ISL68134_16 Datasheet, PDF (14/50 Pages) Intersil Corporation – Digital Dual Output, 7-Phase Configurable PWM

ISL68134
I_OUT
V_OUT
FIGURE 11. DESIRED LOAD TRANSIENT RESPONSE WAVEFORMS
I_OUT
V_OUT
FIGURE 12. LOAD TRANSIENT RESPONSE WHEN R-C TIME
CONSTANT IS TOO SMALL
I_OUT
V_OUT
FIGURE 13. LOAD TRANSIENT RESPONSE WHEN R-C TIME
CONSTANT IS TOO LARGE
SPS CURRENT SENSING
SPS current sense is accomplished by sensing each SPS IMON
output individually using VCCS as a common reference. Connect
all SPS IREF input pins and all ISL68134 CSRTNn input pins
together and tie them to VCCS, then connect the SPS IMONn
output pins to the corresponding ISL68134 CSn input pins. The
signals should be run as differential pairs from the SPS back to
the ISL68134.
Temperature Sensing
The ISL68134 supports temperature sensing via BJT or smart
power stage sense elements. Support for BJT sense elements
utilizes the well known delta Vbe method and allows up to 2
sensors (MMBT3906 or similar) on each temperature sense
input, TMON0 and TMON1. Support for smart power stage
utilizes a linear conversion algorithm and allows 1 sensor
reading per pin. The conversion from voltage to temperature for
smart power stage sensing is user programmable via the
PowerNavigator™ GUI.
SPS temperature sensing measures the temperature dependent
voltage output on the SPS TMON pin. All of the SPS devices
attached to the Output 0 rail have their TMON pins connected to
the ISL68134 TMON0 pin. All of the SPS devices attached to the
Output 1 rail have their TMON pins connected to the ISL68134
TMON1 pin. The reported temperature is that of the highest
temperature SPS of the group.
In addition to the external temperature sense, the IC senses its
own die temperature, which may be monitored via the
PowerNavigator™.
Sensed temperature is utilized in the system for faults, telemetry,
and temperature compensation of sensed current.
Temperature Compensation
The ISL68134 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 ISL68134) 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 ISL68134 supports both corrections.
Figure 14 on page 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). Here, T_DCR = T_ACTUAL
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.
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FN8817.0
September 28, 2016