Modern factories employ automated systems, relying on feedback from numerous sensors throughout the plant to maintain high productivity. These companies use digital fieldbuses to aggregate the vast amounts of data collected by sensors. The more data the sensors collect, the better the system's adaptability and operability.
Therefore, modern industrial sensors using fieldbus connections must detect signals at faster and more accurate rates and output this information as a digital signal, as opposed to traditional analog signals. This functionality requires sensors to use more powerful processors. Furthermore, the increased number of such sensors in factories leads to a smaller form factor. The increased power and smaller form factor force factories to abandon mature linear regulator solutions in favor of switching regulator solutions.
However, using switching regulators presents new challenges. Because inductors require additional space, switching regulators have a large form factor. The relationship between the regulator's switching frequency and the measurement signal frequency must be considered.
Therefore, the layout of the converter is even more critical. Poorly designed switching regulators can increase the noise floor and generate unwanted electromagnetic compatibility (EMC) issues, which will interfere with the detection of small signals.
Fortunately, we now offer DC/DC switching regulators with integrated inductors, which minimizes these challenges. Inductor integration not only reduces the area of the switching node but also makes optimal layout much easier to achieve. The significantly increased switching frequency of the new DC/DC converters allows for the use of small surface-mount inductors and ceramic capacitors, making them among the smallest form factor options available.
The new LMZM23601 power module integrates a DC/DC converter, inductor, Vcc filter capacitor, and boost capacitor into a single 3mm x 3.8mm x 1.6mm package. This allows it to handle input voltages up to 36V and step down from 15V to 2.5V (with fixed 5V and 3.3V options available), while delivering up to 1A of output current. As shown in Figure 1, a complete 1A solution is achieved with minimal on-board space.
Figure 1: The LMZM23601 solution is suitable for 3.3V to 5V outputs with current up to 1A.
The LMZM23601 is compared with traditional linear regulator solutions to meet the following requirements for field transmitter applications:
Input voltage: 10V to 30V, nominal 24V
Output voltage: 3.3V
Output current: 35mA
Temperature range: Ambient temperature -40°C to 85°C
Board area: 4mm*4.5mm
As shown in Table 1, the LMZM23601 offers advantages in package area and thermal performance compared to the Miniature Small Outline Package (MSOP) 8. Note: The RӨJA values specified in Table 1 are for comparative reference only. In practical sensor applications, these values will be higher due to limited board space and copper busbars. Typical RӨJA values in the datasheets have been calculated by the Joint Electronic Equipment Committee (JEDEC) or the Evaluation Module (EVM). For example, the LMZM23601's RӨJA of 45°C/W is calculated based on a 30mm x 30mm dual-layer circuit board.
Table 1: LMZM23601 and Linear Regulator Design Options Classified by Package Type
As shown in Table 2, the power consumption of the linear regulator is (24V-3.3V) x 35mA, which is approximately 0.93W, while the LMZM23601 consumes only 0.116W. The temperature rise of the MSOP-8 packaged linear regulator causes its junction temperature to exceed the standard integrated circuit (IC) junction temperature of 125°C, while according to 45°C/WRӨJA, the junction temperature of the LMZM23601 is 90°C. Even after multiplying RӨJA by a factor of 5, the maximum value of Tj obtained is still lower than this junction temperature.
Table 2: Thermal considerations for 24V to 3.3V conversion at 35mA
This example clearly demonstrates that, from a thermal perspective, linear regulators are not a viable solution. The trade-offs of using a switching approach (even with modules like the LMZM23601) mean that output ripple must be considered. As shown in Figure 2, the peak-to-peak output ripple of a standard LMZM23601 at a 3.3V input is approximately 3mV.
Figure 2: Output ripple of LMZM23601EVM at 3.3V output
To further reduce output ripple, a two-stage filter can be used, as shown in Figure 3. Figure 4 shows that the peak-to-peak value of the output ripple has been reduced from 3mV to below 1mV.
Figure 3: LMZM23601 with secondary filter
Figure 4: Output voltage ripple of LMZM23601 with secondary filter
For industrial sensors that require compact board space, switching regulators are the only viable option. The LMZM23601 integrated inductor not only offers high performance and a solution size smaller than linear regulators, but also achieves the efficiency of a switching regulator.
