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參數(shù)資料
| 型號： | FAN5240 |
| 廠商： | Fairchild Semiconductor Corporation |
| 英文描述： | Multi-Phase PWM Controller for AMD Mobile Athlon TM and Duron TM |
| 中文描述： | 多相PWM控制器的AMD移動Athlon和Duron商標(biāo)商標(biāo) |
| 文件頁數(shù)： | 13/19頁 |
| 文件大?。?/td> | 447K |
| 代理商： | FAN5240 |
PRODUCT SPECIFICATION
FAN5240
REV. 1.1.7 8/29/02
13
Since the tolerance on the current limit is largely dependent
on the ratio of the external resistors it is fairly accurate if the
voltage drop on the Switching Node side of R
SENSE
is an
accurate representation of the load current. When using the
MOSFET as the sensing element, the variation of R
DS(ON)
causes proportional variation in the ISNS. This value not
only varies from device to device, but also has a typical
junction temperature coefficient of about 0.4% / °C (consult
the MOSFET datasheet for actual values), so the actual
current limit set point will decrease propotional to increasing
MOSFET die temperature. The same discussion applies to
the V
DROOP
calculation.
Figure 11. Improving current sensing accuracy
More accurate sensing can be achieved by using a resistor
(R1) instead of the R
DS(ON)
of the FET as shown in Figure
11. This approach causes higher losses, but yields greater
accuracy in both V
DROOP
and I
LIMIT
. R1 is a low value
(e.g. 10m
) resistor.
The current limit (I
LIMIT
) set point chosen needs to accom-
modate ripple current, slew current, and variability in the
MOSFET's R
DS(ON)
.
Slew current (
output voltage to slew upwards during VID code changes,
since the circuit will limit the regulator’s output current by
pulse skipping when I
LIMIT
is reached. The
used earlier in the discussion (set up by the C
SS
) was
500mV/100
μ
S or 5V/mS. Assuming C
OUT
of 4000
μ
F, the
current required to slew C
OUT
at this rate is:
) is the current required for the
term we
which is contributed roughly equally from each phase,
therefore, 1/2 of the slew current comes from a single phase.
The over-current comparator is sampled just after LDRV is
turned on, when the current is near its peak in the cycle.
Assuming 20% inductor ripple current, we can then add 1/2
of the ripple current, or 10%. An additional factor of 1.2
accounts for the inaccuracy in the initial (room temperature)
R
DS(ON)
of the MOSFETs with an additional factor of 1.4 to
accommodate the rise of the MOSFET R
DS(ON)
when oper-
ating with T
J
@ 125°C. With a maximum load current of
12.5A/phase, the target for I
LIMIT
(per phase) would be:
so using equation 11, with R
DS(ON)
= 3m
for the 2 parallel
FDS6688 MOSFETs, R
ILIM
≈
56K:
Over-Voltage Protection
Should the output voltage exceed 2.35V due to an upper
MOSFET failure, or for other reasons, the overvoltage
protection comparator will force the LDRV high. This action
actively pulls down the output voltage and, in the event of
the upper MOSFET failure, will eventually blow the battery
fuse. As soon as the output voltage drops below the thresh-
old, the OVP comparator is disengaged.
This OVP scheme provides a ‘soft’ crowbar function which
helps to tackle severe load transients and does not invert the
output voltage when activated — a common problem for
OVP schemes with a latch.
Over-Temperature Protection
The chip incorporates an over temperature protection circuit
that shuts the chip down when a die temperature of 150°C is
reached. Normal operation is restored at die temperature
below 125°C with internal Power On Reset asserted, result-
ing in a full soft-start cycle.
LDRV
22
PGND
ISNS
21
R
SENSE
R
Q2
I
LIMIT
I
LOAD
>
C
OUT
-------
+
(12a)
C
OUT
-------
-------
C
OUT
-------
4mF
5V/mS
20A
=
=
(12b)
I
LIMIT
1.1
1.2
1.4
12.5A
2
----------
+
>
42A
≈
(12c)
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| FAN5240_06 | 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:Multi-Phase PWM Controller for AMD Mobile Athlon and Duron |
| FAN5240_ADC3116B WAF | 制造商:Fairchild Semiconductor Corporation 功能描述: |
| FAN5240MTC | 功能描述:開關(guān)變換器、穩(wěn)壓器與控制器 DC/DC RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關(guān)頻率:1 MHz 工作溫度范圍: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
| FAN5240MTC_Q | 功能描述:開關(guān)變換器、穩(wěn)壓器與控制器 DC/DC RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關(guān)頻率:1 MHz 工作溫度范圍: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
| FAN5240MTCX | 功能描述:開關(guān)變換器、穩(wěn)壓器與控制器 PWM Controller Two Phase RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關(guān)頻率:1 MHz 工作溫度范圍: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
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