ISL9502CRZ Intersil, ISL9502CRZ Datasheet - Page 18

• Manufacturer Part Number: ISL9502CRZ
• Description: IC CTRLR PWM 2PHASE GPU 48-QFN
• Manufacturer: Intersil

Specifications of ISL9502CRZ

• Pwm Type: Controller
• Number Of Outputs: 1
• Frequency - Max: 500kHz
• Voltage - Supply: 4.75 V ~ 5.25 V
• Buck: Yes
• Boost: No
• Flyback: No
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: No
• Operating Temperature: -10°C ~ 100°C
• Package / Case: 48-VQFN
• Frequency-max: 500kHz
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Duty Cycle: -

In general, the lighter the load, the slower the switching
frequency. Therefore, the switching loss is much reduced for
the light load operation, which is important for conserving the
battery power in the portable application.
Voltage Regulator Thermal Throttling
The ISL9502 features a thermal monitor which senses the
voltage change across an externally placed negative
temperature coefficient (NTC) thermistor.
Proper selection and placement of the NTC thermistor
allows for detection of a designated temperature rise by the
system. Figure 24 shows the thermal throttling feature with
hysteresis. At low temperature, SW1 is on and SW2
connects to the 1.18V side. The total current going into NTC
pin is 60µA. The voltage on NTC pin is higher than threshold
voltage of 1.18V and the comparator output is low. VRHOT#
is pulling up high by the external resistor.
When temperature increases, the NTC resistor value on
NTC pin decreases. Thus, the voltage on NTC pin
decreases to a level lower than 1.18V. The comparator
output changes polarity and turns SW1 off and connects
SW2 to 1.20V. This pulls VRHOT# low and sends the signal
to start thermal throttle. There is a 6µA current reduction on
NTC pin and 20mV voltage increase on threshold voltage of
the comparator in this state. The VRHOT# signal can be
used to change the GPU operation and decrease the power
consumption. When the temperature goes down, the NTC
thermistor voltage will eventually go up. The NTC pin voltage
increases to 1.20V, the comparator output will then be able
to flip back. Such a temperature hysteresis feature of
VRHOT# is illustrated in Figure 25. T
temperature point at which the VRHOT# goes from low to
high due to the system temperature rise. T
lower temperature point at which the VRHOT# goes high
from low because the system temperature decreases to the
normal level.
V
FIGURE 24. CIRCUITRY ASSOCIATED WITH THE THERMAL
NTC
+
-
R
R
NTC
NTC
s
THROTTLING FEATURE IN ISL9502
1.20V
54µA
SW2
6µA
SW1
18
+
1.18V
-
1
INTERNAL TO
represents the higher
ISL9502
2
represents the
VRHOT#
ISL9502
Usually, the NTC thermistor's resistance can be
approximated by the following formula:
T is the temperature of the NTC thermistor and b is a
parameter constant depending on the thermistor material.
T
is derived. The most common temperature for T
For example, there are commercial NTC thermistor products
with b = 2750k, b = 2600k, b = 4500k or b = 4250k.
From the operation principle of the VRHOT# circuit
explained, the NTC resistor satisfies the following equation
group.
From Equation 6 and Equation 7, the following can be
derived,
Using Equation 5 into Equation 8, the required nominal NTC
resistor value can be obtained by:
For some cases, the constant b is not accurate enough to
approximate the NTC resistor value, the manufacturer
provides the resistor ratio information at different
temperature. The nominal NTC resistor value may be
expressed in another way as follows:
where
nominal value. Most datasheet of the NTC thermistor gives
the normalized resistor value based on its value at 25°C.
R
R
R
R
R
R
o
NTC
NTC
NTC
NTC
NTCTo
NTCTo
is the reference temperature in which the approximation
FIGURE 25. TEMPERATURE HYSTERESIS OF VRHOT#
VRHOT#
Logic_1
Logic_0
T ( )
(
(
(
T
T
T
R
Λ
1
2
2
NTC T
)
)
) R
=
=
=
+
+
–
----------------------------------------------------------------------------- -
e
---------------------------------------------------------------------- -
R
R
R
Λ
R
b
–
NTC
NTCTo
S
S
NTC T
2.55kΩ e
•
⎛
⎝
=
=
---------------------- -
T 2
is the normalized NTC resistance to its
(
1.18V
--------------- -
-------------- -
54µA
60µA
–
1.2V
T
+
1
1
2.55kΩ
273
•
2
)
•
e
=
–
⎞
⎠
b
b
=
–
=
2.55kΩ
•
e
•
Λ
R
⎛
⎝
22.22kΩ
b
⎛
⎝
19.67kΩ
NTC T
------------------- -
T
---------------------- -
T
•
o
+
⎛
⎝
---------------------- -
T 1
+
1
1
273
273
–
T
+
2
1
1
273
⎞
⎠
–
-----------------------
To
⎞
⎠
T
+
1
1
273
⎞
⎠
o
T (°C)
is 25°C.
July 17, 2006
(EQ. 10)
(EQ. 5)
(EQ. 6)
(EQ. 7)
(EQ. 8)
(EQ. 9)
FN9275.1