ISL6261ACRZ Intersil, ISL6261ACRZ Datasheet - Page 18

• Manufacturer Part Number: ISL6261ACRZ
• Description: IC CORE CTRLR 1PHASE 40-QFN
• Manufacturer: Intersil

Specifications of ISL6261ACRZ

• Applications: Converter, Intel IMVP-6
• Voltage - Input: 5 ~ 21 V
• Number Of Outputs: 1
• Voltage - Output: 0.3 ~ 1.5 V
• Operating Temperature: -10°C ~ 100°C
• Mounting Type: Surface Mount
• Package / Case: 40-VFQFN, 40-VFQFPN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The NTC thermistor’s resistance is approximately given by
the following formula:
T is the temperature of the NTC thermistor and b is a
constant determined by the thermistor material. T
reference temperature at which the approximation is
derived. The most commonly used T
commercial NTC thermistors, there is b = 2750k, 2600k,
4500k or 4250k.
From the operation principle of VR_TT#, the NTC resistor
satisfies the following equation group:
From Equation 7 and Equation 8, the following can be
derived:
Substitution of Equation 6 into Equation 9 yields the required
nominal NTC resistor value:
In some cases, the constant b is not accurate enough to
approximate the resistor value; manufacturers provide the
resistor ratio information at different temperatures. The
nominal NTC resistor value may be expressed in another
way as follows:
where
nominal value. The normalized resistor value on most NTC
thermistor datasheets is based on the value at +25°C.
Once the NTC thermistor resistor is determined, the series
resistor can be derived by:
R
R
R
R
R
R
R
NTC
s
NTC
NTC
NTC
NTCTo
NTCTo
=
(T
(T
(T
1
60
(
R
.
T
Λ
1
2
20
2
=
=
)
)
)
NTC
)
μA
+
+
V
=
−
R
e
Λ
R
R
R
2
R
( b
−
NTC
(
⋅
NTCTo
s
s
) T
.
NTC
78
T
R
=
=
2
+
NTC
(T
1
is the normalized NTC resistance to its
kΩ
1
1
(T
273
60
54
2
.
.
23
2
20
1
(T
.
78
μA
)
)
μA
⋅
)
⋅
V
V
e
−
−
1
=
e
b
)
kΩ
( b
e
R
⋅
=
Λ
=
=
2
⋅
(
( b
T
.
T
NTC
⋅
22
78
20
20
o
T
+
18
+
1
1
273
1
.
+
kΩ
kΩ
kΩ
78
1
273
(T
273
)
kΩ
1
)
−
)
−
o
R
To
is +25°C. For most
NTC_T
+
1
273
1
)
o
is the
(EQ. 10)
(EQ. 12)
(EQ. 11)
(EQ. 6)
(EQ. 7)
(EQ. 8)
(EQ. 9)
ISL6261A
Once R
at T
One example of using Equations 10, 11 and 12 to design a
thermal throttling circuit with the temperature hysteresis
+100°C to +105°C is illustrated as follows. Since T
and T
Equation 9 gives the required NTC nominal resistance as
The NTC thermistor datasheet gives the resistance ratio as
0.03956 at +100°C and 0.03322 at +105°C. The b value of
4700k in Panasonic datasheet only covers up to +85°C;
therefore, using Equation 11 is more accurate for +100°C
design and the required NTC nominal resistance at +25°C is
438kΩ. The closest NTC resistor value from manufacturers
is 470kΩ. So Equation 12 gives the series resistance as
follows:
The closest standard value is 4.42kΩ. Furthermore,
Equation 13 gives the NTC resistance at T
The NTC branch is designed to have a 470k NTC and a
4.42k resistor in series. The part number of the NTC
thermistor is ERTJ0EV474J. It is a 0402 package. The NTC
thermistor should be placed in the spot that gives the best
indication of the temperature of the voltage regulator. The
actual temperature hysteretic window is approximately
+105°C to +100°C.
T
R
R
R
R
2
s
NTC
NTC_To
NTC
_
2
=
actual
and the actual T
_
2
20
_
T
= +100°C, if we use a Panasonic NTC with b = 4700,
T
NTCTo
2
k
2
=
=
=
Ω
=
431
1
b
. 2
−
. 2
ln(
78
and R
R
78
kΩ
NTC
k
R
Ω
R
k
NTC
_
Ω
NTCTo
s
105
+
is designed, the actual NTC resistance
2
R
+
_
C
temperature can be found in:
T
NTC
2
R
=
)
1
NTC
20
+
_
T
1
k
1
_
Ω
(
=
T
273
1
−
18
15
.
39
+
.
61
T
k
o
Ω
k
)
Ω
2
−
:
=
273
. 4
December 21, 2007
39
1
= +105°C
k
Ω
(EQ. 13)
(EQ. 14)
FN6354.2