Power Tree Planner

Budget input current, regulator losses and output ratings across cascaded supply rails. Record required power-up dependencies before finishing the schematic.

Method, formulas and references

Method

Each load contributes its normal and peak current to its chosen supply. For every regulator, output current is the sum of directly connected loads and the input currents of regulators supplied by that rail. Calculation proceeds from the downstream rails back to the source.

For a buck or boost regulator, Pout = Vout Iout, Pin = Pout / η, Iin = Pin / Vin, and estimated loss = Pin − Pout. Enter efficiency from the device's data at the relevant voltage and load; a single value is only an estimate across operating conditions. Switching-regulator idle current at zero load is not modelled.

For an LDO, Iin ≈ Iout + IQ and estimated loss = Vin Iin − Vout Iout. The planner checks Vin ≥ Vout + the entered dropout requirement. Use worst-case datasheet values for dropout and IQ where appropriate.

The peak budget adds all entered peak currents simultaneously; it does not model transient startup, inrush, switching ripple, current-limit behaviour, or output-voltage tolerance. Power-up dependencies are ordering requirements only, and do not calculate time delays or power-down order. Confirm the actual device data and circuit implementation.

References

  1. Texas Instruments, Power-supply features and sequencing, enable, power-good and soft-start behaviour.
  2. Texas Instruments TIDA-01568, 5-rail power sequencing reference design, example of multi-rail power-tree and startup design.

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