Datasheet

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SLAS233D − JULY 1999 − REVISED JULY 2002
10
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
general function
The TLV5625 is a dual 8-bit, single-supply DAC, based on a resistor-string architecture. It consists of a serial
interface, a speed and power-down control logic, a resistor string, and a rail-to-rail output buffer.
The output voltage (full scale determined by the reference) is given by:
2REF
CODE
2
n
[V]
Where REF is the reference voltage and CODE is the digital input value within the range of 0
10
to 2
n
−1, where
n=8 (bits). The 16-bit data word, consisting of control bits and the new DAC value, is illustrated in the data format
section. A power-on reset initially resets the internal latches to a defined state (all bits zero).
serial interface
A falling edge of CS starts shifting the data bit-per-bit (starting with the MSB) to the internal register on the falling
edges of SCLK. After 16 bits have been transferred or CS
rises, the content of the shift register is moved to the
target latches (DAC A, DAC B, BUFFER, CONTROL), depending on the control bits within the data word.
Figure 2 shows examples of how to connect the TLV5625 to TMS320, SPI, and Microwire.
TMS320
DSP
FSX
CLKX
DX
TLV5625
SCLK
DIN
CS
SPI
I/O
SCK
MOSI
TLV5625
SCLK
DIN
CS
Microwire
I/O
SK
SO
TLV5625
SCLK
DIN
CS
Figure 12. Three-Wire Interface
Notes on SPI and Microwire: Before the controller starts the data transfer, the software has to generate a
falling edge on the pin connected to CS. If the word width is 8 bits (SPI and Microwire) two write operations
must be performed to program the TLV5625. After the write operation(s), the holding registers or the control
register are updated automatically on the 16
th
positive clock edge.
serial clock frequency and update rate
The maximum serial clock frequency is given by:
f
sclkmax
+
1
t
whmin
) t
wlmin
+ 20 MHz
The maximum update rate is:
f
updatemax
+
1
16
ǒ
t
whmin
) t
wlmin
Ǔ
+ 1.25 MHz
Note that the maximum update rate is just a theoretical value for the serial interface, as the settling time of the
TLV5625 should also be considered.