ISL6334D_09 Datasheet, PDF (22/28 Pages) Intersil Corporation – VR11.1, 4-Phase PWM Controller with Phase Dropping, Droop Disabled and Load Current Monitoring Features

ISL6334D
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
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 18 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. 18)
5. Use Equation 19 to calculate the TCOMP factor N:
N
=
2----0---9----x---(_{---T----C----S----C-----}–_{-----T----N----T---C-----})
3xT_NTC + 400
+
4
(EQ. 19)
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 20:
R_TC2
=
-N----x----R----^T----^C----¹-
15 – N
(EQ. 20)
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 16, can be used to cancel the
temperature impact on the IMON voltage.
IM O N
o_C
IS L 6334D
IN T E R N A L
C IR C U IT
FIGURE 16. EXTERNAL TEMPERATURE COMPENSATION
The sensed current will flow out of the IMON pin and develop
a voltage across the resistor equivalent (R_IMON). 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 R_IMON. Due to the non-linear
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 ISL6334D.
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
the next. Principally, the designer will be concerned with
whether components can be mounted on both sides of the
circuit board; whether through-hole components are
permitted; and the total board space available for power
supply circuitry. Generally speaking, the most economical
solutions are those in which each phase handles between
15A and 25A. All surface-mount designs will tend toward the
lower end of this current range. If through-hole MOSFETs
and inductors can be used, higher per-phase currents are
possible. In cases where board space is the limiting
constraint, current can be pushed as high as 40A per phase,
but these designs require heat sinks and forced air to cool
the MOSFETs, inductors and heat-dissipating surfaces.
22
FN6802.1
May 28, 2009