Rainbow Electronics MAX5295 - Manual (Page 26)

MAX5290–MAX5295
Buffered, Fast-Settling, Dual, 12-/10-/8-Bit,
Voltage-Output DACs
26 ______________________________________________________________________________________
SET
,
MID
,
CLR
The SET, MID, and CLR signals force the DAC outputs
to full scale, midscale, or zero scale (Figure 5). These
signals cannot be active at the same time.
The active-low SET input forces the DAC outputs to full
scale when SET is low. When SET is high, the DAC out-
puts follow the data in the DAC registers.
The active-low MID input forces the DAC outputs to mid-
scale when MID is low. When MID is high, the DAC out-
puts follow the data in the DAC registers.
The active-low CLR input forces the DAC outputs to zero
scale when CLR is low. When CLR is high, the DAC out-
puts follow the data in the DAC registers.
If CLR, MID, or SET signals go low in the middle of a write
command, reload the data to ensure accurate results.
Power-Down Lockout (
PDL
)
The PDL active-low software-shutdown lockout input
overrides (not overwrites), the PD_0 and PD_1 shut-
down mode bits. PDL cannot be active at the same
time as SHDN1K or SHDN100K (see the Shutdown
Mode (
SHDN1K , SHDN100K ) section).
If the PD_0 and PD_1 bits command the DAC to shut
down prior to PDL going low, the DAC returns to shut-
down mode immediately after PDL goes high, unless
the PD_0 and PD_1 bits are changed in the meantime.
Shutdown Mode ( S SH HD DN N1 1K K , S SH HD DN N1 10 00 0K K )
The SHDN1K and SHDN100K are active-low signals
that override (not overwrite) the PD_1 and PD_0 bit set-
tings. For the MAX5290/MAX5292/MAX5294, drive
SHDN1K low to select shutdown mode with OUTA and
OUTB internally terminated with 1k
Ω to ground, or drive
SHDN100K low to select shutdown with an internal
100k
Ω termination. For the MAX5291/MAX5293/
MAX5295, drive SHDN1K low for shutdown with 1k
Ω
output termination, or drive SHDN100K low for shut-
down with high-impedance outputs.
Data Output (DOUTRB, DOUTDC0, DOUTDC1)
UPIO1 and UPIO2 can be configured as serial data
outputs, DOUTRB (data out for read back), DOUTDC0
(data out for daisy-chaining, mode 0), and DOUTDC1
(data out for daisy-chaining, mode 1). The differences
between DOUTRB and DOUTDC0 (or DOUTDC1) are
as follows:
• The source of read-back data on DOUTRB is the
DOUT register. Daisy-chain DOUTDC_ data comes
directly from the shift register.
• Read-back data on DOUTRB is only present after a
DAC read command. Daisy-chain data is present on
DOUTDC_ for any DAC write after the first 16 bits
are written.
• The DOUTRB idle state (CS = high) for read back is
high impedance. Daisy-chain DOUTDC_ idles high
when inactive to avoid floating the data input in the
next device in the daisy-chain.
See Figures 1 and 2 for timing details.
t CMS
t
LDL
t S
±0.5 LSB
TOGG
V OUT_
LDAC
PDL
CLR,
MID, OR
SET
PDL AFFECTS DAC OUPTUTS (V OUT_ ) ONLY IF DACS WERE PREVIOUSLY SHUT DOWN.
Figure 5. Asynchronous Signal Timing
t
GP
t LDS
END OF
CYCLE*
GPO_
LDAC
*END-OF-CYCLE REPRESENTS THE RISING EDGE OF CS OR THE 16TH
ACTIVE CLOCK EDGE, DEPENDING ON THE MODE OF OPERATION.
Figure 6. GPO_ and LDAC Signal Timing