ISL6334DIRZ datasheet(21/28 Pages) RENESAS

21 / 28 page

ISL6334D

FN6802 Rev 4.00

Page 21 of 28

Apr 29, 2016

voltage. The VR_FAN signal is set to high when the TM voltage

goes below 33.3% of VCC voltage, and is pulled to GND when the

TM voltage goes back to above 39.1% of VCC voltage. Figure 17

shows the operation of those signals.

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. The 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, the

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 18.

FIGURE 15. BLOCK DIAGRAM OF THERMAL MONITORING

FUNCTION

0.333VCC

0.391VCC

° C

TM1

NTC

VCC

VR_FAN

VR_HOT

FIGURE 16. THE RATIO OF TM VOLTAGE TO NTC TEMPERATURE

WITH RECOMMENDED PARTS

100

120

140

TEMPERATURE (°C)

VR_FAN

VR_HOT

0.451*Vcc

0.391*Vcc

0.333*Vcc

TEMPERATURE

FIGURE 17. VR_HOT AND VR_FAN SIGNAL vs TM VOLTAGE

RTM1

2.75xRNTC T3



(EQ. 15)

RNTC T2



1.267xRNTC T3



(EQ. 16)

RNTC T1



1.644xRNTC T3



(EQ. 17)

FIGURE 18. 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

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