EMC1701 Datasheet, PDF (23/54 Pages) SMSC Corporation – High-Side Current-Sense and Internal 1°C Temperature Monitor

High-Side Current-Sense and Internal 1°C Temperature Monitor
Datasheet
Full Scale Power can be calculated from:
FSP = FSC × FSV
where:
FSP is the Full-Scale Power
FSC is the Full-Scale Current (from
[5]
Equation [1])
FSV is the Full-Scale Voltage (from
Equation [3])
Actual power drawn from the source can be calculated using:
where:
P_SOURCE is the actual power
provided by the source
P_SOURCE =
FSP
×
-^P----^R---^A----^T---^I--^O--
65, 535
measured at SENSE+
FSP is the Full-Scale Power
[6]
(from Equation [5])
P_RATIO is the value read from
the Power Ratio Registers
(see Section 5.20)
For example: Suppose that the actual source voltage is 10.65V and the source current through a 10mΩ
resistor is 1.65A. The FSC value is 2A per Equation [1]; thus, the expected power is 17.573W which
is 36.6% of the FSP value.
Reading the Power Ratio Registers will report P_RATIO as 24,003d (0101_1101_1100_0011b or
5D_C3h), which is 36.6% of the full scale source power. This results in a calculated source power of
17.6W.
4.1.4 Current Peak Detection
The EMC1701-1 includes a hardware set instantaneous current peak detector (this circuitry is also
available in the EMC1701-2 but must be configured via SMBus). The peak detector threshold and
duration values may also be set via the SMBus.
The peak detector supports detection of current spikes that occur faster than the minimum current
sensing conversion time. This allows quick reaction to events requiring system-level response. The
circuitry compares the measured current against a user-defined threshold value and user-defined time
duration. If the measured current exceeds the threshold, an internal timer is started. If the timer
reaches the programmed duration, the THERM pin is asserted (see Figure 4.2 for an example of peak
current detection) and the PEAK status bit set.
The THERM pin will remain asserted until the Peak is no longer detected at which point it will be
released. The PEAK status bit will likewise be cleared.
The Peak Detection circuitry may also assert the ALERT pin. In this case, the ALERT pin must be
configured to operate in Comparator mode. If the ALERT pin is configured to operate in Interrupt mode,
the Peak Detection circuitry will not cause the ALERT pin to be asserted.
The Peak Detection circuitry includes filtering (t_FILTER). When the instantaneous current exceeds the
threshold, it must drop below the threshold for a period of time greater than t_FILTER before the timer is
reset. The Peak Detection circuitry works for current flowing in either direction through the sense
resistor (R_SENSE).
APPLICATION NOTE: The Peak Detector circuitry works independently of the current measurement integration.
SMSC EMC1701
23
DATASHEET
Revision 1.2 (09-27-10)