial command (1001b) or
by applying a negative pulse to the LDAC pin. Any channels
whose toggle select bits are 0 update from input register
LTC2668
CHANNEL 15
LOGIC
WR
LDAC 15
UPD
INPUT REGISTER A
(16 BIT)
16
16
INPUT REGISTER B
(16 BIT)
0
A/B
MUX
1
16
DAC REGISTER 16
16-BIT
SOFTSPAN DAC
TOGGLE SELECT BIT T15
SDI 19
TGB
16-BIT TOGGLE SELECT REGISTER
ONE Tx BIT PER CHANNEL
32-BIT SHIFT REGISTER
SCK
17
CS/LD
16
GLOBAL TOGGLE
BIT (TGB)
TGP
20
Figure 8. Simplified Toggle Block Diagram. Conceptual Only, Actual Circuit May Differ
For more information www.linear.com/LTC2668
2668 F08
2668fa
21
Share Link: 