ISL6336D Datasheet, PDF (24/30 Pages) Intersil Corporation – VR11.1, 6-Phase PWM Controller with Phase Dropping,Droop Disabled and Load Current Monitoring Features

ISL6336D
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, the ISL6336D converts the TM pin voltage
to a 6-bit TM digital signal for temperature compensation. With
the nonlinear A/D converter of ISL6336D, 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 18.
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 19 and that of the actual design. According to the VCC
voltage, ISL6336D 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 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.
The ISL6336D 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
1. Properly choose the voltage divider for the TM pin to match
the TM voltage vs temperature curve with the recommended
curve in Figure 18.
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 Equation 20 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. 20)
5. Use Equation 21 to calculate the TCOMP factor N:
N
=
2----0---9----x---_{---T----C----S----C-----}–_{-----T----N----T---C-----}
3xT_NTC + 400
+
4
(EQ. 21)
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, one does not need the pull-down resistor R_TC2. If
otherwise, obtain R_TC2 using Equation 22:
R_TC2
=
-N----x----R----^T----^C----¹-
15 – N
(EQ. 22)
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.
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 21, can be used to cancel the temperature impact on the
IMON voltage.
IMON
o_C
ISL6336D
INTERNAL
CIRCUIT
FIGURE 21. EXTERNAL TEMPERATURE COMPENSATION
The sensed current will flow out of the IMON pin and develop a
voltage across the resistor equivalent (RIMON). If the resistance
on the IMON pin reduces as the temperature increases, the
temperature impact on the IMON voltage can be compensated.
An NTC resistor can be placed close to the power stage and used
to form a RIMON. Due to the nonlinear temperature
characteristics of the NTC, a resistor network is needed to make
the equivalent resistance on the IMON pin reverse proportional to
the temperature.
The external temperature compensation network can only
compensate the temperature impact on the IMON voltage, while it
has no impact to the sensed current inside ISL6336D. Therefore,
this network cannot compensate for the temperature impact on
the overcurrent protection function.
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FN8320.0
October 6, 2014