ISL62883HRTZ Intersil, ISL62883HRTZ Datasheet - Page 27

• Manufacturer Part Number: ISL62883HRTZ
• Description: IC REG PWM 3PHASE BUCK 40TQFN
• Manufacturer: Intersil

Specifications of ISL62883HRTZ

• Applications: Controller, Intel IMVP-6.5™
• Voltage - Input: 5 V ~ 21 V
• Number Of Outputs: 1
• Voltage - Output: 0.0125 V ~ 1.5 V
• Operating Temperature: -10°C ~ 100°C
• Mounting Type: *
• Package / Case: *
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Figure 26 shows the thermal throttling feature with
hysteresis. An NTC network is connected between the
NTC pin and GND. At low temperature, SW1 is on and
SW2 connects to the 1.20V side. The total current
flowing out of the 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 pulled up by the
external resistor.
When temperature increases, the NTC thermistor
resistance decreases so the NTC pin voltage drops. When
the NTC pin voltage drops below 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 CPU operation and
decrease the power consumption. When the temperature
drops down, the NTC thermistor voltage will go up. If
NTC voltage increases to above 1.24V, the comparator
will flip back. The external resistance difference in these
two conditions is expressed in Equation 49:
One needs to properly select the NTC thermistor value
such that the required temperature hysteresis correlates
to 2.96kΩ resistance change. A regular resistor may
need to be in series with the NTC thermistor to meet the
threshold voltage values.
For example, given Panasonic NTC thermistor with
B = 4700, the 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 required temperature hysteresis is
+105°C to +100°C, the required resistance of NTC will
be:
Therefore a larger value thermistor, such as 470k NTC
should be used.
At +105°C, 470kΩ NTC resistance becomes
(0.03322×470kΩ) = 15.6kΩ. With 60µA on the NTC pin,
the voltage is only (15.6kΩ×60µA) = 0.937V. This value
is much lower than the threshold voltage of 1.20V.
Therefore, a regular resistor needs to be in series with
the NTC. The required resistance can be calculated by
Equation 51:
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. The NTC thermistor
will be placed in the hot spot of the board.
1.24V
--------------- -
54μA
----------------------------------------------------- -
(
1.20V
--------------- - 15.6kΩ
60μA
0.03956 0.03322
–
2.96kΩ
–
1.20V
--------------- -
60μA
–
=
=
2.96k
)
4.4kΩ
=
467kΩ
27
ISL62883, ISL62883B
(EQ. 49)
(EQ. 50)
(EQ. 51)
Current Balancing
Refer to Figures 1 and 2. The ISL62883 achieves current
balancing through matching the ISEN pin voltages. R
and C
phase node voltages. It is recommended to use rather
long R
have minimal ripple and represent the DC current flowing
through the inductors. Recommended values are
R
Layout Guidelines
Table 5 shows the layout considerations. The designators
refer to the reference design shown in Figure 27.
PIN
s
EP
10
11
12
13
1
2
3
4
5
6
7
8
9
= 10kΩ and C
s
s
ISEN3/FB2 A capacitor (C7) decouples it to VSUM-.
C
form filters to remove the switching ripple of the
VR_TT#
PGOOD
s
NAME
RBIAS
ISEN2
ISEN1
COMP
VSEN
PSI#
GND
TABLE 5. LAYOUT CONSIDERATION
NTC
RTN
time constant such that the ISEN voltages
VW
FB
s
Create analog ground plane underneath
the controller and the analog signal
processing components. Don’t let the
power ground plane overlap with the
analog ground plane. Avoid noisy
planes/traces (e.g.: phase node) from
crossing over/overlapping with the analog
plane.
No special consideration
No special consideration
Place the Rbias resistor (R16) in general
proximity of the controller. Low impedance
connection to the analog ground plane.
No special consideration
The NTC thermistor (R9) needs to be
placed close to the thermal source that is
monitor to determine thermal throttling.
Usually it’s placed close to Phase-1 high-
side MOSFET.
Place the capacitor (C4) across VW and
COMP in close proximity of the controller
Place the compensator components (C3,
C6 R7, R11, R10 and C11) in general
proximity of the controller.
Place it in general proximity of the
controller.
An optional capacitor is placed between
this pin and COMP. (It’s only used when
the controller is configured 2-phase). Place
it in general proximity of the controller.
A capacitor (C9) decouples it to VSUM-.
Place it in general proximity of the
controller.
A capacitor (C10) decouples it to VSUM-.
Place it in general proximity of the
controller.
Place the VSEN/RTN filter (C12, C13) in
close proximity of the controller for good
decoupling.
= 0.22µF.
LAYOUT CONSIDERATION
FN6891.3
s