ISL6307A Datasheet, PDF (25/33 Pages) Intersil Corporation – Ultra-high bandwidth 6-Phase PWM Controller with 8 Bit VID Code Capable of Precision RDS(ON) or DCR Differential Current Sensing

ISL6307A
TM
0.39*Vcc
0.33*Vcc
0.28*Vcc
VR_FAN
VR_HOT
T1 T2 T3
Temperature
FIGURE 20. VR_HOTAND VR_FAN SIGNAL VS TM VOLTAGE
Based on the NTC temperature characteristics and the
desired threshold of VR_HOT, the pull-up resistor R_TM1 of
the 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 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 T2 and T1 can be found from the NTC
datasheet.
Temperature Compensation
ISL6307A supports inductor DCR sensing, MOSFET
R_DS(ON) sensing, or resistive sensing techniques. Both
inductor DCR and MOSFET R_DS(ON) have positive
temperature coefficient, which is about +0.38%/°C. Because
the voltage across the inductor or MOSFET is sensed for
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. ISL6307A provides two methods:
integrated temperature compensation and external
temperature compensation.
Integrated Temperature Compensation
When TCOMP voltage is equal or greater than Vcc/15,
ISL6307A 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 21.
V_CC
R_TM1
TM
o_{c RNTC}
V_CC
Non-linear
A/D
Channel current sense
I₆ I₅ I₄ I₃ I₂
D/A ^ki
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 21. 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.
ISL6307A converts the TM pin voltage to a 6-bit TM digital
signal for temperature compensation. With the non-linear
A/D converter of ISL6307A, 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 19.
Depending on the location of the NTC and the air flow, the
NTC may be cooler or hotter than the current sense
component. TCOMP 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 20 and that of the
actual design. ISL6307A converts the TCOMP pin voltage to
a 4-bit TCOMP digital signal as the 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 the TCOMP factor N, the larger the
difference between the NTC temperature and the
temperature of the current sense component.
25
FN9236.0
February 6, 2006