SHUTDOWN OPERATION

A CMOS Logic level signal at the shutdown ( SD) pin will

turn-off the regulator. Pin SD must be actively terminated

through a 10k

Ω pull-up resistor for a proper operation. If this

pin is 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. This pin must be tied to Vin if not used.

DROPOUT VOLTAGE

The dropout voltage of a regulator is defined as the minimum

input-to-output differential required to stay within 2% of the

output voltage. The LP3962EP/LP3965EP use an internal

MOSFET with an Rds(on) of 240m

Ω (typically). For CMOS

LDOs, the dropout voltage is the product of the load current

and the Rds(on) of the internal MOSFET.

REVERSE CURRENT PATH

The internal MOSFET in LP3962EP and LP3965EP 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 200mA continuous

and 1A peak.

MAXIMUM OUTPUT CURRENT CAPABILITY

LP3962 and LP3965 can deliver a continuous current of 1.5

A over the full operating temperature range. A heatsink may

be required depending on the maximum power dissipation

and maximum ambient temperature of the application. Under

all possible conditions, the junction temperature must be

within the range specified under operating conditions. The

total power dissipation of the device is given by:

P

where I

(specified under Electrical Characteristics).

The maximum allowable temperature rise (T

on the maximum ambient temperature (T

cation, and the maximum allowable junction temperature(T

J-

max

):

T

The maximum allowable value for junction to ambient Ther-

mal Resistance,

θ

θ

LP3962 and LP3965 are available in TO-220, TO-263, and

SOT-223 packages. The thermal resistance depends on

amount of copper area or heat sink, and on air flow. If the

maximum allowable value of

θ

≥ 60

˚C/W for TO-220 package,

≥60 ˚C/W for TO-263 package,

and

≥ 140 ˚C/W for SOT-223 package, no heatsink is

needed since the package can dissipate enough heat to

satisfy these requirements. If the value for allowable

θ

below these limits, a heat sink is required.

HEATSINKING TO-220 PACKAGES

The thermal resistance of a TO220 package can be reduced

by attaching it to a heat sink or a copper plane on a PC

board. If a copper plane is to be used, the values of

θ

be same as shown in next section for TO263 package.

The heatsink to be used in the application should have a

heatsink to ambient thermal resistance,

θ

HA

≤θ

θ

θ

In this equation,

θ

junction to the surface of the heat sink and

θ

resistance from the junction to the surface of the case.

θ

about 3˚C/W for a TO220 package. The value for

θ

pends on method of attachment, insulator, etc.

θ

between 1.5˚C/W to 2.5˚C/W. If the exact value is unknown,

2˚C/W can be assumed.

20114708

FIGURE 2. Improving remote load regulation using LP3965EP

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