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參數(shù)資料
| 型號： | SMH4812 |
| 廠商： | Summit Microelectronics, Inc. |
| 元件分類： | 基準電壓源/電流源 |
| 英文描述： | Distributed Power Hot-Swap Controller |
| 中文描述： | 分布式電源熱插拔控制器 |
| 文件頁數(shù)： | 11/19頁 |
| 文件大?。?/td> | 441K |
| 代理商： | SMH4812 |
11
2055 4.0 12/22/00
SMH4812
Preliminary
SUMMIT MICROELECTRONICS, Inc.
APPLICATIONS
Operating at High Voltages
The breakdown voltage of the external active and passive
components limits the maximum operating voltage of the
SMH4812 hot-swap controller. Components that must be
able to withstand the full supply voltage are: the input and
output decoupling capacitors, the protection diode in se-
ries with the DRAIN SENSE pin, the power MOSFET
switch and the capacitor connected between its drain and
gate, the high-voltage transistors connected to the power
good outputs, and the dropper resistor connected to the
controller
’
s V
DD
pin.
Over-Voltage and Under-Voltage Resistors
In the following examples, the three resistors, R1, R2, and
R3, connected to the OV and UV inputs, must be capable
of withstanding the maximum supply voltage of several
hundred volts. The trip voltage of the UV and OV inputs is
2.5V relative to V
SS
. As the input impedance of UV and OV
is very high, large value resistors can be used in the
resistive divider. The divider resistors should be high
stability, 1% metal-film resistors to keep the under-voltage
and over-voltage trip points accurate.
Telecom Design Example
A hot-swap telecom application may use a 48V power
supply with a
–
25% to +50% tolerance (i.e. the 48V supply
can vary from 36V to 72V). The formulae for calculating
R1, R2, and R3 follow.
First a peak current, ID
MAX
, must be specified for the
resistive network. The value of the current is arbitrary, but
it can't be to high (self-heating in R3 will become a
problem), or too low (the value of R3 becomes very large,
and R3 becomes very expensive). To set the calculations
a nominal value of 250μA will be assumed.
With V
OV
(2.5V) being the over-voltage trip point, R1 is
calculated by the formula:
OV
MAX
V
R1
ID
=
.
Substituting:
2.5V
250 A
R1
10k
=
=
.
Next the minimum current that flows through the resistive
divider, ID
MIN
, is calculated from the ratio of minimum and
maximum supply voltage levels:
MAX
VS
MIN
MIN
MAX
ID
VS
ID
×
=
.
Substituting:
MIN
250 A 36V
72V
ID
125 A
=
=
.
Now the value of R3 is calculated from ID
MIN
:
MIN
ID
UV
MIN
VS
V
R3
=
.
V
UV
is the under-voltage trip point, also 2.5V. Substituting:
36V
125 A
2.5V
R3
268k
=
=
.
The closest standard 1% resistor value is 267k
Then R2 is calculated:
(
)
UV
MIN
V
R1 R2
ID
=
,
or
UV
MIN
V
R2
R1
ID
=
.
Substituting:
2.5V
125 A
R2
10k
20k
10k
10k
=
=
=
.
Dropper Resistor Selection
The SMH4812 is powered from the high-voltage supply
via a dropper resistor, R
D
. The dropper resistor must
provide the SMH4812 (and its loads) with sufficient oper-
ating current under minimum supply voltage conditions,
but must not allow the maximum supply current to be
exceeded under maximum supply voltage conditions.
The dropper resistor value is calculated from:
MAX
MIN
DD
D
DD
I
LOAD
I
VS
V
R
=
+
,
where VS
MIN
is the lowest operating supply voltage,
V
DDMAX
is the upper limit of the SMH4812 supply voltage,
I
DD
is minimum current required for the SMH4812 to
operate, and I
LOAD
is any additional load current from the
2.5V and 5V outputs and between V
DD
and V
SS
.
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|---|---|
| SMH4812G | Distributed Power Hot-Swap Controller |
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相關代理商/技術參數(shù) |
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|---|---|
| SMH4812_09 | 制造商:SUMMIT 制造商全稱:SUMMIT 功能描述:Distributed Power Hot-Swap Controller |
| SMH4812G | 制造商:SUMMIT 制造商全稱:SUMMIT 功能描述:Distributed Power Hot-Swap Controller |
| SMH4812S | 制造商:SUMMIT 制造商全稱:SUMMIT 功能描述:Distributed Power Hot-Swap Controller |
| SMH4814 | 制造商:SUMMIT 制造商全稱:SUMMIT 功能描述:Dual Feed Active-ORing Programmable Hot Swap Controller |
| SMH4814NCR00 | 制造商:SUMMIT 制造商全稱:SUMMIT 功能描述:Dual Feed Active-ORing Programmable Hot Swap Controller |
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