MAX543BCPA+

The MAX543 is a 12-bit, current-output, multiplying digital-to-analog converter (DAC) that comes in space-saving 8-pin DIP and 8- or 16-pin surface-mount SO packages. Its 3-wire serial interface saves additional board space and also results in low power dissipation. When used with microprocessors (μPs) with a serial port, the MAX543 minimizes the digital noise feedthrough from its input pins to its output. The serial port can be used as a dedicated analog bus and kept inactive while the MAX543 is in use. Serial interfacing also reduces the complexity of opto- or transformer-isolated applications. The MAX543 contains a 12-bit R-2R type DAC, a serial-in parallel-out shift register, a DAC register and control logic. On the rising edge of the clock (CLK) pulse, the serial input (SRl) data is shifted into the MAX543. When all the data is clocked in, it is transferred into the DAC register by taking the LOAD input low. The MAX543 is specified with a single power supply of either +5V or +15V. With a +5V supply, the digital inputs are TTL and +5V CMOS compatible. High-voltage CMOS compatibility is maintained with a +15V supply. Maxim's MAX543 uses low-tempco thin-film resistors laser trimmed to ±1/4 LSB linearity and better than ±1 LSB gain accuracy. The digital inputs are protected against electrostatic discharge (ESD) damage and can typically withstand over 5,000V of ESD voltages. The MAX543 DAC circuit consists of a laser-trimmed, thin-film R-2R resistor array with NMOS current switches. Binary weighted currents are switched to either Iout or GND depending on the status of each input data bit. Although the current at Iout and GND depends on the digital input code, the sum of the two output currents is always equal to the input current at VREF. The current output (Iout) can be converted into a voltage by adding an external output amplifier. The VREF input accepts a wide range of signals, including fixed and time-varying voltage or current inputs. If a current source is used for the reference input, then a low-tempco external resistor should be used for RFB to minimize gain variation with temperature. The internal feedback resistor (RFB) is compensated with an NMOS switch that matches the NMOS switches used in the R-2R array. This results in excellent supply rejection and gain-temperature coefficient. The Iout pin output capacitance (Cout) is code dependent and is typically 55pF with all switches to GND and 85pF with all switches to Iout. The MAX543's input buffer inverters act as level shifters, converting TTL levels into CMOS logic levels. These input buffers are TTL and 5V-CMOS compatible (0.8V and 2.4V) at VDD = 5V. For VDD = 15V, the input buffers are CMOS compatible (1.5V and 13.5V). At this supply voltage, the input buffers are in their linear region when the input voltages are between 1V and 6V. Therefore, to minimize high supply currents, the digital input voltages should be kept as close to the supply and ground voltages (VDD and GND) as possible.

Applications

• Automatic Calibration
• Motion-Control Systems
• μP - Controlled Systems
• Programmable Amplifiers/Attenuators
• Digitally Controlled Filters

Key features

• 12-Bit Accuracy in 8-Pin MiniDIP or SO
• Fast 3-Wire Serial Interface
• Low INL and DNL (±1/2 LSB Max)
• Gain Accuracy to ±1 LSB Max
• Low Gain Tempco (5 ppm/°C Max)
• Operates with +5V or +15V Supplies
• TTL/CMOS Compatible
• ESD Protected