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Old 13th September 2006, 01:50 PM   #1
jarthel is offline jarthel  Australia
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Default LT1084 and input capacitor

in the LT1084 datasheet, there is a 10uF on the input pin.

I am wondering if this would be similar to the .1uF capacitor on the input pins of the LM117 (from the LM117 datasheet). On the LM117 datasheet, it is said that the .1uF cap is only needed if the input pin is 6inches away from the filter cap.

Thank you for the help
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Old 13th September 2006, 11:47 PM   #2
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Switching regulators have huge dI/dT so any inductance (ESL) in the power buss can kill them. E=L*dI/dT. You need good quality inductor and short leads.
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Old 13th September 2006, 11:49 PM   #3
jarthel is offline jarthel  Australia
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Quote:
Originally posted by sawreyrw
Switching regulators have huge dI/dT so any inductance (ESL) in the power buss can kill them. E=L*dI/dT. You need good quality inductor and short leads.
I do not understand what you are saying. LT1084 is a linear regulator.
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Old 14th September 2006, 07:41 AM   #4
AndrewT is offline AndrewT  Scotland
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Hi,
I would put the 10uF at the input pin regardless of other data sheet conditional recomendations.
Does 1084 have an adjust pin?
If so, then place a good, big cap on the adjust pin as well.
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regards Andrew T.
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Old 14th September 2006, 07:56 AM   #5
Gasho is offline Gasho  Croatia
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In LT1084 generic scheme 10uF is placed on input like smllest recomended value for filtering cap.

LT1084 is manufactured as a series of fixed voltage( voltage sufix behing LT1084 ) and variable voltage regulator.

If you use some preregulator before LT1084 , 10-47uf will be OK , but if LT is the only regulator after stabilisation (greatz) and filtration (Cap only , of LC filter) that cap must be of bigger value (4700-10000uF) to ramove ripples from greatz bridge or discrete diode bridge.
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