ISOURCE (MAX) :=

TJ(MAX) - TA

TJA · VDIODE

ISINK (MAX) :=

TJ(MAX) - TA

TJA · RDS (ON)

16

LM5111

SNVS300H – JULY 2004 – REVISED SEPTEMBER 2016

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Thermal Considerations (continued)

Or the rise in temperature is given by

TRISE = TJ − TA = PD × θJA

(6)

For SOIC package, θJA is estimated as 170°C/W for the conditions of natural convection. For MSOP-PowerPAD,

θJA is typically 60°C/W.

Therefore for SOIC TRISE is equal to

TRISE = 0.236 × 170 = 40.1°C

(7)

11.3.2 Continuous Current Rating of LM5111

The LM5111 can deliver pulsed source/sink currents of 3 A and 5 A to capacitive loads. In applications requiring

continuous load current (resistive or inductive loads), package power dissipation, limits the LM5111 current

capability far below the 5-A sink and 3-A 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

•

RDS(on) is the on resistance of lower MOSFET in the output stage of LM5111

(8)

Consider TJ(max) of 125°C and θJA of 170°C/W for an SO-8 package under the condition of natural convection

and no air flow. If the ambient temperature (TA) is 60°C, and the RDS(on) of the LM5111 output at TJ(max) is 2.5

Ω, this equation yields ISINK(max) of 391 mA which is much smaller than 5-A peak pulsed currents.

Similarly, the maximum continuous source current can be calculated as

where

•

VDIODE is the voltage drop across hybrid output stage which varies over temperature and can be assumed to

be about 1.1 V at TJ(max) of 125°C

(9)

Assuming the same parameters as above, this equation yields ISOURCE(max) of 347 mA.