ISL6334DIRZ datasheet(22/28 Pages) INTERSIL

22 / 28 page

FN6802.2

August 31, 2010

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 (TCSC) 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

TNTC from the NTC datasheet.

5. Use Equation 19 to calculate the TCOMP factor N:

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 RTC1 (typical 10kΩ);

8. If N = 15, one does not need the pull-down resistor RTC2.

If otherwise, obtain RTC2 using Equation 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 RTC2; if the output voltage decreases over 2mV

as the temperature increases, i.e. V1 - V2 > 2mV,

increase N and redesign RTC2.

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.

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 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.

RNTC T

NTC

()

VTMxRTM1

VCC V

–

--------------------------------

(EQ. 18)

209x TCSC T

–

NTC

()

3xTNTC 400

-------------------------------------------------------- 4

(EQ. 19)

RTC2

NxRTC1

15 N

–

-----------------------

(EQ. 20)

IM O N

IS L 6 334 D

IN T E RNAL

CIRCUIT

FIGURE 16. EXTERNAL TEMPERATURE COMPENSATION

ISL6334D

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