AD5300
AD5300 to 68HC11/68L11 Interface
Figure 26 shows a serial interface between the AD5300 and the
68HC11/68L11 microcontroller. SCK of the 68HC11/68L11
drives the SCLK of the AD5300, while the MOSI output drives
the serial data line of the DAC. The SYNC signal is derived
from a port line (PC7). The setup conditions for correct opera-
tion of this interface are as follows: the 68HC11/68L11 should
be configured so that its CPOL bit is a 0 and its CPHA bit is a
1. When data is being transmitted to the DAC, the SYNC line is
taken low (PC7). When the 68HC11/68L11 is configured as
above, data appearing on the MOSI output is valid on the falling
edge of SCK. Serial data from the 68HC11/68L11 is transmit-
ted in 8-bit bytes with only eight falling clock edges occurring in
the transmit cycle. Data is transmitted MSB first. In order to
load data to the AD5300, PC7 is left low after the first eight bits
are transferred, and a second serial write operation is performed
to the DAC and PC7 is taken high at the end of this procedure.
MICROWIRE*
AD5300*
CS
SYNC
SCLK
DIN
SK
SO
*ADDITIONAL PINS OMITTED FOR CLARITY
Figure 28. AD5300 to MICROWIRE Interface
APPLICATIONS
Using REF19x as a Power Supply for AD5300
Because the supply current required by the AD5300 is extremely
low, an alternative option is to use a REF19x voltage reference
(REF195 for 5 V or REF193 for 3 V) to supply the required
voltage to the part—see Figure 29. This is especially useful if
your power supply is quite noisy or if the system supply voltages
are at some value other than 5 V or 3 V (e.g., 15 V). The REF19x
will output a steady supply voltage for the AD5300. If the low
dropout REF195 is used, the current it needs to supply to the
AD5300 is 140 µA. This is with no load on the output of the
DAC. When the DAC output is loaded, the REF195 also needs to
supply the current to the load. The total current required (with
a 5 kΩ load on the DAC output) is
68HC11/68L11*
AD5300*
PC7
SYNC
SCLK
DIN
SCK
MOSI
140 µA + (5 V/5 kΩ) = 1.14 mA
*ADDITIONAL PINS OMITTED FOR CLARITY
The load regulation of the REF195 is typically 2 ppm/mA,
which results in an error of 2.3 ppm (11.5 µV) for the 1.14 mA
current drawn from it. This corresponds to a 0.0006 LSB error.
Figure 26. AD5300 to 68HC11/68L11 Interface
AD5300 to 80C51/80L51 Interface
Figure 27 shows a serial interface between the AD5300 and the
80C51/80L51 microcontroller. The setup for the interface is as
follows: TXD of the 80C51/80L51 drives SCLK of the AD5300,
while RXD drives the serial data line of the part. The SYNC
signal is again 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 AD5300, P3.3 is taken low. The 80C51/80L51 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 this cycle. The 80C51/80L51
outputs the serial data in a format that has the LSB first. The
AD5300 requires its data with the MSB as the first bit received.
The 80C51/80L51 transmit routine takes this into account.
15V
5V
REF195
140A
SYNC
SCLK
DIN
3-WIRE
SERIAL
INTERFACE
V
= 0V TO 5V
OUT
AD5300
Figure 29. REF195 as Power Supply to AD5300
Bipolar Operation Using the AD5300
The AD5300 has been designed for single-supply operation,
but a bipolar output range is also possible using the circuit in
Figure 30. The circuit in Figure 30 will give an output voltage
range of 5 V. Rail-to-rail operation at the amplifier output is
achievable using an AD820 or an OP295 as the output amplifier.
AD5300*
80C51/80L51*
The output voltage for any input code can be calculated as
P3.3
SYNC
D
256
R1 + R2
R2
R1
TXD
RXD
SCLK
DIN
VO = V
×
×
–VDD ×
DD
R1
where D represents the input code in decimal (0 to 255).
With VDD = 5 V, R1 = R2 = 10 kΩ,
*ADDITIONAL PINS OMITTED FOR CLARITY
Figure 27. AD5300 to 80C51/80L51 Interface
10 × D
256
AD5300 to MICROWIRE Interface
VO
=
– 5V
Figure 28 shows an interface between the AD5300 and any
MICROWIRE compatible device. Serial data is shifted out on the
falling edge of the serial clock and is clocked into the AD5300 on
the rising edge of the SK.
This is an output voltage range of 5 V with 00 Hex corresponding
to a –5 V output and FF Hex corresponding to a 5 V output.
D
REV.
–10–
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