www.ti.com

8

6

4

9

5

7

1

2

3

12

14

11

10

13

16

15

DAC7573

GND

A3

A2

A1

A0

SDA

SCL

GPIO-2

GPIO-1

Microcontroller or

Microprocessor

USING REF02 AS A POWER SUPPLY FOR DAC7573

DAC7573

SLAS398 – SEPTEMBER 2003

APPLICATION INFORMATION (continued)

Figure 41. Using GPIO With a Single DAC7573

Bit-banging I

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 DAC7573 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, the above method should not be used.

The SCL line should be high-Z or zero, and a pullup resistor provided as usual. Note also that this cannot be

done on the SDA line in any case, because the DAC7573 drives the SDA line low from time to time, as all I

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 I

production.

Due to the extremely low supply current required by the DAC7573, a possible configuration is to use a REF02

+5 V precision voltage reference to supply the required voltage to the DAC7573'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 DAC7573.

If the REF02 is used, the current it needs to supply to the DAC7573 is 600 µA typical and 900 µA max for

27