DAC8501 Datasheet, PDF (13/18 Pages) Burr-Brown (TI) – Low-Power, Rail-to-Rail Output, 16-Bit Serial Input DIGITAL-TO-ANALOG CONVERTER

POWER-ON RESET
The DAC8501 contains a power-on reset circuit that controls
the output voltage during power-up. On power-up, the DAC
register is filled with zeros and the output voltage is 0V; it
remains there until a valid write sequence is made to the
DAC. This is useful in applications where it is important to
know the state of the output of the DAC when it is in the
process of powering up.
POWER-DOWN MODES
The DAC8501 supports four separate modes of operation
which are programmable by setting two bits (PD1 and PD0)
in the control register. Table I shows how the state of the bits
corresponds to the mode of operation of the device.
PD1 (DB17)
0
—
0
1
1
PD0 (DB16)
0
—
1
0
1
OPERATING MODE
Normal Operation
Power-Down Modes
Output 1kΩ to GND
Output 100kΩ to GND
High-Z
TABLE I. Modes of Operation for the DAC8501.
MICROPROCESSOR
INTERFACING
DAC8501 TO 8051 INTERFACE
Figure 6 shows a serial interface between the DAC8501 and
a typical 8051-type microcontroller. The setup for the inter-
face is as follows: TXD of the 8051 drives SCLK of the
DAC8501, whereas RXD drives the serial data line of the
part. The SYNC signal is derived from a bit-programmable
pin on the port, in this case, port line P3.3 is used. When data
is to be transmitted to the DAC8501, P3.3 is taken LOW. The
8051 transmits data only in 8-bit bytes; thus only eight falling
clock edges occur in the transmit cycle. To load data to the
DAC, P3.3 is left LOW after the first eight bits are transmitted,
and a second write cycle is initiated to transmit the second
byte of data. P3.3 is taken HIGH following the completion of
the third write cycle. The 8051 outputs the serial data in a
format which has the LSB first. The DAC8501 requires its
data with the MSB as the first bit received, therefore the 8051
transmit routine must take this into account, and mirror the
data as needed.
When both bits are set to 0, the part works normally with its
typical current consumption of 250µA at 5V; however, for the
three power-down modes, the supply current falls to 200nA
at 5V (50nA at 3V). Not only does the supply current fall, but
the output stage is also internally switched from the output of
the amplifier to a resistor network of known values, this has
the advantage that the output impedance of the part is known
while the part is in power-down mode. There are three
different options: the output is connected internally to GND
through a 1kΩ resistor; a 100kΩ resistor; or it is left open-
circuited (High-Z), Figure 5 shows the output stage.
Resistor
String DAC
Amplifier
V_FB
V_OUT
80C51/80L51⁽¹⁾
P3.3
TXD
RXD
NOTE: (1) Additional pins omitted for clarity.
DAC8501⁽¹⁾
SYNC
SCLK
D_IN
FIGURE 6. DAC8501 to 80C51/80L51 Interface.
DAC8501 TO Microwire INTERFACE
Figure 7 shows an interface between the DAC8501 and any
Microwire compatible device. Serial data is shifted out on the
falling edge of the serial clock and is clocked into the
DAC8501 on the rising edge of the SK signal.
Power-Down
Circuitry
Resistor
Network
FIGURE 5. Output Stage During Power-Down.
All linear circuitry is shut down when the power-down mode
is activated, however, the contents of the DAC register are
unaffected when in power-down. The time to exit power-
down is typically 2.5µs for V_DD = 5V, and 5µs for V_DD = 3V,
(see the Typical Characteristics for more information).
Microwire^TM
CS
SK
SO
NOTE: (1) Additional pins omitted for clarity.
DAC8501⁽¹⁾
SYNC
SCLK
D_IN
FIGURE 7. DAC8501 to Microwire Interface.
DAC8501
13
SBAS212A
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