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| DAC8574 Datasheet, PDF (38/40 Pages) Texas Instruments – QUAD, 16-BIT, LOW-POWER, VOLTAGE OUTPUT, I2C INTERFACE DIGITAL-TO-ANALOG CONVERTER | |||
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DAC8574
SLAS377A â JANUARY 2003 â REVISED JUNE 2003
APPLICATION INFORMATION (continued)
I2C High Speed Examples (A0, A1, A2, A3 and LDAC pins tied to GND):
EXAMPLE 22: Ramp generation on channel D (Up to Code 7 is shown)
HS Master Code
NOT
REPEATED ADDRESS
START
0001 0000
ACK
START
10011 0000 ACK
Previous VoutD voltage valid
MSB [7â¦0]
LSB [7â¦0]
MSB [7â¦0]
0000 0000 ACK 0000 0000
ACK
0000 0000
ACK
Previous VoutD voltage valid
VoutD = 0 V
MSB [7â¦0]]
LSB [7â¦0]
MSB 7â¦0]
0000 0000 ACK 0000 0010
ACK
0000 0000
ACK
VoutD = 76 µV
VoutD = 2 x 76 µV
MSB [7â¦0]
LSB [7â¦0]
0000 0000 ACK 0000 0100
VoutD = 3 x 76 µV
ACK
VoutD = 4 x 76 µV
MSB [7â¦0]
0000 0000
ACK
MSB [7â¦0]
LSB [7â¦0]
0000 0000 ACK 0000 0110
VoutD = 5 x 76 µV
ACK
VoutD = 6 x 76 µV
MSB [7â¦0]
0000 0000
ACK
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C [7 ⦠0]
0001 0110
ACK
LSB [7â¦0]
0000 0001
LSB [7â¦0]
0000 0011
LSB [7â¦0]
0000 0101
LSB [7â¦0]
0000 0111
ACK
VoutD = 76 µV
ACK
VoutD = 3 x 76
µV
ACK
VoutD = 5 x 76
µV
ACK
VoutD = 7 x 76
µV
LAYOUT
A precision analog component requires careful layout, adequate bypassing, and clean, well-regulated power
supplies.
The power applied to VDD should be well-regulated and low noise. Switching power supplies and dc/dc
converters often have high-frequency glitches or spikes riding on the output voltage. In addition, digital
components can create similar high-frequency spikes as their internal logic switches states. This noise can easily
couple into the DAC output voltage through various paths between the power connections and analog output.
As with the GND connection, VDD should be connected to a positive power-supply plane or trace that is separate
from the connection for digital logic until they are connected at the power-entry point. In addition, a 1 µF to 10 µF
capacitor in parallel with a 0.1 µF bypass capacitor is strongly recommended. In some situations, additional
bypassing may be required, such as a 100 µF electrolytic capacitor or even a Pi filter made up of inductors and
capacitorsâall designed to essentially low-pass filter the â5 V supply, removing the high-frequency noise.
38
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