[Shishuo Design] Teach you a trick to simplify the highly integrated system-level method of designing isolated software configurable I/O channels

The ADP1034 is a high-performance isolated power management unit that contains an isolated flyback regulator, an inverting buck-boost regulator, and a buck regulator, providing three isolated power rails and integrating seven Low power digital isolator. The ADP1034 also features programmable power control (PPC) that allows the voltage on V _OUT1 to be adjusted as needed through a single-wire interface. V _OUT1 supplies the AD74115H AV _DD supply rail from 6V to 28V. V _OUT2 provides 5V to the AD74115H power rails AV _CC and DV _CC . If required, it can also provide supply voltage to an external voltage reference. V _OUT3 supplies the AD74115H AV _SS supply rail from -5V to -24V.

When designing channel-to-channel isolation modules, the primary trade-off is usually between power consumption and channel density. As module size shrinks and channel density increases, power consumption per channel must decrease to meet the module's maximum power budget. In this case, the modules are the ADP1034 and AD74115H, which when used together provide isolated power, data isolation, and software-configurable I/O functionality.

What makes the AD74115H and ADP1034 excellent low-power solutions is the introduction of integrated PPC functionality. The PPC enables the user to adjust the V _OUT1 voltage (AD74115H AV _DD supply voltage) as desired . This method can greatly reduce the power consumption of the module under low load conditions, especially in current output mode. When using the PPC function, the host controller in the system sends the required voltage code to the AD74115H via SPI, which is then passed to the ADP1034 via the one-wire serial interface (OWSI). OWSI implements a CRC check function, which is very robust and can resist EMC interference that may exist in harsh industrial environments.

Looking at the power consumption calculation example, if AV _DD = 24 V and the load is 250Ω, the total module power consumption is 748mW for a current output of 20mA. When using PPC to reduce the AV _DD voltage to 8.6V (load voltage + headroom), the module power consumption is approximately 348mW. This represents a power consumption saving of 400mW within the module.

Example 1 and Example 2 selected the current output use case, driving a 20mA output. The load is 250Ω, the ADC is enabled, and the default measurement configuration is converted at 20 samples per second.

Figure 1. ADP1034 and AD74115H circuit diagram

Example 1 (no PPC):

AD74115H output power = (AV _DD = 24V) × 20 mA = 480 mW

AD74115H input power = AD74115H _QUIESCENT (206 mW) + ADC power consumption (30 mW) + 480 mW =716 mW

Module input power = 716 mW + ADP1034 power consumption (132 mW) = 848 mW

Load power consumption = 20 mA2 × 250 Ω = 100 mW

Total module power consumption = (module input power - load power consumption) = 748 mW

As can be seen in Example 2, when the PPC function is enabled to reduce AV _DD to the required voltage (20 mA × 250 Ω) + 3.6 V headroom = 8.6 V, the power consumption of the module is reduced to 348 mW.

Example 2 (using PPC):

AD74115H output power = (AV _DD = 8.6 V) × 20 mA = 172 mW

AD74115H input power = AD74115H _QUIESCENT (136 mW) + ADC power consumption (30 mW) + 172 mW =338 mW

Module input power = 338 mW + ADP1034 power consumption (100 mW) = 448 mW

Load power consumption = 20 mA2 × 250 Ω = 100 mW Total module power consumption = (module input power - load power consumption) = 348 mW

Figure 2 shows the measured power consumption at 25°C on the AD74115H application board. The measurement results show that the power consumption is slightly lower than the calculated power consumption. The results will vary slightly from device to device.

Figure 2. Measured data: driving 20 mA into 250 Ω load, AVDD = 24 V, AVDD = 8.6 V (using PPC)

Figure 3 shows the power consumption (AV _DD optimized for each load resistor value setting ) of the modules using PPC (ADP1034 and AD74115) versus different load resistor values. Two different voltages are applied to the VINP of the ADP1034 (15V and 24 V) to show the efficiency of the ADP1034. Measurements are taken at 25°C.

Figure 3. Power consumption versus RLOAD at 20 mA output

Figure 4 shows the power consumption (AV _DD optimized for each load resistor value setting ) using PPC at different temperatures versus different load resistor values.

Figure 4. Power consumption versus temperature

Table 1. Typical use case power consumption of AD74115H using PPC

In industrial applications, digital output is considered the most power-hungry use case. The AD74115H supports internal and external current source and sink digital outputs. The ADP1034 provides sufficient power for internal digital output functions, supporting continuous sourcing or sinking of up to 100 mA. In this case, the digital output circuit supply DO_V _DD is connected directly to AV _DD . For currents above 100 mA, the external digital output function must be used, which requires an additional power supply to be connected to DO_V _DD .

To support charging of capacitive loads on initial power-up, a higher short-circuit current limit (~280 mA) can be enabled for a programmable time T1 while using the internal digital output use case. After the T1 time, the second short-circuit current limit value (~140 mA) is deployed. This is a lower current limit value that is valid for the programmable duration T2. During these short circuit conditions, the system requires more current, so care must be taken to ensure that the ADP1034 V _OUT1 voltage does not dip. To ensure no dips, if 24 V DO_V _DD is required , it is recommended to use 24 V as the system supply voltage for the ADP1034. This is the typical voltage requirement for a 24 V relay. For 12 V relays, it is recommended to use a system supply voltage of at least 18 V (ADP1034V _INP ) to ensure sufficient current can be supplied to the load.

Figures 5 and 6 show DO_V _DD versus T1 and T2 short-circuit limits, demonstrating the stability of delivering large currents using the ADP1034.

Figure 5. System power supply = 24 V, DO_VDD voltage = 24V

Figure 6. System power supply = 24 V, DO_VDD voltage = 12V

The ADP1034 uses ADI's patented iCoupler® technology to integrate three isolated power rails, including SPI data and three GPIO isolated channels, in a 7mm × 9mm package. This high level of integration consolidates all channel isolation requirements into a small area on the PCB, helping to solve PCB area challenges and achieve power savings. The controller side of the ADP1034 puts other SPI isolator channels into low-power states when the channels are not in use. This means that the channel is only active when needed. Three isolated GPIO channels are used to isolate the RESET, ALERT, and ADC_RDY pins of the AD74115H, thereby meeting all isolation requirements of the AD74115H without the cost of additional isolator ICs.

Designing a low-power, small-footprint channel-to-channel isolated I/O solution can be a challenge even for some of the most experienced designers in the industry. The ADP1034 and AD74115H system-level solutions address this challenge through high integration and a system-level design approach. A single IC provides three isolated power rails from a single system power supply and provides integrated data isolation, which results in a significant reduction in BOM cost. Coupled with the flexibility of the AD74115H, this system design will meet the requirements of most I/O industrial applications.