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TPS40090 / TPS40091: What is the relationship between the SYNC frequency and the PWM switching frequency?
What is the relationship between the frequency applied to the EN/SYNC pin and the frequency generated at the PWM outputs?
Peter James Miller
Power Management - DC/DC Solutions - Industrial & Communications DC Solutions
Member Group Technical Staff 2008
The TPS40090 controller's internal synchronization circuit uses an internal divide by 2 synchronization circuit to produce a 50% duty cycle SYNC signal and then multiplexes this signal to the PWM outputs.
In 2-phase or 4-phase modes, the PWM output frequency is 1/4 of this divided signal (4-phase multiplexed) generating a 1/8 switching frequency at the PWM output.
In 3-phase mode, the internal frequency is multiplexed over 3 channels to generare a 1/6 switching frequency at the PWM output.
The TPS40130, TPS40131, TPS40132, TPS40140 and TPS40180 use similar clocking schemes, producing the same divide by 8 or divide by 6 relationship between their SYNC or CLKIO inputs and their switching outputs.
Two TPS40090/91 controllers using a 180 degree out of phase 50% duty cycle SYNC pulse train will synchronize 45 degrees out of phase at 1/8 the switching frequency. It is not possible to synchronize two 2-phase TPS40090/91s 90 degrees out of phase (They will be randomly 0 or 90 degrees out of phase, depending on the divide by 2 state at start-up)
Also Note: Since the TPS40130/131/132 uses the same divide by 8 scheme is also used for the TPS40130/131/132, it is not possible to synchronize two TPS40130/131/132 controllers 90 degrees out of phase.
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