LP3985-00

May.-2018

www.lowpowersemi.com

Page 5 of 7

Preliminary Datasheet

LP3985

Applications Information

Like any low-dropout regulator, the external capacitors

used with the LP3985 must be carefully selected for

regulator stability and performance. Using a capacitor

whose value is > 1µF on the LP3985 input and the

amount of capacitance can be increased without limit.

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 LDOs application. The

LP3985 is designed specifically to work with low ESR

ceramic output capacitor in space-saving and

performance consideration. Using a ceramic capacitor

whose value is at least 1µF with ESR is > 25mΩ on the

LP3985 output ensures stability. The LP3985 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 LP3985 and returned to a

clean analog ground.

Thermal Considerations

Thermal protection limits power dissipation in LP3985.

When the operation junction temperature exceeds

150℃, 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

20℃. For continue operation, do not exceed absolute

maximum operation junction temperature 125℃.

The power dissipation definition in device is:

The maximum power dissipation depends on the

thermal resistance of IC package, PCB layout, the rate

of surroundings airflow and temperature difference

between junction to ambient.

The maximum power dissipation can be calculated by

following formula: