ISL6334DIRZ datasheet(22/28 Pages) RENESAS

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ISL6334D

FN6802 Rev 4.00

Page 22 of 28

Apr 29, 2016

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 ISL6334D converts the TM pin voltage

to a 6-bit TM digital signal for temperature compensation. With

the non-linear A/D converter of ISL6334D, 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 16 on page 21.

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 17 on page 21 and that of the actual design. According to

the VCC voltage, ISL6334D 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 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 16.

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 the 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 19, 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

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 19. EXTERNAL TEMPERATURE COMPENSATION

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