TSB41AB3: can it be damaged by shorting data line to ground?

Hello Hardie,

    Yes, this short probably damaged the device, due to this condition may have drawn more current than the maximum supported by TPA0+.

Regards,

Diego.

Thanks Diego,

I did already replace the TSB41AB3 but not before I noticed the short so the new device has probably been damaged also. I'll try probing the removed device with a DMM; hopefully I will see a resistance difference between good and damaged channel pins so that I can confirm that damage has indeed been done. I will then have the confidence to fit a further replacement on my board. I'll post the results here.

Regards,

Graeme

I'm still struggling with this. It is a consumer device using the TSB41AB3 and connecting to a Windows PC with integral IEEE 1394 sockets (VIA chipset). When connected to the PC, there is no response from WIndows at all: no bong and no device appearing in the Device Manager.

After earlier discovering a short-circuit between chassis and TPA0+ I have fixed the s/c and replaced the TSB41AB3. No response from the Windows PC.

I realized the PHY clock frequency was critical and could have changed due to the new PHY being fitted so I checked the SYSCLK frequency and found it to be just outside the 100ppm limit. I trimmed it back to 49.152MHz using the xtal load capacitors. But still no response from the Windows PC.

I have now probed around the TSB41AB3 while powered-up with the cable connection to the PC and again without it. Most of the pin voltages are the same in both states. Here are the ones that are different:

WIth NO cable connection to PC: TPA0+/-=3.3V, TPB0+/-=0.1V, TPbias=3.3V, CNA=3.3V.

With cable connection to PC: TPA0+/-=1.80V, TPB0+/-=1.74V, TPbias=1.83V, CNA=0V.

About 5 minutes after connection, the TPA0+/- and TPB0+/- lines drop down to about 0.15V which I presume is a power-saving mode; they restore after disconnection/re-connection.

All other pins remain the same.

My question is: what is Windows wanting to see from the 1394 connection before it recognizes it as a connection. I would have expected that detection of the bias voltages would be enough for it to know that something had been connected. But does it actually need to COMMUNICATE with the new device before it says "something has been connected"? If so, then maybe my problem is now with the LLC or even the uP?

I'd be grateful for anybody's thoughts on this.

Regards, Graeme

Hello Graeme,

The TSB41AB3 is only a PHY, it will detect the cable connection and de-serialize the 1394 packets into a parallel interface, it could actually work even with no LLC connection acting like a 1394 repeater.

If the system is not recognizing a device on the 1394 bus then the problem is with the LLC-PHY interface or with the uP-LLC interface. Does your system even recognize a 1394 OHCI controller?

Can you send your schematic? Is the LPS signal active? 

Regards.

Thanks Elias,

Windows 7 Device Manager reports the VIA 1394 OHCI Compliant Host Controller as working properly and indeed the PC recognizes other 1394 devices when connected.

I don't have a schematic of the device in question (a photographic scanner) but it uses a Philips SAA7356HL LLC with a Hitachi  H8/3003 uP. The circuit around the PHY seems to follow the TI reference design closely and the cable power is not used (power class 000).

LPS input to the PHY is measured high, being tied to the PHY/LLC supplies through a 1k resistor. 

Other measured voltages around the PHY while connected to the PC are: LREQ=2.4V, CTL0/CTL1=0V, CNA=0V, PD=0.1V, LPS=3.3V, C/LKON=0V, /ISO=3.3V, CPS=0.9V, /RESET=2.8V, R0=0V, R1=1.25V.

Regards,

Graeme

Hello Graeme,

The voltages on the signals above seems correct.

Can you measure the SYSCLK?

Does the TSB41ABe works as a repeater? i.e. if you connect two nodes to the TSB are those two nodes working?

Another options is to ship us your platform for debug.

Are you able to connect an PCI evaluation board? If so we might be able to loan one to you.

Regards.