参数资料
| 型号： | ISL62881HRTZ |
| 厂商： | Intersil |
| 文件页数： | 23/35页 |
| 文件大小： | 0K |
| 描述： | IC REG PWM SGL PHASE 28TQFN |
| 标准包装： | 75 |
| 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： | -10°C ~ 100°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 28-WFQFN 裸露焊盘 |
| 供应商设备封装： | 28-TQFN-EP（4x4） |
| 包装： | 管件 |
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ISL62881, ISL62881B
?
------------------------------ ?
dV fb
× C vid ?
I vid ( t ) = C vid × ------------ × ? 1 – e vid
dV fb C out × LL dV core
C vid × ------------ = ------------------------ × ------------------
R droop
where C out is the total output capacitance.
In the meantime, the R vid -C vid branch current I vid time domain
expression is as shown in Equation 32:
– t
R (EQ. 32)
dt ? ?
? ?
It is desired to let I vid (t) cancel I droop_vid (t). So there are :
(EQ. 33)
dt dt
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
1.24V 1.20V
--------------- – --------------- = 2.96k
and :
R vid × C vid = C out × LL
The result is:
R vid = R droop
(EQ. 34)
(EQ. 35)
resistance difference in these two conditions is shown in
Equation 37:
(EQ. 37)
54 μ A 60 μ A
One needs to properly select the NTC thermistor value such that
dV core
C out × LL
dt
C vid = ------------------------ × ------------------
R droop dV fb
dt
------------------------------------------------------- = 467k Ω
( 0.03956 – 0.03322 )
--------------- – 15.6k Ω = 4.4k Ω
1.20V
and :
------------------ (EQ. 36)
------------
For example: given LL = 3m Ω , R droop = 4.22k Ω , C out = 1320μF,
dV core /dt = 5mV/μs and dV fb /dt = 15mV/μs, Equation 35 gives
R vid = 4.22k Ω and Equation 36 gives C vid = 227pF.
It’s recommended to select the calculated R vid value and start
with the calculated C vid value and tweak it on the actual board to
get the best performance.
During normal transient response, the FB pin voltage is held
constant, therefore is virtual ground in small signal sense. The
R vid -C vid network is between the virtual ground and the real
ground, and hence has no affect on transient response.
Voltage Regulator Thermal Throttling
Figure 24 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 the threshold voltage of 1.20V and the
comparator output is low. VR_TT# is pulled up by the external
resistor.
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 38:
2.96k Ω
(EQ. 38)
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 39:
(EQ. 39)
60 μ A
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.
54μA
64μA
Layout Guidelines
Table 5 shows the layout considerations. The designators refer
NTC
SW1
-
VR_TT#
to the reference designs shown in Figures 25 and 26.
+
V NTC
-
R NTC
+
R s
1.24V
SW2
1.20V
INTERNAL TO
ISL62881
FIGURE 24. CIRCUITRY ASSOCIATED WITH THE THERMAL
THROTTLING FEATURE OF THE ISL62881
23
FN6924.3
June 16, 2011
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