capacitor with an ESR value within the stable range, it would

have to be larger in capacitance (which means bigger and

more costly) than a ceramic capacitor with the same ESR

value. It should also be noted that the ESR of a typical

tantalum will increase about 2:1 as the temperature goes

from 25˚C down to -40˚C, so some guard band must be

allowed.

ENABLE CONTROL

The LP5996 features active high enable pins for each regu-

lator, EN1 and EN2, which turns the corresponding LDO off

when pulled low. The device outputs are enabled when the

enable pins are set to high. When not enabled the regulator

output is off and the device typically consumes 2nA.

If the application does not require the Enable switching

feature, one or both enable pins should be tied to V

the regulator output permanently on.

To ensure proper operation, the signal source used to drive

the enable inputs must be able to swing above and below the

specified turn-on/off voltage thresholds listed in the Electrical

Characteristics section under V

BYPASS CAPACITOR

The internal voltage reference circuit of the LP5996 is con-

nected to the C

external capacitor, connected to this pin, forms a low-pass

filter which reduces the noise level on both outputs of the

device. There is also some improvement in PSSR and line

transient performance. Internal circuitry ensures rapid charg-

ing of the C

ceramic capacitor with either NPO or COG dielectric is rec-

ommended due to their low leakage characteristics and low

noise performance.

SAFE AREA OF OPERATION

Due consideration should be given to operating conditions to

avoid excessive thermal dissipation of the LP5996 or trigger-

ing its thermal shutdown circuit. When both outputs are

enabled,

the

total

power

dissipation

will

be P

each LDO

In general, device options which have a large difference in

output voltage will dissipate more power with both outputs

enabled, due to the input voltage required for the higher

output voltage LDO. In such cases, especially at elevated

ambient temperature, it may not be possible to operate both

outputs at maximum current at the same time.

www.national.com

12