LTM4606 datasheet(14/24 Pages) LINER

14 / 24 page

LTM8050

8050fc

For more information www.linear.com/LTM8050

APPLICATIONS INFORMATION

Table 2. Switching Frequency vs RT Value

SWITCHING FREQUENCY (MHz)

RT VALUE (kΩ)

0.1

432

0.2

215

0.3

137

0.4

93.1

0.5

73.2

0.6

57.6

0.7

51.1

0.8

38.3

0.9

33.2

32.4

1.2

24.9

1.4

1.6

16.2

1.8

2.2

8.06

2.4

7.15

Operating Frequency Trade-offs

It is recommended that the user apply the optimal RT

value given in Table 1 for the input and output operating

condition. System level or other considerations, however,

may necessitate another operating frequency. While the

LTM8050 is flexible enough to accommodate a wide range

of operating frequencies, a haphazardly chosen one may

result in undesirable operation under certain operating or

fault conditions. A frequency that is too high can reduce

efficiency, generate excessive heat or even damage the

LTM8050 if the output is overloaded or short circuited. A

frequencythatistoolowcanresultinafinaldesignthathas

too much output ripple or too large of an output capacitor.

BIAS Pin Considerations

The BIAS pin is used to provide drive power for the internal

power switching stage and operate other internal circuitry.

Forproperoperation,itmustbepoweredbyatleast2.8V.If

the output voltage is programmed to 2.8V or higher, BIAS

may be simply tied to AUX. If VOUT is less than 2.8V, BIAS

can be tied to VIN or some other voltage source. If the BIAS

pin voltage is too high, the efficiency of the LTM8050 may

suffer.TheoptimumBIASvoltageisdependentuponmany

factors, such as load current, input voltage, output voltage

and switching frequency, but 4V to 5V works well in many

applications.Inallcases,ensurethatthemaximumvoltage

at the BIAS pin is less than 25V and that the sum of VIN

and BIAS is less than 72V. If BIAS power is applied from

a remote or noisy voltage source, it may be necessary to

apply a decoupling capacitor locally to the pin.

Load Sharing

Two or more LTM8050’s may be paralleled to produce

highercurrents.Todothis,tietheVIN,FB,VOUTandSHARE

pins of all the paralleled LTM8050’s together. To ensure

thatparalleledmodulesstartuptogether,theRUN/SSpins

may be tied together, as well. If the RUN/SS pins are not

tied together, make sure that the same valued soft-start

capacitors are used for each module. Current sharing

can be improved by synchronizing the LTM8050s. An

example of two LTM8050s configured for load sharing is

given in the Typical Applications section. When n number

of units are connected for parallel operation and a single

feedback resistor is used for all of them, the equation for

the feedback resistor is:

RFB =

394.21

N VOUT –0.79

(

)

kΩ

Burst Mode Operation

To enhance efficiency at light loads, the LTM8050 auto-

matically switches to Burst Mode operation which keeps

the output capacitor charged to the proper voltage while

minimizingtheinputquiescentcurrent.DuringBurstMode

operation, the LTM8050 delivers single cycle bursts of

current to the output capacitor followed by sleep periods

wheretheoutputpowerisdeliveredtotheloadbytheoutput

capacitor. In addition, VINandBIASquiescentcurrentsare

each reduced to microamps during the sleep time. As the

load current decreases towards a no load condition, the

percentage of time that the LTM8050 operates in sleep

mode increases and the average input current is greatly

reduced, resulting in higher efficiency.

Burst Mode operation is enabled by tying SYNC to GND.

To disable Burst Mode operation, tie SYNC to a stable

voltage above 0.7V. Do not leave the SYNC pin floating.

LTM4606 Datasheet(PDF) 14 Page - Linear Technology

LTM4606 Datasheet(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

Datasheet Download

Link URL