ISL6316 Intersil Corporation, ISL6316 Datasheet - Page 22

• Manufacturer Part Number: ISL6316
• Description: Enhanced 4-Phase PWM Controller
• Manufacturer: Intersil Corporation

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, ISL6316 converts the TM pin voltage
to a 6-bit TM digital signal for temperature compensation. With
the non-linear A/D converter of ISL6316, 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.
Depending on the location of the NTC and the airflow, the
NTC may be cooler or hotter than the current sense
component. 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, TCOMP voltage can also
be used to compensate for the difference between the
recommended TM voltage curve in Figure 16 and that of the
actual design. According to the Vcc voltage, ISL6316 converts
the TCOMP pin voltage to a 4-bit TCOMP digital signal as
TCOMP factor N.
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.
ISL6316 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
over current protection functions.
Design Procedure:
R
1. Properly choose the voltage divider for TM pin to match
2. Run the actual board under the full load and the desired
3. After the board reaches the thermal steady state, record
4. Use the following equation to calculate the resistance of
NTC T NTC
www.DataSheet4U.com
the TM voltage Vs temperature curve with the
recommended curve in Figure 15.
cooling condition.
the temperature (T
(inductor or MOSFET) and the voltage at TM and Vcc
pins.
the TM NTC, and find out the corresponding NTC
temperature T
(
)
=
V
------------------------------- -
V
TM
CC
NTC
xR
–
V
TM1
CSC
from the NTC datasheet.
TM
) of the current sense component
22
(EQ. 19)
ISL6316
10. Record the output voltage as V1 immediately after the
11. If the output voltage increases over 2mV as the
The design spreadsheet is available for those calculations.
External Temperature Compensation
By setting the voltage of TCOMP pin to 0, the integrated
temperature compensation function is disabled. One external
temperature compensation network, shown in Figure 18, can
be used to cancel the temperature impact on the droop (i.e.
load line).
N
R
5. Use the following equation to calculate the TCOMP factor
6. Choose an integral number close to the above result for
7. Choose the pull-up resistor R
8. If N = 15, do not need the pull-down resistor R
9. Run the actual board under full load again with the proper
TC2
FIGURE 18. VOLTAGE AT IDROOP PIN WITH A RESISTOR
=
N:
the TCOMP factor. If this factor is higher than 15, use
N = 15. If it is less than 1, use N = 1.
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
209x T
------------------------------------------------------- -
=
3xT
NxR
---------------------- -
(
15 N
NTC
CSC
–
TC1
PLACED FROM IDROOP PIN TO GND WHEN
LOAD CURRENT CHANGES
TC2
IDROOP
+
–
COMP
VDIFF
400
T
; if the output voltage decreases over 2mV
NTC
FB
TC2
)
+
4
by the following equation:
TC2
TC1
.
(typical 10kΩ).
o
c
August 31, 2005
TC2
(EQ. 20)
(EQ. 21)
FN9227.0
,