ISL68137_16 Datasheet, PDF (16/53 Pages) Intersil Corporation – Digital Dual Output, 7-Phase Configurable PWM

ISL68137
Sensed temperature is utilized in the system for faults, telemetry
and temperature compensation of sensed current.
Temperature Compensation
The ISL68137 supports inductor DCR sensing, which generally
requires temperature compensation due to the copper wire used
to form inductors. Copper has a positive temperature coefficient
of approximately 0.39%/°C. Since the voltage across the
inductor is sensed for the output current information, the sensed
current has the same positive temperature coefficient as the
inductor DCR.
Compensating current sense for temperature variation generally
requires that the current sensing element temperature and its
temperature coefficient is known. While temperature coefficient
is generally obtained easily, actual current sense element
temperature is essentially impossible to measure directly.
Instead, a temperature sensor (a BJT for the ISL68137) placed
near the inductors is measured and the current sense element
(DCR) temperature is calculated from that measurement.
Calculating current sense element temperature is equivalent to
applying gain and offset corrections to the temperature sensor
measurement and the ISL68137 supports both corrections.
Figure 15 depicts the block diagram of temperature
compensation. A BJT placed near the inductors used for DCR
sensing is monitored by the IC utilizing the well known delta Vbe
method of temperature sensing. T_SENSE is the direct measured
temperature of the BJT. Because the BJT is not directly sensing
DCR, corrections must be made such that T_DCR reflects the true
DCR temperature. Corrections are applied according to the
relationship shown in Equation 1, where k_SLOPE represents a
gain scaling and T_OFFSET represents an offset correction. These
parameters are provided by the designer via the
PowerNavigator™ GUI:
T_DCR = k_SLOPE  T_SENSE + T_OFFSET
(EQ. 1)
Once T_DCR has been determined, the compensated DCR value
may be determined according to Equation 2, where DCR₂₅ is the
DCR at +25°C and T_C is the temperature coefficient of copper
(3900 ppm/°C). T_DCR = T_ACTUAL here:
DCR_CORR = DCR₂₅  1 + T_C  T_ACTUAL – 25
(EQ. 2)
Thus, the temperature compensated DCR is now used to
determine the actual value of current in the DCR sense element.
IPHASE#
DCR
V_OUT
CSRTNx
CURRENT
SENSE
CSx
TEMPERATURE
COMPENSATION
DCR_CORR
IPHASE#
TMONx
Vbe
VCCS
IC
T_C
k_SLOPE
T_OFFSET
T_SENSE ^{TO TELEMETRY}
FIGURE 15. BLOCK DIAGRAM OF TEMPERATURE COMPENSATION
In the physical PCB design, the temperature sense diode (BJT) is
placed close to the inductor of the phase that is never dropped
during automatic phase drop operation. Additionally, a filter
capacitor no larger than 500pF should be added near the IC
between each TMON pin and VCCS. This is shown in Figure 16.
TMON1
IC
VCCS
TMON0
OPTIONAL AUXILIARY
TEMPERATURE SENSE
SW1
L1
SW5 SW6
L5
L6
OUT1
OPTIONAL AUXILIARY
TEMPERATURE SENSE
SW0
L0
OUT0
FIGURE 16. RECOMMENDED PLACEMENT OF BJT
Lossless Input Current and Power Sensing
Input current telemetry is provided via an input current
synthesizer. By utilizing the IC’s ability to precisely determine its
operational conditions, input current can be synthesized to a high
degree of accuracy without the need for a lossy sense resistor.
Fine-tuning of offset and gain are provided for in the GUI. Note
that input current sense fine-tuning must be done after output
current sense setup is finalized. With a precise knowledge of
input current and voltage, input power may be computed.
Input current and power telemetry is accessed via a PMBus and
easily monitored in the PowerNavigator™ GUI. V_IN is monitored
directly by the VINSEN pin through a 1:5 resistor divider as shown
in Figure 17.
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September 27, 2016