isl6334d Intersil Corporation, isl6334d Datasheet - Page 21

• Manufacturer Part Number: isl6334d
• Description: Vr11.1, 4-phase Pwm Controller With Phase Dropping, Droop Disabled And Load Current Monitoring Features
• Manufacturer: Intersil Corporation

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.
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, 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
o
c
FIGURE 15. BLOCK DIAGRAM OF INTEGRATED
V
V
CC
CC
R
R
R
R
TCOMP
NTC
TM1
TC2
TC1
TM
TEMPERATURE COMPENSATION
NON-LINEAR
4-BIT
D/A
A/D
A/D
k
21
i
I
4
OVERCURRENT
PROTECTION
CHANNEL
CURRENT
SENSE
I
3
I
2
I
1
I
I
I
I
SEN4
SEN3
SEN2
SEN1
ISL6334D
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.
ISL6334D 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 IMON and
overcurrent protection functions.
Design Procedure
10. Record the output voltage as V1 immediately after the
11. If the output voltage increases over 2mV as the
External Temperature Compensation
By pulling the TCOMP pin to GND, the integrated
temperature compensation function is disabled. In addition,
external temperature compensation network on the IMON
pin, shown in Figure 16, can be used to cancel the
temperature impact on the IMON voltage.
1. Properly choose the voltage divider for the TM pin to
2. Run the actual board under the full load and the desired
3. After the board reaches the thermal steady state, record
4. Use Equation 18 to calculate the resistance of the TM
5. Use Equation 19 to calculate the TCOMP factor N:
6. Choose an integral number close to the above result for
7. Choose the pull-up resistor R
8. If N = 15, one does not need the pull-down resistor R
9. Run the actual board under full load again with the proper
match the TM voltage vs temperature curve with the
recommended curve in Figure 13.
cooling condition.
the temperature (T
(inductor or MOSFET) and the voltage at TM and VCC
pins.
NTC, and find out the corresponding NTC temperature
T
the TCOMP factor. If this factor is higher than 15, use
N = 15. If it is less than 1, use N = 1.
If otherwise, obtain R
resistors connected to the TCOMP pin.
output voltage is stable with the full load. Record the
output voltage as V2 after the VR reaches the thermal
steady state.
temperature increases, i.e. V2 - V1 > 2mV, reduce N and
redesign R
as the temperature increases, i.e. V1 - V2 > 2mV,
increase N and redesign R
R
N
R
NTC
NTC T
TC2
=
209x T
------------------------------------------------------- -
(
from the NTC datasheet.
=
NTC
3xT
NxR
---------------------- -
(
15 N
TC2
NTC
)
CSC
–
TC1
=
; if the output voltage decreases over 2mV
V
------------------------------- -
V
+
–
TM
CC
400
T
CSC
NTC
xR
–
TC2
V
TM1
) of the current sense component
)
TM
+
using Equation 20:
4
TC2
TC1
.
(typical 10kΩ);
October 29, 2008
(EQ. 18)
(EQ. 19)
(EQ. 20)
FN6802.0
TC2
.