isl6307b Intersil Corporation, isl6307b Datasheet - Page 25

• Manufacturer Part Number: isl6307b
• Description: 6-phase Vr11 Pwm Controller With 8-bit Vid Code Capable Of Precision Rds On Or Dcr Differential Current Sensing For Applications In Which Supply Voltage Is Higher Than 5v
• Manufacturer: Intersil Corporation

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
temperature T3.
The NTC resistance at the set point T2 and release point T1
of VR_FAN signal can be calculated as:
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
ISL6307B supports inductor DCR sensing, MOSFET
R
inductor DCR and MSOFET R
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
In order to obtain the correct current information, there
should be a way to correct the temperature impact on the
current sense component. ISL6307B provides two methods:
integrated temperature compensation and external
temperature compensation.
Integrated Temperature Compensation
When TCOMP voltage is equal or greater than Vcc/15,
ISL6307B 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.
R
R
R
NTC(T3)
DS(ON)
TM1
NTC T2
NTC T1
(
(
=
2.75xR
)
)
sensing, or resistive sensing techniques. Both
is the NTC resistance at the VR_HOT threshold
=
=
DS(ON)
1.267xR
1.644xR
NTC T3
.
(
NTC T3
NTC T3
)
(
(
)
)
25
DS(ON)
have the positive
(EQ. 18)
(EQ. 19)
(EQ. 20)
ISL6307B
o
c
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, ISL6307B converts the TM pin
voltage to a 6-bit TM digital signal for temperature
compensation. With the non-linear A/D converter of
ISL6307B, 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 16 and that of
the actual design. According to the Vcc voltage, ISL6307B
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
between the NTC temperature and the temperature of the
current sense component.
V
V
CC
CC
FIGURE 18. BLOCK DIAGRAM OF INTEGRATED
R
R
R
R
TCOMP
TM1
NTC
TC2
TC1
TM
Non-linear
TEMPERATURE COMPENSATION
4-bit
A/D
D/A
A/D
k
i
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6
Over current protection
Channel current sense
I
5
Droop, Iout &
I
4
I
3
I
2
March 9, 2006
FN9225.0
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sen6
sen5
sen4
sen3
sen2
sen1