RE: In-rush current specification (?)

[Lame Brooks-G14738 <brooks.lame@motorola.com>]

Regardless of the PCI spec, isn't that 4.5A on 12V for 600uS way over the
1394 limit?  18mJ/3mS=6W;  4.5A*12V=54W.  The 1394 card design can not be
expected to handle that surge; so, some of it will get back to the PCI bus.
-- BrooksL

> -----Original Message-----
> From: Fockler, Joe [mailto:jfockler@ti.com]
> Sent: Thursday, 06 April, 2000 08:42
> To: 'pci-sig@znyx.com'
> Cc: 'Kidwell, Gary'
> Subject: In-rush current specification (?)
> 
> 
> Is there a maximum in-rush energy limit for devices 
> hot-plugged into PCI expansion 
> cards?  The 1394-1995 spec states: 
>         "The inrush energy shall not exceed 18 mJ in 3 ms." 
> but I don't see any inrush spec. in the PCI spec. 
> 
> 
> We've seen some devices that exceed the 500 mA tolerance on 
> the PCI 12 V rail 
> when hot-plugged into a PCI 1394 adapter card.  This in 
> itself doesn't seem to be 
> a problem, but we have seen one PC system that gets reset 
> when a 1394 hard drive 
> is hot-plugged and the inrush current peaks around 4.5A (with 
> a 600 us duration).  
> It looks like the 12 V rail drops and causes the POWER GOOD 
> signal to get deasserted. 
> There is a 750 mA slow fuse on the PCI card 12 V trace. 
> Is the Power Supply Rail Tolerance of 500 mA for the 12 V 
> rail a "Maximum" current? 
> All insight and comments are greatly appreciated. 
> Regards, 
> Joe Fockler 
> Texas Instruments 
> 1394 Host Controller Group 
> 12500 TI Blvd., MS 8731 
> Dallas, TX 75243 
> (214) 480-6064  phone 
> (972) 761-6954  fax 
> email: jfockler@ti.com 
> Visit our Bus Solutions website: 
> http://www.ti.com/sc/1394 
> http://www.ti.com/sc/pci 
>