8-bit bus control, widely used 12-bit general purpose

Function of the circuit

Analog circuits for measurement or control purposes require 12-bit resolution. This circuit uses an 8-bit bus to control the widely used 12-bit DA converter DAC80, which is a very versatile circuit. The output polarity and output voltage range can be easily selected using jumpers.

How the Circuit Works

The data of 8-bit microcomputer is output in 8-bit parallel. Except for the serial input DA converter, the data must be divided into two groups of input and adjusted. The data latch should be 16 bits. First, the four bits of data D7~D4 are latched in the low byte, and the locked 4 bits of data and the high byte are sent to the 12-bit DA converter at the same time with the next clock pulse.

DAC80-CB1-V is a voltage output DA converter with ground-binary input. Its reference voltage is 6.3V, which is connected to the REF-IN terminal. You can also remove the jumper J1 and input from the outside. This method is often used when multiple DACs are needed to make the circuit have tracking characteristics. BP is a bipolar bias terminal. If a bipolar voltage is output, the jumper J2 can be short-circuited and the internal 6.3K resistor can be used to make a 1MA current flow.

Use variable resistors connected to positive and negative RCC to adjust gain and zero. If the power supply is unstable, use a Zener diode to stabilize it and then connect it to VR1 and VR2.

Jumper wires J3 and J4 are used to select the output amplitude. When J3 is short-circuited, a 20VP-P voltage can be output, and when J4 is short-circuited, a 10VP-P voltage can be output. Therefore, when designing the circuit board, the jumper wire jack should be considered. This circuit diagram shows the wiring state of bipolar output and voltage of positive and negative 10V.

Assembly Notes

The 12-bit data input line should be as short as possible and use a shielded line with an outer ground layer to prevent the logic signal from coupling with the analog circuit. Because the pins 1 to 12 of the DAC80 are all logic inputs, a ground line is arranged under the IC.

It should be noted that the summing connection lead 20 and the BP biasing lead 17 are both weak level leads. In order to avoid coupling with other leads, the routing length should be shortened and a shielded wire with an outer layer grounded must be used.

In order to improve the accuracy of the output voltage 0V, the analog and digital grounding must be clearly separated. The ground wires of the two parts can be connected near the DA converter or at the power ground terminal.

Regarding the DA converter: When the input data changes, the internal current also needs to change due to synchronization, so power bypass capacitors C2 and C3 are added near the IC .