LTC6655BHLS8-4.096PBF データシートの表示（PDF） - Linear Technology
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LTC6655BHLS8-4.096PBF Datasheet PDF : 26 Pages
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LTC6655
Applications Information
Bypass and Load Capacitors
The LTC6655 voltage references require a 0.1µF or larger
input capacitor located close to the part to improve power
supply rejection. An output capacitor with a value between
2.7µF and 100µF is also required.
The output capacitor has a direct effect on the stability,
turn-on time and settling behavior. Choose a capacitor
with low ESR to insure stability. Resistance in series
with the output capacitor (ESR) introduces a zero in the
output buffer transfer function and could cause instabil-
ity. The 2.7μF to 100μF range includes several types of
capacitors that are readily available as through-hole and
surface mount components. It is recommended to keep
ESR less than or equal to 0.1Ω. Capacitance and ESR are
both frequency dependent. At higher frequencies capaci-
tance drops and ESR increases. To insure stable operation
the output capacitor should have the required values at
100kHz.
In order to achieve the best performance, caution should
be used when choosing a capacitor. X7R ceramic capaci-
tors are small, come in appropriate values and are rela-
tively stable over a wide temperature range. However,
for a low noise application X7R capacitors may not be
suitable since they may exhibit a piezoelectric effect. The
mechanical vibrations cause a charge displacement in the
ceramic dielectric and the resulting perturbation can look
like noise. If X7R capacitors are necessary, a thorough
bench evaluation should be completed to verify proper
performance.
For very low noise applications where every nanovolt
counts, film capacitors should be considered for their
low noise and lack of piezoelectric effects. Film capaci-
tors such as polyester, polystyrene, polycarbonate, and
polypropylene have good temperature stability. Additional
care must be taken as polystyrene and polypropylene have
an upper temperature limit of 85°C to 105°C. Above these
temperatures, the working voltages need to be derated
according to manufacturer’s specifications. Another type
of film capacitor is polyphenylene sulfide (PPS). These
devices work over a wide temperature range, are stable,
and have large capacitance values beyond 1μF. In general,
film capacitors are found in surface mount and leaded
packages. Table 1 is a partial list of capacitor companies
and some of their available products.
In voltage reference applications, film capacitor lifetime is
affected by temperature and applied voltage. When poly-
ester capacitors are operated beyond their rated tempera-
tures (some capacitors are not rated for operation above
85°C) they need to be derated. Voltage derating is usually
accomplished as a ratio of applied voltage to rated volt-
age limit. Contact specific film capacitor manufacturers to
determine exact lifetime and derating information.
The lifetime of X7R capacitors is long, especially for refer-
ence applications. Capacitor lifetime is degraded by oper-
ating near or exceeding the rated voltage, at high tem-
perature, with AC ripple or some combination of these.
Most reference applications have AC ripple only during
transient events.
Table 1. Film Capacitor Companies
COMPANY
DIELECTRIC
Cornell Dublier
Polyester
Dearborn Electronics
Polyester
Tecate
Polyester
Wima
Polyester
Vishay
Polyester
Vishay
Polycarbonate
Dearborn Electronics
Polyphenylene Sulfide (PPS)
Wima
Polyphenylene Sulfide (PPS)
AVAILABLE CAPACITANCE
0.5µF to 10µF
0.1µF to 12µF
0.01µF to 18µF
10µF to 22µF
1000pF to 15µF
0.01µF to 10µF
0.01µF to 15µF
0.01µF to 6.8µF
TEMPERATURE RANGE
TYPE
–55°C to 125°C
DME
–55°C to 125°C 218P, 430P, 431P, 442P, and 410P
–40°C to 105°C
901, 914, and 914D
–55°C to 100°C
MKS 4, MKS 2-XL
–55°C to 125°C
MKT1820
–55°C to 100°C
MKC1862, 632P
–55°C to 125°C 820P, 832P, 842P, 860P, and 880P
–55°C to 140°C
SMD-PPS
For more information www.linear.com/LTC6655
6655ff
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