isl6334d Intersil Corporation, isl6334d Datasheet - Page 20

• Manufacturer Part Number: isl6334d
• Description: Vr11.1, 4-phase Pwm Controller With Phase Dropping, Droop Disabled And Load Current Monitoring Features
• Manufacturer: Intersil Corporation

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. The VR_FAN signal is set to
high when the TM voltage is lower than 39.1% of VCC
voltage, and is pulled to GND when the TM voltage
increases to above 45.1% of VCC voltage. The VR_FAN
signal is set to high when the TM voltage goes below 33.3%
of VCC voltage, and is pulled to GND when the TM voltage
goes back to above 39.1% of VCC voltage. Figure 14 shows
the operation of those signals.
FIGURE 12. BLOCK DIAGRAM OF THERMAL MONITORING
FIGURE 13. THE RATIO OF TM VOLTAGE TO NTC
°
C
100
90
80
70
60
50
40
30
20
VCC
R
R
TM
TM1
0
NTC
FUNCTION
TEMPERATURE WITH RECOMMENDED PARTS
20
0.391V
0.333V
40
TEMPERATURE (°C)
CC
CC
60
20
80
100
120
VR_FAN
VR_HOT
140
ISL6334D
Based on the NTC temperature characteristics and the
desired threshold of the VR_HOT signal, the pull-up resistor
RTM1 of TM pin is given by Equation 15:
R
temperature T3.
The NTC resistance at the set point T2 and release point T1 of
VR_FAN signal can be calculated as shown in Equations 16
and 17:
With the NTC resistance value obtained from Equations 16
and 17, the temperature value T2 and T1 can be found from
the NTC datasheet.
Temperature Compensation
The ISL6334D supports inductor DCR sensing, or resistive
sensing techniques. The inductor DCR has a positive
temperature coefficient, which is about +0.385%/°C. Since
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. ISL6334D provides two methods:
integrated temperature compensation and external
temperature compensation.
R
R
R
FIGURE 14. VR_HOT AND VR_FAN SIGNAL vs TM VOLTAGE
NTC(T3)
TM1
NTC T2
NTC T1
0.451*Vcc
0.391*Vcc
VR_FAN
VR_HOT
0.333*Vcc
TM
(
(
=
2.75xR
)
)
is the NTC resistance at the VR_HOT threshold
=
=
1.267xR
1.644xR
NTC T3
(
NTC T3
NTC T3
)
(
(
T1
)
)
T2
T3
TEMPERATURE
October 29, 2008
(EQ. 15)
(EQ. 16)
(EQ. 17)
FN6802.0