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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: The strange thing ... posted by langel on August 12, 2007 at 04:46:43:
Basically the same negative feedback design. They still require a certain amount of esr for capacitive loads to give them a phase margin, hence the rec for a nominal value tantalum cap. What is recommended in the data sheet is output capacitance with a stable esr value, but the acceptable range would depend somewhat on the type of load, that is, if you don't use it with just a low esr cap on the output as the only load, then you probably don't need to worry...STABILITY CONSIDERATION
Stability consideration primarily concern the phase response
of the feedback loop. In order for stable operation, the loop
must maintain negative feedback. The LM1086 requires a
certain amount series resistance with capacitive loads. This
series resistance introduces a zero within the loop to increase
phase margin and thus increase stability. The equivalent
series resistance (ESR) of solid tantalum or aluminum
electrolytic capacitors is used to provide the appropriate zero
(approximately 500 kHz).The Aluminum electrolytic are less expensive than tantalums,
but their ESR varies exponentially at cold temperatures;
therefore requiring close examination when choosing
the desired transient response over temperature. Tantalums
are a convenient choice because their ESR varies less than
2:1 over temperature.The recommended load/decoupling capacitance is a 10uF
tantalum or a 50uF aluminum. These values will assure
stability for the majority of applications.
Edits: 08/12/07 08/12/07
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