LP3980 datasheet(6/10 Pages) POWER

6 / 10 page

LP3980-00

Jul.-2018

Email: marketing@lowpowersemi.com

www.lowpowersemi.com

Page 6 of 10

Preliminary Datasheet

LP3980

Applications Information

Like any low-dropout regulator, the external

capacitors used with the LP3980 must be carefully

selected for regulator stability and performance.

Using a capacitor whose value is > 1µF on the

LP3980 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 LP3980 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 1µF with ESR is > 25mΩ on the

LP3980 output ensures stability. The LP3980 still

works well with output capacitor of other types due to

the wide stable ESR range. Figure 1 shows the

curves of allowable ESR range as a function of load

current for various output capacitor values. 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 LP3980 and

returned to a clean analog ground.

Enable Function

The

LP3980

features

LDO

regulator

enable/disable function. To assure the LDO regulator

will switch on, the EN turn on control level must be

greater than 1.2 volts. The LDO regulator will go into

the shutdown mode when the voltage on the EN pin

falls below 0.4 volts. For to protecting the system, the

LP3980 have a quick-discharge function. If the

enable function is not needed in a specific

application, it may be tied to VIN to keep the LDO

regulator in a continuously on state.

Thermal Considerations

Thermal protection limits power dissipation in

LP3980. 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 :

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 junctions to ambient.

The maximum power dissipation can be calculated

by following formula:

PD(MAX) = ( TJ(MAX) − TA ) / θJA

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