ISL6334AR5368 Datasheet, PDF (23/31 Pages) Intersil Corporation – VR11.1, 4-Phase PWM Controller with Light Load Efficiency Enhancement and Load Current Monitoring Features

ISL6334AR5368
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.
VCC
VR_FAN
R_TM1
TM
0.391V_CC
VR_HOT
o_c
R
NTC
0.333V_CC
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
0.451*Vcc
0.391*Vcc
0.333*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 the VR_HOT signal, the pull-up resistor
RTM1 of TM pin is given by Equation 18:
R_TM1 = 2.75xR_NTC(T3)
(EQ. 18)
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 as shown in Equations 19
and 20:
R_NTC(T2) = 1.267xR_NTC(T3)
(EQ. 19)
R_NTC(T1) = 1.644xR_NTC(T3)
(EQ. 20)
With the NTC resistance value obtained from Equations 19
and 20, the temperature value T2 and T1 can be found from
the NTC datasheet.
Temperature Compensation
The ISL6334AR5368 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. ISL6334AR5368 provides two
methods: integrated temperature compensation and external
temperature compensation.
Integrated Temperature Compensation
When the TCOMP voltage is equal or greater than VCC/15,
ISL6334AR5368 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.
23
FN6839.2
September 7, 2010