LTM4614EVPBF datasheet(12/20 Pages) LINER

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LTM4614

4614fa

APPLICATIONS INFORMATION

Parallel Switching Regulator Operation

The LTM4614 switching regulators are inherently current

mode control. Paralleling will have very good current

sharing. This will balance the thermals on the design.

Figure 13 shows a schematic of a parallel design. The

voltage feedback equation changes with the variable N

as channels are paralleled.

The equation:

OUT = 0.8V •

4.99k

N is the number of paralleled channels.

Thermal Considerations and Output Current Derating

The power loss curves in Figures 5 and 6 can be used

in coordination with the load current de-rating curves in

Figures 7 to 10 for calculating an approximate

θJA thermal

resistance for the LTM4614 with various heat sinking

and airﬂow conditions. Both of the LTM4614 outputs

are at full 4A load current, and the power loss curves in

Figures 5 and 6 are combine power losses plotted for both

output voltages up to 4A each. The 4A output voltages are

1.2V and 3.3V. These voltages are chosen to include the

lower and higher output voltage ranges for correlating

the thermal resistance. Thermal models are derived from

several temperature measurements in a controlled tem-

perature chamber along with thermal modeling analysis.

The junction temperatures are monitored while ambient

temperature is increased with and without airﬂow. The

junctions are maintained at ~120°C while lowering output

current or power while increasing ambient temperature.

The 120°C is chosen to allow for a 5°C margin window

relative to the maximum 125°C. The decreased output

current will decrease the internal module loss as ambi-

ent temperature is increased. The power loss curves in

Figures 5 and 6 show this amount of power loss as a

function of load current that is speciﬁed for both chan-

nels The monitored junction temperature of 120°C minus

the ambient operating temperature speciﬁes how much

Figure 5. 1.2V Power Loss

Figure 6. 3.3V Power Loss

2.5

2.0

1.0

1.5

0.5

4614 F05

LOAD CURRENT (A)

VIN = 5V

3.0

2.0

2.5

1.0

1.5

0.5

4614 F06

LOAD CURRENT (A)

VIN = 5V

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