ISL6334 Datasheet, PDF (24/30 Pages) Intersil Corporation – VR11.1, 4-Phase PWM Controller with Light Load Efficiency Enhancement and Load Current Monitoring

ISL6334, ISL6334A
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, ISL6334, ISL6334A 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, the larger the difference
between the NTC temperature and the temperature of the
current sense component.
ISL6334, ISL6334A 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 the TM pin to
match the TM voltage vs temperature curve with the
recommended curve in Figure 13.
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 21 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
T
M
(EQ. 21)
5. Use Equation 22 to calculate the TCOMP factor N:
N
=
2----0---9----x---(_{---T----C----S----C-----}–_{-----T----N----T---C-----})
3xT_NTC + 400
+
4
(EQ. 22)
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 23:
R_TC2
=
-N----x----R----^T----^C----¹-
15 – N
(EQ. 23)
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,
one external temperature compensation network, shown in
Figure 16, can be used to cancel the temperature impact on
the droop (i.e., load line).
COMP
IS L 6 3 3 4 ,
IS L 6 3 3 4 A
IN TER N A L
C IR C U IT
FB
o_C
IS E N
V D IFF
FIGURE 16. EXTERNAL TEMPERATURE COMPENSATION
The sensed current will flow out of the FB pin and develop a
droop voltage across the resistor equivalent (R_FB) between
the FB and VDIFF pins. If R_FB resistance reduces as the
temperature increases, the temperature impact on the droop
can be compensated. An NTC resistor can be placed close to
the power stage and used to form R_FB. Due to the non-linear
temperature characteristics of the NTC, a resistor network is
needed to make the equivalent resistance between the FB
and VDIFF pins reverse proportional to the temperature.
The external temperature compensation network can only
compensate the temperature impact on the droop, while it has
no impact to the sensed current inside ISL6334, ISL6334A.
Therefore, this network cannot compensate for the
temperature impact on the overcurrent protection function.
General Design Guide
This design guide is intended to provide a high-level
explanation of the steps necessary to create a multiphase
power converter. It is assumed that the reader is familiar with
many of the basic skills and techniques referenced in the
following. In addition to this guide, Intersil provides complete
reference designs, which include schematics, bills of
materials, and example board layouts for all common
microprocessor applications.
Power Stages
The first step in designing a multiphase converter is to
determine the number of phases. This determination
depends heavily upon the cost analysis, which in turn
depends on system constraints that differ from one design to
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FN6482.0
February 26, 2008