ISL6327 Datasheet, PDF (22/30 Pages) Intersil Corporation – Enhanced 6-Phase PWM Controller with 8-Bit VID Code and Differential Inductor DCR or Resistor Current Sensing

ISL6327
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
and 20, the temperature value T2 and T1 can be found from
the NTC datasheet.
Temperature Compensation
ISL6327 supports inductor DCR sensing, or resistive
sensing techniques. The inductor DCR have the positive
temperature coefficient, which is about +0.38%/°C. Because
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. ISL6327 provides two methods:
integrated temperature compensation and external
temperature compensation.
Integrated Temperature Compensation
When TCOMP voltage is equal or greater than Vcc/15,
ISL6327 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.
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 15. 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, ISL6327 converts the TM pin voltage
to a 6-bit TM digital signal for temperature compensation.
With the non-linear A/D converter of ISL6327, 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 13.
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 14 and that of
the actual design. According to the VCC voltage, ISL6327
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.
ISL6327 multiplexes the TCOMP factor N with the TM digital
signal to obtain the adjustment gain to compensate the
temperature impact on the sensed channel current. The
compensated channel current signal is used for droop and
overcurrent protection functions.
Design Procedure
1. Properly choose the voltage divider for TM pin to match
the TM voltage vs. temperature curve with the
recommended curve in Figure 13.
2. Run the actual board under the full load and the desired
cooling condition.
3. After the board reaches the thermal steady state, record
the temperature (T_CSC) of the current sense component
(inductor) and the voltage at TM and VCC pins.
4. Use the following equation to calculate the resistance of
the TM NTC, and find out the corresponding NTC
temperature T_NTC from the NTC datasheet.
R_NTC(TNTC)
=
V-----_{T---M-----x----R----T----M-----1-}
V_CC – V_TM
(EQ. 21)
22
FN9276.2
December 20, 2006