ISL6316_06 Datasheet, PDF (22/29 Pages) Intersil Corporation – Enhanced 4-Phase PWM Controller with 6-Bit VID Code Capable of Precision rDS(ON) or DCR Differential Current Sensing for VR10 Application

ISL6316
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
overcurrent protection functions.
Design Procedure:
1. Properly choose the voltage divider for TM pin to match
the TM voltage Vs temperature curve with the
recommended curve in Figure 15.
2. Run the actual board under the full load and the desired
cooling condition.
3. After the board reaches the thermal steady state, record
the temperature (T_CSC) of the current sense component
(inductor or MOSFET) and the voltage at TM and VCC
pins.
4. Use the following equation to calculate the resistance of
the TM NTC, and find out the corresponding NTC
temperature T_NTC from the NTC datasheet.
R_NTC(TNTC)
=
V-----_{T---M-----x----R----T----M-----1-}
V_CC – V_TM
(EQ. 19)
5. Use the following equation to calculate the TCOMP factor
N:
N
=
2----0---9----x---(_{---T----C----S----C-----}–_{-----T----N----T---C-----})
3xT_NTC + 400
+
4
(EQ. 20)
6. Choose an integral number close to the above result for
the TCOMP factor. If this factor is higher than 15, use
N = 15. If it is less than 1, use N = 1.
7. Choose the pull-up resistor R_TC1 (typical 10kΩ).
8. If N = 15, do not need the pull-down resistor R_TC2,
otherwise obtain R_TC2 by the following equation:
R_TC2
=
-N----x----R----^T----^C----¹-
15 – N
(EQ. 21)
9. Run the actual board under full load again with the proper
resistors connected to the TCOMP pin.
10. Record the output voltage as V1 immediately after the
output voltage is stable with the full load; Record the
output voltage as V2 after the VR reaches the thermal
steady state.
11. If the output voltage increases over 2mV as the
temperature increases, i.e. V2 - V1 > 2mV, reduce N and
redesign R_TC2; if the output voltage decreases over 2mV
as the temperature increases, i.e. V1 - V2 > 2mV,
increase N and redesign R_TC2.
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).
COMP
FB
IDROOP
o_c
VDIFF
FIGURE 18. VOLTAGE AT IDROOP PIN WITH A RESISTOR
PLACED FROM IDROOP PIN TO GND WHEN
LOAD CURRENT CHANGES
The sensed current will flow out of IDROOP pin and develop
the droop voltage across the equivalent resistor (R_FB)
between FB and VDIFF pins. If RFB resistance reduces as
the temperature increases, the temperature impact on the
droop can be compensated. An NTC resistor can be placed
22
FN9227.1
December 12, 2006