ISL6334B Datasheet, PDF (23/30 Pages) Intersil Corporation – VR11.1, 4-Phase PWM Controller with Phase Dropping, Droop Disabled and Load Current Monitoring Features

ISL6334B, ISL6334C
100
90
80
70
60
50
40
30
20
0 20 40 60 80 100 120 140
TEMPERATURE (°C)
FIGURE 13. THE RATIO OF TM VOLTAGE TO NTC
TEMPERATURE WITH RECOMMENDED PARTS
We recommend using those resistors for the accurate
temperature compensation.
There is an comparator with hysteresis to compare the TM
pin voltage to the fixed threshold for the VR_HOT signal.
The VR_HOT signal is set to high when the TM voltage goes
below 33.3% of VCC voltage, and is pulled to GND when the
TM voltage goes back to above 39.1% of VCC voltage.
Figure 14 shows the operation of those signals.
TM
0.391*Vcc
0.333*Vcc
VR_HOT
TEMPERATURE
T2 T3
FIGURE 14. VR_HOT 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 18:
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 can be calculated as
shown in Equations 19:
R_NTC(T2) = 1.267xR_NTC(T3)
(EQ. 19)
With the NTC resistance value obtained from Equations 18
and 19, the temperature value T3 and T2 can be found from
the NTC datasheet.
Temperature Compensation
The ISL6334B, ISL6334C 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. ISL6334B, ISL6334C provides
two methods: integrated temperature compensation and
external temperature compensation.
Integrated Temperature Compensation
When the TCOMP voltage is equal or greater than VCC/15,
ISL6334B, ISL6334C 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, ISL6334B, ISL6334C converts the
TM pin voltage to a 6-bit TM digital signal for temperature
compensation. With the non-linear A/D converter of
ISL6334B, ISL6334C, 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.
23
FN6689.2
August 31, 2010