ISL6334A_14 Datasheet, PDF (24/31 Pages) Intersil Corporation – VR11.1, 4-Phase PWM Controller with Light Load Efficiency Enhancement and Load Current Monitoring Features

ISL6334, ISL6334A
The NTC resistance at the set point T2 and release point T1 of
VR_FAN signal can be calculated as shown in Equations 19
and 20:
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
The ISL6334, ISL6334A supports inductor DCR sensing, or
resistive sensing techniques. The inductor DCR has a
positive temperature coefficient, which is about +0.385%/°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. ISL6334, ISL6334A provides two
methods: integrated temperature compensation and external
temperature compensation.
Integrated Temperature Compensation
When the TCOMP voltage is equal or greater than VCC/15,
ISL6334, ISL6334A 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
R
NTC
V_CC
R
TC1
TCOMP
R
TC2
NON-LINEAR
A/D
CHANNEL
CURRENT
SENSE
I₄
I₃
I₂
I_sen4
I_sen3
I_sen2
I_sen1
I₁
D/A
k_i
4-BIT
A/D
DROOP AND
OVERCURRENT
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, ISL6334, ISL6334A converts the TM
pin voltage to a 6-bit TM digital signal for temperature
compensation. With the non-linear A/D converter of
ISL6334, ISL6334A, 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 13.
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
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, ISL6334, ISL6334A converts the TCOMP pin
voltage to a 4-bit TCOMP digital signal as TCOMP factor N.
The 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.
ISL6334, ISL6334A 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 the 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 or MOSFET) and the voltage at TM and VCC
pins.
4. Use Equation 21 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)
5. Use Equation 22 to calculate the TCOMP factor N:
N
=
2----0---9----x---(_{---T----C----S----C-----}–_{-----T----N----T---C-----})
3xT_NTC + 400
+
4
(EQ. 22)
24
FN6482.2
February 1, 2013