isl6306 Intersil Corporation, isl6306 Datasheet - Page 25

• Manufacturer Part Number: isl6306
• Description: 4-phase Pwm Controller With 8-bit Dac Code Capable Of Precision Rds On Or Dcr Differential Current Sensing
• 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 18 &
19, the temperature value T2 and T1 can be found from the
NTC datasheet.
R
R
R
FIGURE 16. VR_HOT AND VR_FAN SIGNAL vs TM VOLTAGE
NTC(T3)
TM1
NTC T2
NTC T1
FIGURE 15. THE RATIO OF TM VOLTAGE TO NTC
VR_HOT
VR_FAN
0.39*Vcc
0.33*Vcc
0.28*Vcc
100%
90%
80%
70%
60%
50%
40%
30%
20%
(
(
TM
=
2.75xR
)
)
is the NTC resistance at the VR_HOT threshold
0
=
=
1.267xR
1.644xR
TEMPERATURE WITH RECOMMENDED PARTS
NTC T3
20
(
NTC T3
NTC T3
V
)
40
TM
Tem perature (
(
(
/ V
TEMPERATURE (°C)
V
CC
)
)
TM
25
60
T1
vs. Tem perature
/V
CC
T2
vs TE
80
T3
o
C)
100
TEMPERATURE (°C)
Temperature
120
(EQ. 17)
(EQ. 18)
(EQ. 19)
140
ISL6306
o
c
Temperature Compensation
ISL6306 supports inductor DCR sensing, MOSFET r
sensing, or resistive sensing techniques. Both inductor DCR
and MOSFET r
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. ISL6306 provides two methods:
integrated temperature compensation and external
temperature compensation.
Integrated Temperature Compensation
When TCOMP voltage is equal or greater than VCC/15,
ISL6306 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 17.
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, ISL6306 converts the TM pin voltage
to a 6-bit TM digital signal for temperature compensation.
With the non-linear A/D converter of ISL6306, 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 15.
DS(ON)
V
V
FIGURE 17. BLOCK DIAGRAM OF INTEGRATED
CC
CC
R
R
R
R
TCOMP
NTC
TC2
TM1
TC1
.
TM
TEMPERATURE COMPENSATION
DS(ON)
NON-LINEAR
Non-linear
4-BIT
4-bit
A/D
A/D
D/A
A/D
A/D
have the positive temperature
k
i
DROOP AND OVERCURRENT
Over current protection
I
Channel current
4
PROTECTION
CHANNEL
CURRENT
Droop &
sense
SENSE
I
3
I
2
December 8, 2006
DS(ON)
I
1
FN9226.1
I
I
I
I
sen4
sen3
sen2
sen1