EMC1701 datasheet(21/54 Pages) SMSC

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High-Side Current-Sense and Internal 1°C Temperature Monitor

Datasheet

SMSC EMC1701

Revision 1.2 (09-27-10)

DATASHEET

4.1

Source Monitoring

The EMC1701 includes circuitry for both source current sensing and source voltage measurement.

From these measurements, a ratiometric value corresponding to the power delivered at the SENSE+

pin is provided.

4.1.1

Current Measurement

The EMC1701 includes a high-side current sensing circuit. This circuit measures the voltage, VSENSE,

induced across a fixed external current sense resistor, RSENSE, and stores a representative voltage as

a signed 11-bit number in the Sense Voltage Registers (see Section 5.18).

This circuitry is able to measure the direction of current flow (from SENSE+ to SENSE- or from

SENSE- to SENSE+). Current flowing from SENSE+ to SENSE- is defined as positive current. Current

flowing from SENSE- to SENSE+ is defined as negative.

The EMC1701 contains user programmable bipolar Full Scale Sense Ranges (FSSR) of ±10mV,

±20mV, ±40mV, or ±80mV (see Section 5.16). The default for this setting is ±80mV.

Each VSENSE measurement is averaged over a user programmable time (see Section 5.16). It is

compared against programmable high and low limits (see Section 5.21). If VSENSE exceeds (or drops

below) the respective limits, the ALERT pin may be asserted (the default operation is to enable current

sense interrupts on the ALERT pin).

The EMC1701 also contains user programmable current peak detection circuitry (see Section 4.1.4)

that will assert the THERM pin if a current spike is detected larger than the programmed threshold and

of longer duration than the programmed time. This circuitry is independent of VSENSE.

Full Scale Current (FSC) can be calculated from:

Actual source current through RSENSE can then be calculated using:

For example: Suppose the system is drawing 1.65A through a 10m

Ω resistor and the FSR is set for

20mV. Therefore, by Equation [1], the FSC is 2A.

For a positive voltage the Sense Voltage Registers are read, ignoring the lower four bits since they are

always zero, as 69_8h (0110_1001_1000b or 1688d) which is 82.5% of the full scale source current.

This results in a calculated source current of 1.649A using Equation [2].

where:

[1]

FSC is the Full-Scale Current

FSR, the Full Scale Range, is either

10mV, 20mV, 40mV or 80mV (see

Section 5.16)

RSENSE is the external sense resistor

value

where:

[2]

ISOURCE is the actual source current

FSC is the Full-Scale Current value

(from Equation [1])

VSENSE is the value read from the Sense

Voltage Registers, ignoring the four

lowest bits which are always zero (see

Section 5.18)

FSC

FSR

SENSE

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

SOURCE

FSC

SENSE

2 047

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