ISL6334B datasheet(23/30 Pages) INTERSIL

Part #	ISL6334B

Description	VR11.1, 4-Phase PWM Controller with Phase Dropping, Droop Disabled and Load Current Monitoring Features

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Manufacturer	INTERSIL [Intersil Corporation]

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23

FN6689.2

August 31, 2010

We recommend using those resistors for the accurate

temperature compensation.

There is an comparator with hysteresis to compare the TM

pin voltage to the fixed threshold for the VR_HOT signal.

The VR_HOT 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 14 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 18:

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

temperature T3.

The NTC resistance at the set point T2 can be calculated as

shown in Equations 19:

With the NTC resistance value obtained from Equations 18

and 19, the temperature value T3 and T2 can be found from

the NTC datasheet.

Temperature Compensation

The ISL6334B, ISL6334C 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. ISL6334B, ISL6334C provides

two methods: integrated temperature compensation and

external temperature compensation.

Integrated Temperature Compensation

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

ISL6334B, ISL6334C 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, ISL6334B, ISL6334C converts the

TM pin voltage to a 6-bit TM digital signal for temperature

compensation. With the non-linear A/D converter of

ISL6334B, ISL6334C, 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.

FIGURE 13. THE RATIO OF TM VOLTAGE TO NTC

TEMPERATURE WITH RECOMMENDED PARTS

20

30

40

50

60

70

80

90

100

0

20

40

60

80

100

120

140

TEMPERATURE (°C)

TM

VR_HOT

0.391*Vcc

0.333*Vcc

TEMPERATURE

T2

T3

FIGURE 14. VR_HOT SIGNAL vs TM VOLTAGE

R

TM1

2.75xR

NTC T3

()

=

(EQ. 18)

R

NTC T2

()

1.267xR

NTC T3

()

=

(EQ. 19)

FIGURE 15. BLOCK DIAGRAM OF INTEGRATED

TEMPERATURE COMPENSATION

oc

R

TM1

R

NTC

TM

R

TC1

R

TC2

TCOMP

V

CC

NON-LINEAR

A/D

4-BIT

A/D

DROOP AND

OVERCURRENT

PROTECTION

I

1

I

2

I

3

I

4

k

i

D/A

CHANNEL

CURRENT

SENSE

I

sen4

I

sen3

I

sen2

I

sen1

V

CC

ISL6334B, ISL6334C

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ISL6334B Datasheet(PDF) 23 Page - Intersil Corporation

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