Datasheet

 2013 Microchip Technology Inc. DS22331A-page 65
MCP19111
10.0 RELATIVE EFFICIENCY
MEASUREMENT
With a constant input voltage, output voltage and load
current, any change in the high-side MOSFET on-time
represents a change in the system efficiency. The
MCP19111 is capable of measuring the on-time of the
high-side MOSFET. Therefore, the relative efficiency of
the system can be measured and optimized by
changing the system parameters, such as switching
frequency, driver dead time or high-side drive strength.
10.1 Relative Efficiency Measurement
Procedure
To measure the relative efficiency, the RELEFF regis-
ter, ABECON<MEASEN> and ABECON<RECIREN>
bits, and the ADC RELEFF input are used. The
following steps outlines the measurement process:
1. Set the ABECON<RECIREN> bit to enable the
measurement circuitry.
2. Clear the ABECON<MEASEN> bit.
3. With the ADC, read the RELEFF channel and
store this reading as the High.
4. With the ADC, read the VZC channel and store
this reading as the Low.
5. Set the ABECON<MEASEN> bit to initiate a
measurement cycle.
6. Monitor the RELEFF<MSDONE> bit. When set,
it indicates the measurement is complete.
7. When the measurement is complete, use the ADC
to read the RELEFF channel. This value becomes
the Fractional variable in Equation 10 1. This
reading should be accomplished approximately
50ms after the RELESS<MSDONE> bit is set.
8. Read the value of the RE<6:0> bits in the
RELEFF register and store the reading as
Whole.
9. Clear the ABECON<MEASEN> bit.
10. The relative efficiency is then calculated by the
following equation:
EQUATION 10-1:
Note 1: The RELEFF<MSDONE> bit is set and
cleared automatically.
Whole
Fractional Low–
High Low–
--------------------------------------------------+


PR2 1+
--------------------------------------------------------------------------------
Where:
Whole = Value obtained in Step 8 of the
measurement procedure
Fractional = Value obtained in Step 7 of the
measurement procedure
High = Value obtained in Step 3 of the
measurement procedure
Low = Value obtained in Step 4 of the
measurement procedure
Duty_Cycle =
REGISTER 10-1: RELEFF: RELATIVE EFFICIENCY MEASUREMENT REGISTER
R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0
MSDONE RE6 RE5 RE4 RE3 RE2 RE1 RE0
bit 7 bit 0
Legend:
R = Readable bit P = Programmable bit U = Unimplemented bit, read as ‘0’
-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is cleared x = Bit is unknown
bit 7 MSDONE: Relative efficiency measurement done bit
1 = Relative efficiency measurement is complete
0 = Relative efficiency measurement is not complete
bit 6-0 RE<6:0>: Whole clock counts for relative efficiency measurement result