参数资料
型号: MAX5920CESA+T
厂商: Maxim Integrated
文件页数: 15/18页
文件大小: 310K
描述: IC HOT-SWAP CTRLR -48V 8-SOIC
标准包装: 2,500
类型: 热交换控制器
应用: 通用
内部开关:
电源电压: -20 V ~ -80 V
工作温度: -40°C ~ 85°C
安装类型: 表面贴装
封装/外壳: 8-SOIC(0.154",3.90mm 宽)
供应商设备封装: 8-SOIC
包装: 带卷 (TR)
Applications Information
Sense Resistor
The circuit-breaker current-limit threshold is set to 50mV
(typically). Select a sense resistor that causes a drop
equal to or above the current-limit threshold at a current
level above the maximum normal operating current.
Typically, set the overload current to 1.5 to 2.0 times the
nominal load current plus the load-capacitance charging
current during startup. Choose the sense resistor power
rating to be greater than (V
CL
)
2
/ R
SENSE
.
Component Selection Procedure
"   Determine load capacitance:
C
L
= C2 + C3 + module input capacitance
"   Determine load current, I
LOAD
.
"   Select circuit-breaker current, for example:
I
CB
= 2 x I
LOAD
"   Calculate R
SENSE
:
Realize that I
CB
varies ?0% due to trip-voltage
tolerance.
"   Set allowable inrush current:
"   Determine value of C2:
"   Calculate value of C1:
"   Determine value of R3:
"  Set R2 = 10&.
"  If an optocoupler is utilized as in Figure 14, deter-
mine the LED series resistor:
Although the suggested optocoupler is not specified for
operation below 5mA, its performance is adequate for
36V temporary low-line voltage where LED current
would then be H2.2mA to 3.7mA. If R7 is set as high as
51k&, optocoupler operation should be verified over
the expected temperature and input voltage range to
ensure suitable operation when LED current H0.9mA for
48V input and H0.7mA for 36V input.
If input transients are expected to momentarily raise the
input voltage to >100V, select an input transient-volt-
age-suppression diode (TVS) to limit maximum voltage
on the MAX5920 to less than 100V. A suitable device is
the Diodes Inc. SMAT70A telecom-specific TVS.
Select Q1 to meet supply voltage, load current, efficien-
cy, and Q1 package power-dissipation requirements:
BV
DSS
e 100V
I
D(ON)
e 3 x I
LOAD
DPAK, D
2
PAK, or TO-220AB
The lowest practical R
DS(ON)
, within budget constraints
and with values from 14m& to 540m&, are available at
100V breakdown.
Ensure that the temperature rise of Q1 junction is not
excessive at normal load current for the package select-
ed. Ensure that I
CB
current during voltage transients
does not exceed allowable transient-safe operating-area
limitations. This is determined from the SOA and tran-
sient-thermal-resistance curves in the Q1 manufacturers
data sheet.
Example 1:
I
LOAD
= 2.5A, efficiency = 98%, then V
DS
= 0.96V is
acceptable, or R
DS(ON)
d 384m& at operating temper-
ature is acceptable. An IRL520NS 100V NMOS with
R
DS(ON)
d 180m& and I
D(ON)
= 10A is available in
D
2
PAK. (A Vishay Siliconix SUD40N10-25 100V NMOS
with R
DS(ON)
d 25m& and I
D(ON)
= 40A is available in
DPAK, but may be more costly because of a larger die
size).
Using the IRL520NS, V
DS
d 0.625V even at +80癈 so
efficiency e 98.6% at 80癈. P
D
d 1.56W and junction
temperature rise above case temperature would be 5癈
due to the package ?/DIV>
JC
= 3.1癈/W thermal resistance.
Of course, using the SUD40N10-25 would yield an effi-
ciency greater than 99.8% to compensate for the
increased cost.
R
V
V
mA   I
mA
IN NOMINAL
LED
7
2
3
5
   
(
)
=

d
d
R
s
C
typically  k
3
2
150
1
d
?/DIV>
 (
     )
&
C
C    C    x
V
V
V
gd
IN MAX
GS TH
GS TH
1
2
=
+

?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
(
)
(
)
(   )
(   )
C
A x C
I
L
INRUSH
2
45
=
?/DIV>
I
x
mV
R
I
or
I
I
x I
INRUSH
SENSE
LOAD
INRUSH
LOAD
CB MIN
d

+
d
0 8
40
0 8
.
.
(
)
R
mV
I
SENSE
CB
=
50
-48V Hot-Swap Controller
with External R
SENSE
______________________________________________________________________________________   15
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