The DAC7617 is a quad, serial input, 12-bit, voltage output digital-to-analog converter (DAC), with guar and 12-bit monotonic performance over the -40°C to +85°C temperature range. Asynchronous reset clears all registers with either medium scale (800H) or zero scale (000H), selectable via the RESETSEL pin. The single DAC input is double buffered, enabling simultaneous updates to all DAC outputs. The device is powered from a single +3V supply. Low power consumption and small size make the DAC7617 ideal for automatic test equipment, DAC-per-pin programming aggregates, data acquisition systems and closed-loop servo control. The device is available in SO-16 and SSOP-20 packages and is guaranteed over the -40°C to +85°C temperature range.

working principle

The DAC7617 is a quad, serial input, 12-bit, voltage output DAC. The architecture is a typical R-2R ladder configuration followed by an op amp used as a buffer. Each DAC has its own R-2R ladder network and outputs op amps, but all have a common reference voltage input. The minimum output voltage ("zero scale") and maximum output voltage ("full scale") are set by external reference voltages (VREFL and VREFH respectively). The digital input is a 16-bit serial word containing the 12-bit DAC code and a 2-bit address used to select one of the four DACs (the two remaining code bits are unused). The converter can be powered from a single +3V supply. Each device provides a reset function that diately sets all DAC output voltages and internal registers to zero-scale (code 000H) or mid-scale (code 800H). The reset code is selected by the state of the RESETSEL pin (LOW = 000H, HIGH = 800H). The figure below shows the basic operation of the DAC7617.

Analog output

The output of the DAC7617 can swing to ground. Note that the settling time of the output op amp will be longer with voltages very close to ground. Also, care must be taken when measuring zero-scale error. If the output amplifier has a negative offset, the output voltage may not be suitable for changing the first few digital input codes (000H, 001H, 002H, etc.) since the output voltage cannot go below ground. The behavior of the output amplifier can be in some critical applications. In a short-circuit condition (DAC output short to VDD), the output amplifier can sink significantly more current than it can source.

layout

Precision analog components require careful layout, AD- is equivalent to a bypass, clean, well regulated power supply. Since the DAC7617 provides single-supply operation, it can often be used in close proximity to digital logic, microcontrollers, microprocessors and digital signal processors. The more digital logic is present in the design and the higher the switching speed, the harder it will be to keep digital noise from appearing at the converter's output. Due to the single ground pin of the DAC7617, all return currents, both digital and analog, must flow through the GND pin. Ideally, the ground would be connected directly to the analog ground plane. The planes will be disconnected from the ground connections used for the digital compo system until they are connected at the power input point of the system (see diagram below).

The supply applied to V DD should be well regulated and low noise. Switching power supplies and DC/DC converters will often have high frequency glitches or spikes riding on the output voltage. Additionally, digital components can create similar high-frequency spikes as their internal logic switch states. This noise can easily couple into the DAC output through various paths between the power connections and the analog output. As the connection to GND, VDD should be connected to a +3V, power plane or traces are separate digital logic connections until they are connected at the power input point. Also, 1µF to 10µF and 0.1µF capacitors shown in Figure 3 are strongly recommended. In some cases additional bypassing may be required, such as a 100 µF electrolytic capacitor, or even a pi filter consisting of an inductor and capacitor, all designed to essentially low pass the +3V supply, removing high frequency noise.