EMC1702 Datasheet, PDF (21/57 Pages) SMSC Corporation – High-Side Current-Sense and Dual 1°C Temperature Monitor

High-Side Current-Sense and Dual 1°C Temperature Monitor
Datasheet
4.1 Source Monitoring
The EMC1702 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 EMC1702 includes a high-side current sensing circuit. This circuit measures the voltage, V_SENSE,
induced across a fixed external current sense resistor, R_SENSE, and stores a representative voltage as
a signed 11-bit number in the Sense Voltage Registers (see Section 5.22).
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 EMC1702 contains user programmable bipolar Full Scale Sense Ranges (FSSR) of ±10mV,
±20mV, ±40mV, or ±80mV (see Section 5.20). The default for this setting is ±80mV.
Each V_SENSE measurement is averaged over a user programmable time (see Section 5.20). It is
compared against programmable high and low limits (see Section 5.25). If V_SENSE 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 EMC1702 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 V_SENSE.
Full Scale Current (FSC) can be calculated from:
FSC
=
-----^F----^S----^R--------
R_SENSE
where:
FSC is the Full-Scale Current
FSR, the Full Scale Range, is either
10mV, 20mV, 40mV or 80mV (see
[1]
Section 5.20)
R_SENSE is the external sense resistor
value
Actual source current through R_SENSE can then be calculated using:
I_SOURCE =
FSC
×
-^V----^S---^E----^N---^S----^E-
2, 047
where:
I_SOURCE is the actual source current
FSC is the Full-Scale Current value
(from Equation [1])
[2]
V_SENSE is the value read from the Sense
Voltage Registers, ignoring the four
lowest bits which are always zero (see
Section 5.22)
For example: Suppose the system is drawing 1.65A through a 10mΩ 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].
SMSC EMC1702
21
DATASHEET
Revision 1.2 (09-27-10)