LP2966EP datasheet(13/15 Pages) NSC

13 / 15 page

Applications Information (Continued)

ERROR and the output voltage. In this example, the input

voltage is changed to demonstrate the functionality of the

Error Flag.

The internal error flag comparators have open drain output

stages. Hence, the ERROR pins should be pulled high

through a pull up resistor. Although the ERROR pin can sink

current of 1mA, this current adds to the battery drain. Hence,

the value of the pull up resistor should be in the range of

100k

Ω to 1MΩ. The ERROR pins must be connected to

ground if this function is not used. It should also be noted

that when the shutdown pins are pulled low, the ERROR pins

are forced to be invalid for reasons of saving power in

shutdown mode.

SHUTDOWN OPERATION

The two LDO regulators in the LP2966EP have independent

shutdown. A CMOS Logic level signal at the shutdown( SD)

pin will turn-off the corresponding regulator. Pins SD1 and

SD2 must be actively terminated through a 100k

Ω pull-up

resistor for a proper operation. If these pins are driven from

a source that actively pulls high and low (such as a CMOS

rail to rail comparator), the pull-up resistor is not required.

These pins must be tied to Vin if not used.

DROP-OUT VOLTAGE

The drop-out voltage of a regulator is defined as the mini-

mum input-to-output differential required to stay within

100mV of the output voltage measured with a 1V differential.

The LP2966EP uses an internal MOSFET with an Rds(on) of

Ω. For CMOS LDOs, the drop-out voltage is the product of

the load current and the Rds(on) of the internal MOSFET.

REVERSE CURRENT PATH

The internal MOSFET in the LP2966EP has an inherent

parasitic diode. During normal operation, the input voltage is

higher than the output voltage and the parasitic diode is

reverse biased. However, if the output is pulled above the

input in an application, then current flows from the output to

the input as the parasitic diode gets forward biased. The

output can be pulled above the input as long as the current

in the parasitic diode is limited to 150mA.

MAXIMUM OUTPUT CURRENT CAPABILITY

Each output in the LP2966EP can deliver a current of more

than 150mA over the full operating temperature range. How-

ever, the maximum output current capability should be der-

ated by the junction temperature. Under all possible condi-

tions, the junction temperature must be within the range

specified under operating conditions. The LP2966EP is

available in MSOP-8 package. This package has a junction

to ambient temperature coefficient (

ja) of 235 ˚C/W with

minimum amount of copper area. The total power dissipation

of the device is approximately given by:

D =(Vin -VOUT1)IOUT1 +(Vin-VOUT2)IOUT2

The maximum power dissipation, P

Dmax, that the device can

tolerate can be calculated by using the formula

Dmax =(Tjmax -TA)/

where T

jmax is the maximum specified junction temperature

(125˚C), and T

A is the ambient temperature.

The following figures show the variation of thermal coeffi-

cient with different layout scenarios.

20099335

FIGURE 3. Error Flag Operation

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