ISL68137_16 Datasheet, PDF (15/53 Pages) Intersil Corporation – Digital Dual Output, 7-Phase Configurable PWM

ISL68137
V_PHASE
R_{SENSE ESL}
V_OUT
R
ESL
RSENSE
 RC
IC
CSRTNn
C
CSn
CURRENT
SENSE
FIGURE 10. SENSE RESISTOR IN SERIES WITH INDUCTOR
A current sensing resistor has a distributed parasitic inductance,
known as ESL (Equivalent Series Inductance, typically less than
4nH). Consider the ESL as a separate lumped quantity, as shown
in Figure 10. The phase current I_L, flowing through the inductor,
will also pass through the ESL. Similar to DCR sensing described
previously, a simple R-C network across the current sense
resistor extracts the R_SENSE voltage. Simply match the
ESL/R_SENSE time constant to the R-C time constant.
Figure 11 shows the sensed waveforms with and without
matching RC when using resistive sense. PCB layout should be
treated similar to that described for DCR sense.
MATCHED RC
MISMATCHED RC
FIGURE 11. VOLTAGE ACROSS R WITH AND WITHOUT RC
L/DCR OR ESL/R_SEN MATCHING
Assuming the compensator design is correct, Figure 12 shows the
expected load transient response waveforms if L/DCR or
ESL/R_SEN is matching the R-C time constant. When the load
current I_OUT has a square change, the output voltage V_OUT also
has a square response, except for the potential overshoot at load
release. However, there is always some uncertainty in the true
parameter values involved in the time constant matching and
therefore, fine-tuning is generally required.
If the R-C time constant is too large or too small, V_C(t) will not
accurately represent real-time I_OUT(t) and will worsen the
transient response. Figure 13 shows the load transient response
when the R-C timing constant is too small. In this condition, V_OUT
will sag excessively upon load insertion and may create a system
failure or early overcurrent trip. Figure 14 shows the transient
response when the R-C timing constant is too large. V_OUT is
sluggish in drooping to its final value. Use these general guides if
fine-tuning is needed.
I_OUT
V_OUT
FIGURE 12. DESIRED LOAD TRANSIENT RESPONSE WAVEFORMS
I_OUT
V_OUT
FIGURE 13. LOAD TRANSIENT RESPONSE WHEN R-C TIME
CONSTANT IS TOO SMALL
I_OUT
V_OUT
FIGURE 14. 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 ISL68137 CSRTNn input pins
together and tie them to VCCS, then connect the SPS IMONn
output pins to the corresponding ISL68137 CSn input pins. The
signals should be run as differential pairs from the SPS back to
the ISL68137.
Temperature Sensing
The ISL68137 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 two
sensors (MMBT3906 or similar) on each temperature sense
input, TMON0 and TMON1. Support for smart power stage
utilizes a linear conversion algorithm and allows one 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 ISL68137 TMON0 pin. All of the SPS devices attached to the
Output 1 rail have their TMON pins connected to the ISL68137
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 PowerNavigator™.
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FN8757.0
September 27, 2016