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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:

Set the ABECON<RECIREN> bit to enable the

measurement circuitry.

Clear the ABECON<MEASEN> bit.

With the ADC, read the RELEFF channel and

store this reading as the High.

With the ADC, read the VZC channel and store

this reading as the Low.

Set the ABECON<MEASEN> bit to initiate a

measurement cycle.

Monitor the RELEFF<MSDONE> bit. When set,

it indicates the measurement is complete.

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.

Read the value of the RE<6:0> bits in the

RELEFF register and store the reading as

Whole.

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



--------------------------------------------------------------------------------

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 =

RELEFF: RELATIVE EFFICIENCY MEASUREMENT REGISTER

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

= Relative efficiency measurement is complete

= Relative efficiency measurement is not complete

bit 6-0

RE<6:0>: Whole clock counts for relative efficiency measurement result

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