參數(shù)資料
型號: LTC4245CG#TRPBF
廠商: Linear Technology
文件頁數(shù): 15/36頁
文件大?。?/td> 431K
描述: IC CNTRLR HOT SWAP 36-SSOP
標(biāo)準(zhǔn)包裝: 1,000
類型: 熱交換控制器
應(yīng)用: CompactPCI?
內(nèi)部開關(guān):
電源電壓: 3.3V,5V,12V
工作溫度: 0°C ~ 70°C
安裝類型: 表面貼裝
封裝/外殼: 36-SSOP(0.209",5.30mm 寬)
供應(yīng)商設(shè)備封裝: 36-SSOP
包裝: 帶卷 (TR)
LTC4245
15
4245fa
The typical LTC4245 application is in a high availability sys-
tem where boards using multiple supplies are hot plugged.
The device enables the system to periodically monitor board
power consumption and fault status over the I
2
C interface.
Boards in CompactPCI and PCI Express systems typically
utilize three to four supplies. Figure 1 shows the LTC4245
being used in a CompactPCI application.
The following sections describe the turn on, turn off and
fault response behavior of the LTC4245. The ADC and I
2
C
interface are discussed next. External component selection
is discussed in detail in the Design Example section.
CPCI Connection Pin Sequence
The staggered lengths of the CPCI male connector pins on
the backplane ensures that all power supplies are physi-
cally connected to the LTC4245 before back-end power
is allowed to ramp up (BD_SEL# asserted low). The long
pins, which include 5V, 3.3V, V(I/O) and GND, mate  rst.
The short BD_SEL# pin mates last. At least one long 3.3V
power pin must be connected to the LTC4245 in order for
the PRECHARGE pin voltage to be available before the
CPCI bus pins mate.
The following is a typical hot plug sequence.
   1. ESD clips make contact.
   2. Long power and ground pins make contact and Early
      Power is established. The 1V precharge voltage
      becomes valid at this stage. Power is also applied
      to the pull-up resistors connected to the HEALTHY#
      and BD_SEL# signals. LOCAL_PCI_RST# is held
      in reset. All power switches are held off at this stage
      of insertion.
   3. Medium length pins make contact. The 12V and 12V
      connector pins make contact at this stage. The
      internal low voltage supply of the LTC4245 (INTV
CC
)
      powers up from the 12V supply. An internal 10糀
      pull-up from INTV
CC
 to BD_SEL# turns on. Other
      connector pins that mate are HEALTHY#, PCI_RST#
      and the bus I/O pins (which are precharged to 1V).
   4. Short pins make contact. If the BD_SEL# signal is
      grounded on the backplane, the plug-in board
      power-up cycle may begin immediately. If the ON pin
      is tied high then turn-on is automatic, else the LTC4245
      waits for a serial bus turn-on command. System
      backplanes that do not ground the BD_SEL# signal
      will instead have circuitry that detects when
   
BD_SEL# makes contact with the plug-in board. The
      system logic can then control the power up process
      by pulling BD_SEL# low. The precharge potential may
      be optionally disconnected from the CPCI bus signals
      at this stage.
Turn-On
The back-end power planes are isolated from the input
power planes by external N-channel pass transistors Q1
through Q4. Sense resistors R1 to R4 provide current
fault detection. Resistors R5 to R8 prevent high frequency
oscillations in MOSFETs Q1 to Q4 respectively.
The following conditions must be satis ed for a duration of
100ms before the external switches can be turned on.
   1. All input supplies and the internally generated supply,
      INTV
CC
, must exceed their undervoltage lockout
      thresholds. The V
EE
 undervoltage lockout can be
      disabled by not tying the CFG pin low.
   2. No undervoltage, overcurrent or PGI fault bits must
      be set unless the corresponding auto-retry is enabled.
      When 12V
IN
 powers up for the  rst time, INTV
CC
 
      rises above its undervoltage threshold which
      generates a 60約 to 120約 internal power-on-reset
      pulse. During reset, the fault registers are cleared
      and the control bits are initialized. If INTV
CC
 is already
      up, then the I
2
C interface can be used to clear the
      fault bits or set the auto-retry bits.
   3. The BD_SEL# pin must be pulled low.
When these initial conditions are satis ed, the ON pin is
checked. If it is high, the four FET On control bits (D0 to
D3) are set either simultaneously (the default state) or
in a 12V, 5V, 3.3V, 12V sequence (register bit C6 set).
If ON is low, the external switches turn on when the ON
pin is brought high or if a serial bus turn-on command
is received. Figure 2 shows all supplies turning on after
BD_SEL# goes low.
APPLICATIO  S I FOR  ATIO
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