voltage regulator

[[email protected]]

Hi, I am a grad student at Stanford. I am trying to make a ECL to TTL
converter board. So, I will use MC10H125. These chips need -5.2V. And I
am trying to get this from NIM crate's power supply of -6V. I am
wondering which voltage regulator to use. I was thinking of LM2990-5.2,
but the dropout voltage could be as much as 1V in which case, it won't
work. Any advice would be appreciated. Thank you.

 

[Klaus Bahner]

Hi, I am a grad student at Stanford. I am trying to make a ECL to TTL
converter board. So, I will use MC10H125. These chips need -5.2V. And I
am trying to get this from NIM crate's power supply of -6V. I am
wondering which voltage regulator to use. I was thinking of LM2990-5.2,
but the dropout voltage could be as much as 1V in which case, it won't
work. Any advice would be appreciated. Thank you.

How many 10H125 are you going to use? The max 1V drop out voltage of the
LM2990 is for a maximum current of 1A, i.e. about 25 10H125 if I
remember their supply current requirements correctly. If you are only
going to use a couple of them you should be fine.
Besides that NIM crates also have higher output voltages rails, which
would make it unnecessary to us an LDO regulator anyway, provided your
total ECL chip count is low enough to keep the supply current low enough
for a linear regulator. If not you may consider a switching regulator,
e.g. one of National's Simple Switcher in inverting configuration. Using
one of their adjustable Simple Switchers you can generate the -5.2
from e.g. the +6V rail.

HTH
Klaus

 

[[email protected]]

Thank you for your quick reply. I will need 8 of 10H125. Would you
still use LM2990-5.2? I was also thinking of using -12V from the NIM
power supply, but it would be wasteful... And, I will investigate
switching regulator.

 

[John Larkin]

Hi, I am a grad student at Stanford. I am trying to make a ECL to TTL
converter board. So, I will use MC10H125. These chips need -5.2V. And I
am trying to get this from NIM crate's power supply of -6V. I am
wondering which voltage regulator to use. I was thinking of LM2990-5.2,
but the dropout voltage could be as much as 1V in which case, it won't
work. Any advice would be appreciated. Thank you.

In both CAMAC and NIM, it was traditional to use a single diode to
drop the +-6 to approximately 5. 1N5400 or something, good enough.

John

 

[Peter Bennett]

Hi, I am a grad student at Stanford. I am trying to make a ECL to TTL
converter board. So, I will use MC10H125. These chips need -5.2V. And I
am trying to get this from NIM crate's power supply of -6V. I am
wondering which voltage regulator to use. I was thinking of LM2990-5.2,
but the dropout voltage could be as much as 1V in which case, it won't
work. Any advice would be appreciated. Thank you.

Just use a normal rectifier diode (1N4005 or similar) in series with
the -6 supply - this will give an 0.7 volt drop which will give you
"close enough" to -5.2 volts.

We have lots of commercial CAMAC modules that just use a diode off the
+6 bus to provide power to TTL circuits.


--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
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[Joerg]

Hello John,

In both CAMAC and NIM, it was traditional to use a single diode to
drop the +-6 to approximately 5. 1N5400 or something, good enough.

One situation where that could be a problem is noise sensitive gear. We
had an ECL memory bank driver modulate a wimpy -5.2V rail in an
ultrasound machine. Since it was doing that at the video repetition rate
there was no way to sufficiently filter this out other than design a
stiff regulator. That got rid of the noise.

Regards, Joerg

 

[Joerg]

Hello Peter,

We have lots of commercial CAMAC modules that just use a diode off the
+6 bus to provide power to TTL circuits.

Doesn't that exceed the tolerance limits a little? While most CMOS would
be ok the old LS series isn't guaranteed to work properly above 5.25V.

Regards, Joerg

 

[Fred Bloggs]

Hi, I am a grad student at Stanford. I am trying to make a ECL to TTL
converter board. So, I will use MC10H125. These chips need -5.2V. And I
am trying to get this from NIM crate's power supply of -6V. I am
wondering which voltage regulator to use. I was thinking of LM2990-5.2,
but the dropout voltage could be as much as 1V in which case, it won't
work. Any advice would be appreciated. Thank you.

You don't need any voltage regulation because the ECL inputs are
referenced to GND, and the VEE deviation from nominal -5.2 is a common
mode effect that does not influence the signal thresholds.

From the ON Semi family characteristics app note:"Power supply
regulation which will achieve 10% regulation or better at the device
level is recommended. The –5.2 V power supply potential will result in
best circuit speed. Other values for VEE may be used. A more negative
voltage will increase noise margins at a cost of increased
power dissipation. A less negative voltage will have just the
opposite effect. (Noise margins and performance
specifications of MECL 10H are unaffected by variations in
VEE because of the internal voltage regulation.)"

Plan on 8x50=400mA Vee sink current, include a feel good 1uF power entry
capacitor on the board, and 0.001u bypass Vee to GND every few chips or
so depending on board type and layout. Do the same for Vcc. Add a
Schottky 3A diode in series with -6V if -5.x makes you feel better.

 

[Fred Bloggs]

Hello Peter,



Doesn't that exceed the tolerance limits a little? While most CMOS would
be ok the old LS series isn't guaranteed to work properly above 5.25V.

Regards, Joerg

The LS family is not guaranteed to work properly, period. Max Vcc is
7.0V, where did you get 5.25V from? -You could be thinking noise margin
degradation for > |+/-5%| Vcc deviation of commercial grade, and that
over 0-70C.

 

[Joerg]

Hello Fred,

The LS family is not guaranteed to work properly, period. Max Vcc is
7.0V, where did you get 5.25V from? -You could be thinking noise margin
degradation for > |+/-5%| Vcc deviation of commercial grade, and that
over 0-70C.

Page 6 is where I got it from:
http://focus.ti.com/lit/ds/symlink/sn74ls04.pdf

7V is the abs max but they never guarantee it to function that high,
just that it doesn't instantly die. I guess it depends on the
application but in mine (mostly med) you can never operate outside the
min-max values as stated in the data sheet under "recommended operating
conditions". Anything else would get flagged.

Regards, Joerg