Antimouse (22.08.2016 17:39, просмотров: 212) ответил AU08 на LP2985 c десятикратным запасом по току и ESR выходных конденсаторов.
я бы поставил 4.7-10мкФ X5R, тем более, что ток видимо малюсенький (если говорите, что с запасом по характеристике ESR(load current) ) The LP2985-N was designed to work with ceramic capacitors on the output to take advantage of the benefits
they offer: for capacitance values in the 2.2 μF to 4.7 μF range, ceramics are the least expensive and also have
the lowest ESR values (which makes them best for eliminating high-frequency noise). The ESR of a typical 2.2
μF ceramic capacitor is in the range of 10 mΩ to 20 mΩ, which easily meets the ESR limits required for stability
by the LP2985-N.
One disadvantage of ceramic capacitors is that their capacitance can vary with temperature. Most large value
ceramic capacitors (≥ 2.2 μF) are manufactured with the Z5U or Y5V temperature characteristic, which results in
the capacitance dropping by more than 50% as the temperature goes from 25°C to 85°C.
This could cause problems if a 2.2 μF capacitor were used on the output since it will drop down to approximately
1 μF at high ambient temperatures (which could cause the LM2985 to oscillate). If Z5U or Y5V capacitors are
used on the output, a minimum capacitance value of 4.7 μF must be observed.
A better choice for temperature coefficient in ceramic capacitors is X7R, which holds the capacitance within
±15%. Unfortunately, the larger values of capacitance are not offered by all manufacturers in the X7R dielectric.
Tantalum capacitors are less desirable than ceramics for use as output capacitors because they are more
expensive when comparing equivalent capacitance and voltage ratings in the 1 μF to 4.7 μF range.
Another important consideration is that Tantalum capacitors have higher ESR values than equivalent size
ceramics. This means that while it may be possible to find a Tantalum capacitor with an ESR value within the
stable range, it would have to be larger in capacitance (which means bigger and more costly) than a ceramic
capacitor with the same ESR value.
It should also be noted that the ESR of a typical Tantalum will increase about 2:1 as the temperature goes from
25°C down to −40°C, so some guard band must be allowed.