LP3989 datasheet(7/8 Pages) POWER

7 / 8 page

LP3989-01

Aug.-2014

Email: marketing@lowpowersemi.com

www.lowpowersemi.com

Page 7 of 8

Preliminary Datasheet

LP3989

VOUT(V)

R2(KΩ)

R1(KΩ)

1.2

25.5

1.5

44.6

1.8

63.8

70.5

2.5

99.9

2.8

117.5

90.8

3.3

103.1

3.5

111.4

132.0

4.2

140.3

4.5

152.6

Considering the practical application, we may add a

small capacitor with R1 in parallel which could be 22pF

or 47pF.

Thermal Considerations(for SOT23-5)

Thermal protection limits power dissipation in LP3989.

When the operation junction temperature exceeds

150°C, the OTP circuit starts the thermal shutdown

function turn the pass element off. The pass element

turns on again after the junction temperature cools by

25°C. For continue operation, do not exceed absolute

maximum operation junction temperature 125°C.

The power dissipation definition in device is:

PD = (VIN−VOUT) x IOUT + VIN x IQ

The maximum power dissipation depends on the

thermal resistance of IC package, PCB layout, the rate

of surroundings airflow and temperature difference

between junction and ambient.

The maximum power dissipation can be calculated by

following formula:

PD(MAX) = ( TJ(MAX) − TA ) /θJA

Where TJ(MAX) is the maximum operation junction

temperature 125°C, TA is the ambient temperature and

the θJA is the junction to ambient thermal resistance.

For recommended operating conditions specification

of LP3989, where TJ(MAX) is the maximum junction

temperature of the die (125°C) and TA is the maximum

ambient temperature. The junction to ambient thermal

resistance (θJA is layout dependent) for SOT23-5

package is 195°C/W.

PD(MAX) = (125°C−25°C) / 195 = 500mW (SOT23-5)

The maximum power dissipation depends on

operating ambient temperature for fixed TJ(MAX) and

thermal resistance θJA. Considering the PCB thermal

feather, the PD(MAX) may be higher than 500mW.

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