Cirrus Logic AN368 - Manual (Page 22)

AN368
22 AN368REV2
g. Automated Resonant Period Measurements
To ensure accuracy of the T2 duration measurements within the CS1630 controller, the resonant period T
RES
of the power train can be automatically measured during the T3 time (secondary current equals zero) of the
switching cycle. To enable the automated resonant period measurement, set the PROBE bit within register
Config7 at Address 39 to a value of ‘1’. To measure the resonant period, the controller forces DCM operation
at selected multiples of TT and measures the duration between the first and second zero-crossing detections.
The frequency of the automated resonant period measurements is configurable through the PRCNT[3:0] bits
in register Config7 at Address 39. The number of channel 1 switching cycles TT
Cycles
between resonant period
measurements is set by Equation 42.
To force a resonant period measurement every 47 switching cycles, TT
Cycles
, a value of 2 is programmed into
the PRCNT[3:0] bits.
If the automated resonant period measurement is not desired, the controller supports the option to manually
program the resonant period. In this case, the PROBE bit is disabled with a value of ‘0’, and the value of one-
quarter of the resonant period T
RES
is programmed using the PRCNT[3:0] bits in Equation 43.
If the resonant period T
RES
is 800ns, a value of ‘2’ is programmed into bits PRCNT[3:0].
T
RES
Figure 6. Waveforms of the Resonant Frequency
[Eq. 42] TT
Cycles
16 P  RCNT[3:0]   15 + =
[Eq. 43]
T
RES
4
--------------- 2 PRCNT[3:0] 50ns   =