JAJSKX2A August 2019 – May 2021 TPS53676
PRODUCTION DATA
In any practical multiphase printed circuit board design, some power stages are physically located near to, or between other phases. Power stages physically located between two other power stages experience mutual heating as a result of power dissipation from adjacent power stages. Hence, even though the controller device regulates the DC current sharing of each phase, the temperature of each power stage may be different.
Optionally, adjust the per-phase current sharing ratio KT for each phase using the ISHARE_CONFIG command. This open-loop adjustment allows the designer to balance the temperature of each phase to compensate for mutual heating and non-uniform ground copper for heat spreading. The per-phase current limit of each phase is not affected by this setting. Refer to the Technical Reference Manual for a register map of ISHARE_CONFIG.
Thermal balancing is accomplished by scaling the gain of each phase current, as provided to the current sharing amplifier, in the on-time generator circuit for each phase. Refer to GUID-12F9C7D9-6273-42FD-BC8D-20C4C43EF14A.html#T5605938-11 for more information. Each phase has an independently programmable gain KT. Current share gain is assigned according to the logical phase number (PHASE setting) for each phase. The current carried by each phase when thermal balancing is active, can be calculated according to #T5743756-15.
First, calculate the effective thermal phase number, NT as shown below. Note this value changes with different numbers of operational phases, when phase shedding is enabled.
where
Then each phase carries a portion of the total current, ISUM, as shown in #T5958955-4.
where
Then, the current sharing ratio, comparing one phase to another is given by #T5958955-5.
where
Example: Balancing phase temperature for 7-phase converter
Consider a 7-phase converter with the following thermal balance gains assigned:
PHASE | Thermal Balance Gain Ki | VALUE | PHASE | Thermal Balance Gain Ki | VALUE | |
---|---|---|---|---|---|---|
Phase 1 | K1 | 0.8 | Phase 5 | K5 | 1.0 | |
Phase 2 | K2 | 0.9 | Phase 6 | K6 | 0.9 | |
Phase 3 | K3 | 1.0 | Phase 7 | K7 | 0.8 | |
Phase 4 | K4 | 1.0 |
Calculate NT according to #T5958955-6.
Phases 1 and 7 have the same thermal balance gain, and carry the same proportion of the total current. Phases 2 and 6 have the same thermal balance gain and carry the same proportion of total current. Similarly, phases 3, 4, and 5 carry the same proportion of total current. #T5958955-7, #T5958955-8, and #T5958955-9 show the expected phase currents as a fraction of the total current ISUM.
The ratios of two phase currents can be easily calculated as shown in #T5958955-10 and #T5958955-11.