EMC1702 datasheet(23/60 Pages) MICROCHIP

23 / 60 page

EMC1702

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2020 Microchip Technology Inc.

DS20006455A

For a negative voltage the Sense Voltage Registers are read as 96_8h, also ignoring the lower four

bits since they are always zero. To calculate source current the binary value is first converted from

two’s complement by inverting the bits and adding one:

96_8h = 1001_0110_1000b. Inverting equals 0110_1001_0111b (69_7h) and adding one gives

0110_1001_1000b (69_8h).

This results in the same calculated value as in the positive voltage case.

4.1.2

Voltage Measurement

Source voltage is measured on the supply side of the RSENSE resistor (SENSE+) and stored as an

unsigned 11-bit number in the Source Voltage Registers as VSOURCE (see Section 5.23).

Each VSOURCE measurement is averaged over a user programmable time (see Section 5.6 and

Section 5.19). The measurement is delayed by the programmed conversion rate. VSOURCE is

compared against programmable high, low, and critical limits (see Section 5.15, Section 5.16, and

Section 5.17). If the value meets or exceeds the high limits or drops below the low limits, the ALERT

pin may be asserted (default is to enable this function). If the value meets or exceeds the critical limit,

the THERM pin will be asserted (see Section 5.27).

Full Scale Voltage (FSV) is given by the maximum value of the Source Voltage Registers:

Actual source voltage at the SENSE+ pin can be calculated using:

For example: Suppose that the actual source voltage is 10.65V. The Source Voltage Registers are read

as VSOURCE = 71_Ah (0111_0001_1010b or 1818d) which is 44.4% of the full scale source voltage.

This results in a calculated source voltage of 10.65V using Equation [4].

Note that the actual source voltage may also be determined by scaling each bit set by the indicated

bit weighting as described in Section 5.23.

4.1.3

Power Calculation

The EMC1702 may be used to determine the average power provided at the source side of RSENSE

(SENSE+) using the value, PRATIO, contained in the Power Ratio Registers (see Section 5.24). The

value represents the % of maximum calculable power.

PRATIO is mathematically generated by multiplying the absolute values of VSENSE and VSOURCE (see

Section 4.1.1 and Section 4.1.2) and stored as a shifted 16-bit unsigned number. PRATIO is updated

whenever either VSENSE or VSOURCE is updated.

where:

[3]

FSV is the Full-Scale Voltage (a

constant)

where:

[4]

Source Voltage is the voltage at the

SENSE+ pin

FSV is the Full-Scale Voltage (from

Equation [3])

VSOURCE is the digital value read from

the Source Voltage Registers. Note that

the lowest five bits are always zero (see

Section 5.23)

FSV

23.9883V

Source Voltage

FSV

VSOURCE

4 094

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