LP3993 datasheet(5/7 Pages) POWER

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LP3993-02

May.-2019

Email: marketing@lowpowersemi.com

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Page 5 of 7

Preliminary Datasheet

LP3993

Applications Information

ike any low-dropout regulator, the external capacitors

used with the LP3993 must be carefully selected for

regulator stability and performance. Using a capacitor

whose value is ≥ 10µF on the LP3993 input. The

input capacitor must be located a distance of not more

than 0.5 inch from the input pin of the IC and returned

to a clean analog ground. Any good quality ceramic or

tantalum can be used for this capacitor. The capacitor

with larger value and lower ESR (equivalent series

resistance) provides better PSRR and line-transient

response. The output capacitor must meet both

requirements for minimum amount of capacitance and

ESR in all LDO`s application. The LP3993 is designed

specifically to work with low ESR ceramic output

capacitor

space-saving

and

performance

consideration. Using a ceramic capacitor whose value

is at least 10µF with ESR is > 25mΩ on the LP3993

output ensures stability. The LP3993 still works well

with output capacitor of other types due to the wide

stable ESR range. Output capacitor of larger

capacitance can reduce noise and improve load

transient response, stability, and PSRR. The output

capacitor should be located not more than 0.5 inch

from the VOUT pin of the LP3993 and returned to a

clean analog ground.

Thermal Considerations

Thermal protection limits power dissipation in LP3993.

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.

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 LP3993, the junction to ambient thermal resistance

(θJA is layout dependent) for LP3993 showed below.

SOT23-3 : 250℃/W

SOT89-3 : 165℃/W

And，

PD=(125°C−25°C)/250℃/W= 400mW (SOT23-3)

PD=(125°C−25°C)/165℃/W= 600mW (SOT89-3)

The maximum power dissipation depends on

operating ambient temperature for fixed TJ(MAX) and

thermal resistance θJA.

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