ISL6326 Datasheet, PDF (22/30 Pages) Intersil Corporation – 4-Phase PWM Controller with 8-Bit DAC Code Capable of Precision rDS ON or DCR Differential Current Sensing

ISL6326
V_TM/V_CC vs TEMPERATURE
100
90
80
70
60
50
40
30
20
0
20 40 60 80 100 120 140
TEMPERATURE (°C)
FIGURE 12. THE RATIO OF TM VOLTAGE TO NTC
TEMPERATURE WITH RECOMMENDED PARTS
TM
0.39*V_CC
0.33*V_CC
0.28*V_CC
VR_FAN
VR_HOT
TEMPERATURE
T1 T2 T3
FIGURE 13. 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
R_TM1 of TM pin is given by Equation 17:
R_TM1 = 2.75xR_NTC(T3)
(EQ. 17)
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 in Equations 18 and 19:
R_NTC(T2) = 1.267xR_NTC(T3)
(EQ. 18)
R_NTC(T1) = 1.644xR_NTC(T3)
(EQ. 19)
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
ISL6326 supports inductor DCR sensing, or resistive
sensing techniques. The inductor DCR has a positive
temperature coefficient, which is about +0.38%/°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. ISL6326 provides two methods:
1. Integrated temperature compensation
2. External temperature compensation
Integrated Temperature Compensation
When the TCOMP voltage is equal or greater than VCC/15,
ISL6326 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 14.
V_CC
R_TM1
TM
°C _RNTC
V_CC
NON-LINEAR
A/D
CHANNEL CURRENT
SENSE
I4
I3
I2
I1
ISEN4
ISEN3
ISEN2
ISEN1
D/A
ki
R_TC1
TCOMP
R_TC2
4-BIT
A/D
DROOP AND
OVERCURRENT PROTECTION
FIGURE 14. BLOCK DIAGRAM OF INTEGRATED
TEMPERATURE COMPENSATION
When the TM NTC is placed close to the current sense
component (inductor), the temperature of the NTC will track
the temperature of the current sense component. Therefore
the TM voltage can be utilized to obtain the temperature of
the current sense component.
Based on VCC voltage, ISL6326 converts the TM pin voltage
to a 6-bit TM digital signal for temperature compensation.
With the non-linear A/D converter of ISL6326, the TM digital
signal is linearly proportional to the NTC temperature. For
accurate temperature compensation, the ratio of the TM
voltage to the NTC temperature of the practical design
should be similar to that in Figure 12.
Depending on the location of the NTC and the airflow, the
NTC may be cooler or hotter than the current sense
component. The TCOMP pin voltage can be utilized to
correct the temperature difference between NTC and the
current sense component. When a different NTC type or
different voltage divider is used for the TM function, the
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FN9262.1
May 5, 2008