DAC7574IDGSR Datasheet, PDF (28/35 Pages) Texas Instruments – QUAD, 12-BIT, LOW-POWER, VOLTAGE OUTPUT, I2C INTERFACE DIGITAL-TO-ANALOG CONVERTER

DAC7574
SLAS375 – JUNE 2003
www.ti.com
APPLICATION INFORMATION (continued)
POWER SUPPLY REJECTION
The positive reference voltage input of DAC7574 is internally tied to the power supply pin of the device. This
increases I²C system flexibility, creating room for an extra I²C address pin in a low pin-count package. To
eliminate the supply noise appearing at the DAC output, the user must pay close attention to how DAC7574 is
powered. The supply to DAC7574 must be clean and well regulated. For best performance, use of a precision
voltage reference is recommended to supply power to DAC7574. This is equivalent to providing a precision
external reference to the device. Due to low power consumption of DAC7574, load regulation errors are
negligible. In order to avoid excess power consumption at the Schmitt-triggered inputs of DAC7574, the precision
reference voltage should be close to the I²C bus pullup voltage. For 3-V, 3.3-V and 5-V I²C bus pullup voltages,
REF2930, REF2933 and REF02 precision voltage references are recommended respectively. These precision
voltage references can be used to supply power for multiple devices on a system.
USING REF02 AS A POWER SUPPLY FOR DAC7574
Due to the extremely low supply current required by the DAC7574, a possible configuration is to use a REF02
+5 V precision voltage reference to supply the required voltage to the DAC7574’s supply input as well as the
reference input, as shown in Figure 42. This is especially useful if the power supply is quite noisy or if the system
supply voltages are at some value other than 5 V. The REF02 outputs a steady supply voltage for the DAC7574.
If the REF02 is used, the current it needs to supply to the DAC7574 is 600 µA typical and 900 µA max for
V_DD = 5 V. When a DAC output is loaded, the REF02 also needs to supply the current to the load. The total
typical current required (with a 5-kΩ load on a single DAC output) is:
600 µA + (5 V / 5 kΩ) = 1.6 mA
The load regulation of the REF02 is typically 0.005%/mA, which results in an error of 400µV for 1.6-mA of current
drawn from it. This corresponds to a 0.33 LSB error for a 0 V to 5 V output range.
15 V
5V
REF02
1.6 mA
I²C
Interface
SCL
SDA
V_DD
DAC7574
V_OUT = 0 V to 5 V
Figure 42. REF02 Power Supply
LAYOUT
A precision analog component requires careful layout, adequate bypassing, and clean, well-regulated power
supplies.
The power applied to V_DD 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.
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