ISL6307 Datasheet, PDF (26/34 Pages) Intersil Corporation – 6-Phase PWM Controller with 8 Bit VID Code Capable of Precision RDS(ON) or DCR Differential Current

ISL6307
TM
0.39*Vcc
0.33*Vcc
0.28*Vcc
VR_FAN
VR_HOT
T1 T2 T3
Temperature
FIGURE 17. VR_HOTAND 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:
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:
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 &
20, the temperature value T2 and T1 can be found from the
NTC datasheet.
Temperature Compensation
ISL6307 supports inductor DCR sensing, MOSFET R_DS(ON)
sensing, or resistive sensing techniques. Both inductor DCR
and MSOFET R_DS(ON) have the positive temperature
coefficient, which is about +0.38%/°C. Because the voltage
across inductor or MOSFET is sensed for the output current
information, the sensed current has the same positive
temperature coefficient as the inductor DCR or MOSFET
R_DS(ON).
In order to obtain the correct current information, there
should be a way to correct the temperature impact on the
current sense component. ISL6307 provides two methods:
integrated temperature compensation and external
temperature compensation.
Integrated Temperature Compensation
When TCOMP voltage is equal or greater than Vcc/15,
ISL6307 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 18.
V_CC
R_TM1
TM
o_{c RNTC}
V_CC
Non-linear
A/D
D/A ^ki
Channel current sense
I₆ I₅ I₄ I₃ I₂
I_sen6
I_sen5
I_sen4
I_sen3
I_sen2
I_sen1
I₁
R_TC1
TCOMP
R_TC2
4-bit
A/D
Droop, Iout &
Over current protection
FIGURE 18. BLOCK DIAGRAM OF INTEGRATED
TEMPERATURE COMPENSATION
When the TM NTC is placed close to the current sense
component (inductor or MOSFET), 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, ISL6307 converts the TM pin voltage
to a 6-bit TM digital signal for temperature compensation.
With the non-linear A/D converter of ISL6307, 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 16.
Depending on the location of the NTC and the air-flowing,
the NTC may be cooler or hotter than the current sense
component. 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, TCOMP voltage
can also be used to compensate for the difference between
the recommended TM voltage curve in Figure 17 and that of
the actual design. According to the Vcc voltage, ISL6307
converts the TCOMP pin voltage to a 4-bit TCOMP digital
signal as TCOMP factor N.
TCOMP factor N is an integer between 0 and 15. The
integrated temperature compensation function is disabled for
N = 0. For N = 4, the NTC temperature is equal to the
temperature of the current sense component. For N < 4, the
NTC is hotter than the current sense component. The NTC is
cooler than the current sense component for N > 4. When
N > 4, the larger TCOMP factor N, the larger the difference
26
FN9224.0
March 9, 2006