ISL6260CCRZ Datasheet, PDF (22/28 Pages) Intersil Corporation – Multiphase PWM Regulator for IMVP-6+ Mobile CPUs

ISL6260C
converter operating in CCM can be determined using the
following relationship, where Rfset is in kΩ and the switching
period is in μs.
Rfset(kΩ) = (Period(μs) – 0.29) × 2.33
(EQ. 4)
In discontinuous conduction mode, (DCM), the ISL6260C
runs in period stretching mode. It should be noted that the
switching frequency in the Electrical Specification Table is
tested with the error amplifier output or Comp pin voltage at
2V. When Comp pin voltage is lower, the switching
frequency will not be at the tested value but can still maintain
the output voltage ripple within spec.
Voltage Regulator Thermal Throttling
lntel™ IMVP-6+™ technology supports thermal throttling of
the processor to prevent catastrophic thermal damage to the
voltage regulator. The ISL6260C feature a thermal monitor
which senses the voltage change across an externally
placed negative temperature coefficient (NTC) thermistor,
see Figure 45. Proper selection and placement of the NTC
thermistor allows for detection of a designated temperature
rise by the system.
Figure 45 shows the thermal throttling feature with
hysteresis. At low temperature, SW1 is on and SW2
connects to the 1.20V side. The total current going from NTC
pin is 60µA. The voltage on NTC pin is higher than threshold
voltage of 1.20V and the comparator output is low. VR_TT#
is pulling up high by the external resistor.
54µA 6µA
NTC
+
V_NTC
-
R_NTC
R_s
1.24V
SW1
VR_TT#
-
+
SW2
1.20V
INTERNAL TO
ISL6260C
CPU operation and decrease the power consumption. When
the temperature goes down, the NTC thermistor voltage will
eventually go up. If NTC voltage increases to 1.24V, the
comparator will then be able to flip back. The external
resistance difference in these two conditions is:
1_-5---.4_--2_--μ-4_---A-V_{-- – -}16_---.0_--2_--μ-0_---A-V_{-- = 2.96k}
(EQ. 5)
Therefore, proper NTC thermistor has to be chosen such
that 2.96k resistor change will be corresponding to required
temperature hysteresis. Regular external resistor may need
to be in series with NTC resistors to meet the threshold
voltage values.
The following is an example.
For Panasonic NTC thermistor with B = 4700, its resistance
will drop to 0.03322 of its nominal at +105°C, and drop to
0.03956 of its nominal at +100°C. If the requirement for the
temperature hysteresis is (+105°C to +100°C), the required
resistance of NTC will be:
(^---0^---.^--0^---3^----9^{---25---.6--9---6}–----^k-0^--Ω-.^--0^---3^---3^----2^---2^----) ^{= 467kΩ}
(EQ. 6)
Therefore a larger value thermistor, such as 470k NTC
should be used.
At 105°C, 470k NTC resistance becomes
(0.03322*470k) = 15.6k. With 60µA on NTC pin, the voltage
is only (15.6k*60µA) = 0.937V. This value is much lower than
the threshold voltage of 1.20V. Therefore, a resistor is
needed to be in series with the NTC. The required resistance
can be calculated by:
1_-6---.0_--2_--μ-0_---A-V_{-- – 15.6kΩ = 4.4kΩ}
(EQ. 7)
4.42k is a standard resistor value. Therefore, the NTC
branch should have a 470k NTC and 4.42k resistor in series.
The part number for the NTC thermistor is ERTJ0EV474J. It
is a 0402 package. NTC thermistor will be placed in the hot
spot of the board.
FIGURE 45. CIRCUITRY ASSOCIATED WITH THE THERMAL
THROTTLING FEATURE OF THE ISL6260C
When temperature increases, the NTC thermistor resistance
on NTC pin decreases. The voltage on NTC pin decreases
to a level lower than 1.20V. The comparator changes polarity
and turns SW1 off and throws SW2 to 1.24V. This pulls
VR_TT# low and sends the signal to start thermal throttle.
There is a 6µA current reduction on NTC pin and 40mV
voltage increase on threshold voltage of the comparator in
this state. The VR_TT# signal will be used to change the
22
FN9259.3
June 21, 2010