Question about diodes - which one should I use?

I'm right now attempting to reverse-engineer a computer memory card. It is basically a SRAM card with a battery backup.

+5VDC is taken from the host system's expansion slot, and basically powers everything up, including the SRAM modules. When the +5VDC is no longer available (i.e. the computer is turned off,) the battery saves the contents of the SRAM modules.

The battery is used to protect the contents of the SRAM modules from getting lost. It is a 3V lithium battery, and is rechargable.

Between the VCC pin on the SRAM modules and the +5VDC rail from the host system, there sits a diode I can only partially identify. On the diode, I can only read "3A" and "ITT". The cathode end connects to the SRAM VCC pin, while the anode connects to the +5VDC rail. I believe the diode is being used to avoid the battery voltage from flowing into the host system.

What would be a good diode to use in this situation?

 

On Thursday, December 24, 2015 at 8:32:01 AM UTC-10, John Larkin wrote:

On Wed, 23 Dec 2015 13:21:52 -0800 (PST), groink1@gmail.com wrote:

I'm right now attempting to reverse-engineer a computer memory card. It is basically a SRAM card with a battery backup.

+5VDC is taken from the host system's expansion slot, and basically powers everything up, including the SRAM modules. When the +5VDC is no longer available (i.e. the computer is turned off,) the battery saves the contents of the SRAM modules.

The battery is used to protect the contents of the SRAM modules from getting lost. It is a 3V lithium battery, and is rechargable.

Between the VCC pin on the SRAM modules and the +5VDC rail from the host system, there sits a diode I can only partially identify. On the diode, I can only read "3A" and "ITT". The cathode end connects to the SRAM VCC pin, while the anode connects to the +5VDC rail. I believe the diode is being used to avoid the battery voltage from flowing into the host system.

What would be a good diode to use in this situation?

The classic (practically only) ITT part was the SD103 schottky diode.
That may be it.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

Thank you! I'll check the SD103 out.

 

[John Larkin]

On Wed, 23 Dec 2015 13:21:52 -0800 (PST), groink1@gmail.com wrote:

I'm right now attempting to reverse-engineer a computer memory card. It is basically a SRAM card with a battery backup.

+5VDC is taken from the host system's expansion slot, and basically powers everything up, including the SRAM modules. When the +5VDC is no longer available (i.e. the computer is turned off,) the battery saves the contents of the SRAM modules.

The battery is used to protect the contents of the SRAM modules from getting lost. It is a 3V lithium battery, and is rechargable.

Between the VCC pin on the SRAM modules and the +5VDC rail from the host system, there sits a diode I can only partially identify. On the diode, I can only read "3A" and "ITT". The cathode end connects to the SRAM VCC pin, while the anode connects to the +5VDC rail. I believe the diode is being used to avoid the battery voltage from flowing into the host system.

What would be a good diode to use in this situation?

The classic (practically only) ITT part was the SD103 schottky diode.
That may be it.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Michael Black]

On Thu, 24 Dec 2015, John Larkin wrote:

On Wed, 23 Dec 2015 13:21:52 -0800 (PST), groink1@gmail.com wrote:

I'm right now attempting to reverse-engineer a computer memory card. It is basically a SRAM card with a battery backup.

+5VDC is taken from the host system's expansion slot, and basically powers everything up, including the SRAM modules. When the +5VDC is no longer available (i.e. the computer is turned off,) the battery saves the contents of the SRAM modules.

The battery is used to protect the contents of the SRAM modules from getting lost. It is a 3V lithium battery, and is rechargable.

Between the VCC pin on the SRAM modules and the +5VDC rail from the host system, there sits a diode I can only partially identify. On the diode, I can only read "3A" and "ITT". The cathode end connects to the SRAM VCC pin, while the anode connects to the +5VDC rail. I believe the diode is being used to avoid the battery voltage from flowing into the host system.

What would be a good diode to use in this situation?

The classic (practically only) ITT part was the SD103 schottky diode.
That may be it.

And of course, a schottky diode has a lower voltage drop than a silicon
diode.

Michael

 

[John Larkin]

On Thu, 24 Dec 2015 23:33:00 -0500, Michael Black <et472@ncf.ca>
wrote:

On Thu, 24 Dec 2015, John Larkin wrote:

On Wed, 23 Dec 2015 13:21:52 -0800 (PST), groink1@gmail.com wrote:

I'm right now attempting to reverse-engineer a computer memory card. It is basically a SRAM card with a battery backup.

+5VDC is taken from the host system's expansion slot, and basically powers everything up, including the SRAM modules. When the +5VDC is no longer available (i.e. the computer is turned off,) the battery saves the contents of the SRAM modules.

The battery is used to protect the contents of the SRAM modules from getting lost. It is a 3V lithium battery, and is rechargable.

Between the VCC pin on the SRAM modules and the +5VDC rail from the host system, there sits a diode I can only partially identify. On the diode, I can only read "3A" and "ITT". The cathode end connects to the SRAM VCC pin, while the anode connects to the +5VDC rail. I believe the diode is being used to avoid the battery voltage from flowing into the host system.

What would be a good diode to use in this situation?

The classic (practically only) ITT part was the SD103 schottky diode.
That may be it.

And of course, a schottky diode has a lower voltage drop than a silicon
diode.

Michael

Sometimes.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Tim Wescott]

On Thu, 24 Dec 2015 23:33:00 -0500, Michael Black wrote:

On Thu, 24 Dec 2015, John Larkin wrote:

On Wed, 23 Dec 2015 13:21:52 -0800 (PST), groink1@gmail.com wrote:

I'm right now attempting to reverse-engineer a computer memory card.
It is basically a SRAM card with a battery backup.

+5VDC is taken from the host system's expansion slot, and basically
powers everything up, including the SRAM modules. When the +5VDC is no
longer available (i.e. the computer is turned off,) the battery saves
the contents of the SRAM modules.

The battery is used to protect the contents of the SRAM modules from
getting lost. It is a 3V lithium battery, and is rechargable.

Between the VCC pin on the SRAM modules and the +5VDC rail from the
host system, there sits a diode I can only partially identify. On the
diode, I can only read "3A" and "ITT". The cathode end connects to the
SRAM VCC pin, while the anode connects to the +5VDC rail. I believe
the diode is being used to avoid the battery voltage from flowing into
the host system.

What would be a good diode to use in this situation?

The classic (practically only) ITT part was the SD103 schottky diode.
That may be it.

And of course, a schottky diode has a lower voltage drop than a silicon
diode.

Michael

Higher leakage, too -- so it's not necessarily a slam-dunk.

--
www.wescottdesign.com