Power Distribution Module (PDMs) Design Guide 5-5-17 – Introduction Designing with Cobham PDMs is extremely quick and easy once you learn the basics. The interchangeable modular approach to power system design reduces NRE costs and schedule, with greater flexibility later in your program when requirement changes can be the most impactful. This design guide teaches you the all the basics you will need, from architecting your power system, how to analyze your system AC and DC performance, as well as designing EMI filtering for PDMs. Table 1 shows you the Cobham offering of PDM modules. TABLE 1: Cobham PDM Products Figure 1: Basic IRM and iPOL Connections System Architecture When designing with PDMs, it is assumed that the following requirements are known: Input voltage range, required output voltages and tolerances, and load currents (at least a maximum). Other requirements that may influence the architecture are: specific efficiency requirements, unusual transient requirements, and sequencing requirements. The simplest design approach is to use a single IRM and a single iPOL to produce each voltage required. For each output voltage required, select an iPOL using the following the equation: Vib = Vout / K; Where Vib is the intermediate bus voltage which is the output voltage of the IRM, Vout is the required voltage and K is the K factor of iPOL. Note: Vib needs to be between 26 and 48V for proper use of the IRM. See Table 2 for a list of common user voltages and the K factors that produce the Vib within the IRM output voltage range. Once the iPOL is chosen only two resistor values need to be calculated, ROS and Rg. The equation for ROS is found in the IRM datasheet and the calculation for Rg is found in anpdm100 (Note: The values of RAL1 and RAL2 are found in anpdm100 as well). Finally, choose your IRM based on your input voltage range. The values of ROS and Rg remain the same for each of the IRMs. At this point, the calculations for the design of a DC-DC converter are complete.
Power Distribution Module (PDMs) Design Guide – 5-5-17 Introduction Designing with Cobham PDMs is extremely quick and easy once you learn the basics. The interchangeable modular approach to power system design reduces NRE costs and schedule, with greater flexibility later in your program when requirement changes can be the most impactful. This design guide teaches you the all the basics you will need, from architecting your power system, how to analyze your system AC and DC performance, as well as designing EMI filtering for PDMs. Table 1 shows you the Cobham offering of PDM modules. TABLE 1: Cobham PDM Products Figure 1: Basic IRM and iPOL Connections System Architecture When designing with PDMs, it is assumed that the following requirements are known: Input voltage range, required output voltages and tolerances, and load currents (at least a maximum). Other requirements that may influence the architecture are: specific efficiency requirements, unusual transient requirements, and sequencing requirements. The simplest design approach is to use a single IRM and a single iPOL to produce each voltage required. For each output voltage required, select an iPOL using the following the equation: Vib = Vout / K; Where Vib is the intermediate bus voltage which is the output voltage of the IRM, Vout is the required voltage and K is the K factor of iPOL. Note: Vib needs to be between 26 and 48V for proper use of the IRM. See Table 2 for a list of common user voltages and the K factors that produce the Vib within the IRM output voltage range. Once the iPOL is chosen only two resistor values need to be calculated, ROS and Rg. The equation for ROS is found in the IRM datasheet and the calculation for Rg is found in anpdm100 (Note: The values of RAL1 and RAL2 are found in anpdm100 as well). Finally, choose your IRM based on your input voltage range. The values of ROS and Rg remain the same for each of the IRMs. At this point, the calculations for the design of a DC-DC converter are complete.
PDM_Design_Guide_and_Worst_Case_Volt_Reg_Spreadsheet.docx