SLEEP MODE
Reset, Power-On Reset and Brown-Out
The DAC1220 contains an internal power-on reset circuit. If
the power supply ramp rate is greater than 50mV/ms, this
circuit will be adequate to ensure the device powers up
correctly. Due to oscillator settling considerations, commu-
nication to and from the DAC1220 should not occur for at
least 25ms after power is stable.
The Sleep Mode is entered after the bit combination 10 has
been written to the CMR Operation Mode bits (MD1 and
MD0). This mode ends when these bits are changed to a
value other than 10.
Communication with the DAC1220 can continue during
Sleep Mode. When a new mode (other than Sleep) has been
entered, the DAC1220 will execute a very brief internal
power-up sequence of the analog and digital circuitry. In
addition, the settling of the external VREF and other circuitry
must be taken into account to determine the amount of time
required to resume normal operation.
If this requirement cannot be met or if the circuit has brown-
out considerations, the timing diagram of Figure 3 can be
used to reset the DAC1220. This accomplishes the reset by
controlling the duty cycle of the SCLK input.
Sleep mode is the default state after power on or reset. The
output is high impedance during sleep mode.
The output is turned off in sleep mode.
I/O Recovery
If serial communication stops during an instruction or data
transfer for longer than 100ms (for fXIN = 2.5MHz), the
DAC1220 will reset its serial interface. This will not affect
the internal registers. The main controller must not continue
the transfer after this event, but must restart the transfer from
the beginning. This feature is very useful if the main control-
ler can be reset at any point. After reset, simply wait 200ms
(for fXIN = 2.5MHz) before starting serial communication.
SERIAL INTERFACE
The DAC1220 includes a flexible serial interface which can
be connected to microcontrollers and digital signal proces-
sors in a variety of ways. Along with this flexibility, there is
also a good deal of complexity. This section describes the
trade-offs between the different types of interfacing methods
in a top-down approach—starting with the overall flow and
control of serial data, moving to specific interface examples,
and then providing information on various issues related to
the serial interface.
Isolation
The serial interface of the DAC1220 provides for simple
isolation methods. An example of an isolated two-wire
interface is shown in Figure 4.
t1: > 512 • tXIN
Reset On
Falling Edge
< 800 • tXIN
t2: > 10 • tXIN
t2
t2
t3: > 1024 • tXIN
< 1800 • tXIN
SCLK
t1
t3
t4
t4: ≥ 2048 • tXIN
< 2400 • tXIN
FIGURE 3. Resetting the DAC1220.
Isolated
Power
DVDD
Opto
Coupler
8051
P1.1
P1.0
DAC1220
C1
12pF
1
DVDD
XOUT
XIN
SCLK 16
SDIO 15
CS 14
Opto
Coupler
2
XTAL
3
4
C2
DGND
AVDD
DNC
DNC
DNC
AGND 13
VREF 12
VOUT 11
C2 10
12pF
AVDD
VREF
5
6
7
8
= Isolated
= DGND
= AGND
VOUT
C2
C1
C1
9
FIGURE 4. Isolation for Two-Wire Interface
®
10
DAC1220
BB [ BURR-BROWN CORPORATION ]
