ISL6327A Datasheet, PDF (21/29 Pages) Intersil Corporation – Enhanced 6-Phase PWM Controller with 8-Bit VID Code and Differential Inductor DCR or Resistor Current Sensing

ISL6327A
The diagram of thermal monitoring function block is shown in
Figure 12. One NTC resistor should be placed close to the
power stage of the voltage regulator to sense the operational
temperature, and one pull-up resistor is needed to form the
voltage divider for TM pin. As the temperature of the power
stage increases, the resistance of the NTC will reduce,
resulting in the reduced voltage at TM pin. Figure 13 shows
the TM voltage over the temperature for a typical design with
a recommended 6.8kΩ NTC (P/N: NTHS0805N02N6801
from Vishay) and 1kΩ resistor RTM1. We recommend using
those resistors for the accurate temperature compensation.
There are two comparators with hysteresis to compare the
TM pin voltage to the fixed thresholds for VR_FAN and
VR_HOT signals respectively. VR_FAN signal is set to high
when TM voltage is lower than 33% of VCC voltage, and is
pulled to GND when TM voltage increases to above 39% of
V_CC voltage. VR_HOT is set to high when TM voltage goes
below 28% of VCC voltage, and is pulled to GND when TM
voltage goes back to above 33% of VCC voltage. Figure 14
shows the operation of those signals.
VCC
+
-
VR_FAN
R_TM1
TM
C
R_NTC
0.33*VCC
+
-
0.28*VCC
VR_HOT
FIGURE 12. BLOCK DIAGRAM OF THERMAL MONITORING
FUNCTION
100
90
80
70
60
50
40
30
20
0
20 40 60 80 100 120 140
TEMPERATURE (°C)
FIGURE 13. THE RATIO OF TM VOLTAGE TO NTC
TEMPERATURE WITH RECOMMENDED PARTS
TM
0.39*VCC
0.33*VCC
0.28*VCC
VR_FAN
VR_HOT
TEMPERATURE
T1 T2 T3
FIGURE 14. VR_HOT AND VR_FAN SIGNAL vs TM VOLTAGE
Based on the NTC temperature characteristics and the
desired threshold of VR_HOT signal, the pull-up resistor
RTM1 of TM pin is given by Equation 16:
R_TM1 = 2.75xR_NTC(T3)
(EQ. 16)
R_NTC(T3) is the NTC resistance at the VR_HOT threshold
temperature T3.
The NTC resistance at the set point T2 and release point T1 of
VR_FAN signal can be calculated using Equations 17 and 18:
R_NTC(T2) = 1.267xR_NTC(T3)
(EQ. 17)
R_NTC(T1) = 1.644xR_NTC(T3)
(EQ. 18)
With the NTC resistance value obtained from Equations 17
and 18, the temperature value T2 and T1 can be found from
the NTC datasheet.
Temperature Compensation
ISL6327A supports inductor DCR sensing, or resistive
sensing techniques. The inductor DCR have the positive
temperature coefficient, which is about +0.38%/°C. Because
the voltage across inductor is sensed for the output current
information, the sensed current has the same positive
temperature coefficient as the inductor DCR.
In order to obtain the correct current information, there
should be a way to correct the temperature impact on the
current sense component. ISL6327A provides two methods:
integrated temperature compensation and external
temperature compensation.
Integrated Temperature Compensation
When TCOMP voltage is equal or greater than VCC/15,
ISL6327A will utilize the voltage at TM and TCOMP pins to
compensate the temperature impact on the sensed current.
The block diagram of this function is shown in Figure 15.
21
FN6833.0
February 17, 2009