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Explorer
Explorer
9,284 Views
Registered: ‎07-23-2009

SPARTAN 3A PCI 5V interface

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Hello all,

 

I have to upgrade an existing board of my company which uses a old Quicklogic FPGA and that has a PCI 5Vdc compatible interface.

I would like to use a Xilinx FPGA with Xilinx PCI 32 bit IPcore ad I would use a SPARTAN 3A FPGA because it is well supported by ISE toolsuite than SPARTAN II (5Vdc PCI compatible) that is not supported.

The problem is that this family is designed to support 3.3Vdc PCI interface and all PC motherboards have 5 Vdc PCI interface ports.

 

Is not a problem if my board is NOT PCI compliant.

 

I have found  this appnotes from xilinx (Connecting Devices in the Virtex and Spartan Families to a 3.3V or 5V PCI Bus) to interface easily

Virtex 2 and Spartan Families to a 3.3V or 5V PCI Bus but SPARTAN 3A family is not drectly menthioned here. I have found this link in SPARTAN 3A family page but I do not have any confirmation that this method could work with this family.

There are a lots of ICs that work in the same way of IDT QuickSwitch like Texas-Instruments SN74CBT3T16211 but I would like to understand if they are bidirectional and if they works like serial resistor or integrate clamp diodes or clamping circuitsthat can protect a SPARAN 3A I/O pin when PCI signals are driven by a 5VDC source (PC side).

 

Can anybody help me?


 

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Explorer
Explorer
10,953 Views
Registered: ‎07-23-2009

Re: SPARTAN 3A PCI 5V interface

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Xilinx answered to my webcase question:

 

Deepesh said:

 

Hi Emanuele,

Regarding your following question:

1_ Are Spartan3A I/O able to support the solution menthioned above?

I have checked. It shouldn't be problem. The solution should still work.
However, we haven't tested it here.

 

the question was regarding the xapp646 and the possibility to use quickswitch with spartan 3A for PCI 5V-->3.3V bus interface.

 

Now I am answering about new SPARTAN 6 familiy (with the same question).

 

Anyway, a guy from Silica told me that Spartan 6 device will be able to be purchased from the Q1 of 2010. XC6SLX9 from Q2 -.-''

 

 

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Instructor
Instructor
9,270 Views
Registered: ‎08-14-2007

Re: SPARTAN 3A PCI 5V interface

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The QuickSwitch approach should work with any 3.3V logic part including Spartan 3A.

The main difference between the Spartan 3A and the other series in the app note is that

the 3A does not have the clamp diodes to Vcco, so you need to be careful not to exceed

the 3.6V maximum input voltage.  The QuickSwitch and simular parts are simple FET

switches, without a charge pump on the gate.  Thus when the channel voltage gets

close to VDD (of the Quickswitch) the FET switches off preventing signals from driving

above the cutoff voltage (Vdd - Vgs on).  BE CAREFUL when selecting these parts.

TI has a series of parts that runs on 3.3V, but DOES have a charge pump for the gate

so it can PASS 5V SIGNALS THROUGH!  Selecting the Vdd for the QuickSwitch is

a bit tricky.  It usually wants to be around 4V for this application.  I think this is

covered in the app note.

 

Regards,

Gabor

-- Gabor
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Adventurer
Adventurer
9,267 Views
Registered: ‎03-16-2009

Re: SPARTAN 3A PCI 5V interface

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Hi!

 

See my list of solution that I compose sometimes ago:

 

IDT:
1) QS34X245Q3G -32 Bit/QVSOP-80
2) QS3861PAG - 10 Bit/TSSOP-24
3) QS3384PAG - 10 Bit/TSSOP-24
3) QS32X861Q1G - 20 Bit/QSOP-48
4) QS32X384Q1G - 20 Bit/QSOP-48
5) QS3306AS1G 2 Bit/SOIC-8

 

Faichild:
1) FST16211MTD - 24 Bit/TSSOP-56
2) FSTD16211MTD - 24 Bit/TSSOP-56
3) FST34X2245QSPX - 32 Bit/QVSOP-80
4) NC7SZ384M5X - 1 Bit/SOT-23
4) NC7SZ384P5X - 1 Bit/SC-70
5) NC7WB3125K8X -2 Bit/US-8
6) FST3384MTC - 10 Bit/TSSOP-24

 

TI:
1) 74CBTD1G125DCK - 1 Bit/SC-70
2) 74CBTD1G125DBV - 1Bit/SOT-23
3) 74CBTD3306PW - 2 Bit/TSSOP-8
4) 74CBTD3306D - 2 Bit/SOIC-8
5) 74CBTD3384DGV - 10 Bit/TVSOP-24
6) 74CBTD3384DW - 10 Bit/SOIC-24
7) 74CBTD3384PW - 10 Bit/TSSOP-24

 

Pericom:
1) PI5C3384LE - 10 Bit/TSSOP-24
2) PI53861Q - 10 Bit/SSOP-24


PRICES from "findchips":
TI:
SN74CBTD3384PW  0.40 | 1ku
SN74CBTD16211DGGR 2.64 | 1ku
SN74CBTD3306PW  0.31 | 1ku


NXP:
CBTD3384  0.38 | 1ku
CBTD16211DGG  0.90 | 1ku
CBT3306PW  0.49 | 1ku

 

I select 2x CBTD3384  and 1x CBT3306PW  for my design (PCI Master\Target). Both part have a internal diode. So you can connect chip VDD to 5VDC directly.

Some attention about powering PCI board: old motherboard haven`t a 3.3V on PCI connector.

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Instructor
Instructor
9,263 Views
Registered: ‎08-14-2007

Re: SPARTAN 3A PCI 5V interface

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We do a lot of PCI board designs here and see lots of systems.  My experience is

that you need to go pretty far back to find a motherboard with no 3.3V on the

PCI connector, however most of our cards still have 5V to 3.3V converters

to handle this.

 

Another point.  Most newer systems are PCI express based.  The remaining

PCI slots are considered "legacy" slots and may not have the performance

you want in some cases.  I have also come across systems with only

3.3V PCI slots, so it would be wise to design the board as "universal"

rather than 5V.  This reduces the available number of Vcc pins since

the VCCio pins cannot be used to power circuitry in the universal

card.  64-bit slots are almost all 3.3V.

 

Regards,

Gabor

-- Gabor
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Explorer
Explorer
9,250 Views
Registered: ‎07-23-2009

Re: SPARTAN 3A PCI 5V interface

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Thank you all for the answers.

I am looking to the data sheet for TI if the mentioned sn74cb3t16211

 

the fact is that i am a little bit confused because the flowing of the signals is given only from port A to port B but is written that this device is BIDIRECTIONAL.

Anyway if I connect port A to 5vdc PCI bus and port B to my Spartan 3A FPGA, I think that communication bidirectional.

if I think to a single MOS with the SOURCE connected to port B and the DRAIN to port A with a Vgate = Vcc+Vt (where Vcc of TI chip is 3.3 V) as menthioned in data sheet I can have 2 scenarios:

 

1_ 5V PCI signal is driven port A (drain) of my switch. I can read the signal at port B with a level that is about 3.3V (Vgate-Vsource = Vcc + Vt - Vt). In this way the mos is in saturation region (Vgs > Vt at port B but Vgd < Vt at port A, negative 5V-3.3V-Vt)

2_ I drive port B with my FPGA (with port A an high impedance) the mos is in ohmic region (rdson) and the signal pass through it to port A because Vgs > Vt and Vgd > Vt

 

for this reason i am not able to understand this phrase from Gszakacs:

TI has a series of parts that runs on 3.3V, but DOES have a charge pump for the gate

so it can PASS 5V SIGNALS THROUGH!

 

If I drive port A with 5V and Vdd of TI quickswitch is 3.3Vthe information pass through but not over 3.3 V, this is due to what i explained overe here :)

 

I read in this appnote from xilinx http://www.xilinx.com/support/documentation/application_notes/xapp311.pdf on page 3 that the problem for a 3.3V PCI FPGA pin that want drive a 5V input pin of a PCI bus, is that maybe the mos of the output pin is not able to load enough current due to he small dimensions of W/L (and then the equivalent resistance) or in other words if the pull up transistor is sufficently large.

 

how can I know if  spartan 3A Output pins can drive a 5V PCI  input?

 

Sincerly,

Emanuele

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Explorer
Explorer
9,178 Views
Registered: ‎07-23-2009

Re: SPARTAN 3A PCI 5V interface

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No news?

 

:(

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Explorer
Explorer
10,954 Views
Registered: ‎07-23-2009

Re: SPARTAN 3A PCI 5V interface

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Xilinx answered to my webcase question:

 

Deepesh said:

 

Hi Emanuele,

Regarding your following question:

1_ Are Spartan3A I/O able to support the solution menthioned above?

I have checked. It shouldn't be problem. The solution should still work.
However, we haven't tested it here.

 

the question was regarding the xapp646 and the possibility to use quickswitch with spartan 3A for PCI 5V-->3.3V bus interface.

 

Now I am answering about new SPARTAN 6 familiy (with the same question).

 

Anyway, a guy from Silica told me that Spartan 6 device will be able to be purchased from the Q1 of 2010. XC6SLX9 from Q2 -.-''

 

 

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