参数资料
型号: ISL62882IRTZ
厂商: Intersil
文件页数: 28/42页
文件大小: 0K
描述: IC REG PWM 2PHASE BUCK 40TQFN
标准包装: 60
应用: 控制器,Intel IMVP-6.5?
输入电压: 5 V ~ 25 V
输出数: 1
输出电压: 0.013 V ~ 1.5 V
工作温度: -40°C ~ 100°C
安装类型: 表面贴装
封装/外壳: 40-WFQFN 裸露焊盘
供应商设备封装: 40-TQFN-EP(5x5)
包装: 管件
ISL62882, ISL62882B
Figure 29 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
Current Balancing
Refer to Figures 1 and 2. The ISL62882 achieves current
balancing through matching the ISEN pin voltages. R s and C s
form filters to remove the switching ripple of the phase node
voltages. It is recommended to use rather long R s C s time
constant such that the ISEN voltages have minimal ripple and
represent the DC current flowing through the inductors.
Recommended values are R s = 10k Ω and C s = 0.22μF.
Layout Guidelines
Table 6 shows the layout considerations. The designators refer to
the reference design shown in Figure 31.
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 shown in
PIN
EP
NAME
GND
TABLE 6. LAYOUT CONSIDERATION
LAYOUT CONSIDERATION
Create analog ground plane underneath the
controller and the analog signal processing
components. Don’t let the power ground plane
--------------- – --------------- = 2.96k
Equation 44:
1.24V 1.20V
54 μ A 60 μ A
(EQ. 44)
1
PGOOD
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
One needs to properly select the NTC thermistor value such that
the required temperature hysteresis correlates to 2.96k Ω
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 as shown in Equation 45:
2
3
4
5
PSI#
RBIAS
VR_TT#
NTC
No special consideration
Place the R BIAS 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.
------------------------------------------------------- = 467k Ω
2.96k Ω
( 0.03956 – 0.03322 )
(EQ. 45)
6
VW
Place the capacitor (C4) across VW and COMP in
close proximity of the controller
Therefore, a larger value thermistor such as 470k NTC should be
used.
At +105°C, 470k Ω NTC resistance becomes
(0.03322 × 470k Ω ) = 15.6k Ω . With 60μA on the NTC pin, the
voltage is only (15.6k Ω × 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 46:
7
8
9
10
11
COMP
FB
FB2
ISEN2
ISEN1
Place the compensator components (C3, C5, C6
R7, R11, R10 and C11) 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.
--------------- – 15.6k Ω = 4.4k Ω
1.20V
60 μ A
(EQ. 46)
12
13
VSEN
RTN
Place the VSEN/RTN filter (C12, C13) in close
proximity of the controller for good decoupling.
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.
28
FN6890.4
June 21, 2011
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