参数资料
型号: MAX5957AETN+T
厂商: Maxim Integrated
文件页数: 20/25页
文件大小: 634K
描述: IC TRPL PCI EXP/HOT-PLUG 56-TQFN
产品培训模块: Lead (SnPb) Finish for COTS
Obsolescence Mitigation Program
标准包装: 2,500
类型: 热交换控制器
应用: 通用型,PCI Express?
内部开关:
电源电压: 3.3V,12V
工作温度: -40°C ~ 85°C
安装类型: 表面贴装
封装/外壳: 56-WFQFN 裸露焊盘
供应商设备封装: 56-TQFN-EP(7x7)
包装: 带卷 (TR)
Triple PCI Express, Hot-Plug Controllers
20   ______________________________________________________________________________________
External MOSFET Gate Drivers
(12G_ and 3.3G_)
The gate drive for the external MOSFETs is provided at
12GA, 12GB, 12GC, 3.3GA, 3.3GB, and 3.3GC. 12G_
is the gate drive for the 12V main supply and is boost-
ed to 5.3V above V
12VIN
by its internal charge pump.
During turn-on, 12G_ sources 5礎 into the external
gate capacitance to control the turn-on time of the
external MOSFET. During turn-off, 12G_ sinks 150礎
from the external gate capacitance to quickly turn off
the external MOSFET. During short-circuit events, an
internal 120mA current sink activates to rapidly bring
the load current into the regulation limits.
3.3G_ is the gate drive for the 3.3V main supplys MOS-
FET and is driven to 5.5V above the 3.3V main supply.
The power for 3.3G_ is supplied from 12VIN and has no
internal charge pump. During turn-on, 3.3G_ sources
5礎 into the external gate capacitance to control the
turn-on time of the external MOSFET. During turn-off,
3.3G_ sinks 150mA to quickly turn off the external
MOSFET. During short-circuit events, an internal
120mA current sink activates to rapidly turn off the
appropriate external MOSFET.
Auxiliary Supply (3.3VAUXIN)
3.3VAUXIN provides power to the auxiliary outputs as
well as the internal logic and references. The drains of
the internal auxiliary MOSFETs connect to 3.3AUXIN
through internal sense resistors and the sources con-
nect to the auxiliary outputs (3.3VAUXO_). Both
MOSFETs have typical on-resistance of 0.2&. Each
channels internal charge pump boosts the gate-drive
voltage to fully turn on the internal n-channel MOSFETs.
The auxiliary supplies have an internal current limit set
to 450mA (MAX5957), 700mA (MAX5958).
Applications Information
Setting the Power-On Reset
t
FAULT
is the time an overcurrent or overtemperature
fault must remain for the MAX5957/MAX5958 to disable
the main or auxiliary channels of a particular slot.
Program the fault timeout period (t
FAULT
) by connect-
ing a resistor (R
TIM
) from TIM to GND. t
FAULT
can be
calculated by the following equation:
t
FAULT
= (166ns / &) x R
TIM
The t
FAULT
programmed time duration must be chosen
according to the total capacitance load connected to
the 12G_ and 3.3G_ pins. To properly power up the
main supply outputs, the following constraints need to
be taken:
t
SU
e (V
GATE
x C
LOAD
) / I
CHG
where t
SU
= 2 x t
FAULT
and where:
"  I
CHG
= 5礎.
"  V
GATE
= 4.8V + V
12VIN
for 12G_ and V
GATE
= 6.8V
+ V
3.3VIN
for 3.3G_.
"  C
LOAD
is the total capacitance load at the gate.
Maximum and minimum values for R
TIM
are 500& and
500k&, respectively. Leave TIM floating for a default
t
FAULT
of 10ms.
Timeout Period (t
POR_HL
)
t
POR_HL
is the time from when the gate voltages of all
outputs of a slot reach their power-good threshold to
when PWRGD_ pulls low. Program the POR timeout
period (t
POR
) by connecting a resistor (R
PORADJ
) from
PORADJ to GND. t
POR_HL
can be calculated by the fol-
lowing equation:
t
POR_HL
= (2.5祍 / &) x R
PORADJ
Maximum and minimum values for R
PORADJ
are 500&
and 500k&, respectively. Leave PORADJ floating for a
default t
POR
of 150ms. Connect PORADJ to GND in
order to completely skip the power-on delay time prior
to the PWRGD_ assertion.
Component Selection
Select the external n-channel MOSFET according to the
applications current requirement. Limit the switch
power dissipation by choosing a MOSFET with an
R
DS_ON
low enough to have a minimum voltage drop at
full load. High R
DS_ON
causes larger output ripple if
there are pulsed loads. High R
DS_ON
can also trigger
an external undervoltage fault at full load. Determine
the MOSFETs power-rating requirement to accommo-
date a short-circuit condition on the board during start-
up. Table 3 lists the MOSFETs and sense resistor
manufacturers.
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