Datasheet

Data Sheet AD5381
Rev. D | Page 15 of 40
Mnemonic Function
REFOUT/REFIN
The AD5381 contains a common REFOUT/REFIN pin. When the internal reference is selected, this pin is the reference
output. If the application requires an external reference, it can be applied to this pin and the internal reference can
be disabled via the control register. The default for this pin is a reference input.
VOUT39/MON_OUT
This pin has a dual function. It acts as a buffered output for Channel 39 in default mode. However, when the monitor
function is enabled, this pin acts as the output of a 39-to-1 channel multiplexer that can be programmed to
multiplex one of Channels 0 to 38 to the MON_OUT pin. The MON_OUT pin’s output impedance is typically 500 Ω
and is intended to drive a high input impedance like that exhibited by SAR ADC inputs.
SER/
PAR
Interface Select Input. This pin allows the user to select whether the serial or parallel interface is used. If it is tied high,
the serial interface mode is selected and Pin 97 (
SPI
/I
2
C) is used to determine if the interface mode is SPI or I
2
C.
Parallel interface mode is selected when SER/
PAR
is low.
CS
/(
SYNC
/AD0) In parallel interface mode, this pin acts as chip select input (level sensitive, active low). When low, the AD5381
is selected.
Serial Interface Mode. This is the frame synchronization input signal for the serial clock and data.
I
2
C Mode. This pin acts as a hardware address pin used in conjunction with AD1 to determine the software address
for the device on the I
2
C bus.
WR
/(DCEN/AD1) Multifunction Pin. In parallel interface mode, this pin acts as write enable. In serial interface mode, this pin acts as a
daisy-chain enable in SPI mode and as a hardware address pin in I
2
C mode.
Parallel Interface Write Input (edge sensitive). The rising edge of
WR
is used in conjunction with
CS
low, and the
address bus inputs to write to the selected device registers.
Serial Interface. Daisy-chain select input (level sensitive, active high). When high, this signal is used in conjunction
with SER/
PAR
high to enable the SPI serial interface daisy-chain mode.
I
2
C Mode. This pin acts as a hardware address pin used in conjunction with AD0 to determine the software address
for this device on the I
2
C bus.
DB11–DB0 Parallel Data Bus. DB11 is the MSB and DB0 is the LSB of the input data-word on the AD5381.
A5–A0
Parallel Address Inputs. A5 to A0 are decoded to address one of the AD5381’s 40 input channels. Used in conjunction
with the REG1 and REG0 pins to determine the destination register for the input data.
REG1, REG0
In parallel interface mode, REG1 and REG0 are used in decoding the destination registers for the input data. REG1
and REG0 are decoded to address the input data register, offset register, or gain register for the selected channel and
are also used to decide the special function registers.
SDO/(
A
/B) Serial Data Output in Serial Interface Mode. Three-stateable CMOS output. SDO can be used for daisy-chaining a
number of devices together. Data is clocked out on SDO on the rising edge of SCLK, and is valid on the falling edge
of SCLK.
When operating in parallel interface mode, this pin acts as the A or B data register select when writing data to the
AD5381’s data registers with toggle mode selected (see the Toggle Mode Function section). In toggle mode, the
LDAC is used to switch the output between the data contained in the A and B data registers. All DAC channels
contain two data registers. In normal mode, Data Register A is the default for data transfers.
BUSY
Digital CMOS Output.
BUSY
goes low during internal calculations of the data (x2) loaded to the DAC data register.
During this time, the user can continue writing new data to the x1, c, and m registers, but no further updates to the
DAC registers and DAC outputs can take place. If
LDAC
is taken low while
BUSY
is low, this event is stored.
BUSY
also
goes low during power-on reset, and when the
RESET
pin is low. During this time, the interface is disabled and any
events on
LDAC
are ignored. A
CLR
operation also brings
BUSY
low.
LDAC
Load DAC Logic Input (Active Low). If
LDAC
is taken low while
BUSY
is inactive (high), the contents of the input
registers are transferred to the DAC registers and the DAC outputs are updated. If
LDAC
is taken low while
BUSY
is
active and internal calculations are taking place, the
LDAC
event is stored and the DAC registers are updated when
BUSY
goes inactive. However any events on
LDAC
during power-on reset or on
RESET
are ignored.
CLR
Asynchronous Clear Input. The
CLR
input is falling edge sensitive. When
CLR
is activated, all channels are updated
with the data contained in the
CLR
code register.
BUSY
is low for a duration of 35 µs while all channels are being
updated with the
CLR
code.
RESET
Asynchronous Digital Reset Input (Falling Edge Sensitive). The function of this pin is equivalent to that of the power-
on reset generator. When this pin is taken low, the state machine initiates a reset sequence to digitally reset the x1,
m, c, and x2 registers to their default power-on values. This sequence typically takes 270 µs. The falling edge of
RESET
initiates the
RESET
process and
BUSY
goes low for the duration, returning high when
RESET
is complete. While
BUSY
is low, all interfaces are disabled and all
LDAC
pulses are ignored. When
BUSY
returns high, the part resumes normal
operation and the status of the
RESET
pin is ignored until the next falling edge is detected.