LTM8049 datasheet(27/34 Pages) LINER

27 / 34 page

LTM4651

4651f

For more information www.linear.com/LTM4651

Figure 28. 5V to –24V Derating

Curve, with BGA Heat Sink

Figure 29. 12V to –24V Derating

Curve, with BGA Heat Sink

Figure 30. 24V to –24V Derating

Curve, with BGA Heat Sink

APPLICATIONS INFORMATION—DERATING CURVES

APPLICATIONS INFORMATION

Safety Considerations

The LTM4651 does not provide galvanic isolation from VIN

to VOUT–. There is no internal fuse. If required, a slow blow

fuse with a rating twice the maximum input current needs

to be provided to protect the unit from catastrophic failure.

The fuse or circuit breaker, if used, should be selected to

limit the current to the regulator in case of a MT MOSFET

fault. If MT fails, the system’s input supply will source

very large currents to PGND through MT. This can cause

excessive heat and board damage depending on how

much power the input voltage can deliver to this system.

A fuse or circuit breaker can be used as a secondary fault

protector in this situation. The LTM4651 does feature

overcurrent and overtemperature protection.

Layout Checklist/Example

The high integration of LTM4651 makes the PCB board

layout straightforward. However, to optimize its electrical

and thermal performance, some layout considerations

are still necessary.

• Use large PCB copper areas for high current paths,

including VIN, PGND and VOUT–. Doing so helps to

minimize the PCB conduction loss and thermal stress.

• Place high frequency ceramic input and output (and, if

used, input-to-output) capacitors next to the VIN, VD,

PGNDandVOUT–pinstominimizehighfrequencynoise.

• Place a dedicated power ground layer underneath the

LTM4651.

• To minimize the via conduction loss and reduce module

thermal stress, use multiple vias for interconnection

between top layer and other power layers.

• Do not put vias directly on pads, unless they are capped

or plated over.

• Use a separate SVOUT– copper plane for components

connected to signal pins. Connect SVOUT– to VOUT–

directly under the module.

• For parallel module applications, connect the VOUT–,

GNDSNS,RUN,ISETa,COMPaandPGOODpinstogether

as shown in Figure 41.

• Bring out test points on the signal pins for monitoring.

Figure 31 gives a good example of the recommended

LTM4651 layout.

0LFM

200LFM

400LFM

AMBIENT TEMPERATURE (°C)

100

120

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

4651 F28

0LFM

200LFM

400LFM

AMBIENT TEMPERATURE (°C)

100

120

0.125

0.250

0.375

0.500

0.625

0.750

0.875

1.000

1.125

1.250

4651 F29

0LFM

200LFM

400LFM

AMBIENT TEMPERATURE (°C)

100

120

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

4651 F30

LTM8049 Datasheet(PDF) 27 Page - Linear Technology

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