DAC5573 Datasheet, PDF (27/30 Pages) Texas Instruments – QUAD, 8-BIT, LOW-POWER, VOLTAGE OUTPUT, INTERFACE DIGITAL-TO-ANALOG CONVERTER

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APPLICATION INFORMATION (continued)
Microcontroller or
Microprocessor
GPIO-1
GPIO-2
IOV_DD
DAC5573
SLAS401 – NOVEMBER 2003
DAC5573
1 VOUTA
A3 16
2 VOUTB
A2 15
3 V_REFH
4 V_DD
A1 14
A0 13
5 V_REFL
6 GND
IOV_DD 12
SDA 11
7 V_{OUTC SCL} 10
8 V_OUTD L_DAC 9
NOTE: DAC5573 power and input/output connections are omitted for clarity, except I²C Inputs.
Figure 39. Using GPIO With a Single DAC5573
Bit-banging I²C with GPIO pins can be done by setting the GPIO line to zero and toggling it between input and
output modes to apply the proper bus states. To drive the line low, the pin is set to output a zero; to let the line
go high, the pin is set to input. When the pin is set to input, the state of the pin can be read; if another device is
pulling the line low, this reads as a zero in the port's input register.
Note that no pullup resistor is shown on the SCL line. In this simple case the resistor is not needed. The
microcontroller can simply leave the line on output, and set it to one or zero as appropriate. It can do this
because the DAC5573 never drives its clock line low. This technique can also be used with multiple devices, and
has the advantage of lower current consumption due to the absence of a resistive pullup.
If there are any devices on the bus that may drive their clock lines low, do not use the above method. The SCL
line must be high-Z or zero, and a pullup resistor must be provided as usual. Note also that this cannot be done
on the SDA line in any case, because the DAC5573 drives the SDA line low from time to time, as all I²C devices
do.
Some microcontrollers have selectable strong pullup circuits built in to their GPIO ports. In some cases, these
can be switched on and used in place of an external pullup resistor. Weak pullups are also provided on some
microcontrollers, but usually these are too weak for I²C communication. Test any circuit before committing it to
production.
USING REF02 AS A POWER SUPPLY FOR DAC5573
Due to the extremely low supply current required by the DAC5573, a possible configuration is to use a REF02
+5-V precision voltage reference to supply the required voltage to the DAC5573 supply input as well as the
reference input, as shown in Figure 40. 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 DAC5573.
If the REF02 is used, the current it needs to supply to the DAC5573 is 600 µA typical and 900 µA max for
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