For the auditory alarm implementation, two DAC53701 devices are required: one device to generate the pulse envelope and the burst, and the second device to generate the pulse frequency, as shown in Figure 9-7. The signals coming from both DACs are combined together using amplifier OP1 that has a shutdown pin, for example, the TLV9002S or OPA363. The combined signal is then ac-coupled to an audio amplifier, such as the TPA6211A1https://www.ti.com/product/TPA6211A1, to drive the speaker. The TPA6211A1 is an integrated Class-AB amplifier that can drive up to 3 W of output power with very little distortion. As per medical alarm standard IEC60601-1-8, the pulse frequency must be greater than 150 Hz, and must have at least four harmonic components that are within ±15 dB of each other. As a result of the square-wave pulse frequency and the mixing done by OP1, the speaker output generates multiple harmonics of the fundamental pulse frequency. The DACx3701 provide a range of timing options for the pulse frequency and envelope, and various options to program the pulse frequency and envelope timings. See Section 8.4.4 for the alarm configuration options. Calculate the frequency of a square wave or pulse frequency using Equation 3. The square-wave function has a limited number of frequencies because this function is programmed by the SLEW_RATE bit alone. To get a higher number of frequencies, generate a triangular waveform with comparator mode output. Generate the triangular waveform using Equation 4. Set the DAC output in the comparator mode by fixing the FB pin to the midscale of the DAC using a resistive voltage divider from V_DD. Select V_DD as the reference in this case using the GENERAL_CONFIG register (see Section 8.6.2).

The following pseudocode helps to get started with a medical alarm application using two DACs:

//SYNTAX: WRITE <REGISTER NAME (Hex code)>, <MSB DATA>, <LSB DATA>
//Power-up the first DAC, enable VDD reference
//SLEW_RATE: 1.6384 ms (Square wave frequency: 610 Hz)
WRITE GENERAL_CONFIG(0xD1), 0xD1, 0x58
//Set MARGIN_HIGH on the first DAC
WRITE DAC_MARGIN_HIGH(0x25), 0x0F, 0xFC
//Set MARGIN_LOW on the first DAC
WRITE DAC_MARGIN_LOW(0x26), 0x00, 0x00
//Trigger square wave generation on the first DAC
WRITE TRIGGER(0xD3), 0x01, 0x00
//Power-up the second DAC, enable VDD reference
//CODE_STEP: 8 LSB, SLEW_RATE: 204.8 µs x 1.75 = 358.4 µs (Envelope rise/fall times for full-scale: ~26 ms)
WRITE GENERAL_CONFIG(0xD1), 0x1A, 0xE8
//OPTION-1: Configure the second DAC for low-priority alarm with minimum time settings and trigger
WRITE CONFIG2(0xD2), 0x01, 0x00
//OPTION-2: Configure the second DAC for medium-priority alarm with minimum time settings and trigger
WRITE CONFIG2(0xD2), 0x02, 0x00
//OPTION-3: Configure the second DAC for high-priority alarm with minimum time settings and trigger
WRITE CONFIG2(0xD2), 0x04, 0x00
//Set MARGIN_HIGH on the second DAC
WRITE DAC_MARGIN_HIGH(0x25), 0x0F, 0xFC
//Set MARGIN_LOW on the second DAC
WRITE DAC_MARGIN_LOW(0x26), 0x00, 0x00