Datasheet

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DAC8554
SLAS431B – JUNE 2005 – REVISED OCTOBER 2006
The DAC8554 also supports a number of different Power-down/data selection is as follows:
load commands. The load commands include
DB16 is a power-down flag. If this flag is set, then
broadcast commands to address all the DAC8554s
DB15 and DB14 select one of the four power-down
on an SPI bus. The load commands can be
modes of the device as described in Table 1 . If DB16
summarized as follows:
= 1, DB15 and DB14 no longer represent the two
DB21 = 0 and DB20 = 0: Single-channel store. MSBs of data, but represent a power-down condition
The temporary register (data buffer) corresponding to described in Table 1 . Similar to data, power-down
a DAC selected by DB18 and DB17 is updated with conditions can be stored at the temporary registers
the contents of SR data (or power-down). of each DAC. It is possible to update DACs
simultaneously either with data, power-down, or a
DB21 = 0 and DB20 = 1: Single-channel update.
combination of both.
The temporary register and DAC register
corresponding to a DAC selected by DB18 and DB17 Refer to Table 2 for more information.
are updated with the contents of SR data (or
power-down). Table 1. DAC8554 Power-Down Modes
PD0 PD1 PD2
DB21 = 1 and DB20 = 0: Simultaneous update. A
(DB16) (DB15) (DB14) OPERATING MODE
channel selected by DB18 and DB17 gets updated
1 0 0 Output high impedance
with the SR data, and simultaneously, all the other
channels get updated with previous stored data (or
1 0 1 Output typically 1k Ω to GND
power-down) from temporary registers.
1 1 0 Output typically 100k Ω to GND
1 1 1 Output high impedance
DB21 = 1 and DB20 = 1: Broadcast update. All the
DAC8554s on the SPI bus respond, regardless of
address matching. If DB18 = 0, then SR data gets
ignored, all channels from all DAC8554s get updated
with previously stored data (or power-down). If DB18
= 1, then SR data (or power-down) updates all
channels of all DAC8554s in the system. This
broadcast update feature allows the simultaneous
update of up to 16 channels.
Table 2. Control Matrix
DB23 DB22 DB21 DB20 DB19 DB18 DB17 DB16 DB15 DB14 DB13-DB0
Don't
A1 A0 LD 1 LD 0 Care DAC Sel 1 DAC Sel 0 PD0 MSB MSB-1 MSB-2...LSB
(Address Select) DESCRIPTION
0/1 0/1 This address selects 1 of 4 possible devices on a
single SPI data bus based on each device's address
See Below pin(s) state.
0 0 X 0 0 0 Data Write to buffer A with data
0 0 X 0 1 0 Data Write to buffer B with data
0 0 X 1 0 0 Data Write to buffer C with data
0 0 X 1 1 0 Data Write to buffer D with data
Write to buffer (selected by DB17 and DB18) with
0 0 X (00, 01, 10, or 11) 1 See Table 1 0
power-down command
A0 and A1 should
correspond to the
Write to buffer with data and load DAC (selected by
0 1 X (00, 01, 10, or 11) 0 Data
package address
DB17 and DB18)
set via pins 13
Write to buffer with power-down command and load
and 14.
0 1 X (00, 01, 10, or 11) 1 See Table 1 0
DAC (selected by DB17 and DB18)
Write to buffer with data (selected by DB17 and DB18)
1 0 X (00, 01, 10, or 11) 0 Data and then load all DACs simultaneously from their
corresponding buffers.
Write to buffer with power-down command (selected by
1 0 X (00, 01, 10, or 11) 1 See Table 1 0 DB17 and DB18) and then load all DACs
simultaneously from their corresponding buffers.
Broadcast Modes
Simultaneously update all channels of all DAC8554
X X 1 1 X 0 X X X devices in the system with data stored in each
channels temporary register.
X X 1 1 X 1 X 0 Data Write to all devices and load all DACs with SR data
Write to all devices and load all DACs with
X X 1 1 X 1 X 1 See Table 1 0
power-down command in SR.
16
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