ISL6334D_14 Datasheet, PDF (21/28 Pages) Intersil Corporation – VR11.1, 4-Phase PWM Controller with Phase Dropping, Droop Disabled and Load Current Monitoring Features

ISL6334D
TM
0.451*Vcc
0.391*Vcc
0.333*Vcc
VR_FAN
VR_HOT
TEMPERATURE
T1 T2 T3
FIGURE 14. VR_HOT AND VR_FAN SIGNAL vs TM VOLTAGE
Based on the NTC temperature characteristics and the
desired threshold of the VR_HOT signal, the pull-up resistor
RTM1 of TM pin is given by Equation 15:
R_TM1 = 2.75xR_NTC(T3)
(EQ. 15)
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 shown in Equations 16
and 17:
R_NTC(T2) = 1.267xR_NTC(T3)
(EQ. 16)
R_NTC(T1) = 1.644xR_NTC(T3)
(EQ. 17)
With the NTC resistance value obtained from Equations 16
and 17, the temperature value T2 and T1 can be found from
the NTC datasheet.
Temperature Compensation
The ISL6334D 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. The ISL6334D provides two
methods: integrated temperature compensation and external
temperature compensation.
Integrated Temperature Compensation
When the TCOMP voltage is equal or greater than VCC/15,
ISL6334D 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.
21
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
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, the ISL6334D converts the TM pin
voltage to a 6-bit TM digital signal for temperature
compensation. With the non-linear A/D converter of
ISL6334D, 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, ISL6334D 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 is, the larger the difference
between the NTC temperature and the temperature of the
current sense component.
FN6802.3
November 22, 2013