LT1963 datasheet(14/28 Pages) LINER

14 / 28 page

LT3089

3089f

For more information www.linear.com/LT3089

APPLICATIONS INFORMATION

In LT3089 applications with long wires or PCB traces, the

inductive reactance may cause instability. In some cases,

adding series resistance to the input and output lines (as

showninFigure4)maysufficientlydampenthesepossible

high-Q lines and provide stability. The user must evaluate

therequiredresistorvaluesagainstthedesign’sheadroom

constraints. In general, operation at low output current

levels (<20mA) automatically requires higher values of

programming resistors and may provide the necessary

damping without additional series impedance.

If the line impedances in series with the LT3089 are

complex enough such that series damping resistors are

not sufficient, a frequency compensation network may be

necessary. Several options may be considered.

Figure 5 depicts the simplest frequency compensation

networks as a single capacitor across the two terminals

of the current source. Some applications may use the

capacitance to stand off DC voltage but allow the transfer

of data down a signal line.

For some applications, pure capacitance may be unac-

ceptable or present a design constraint. One circuit

example typifying this is an “intrinsically-safe” circuit in

which an overload or fault condition potentially allows the

capacitor’s stored energy to create a spark or arc. For ap-

plications where a single capacitor is unacceptable, Figure

5 alternately shows a series RC network connected across

the two terminals of the current source. This network has

the added benefit of limiting the discharge current of the

capacitor under a fault condition, preventing sparks or

arcs. In many instances, a series RC network is the best

solutionforstabilizingtheapplicationcircuit.Typicalresis-

tor values will range from 100Ω to 5k. Once again, Linear

Technology strongly recommends testing stability in situ

foranyLT3089applicationacrossalloperatingconditions,

especiallyonesthatpresentcompleximpedancenetworks

at the input and output of the current source.

If an application refers the bottom of the LT3089 current

source to GND, it may be necessary to bypass the top

of the current source with a capacitor to GND. In some

cases, this capacitor may already exist and no additional

capacitance is required. For example, if the LT3089 was

used as a variable current source on the output of a power

supply, the output bypass capacitance would suffice to

provide LT3089 stability. Other applications may require

the addition of a bypass capacitor. A series RC network

may also be used as necessary, and depends on the ap-

plication requirements.

SET

OUT

–

LT3089

50µA

RSET

ROUT

RSERIES

LONG LINE

REACTANCE/INDUCTANCE

3089 F04

LONG LINE

REACTANCE/INDUCTANCE

Figure 4. Adding Series Resistance Decouples

and Dampens Long Line Reactances

Figure 5. Compensation from Input to Output

of Current Source Provides Stability

3089 F05

SET

OUT

–

LT3089

50µA

CCOMP OR

RSET

ROUT

RCOMP

CCOMP

LT1963 датащи(PDF) 14 Page - Linear Technology

LT1963 датащи(HTML) 14 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

датащи скачать

ссылки URL