SLUAA12 March 2020 TPS53681
- Selection Considerations for Output Capacitors of Multiphase Voltage Regulators Part 1
3.2.3 Criteria for Loop Saturation
Judgement for loop saturation depends on the relationship of desired slew rate of Isum rising/falling and maximum supported slew rate for Isum rising/falling, under the assumption of unsaturated loop (linear system response).
The maximum desired slew rate of Isum named kde_max, is decided by the nature response of Gii_CL(s) emulated first-order system, while the maximum supported slew rate for Isum named kmax, is decided by controller limitations and circuit parameters together. Upward and downward load step have different kmax value.
Figure 11. Nature Response of Gii_CL(s) Linear System Below tables are used to simply but roughly judge, what status the response should be like, under linear system assumption.
Table 3. Criteria for Slew Rate Relationship
| Condition 1 | Condition 2 | Condition 3 | |
|---|---|---|---|
| t0 | t0<<τ | Somewhere in between | t0>3~5τ |
| Response waveform in Figure 11 | Right | Somewhere in between | Left |
| Desired max slew rate: kde_max | A/τ | Somewhere in between | k |
Table 4. Criteria for Loop Saturation
| Slew Rate Comparison | Loop Status |
|---|---|
| kmax>kde_max | Unsaturated |
| kmax<kde_max | Partially or fully saturated |