LM5110

SNVS255A – MAY 2004 – REVISED MAY 2004

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Assuming negligible gate resistance, the total power dissipated in the MOSFET driver due to gate charge is

approximated by

where

•

The power dissipation in the driver due to charging and discharging of MOSFET gate capacitances at switching

If both channels of the LM5110 are operating at equal frequency with equivalent loads, the total losses will be

twice as this value which is 0.216W.

In addition to the above gate charge power dissipation, - transient power is dissipated in the driver during output

interval of time through the output totem-pole N and P channel MOSFETs. The final component of power

dissipation in the driver is the power associated with the quiescent bias current consumed by the driver input

stage and Under-voltage lockout sections.

Characterization of the LM5110 provides accurate estimates of the transient and quiescent power dissipation

components. At 300 kHz switching frequency and 30 nC load used in the example, the transient power will be 8

Therefore the total power dissipation

We know that the junction temperature is given by

Or the rise in temperature is given by

For SOIC-8 package

For WSON-10 package, the integrated circuit die is attached to leadframe die pad which is soldered directly to

the printed circuit board. This substantially decreases the junction to ambient thermal resistance (

thereby reduced to just 9.5 degrees.

CONTINUOUS CURRENT RATING OF LM5110

The LM5110 can deliver pulsed source/sink currents of 3A and 5A to capacitive loads. In applications requiring

continuous load current (resistive or inductive loads), package power dissipation, limits the LM5110 current

capability far below the 5A sink/3A source capability. Rated continuous current can be estimated both when

sourcing current to or sinking current from the load. For example when sinking, the maximum sink current can be

calculated as

where

•

2.5

Similarly, the maximum continuous source current can be calculated as

10

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