ISL6334DIRZ datasheet(21/28 Pages) INTERSIL

21 / 28 page

FN6802.2

August 31, 2010

Based on the NTC temperature characteristics and the

desired threshold of the VR_HOT signal, the pull-up resistor

RTM1 of TM pin is given by Equation 15:

RNTC(T3) is the NTC resistance at the VR_HOT threshold

temperature T3.

The NTC resistance at the set point T2 and release point T1 of

VR_FAN signal can be calculated as shown in Equations 16

and 17:

With the NTC resistance value obtained from Equations 16

and 17, the temperature value T2 and T1 can be found from

the NTC datasheet.

Temperature Compensation

The ISL6334D supports inductor DCR sensing, or resistive

sensing techniques. The inductor DCR has a positive

temperature coefficient, which is about +0.385%/°C. Since

the voltage across inductor is sensed for the output current

information, the sensed current has the same positive

temperature coefficient as the inductor DCR.

In order to obtain the correct current information, there

should be a way to correct the temperature impact on the

current sense component. ISL6334D provides two methods:

integrated temperature compensation and external

temperature compensation.

Integrated Temperature Compensation

When the TCOMP voltage is equal or greater than VCC/15,

ISL6334D will utilize the voltage at TM and TCOMP pins to

compensate the temperature impact on the sensed current.

The block diagram of this function is shown in Figure 15.

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, 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 13.

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 14 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.

FIGURE 14. VR_HOT AND VR_FAN SIGNAL vs TM VOLTAGE

VR_FAN

VR_HOT

0.451*Vcc

0.391*Vcc

0.333*Vcc

TEMPERATURE

RTM1

2.75xRNTC T3

()

(EQ. 15)

RNTC T2

()

1.267xRNTC T3

()

(EQ. 16)

RNTC T1

()

1.644xRNTC T3

()

(EQ. 17)

FIGURE 15. BLOCK DIAGRAM OF INTEGRATED

TEMPERATURE COMPENSATION

TM1

NTC

TC1

TC2

TCOMP

NON-LINEAR

A/D

4-BIT

A/D

OVERCURRENT

PROTECTION

D/A

CHANNEL

CURRENT

SENSE

SEN4

SEN3

SEN2

SEN1

ISL6334D

ISL6334DIRZ Datasheet(PDF) 21 Page - Intersil Corporation

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