The Error signal becomes low as V

goes high at about 5V input, where the output equals 4.75V.

Since the dropout voltage is load dependent, the

input volt-

age trip points will vary with load current, but the output volt-

age trip point does not.

The comparator has an open-collector output which requires

an external pull-up resistor. This resistor may be connected

to the LP2960 output or another supply voltage.

Best operation is obtained by connecting the pull-up to the

LP2960 output. If the pull-up resistor is connected to an ex-

ternal 5V supply, the error flag will incorrectly signal “HIGH”

whenever V

In selecting a value for the pull-up resistor, note that while

the output can sink 400 µA, this current adds to battery drain.

Suggested values range from 100 k

Ω–1 MΩ. The resistor is

not required if the output is unused.

If a large output capacitance is used, a false logic “HIGH”

can be generated when V

put becomes a high impedance, causing the voltage at the

error output to rise to its pull-up value. If the pull-up resistor

is connected to V

(which is a logic “HIGH” signal

incorrectly signifying the out-

put is in regulation).

The user may wish to divide down the error flag voltage us-

ing equal-value resistors (10 k

Ω suggested) to ensure a

low-level logic signal during any fault condition, while still al-

lowing a valid high logic level during normal operation.

AUXILIARY COMPARATOR

The LP2960 contains an auxiliary comparator whose invert-

ing input is connected to the 1.23V reference. The auxiIiary

comparator has an open-collector output whose electrical

characteristics are similar to the dropout detection compara-

tor. The non-inverting input and output are brought out for

external connections.

SHUTDOWN INPUT

A logic-level signal will shut off the regulator output when a

To prevent possible mis-operation, the Shutdown input must

be

actively

terminated.

If

the

input

is

driven

from

open-collector logic, a pull-up resistor (20 k

Ω–100 kΩ rec-

ommended) should be connected from the Shutdown input

to the regulator input.

If the Shutdown input is driven from a source which actively

pulls low and high (like an op-amp), the puIl-up resistor is not

required, but may be used.

If the Shutdown input is to be unused, the cost of the pull-up

resistor can be saved by tying the Shutdown input directly to

the regulator input.

IMPORTANT: Since the Absolute Maximum Ratings state

that the Shutdown input can not go more than 0.3V below

ground, the reverse-battery protection feature which protects

the regulator input is sacrificed if the Shutdown input is tied

directly to the regulator input.

If reverse-battery protection is required in an application,

the

pull-up resistor between the Shutdown input and the regula-

tor input must be used.

GROUND CONNECTIONS

The pins designated GND (see

Connection Diagrams) must

be connected to the high-current ground point in the circuit.

The GND pins are electrically connected (through the lead

frame) to the die substrate, making them ideal for conducting

ground current or heat (see

Heatsinking).

The parts in the surface-mount (M) package also have an

Analog Ground pin, which is the ground point on the die for

the regulator reference circuitry.

Along with the Sense pin, the availability of the Analog

Ground pin allows the designer the ability to use “remote”

sensing and eliminate output voltage errors due to IR drops

occurring along PC board traces.

IMPORTANT: The Analog Ground pin must be connected to

circuit ground at some point for the regulator to operate.

If remote sensing is not needed, the Analog Ground pin can

simply be pin-strapped to the adjacent GND pin.

HEATSINKING

A heatsink may be required with the LP2960 depending on

the maximum power dissipation and maximum ambient tem-

perature of the application. Under alI possible operating con-

ditions, the junction temperature must be within the range

specified under Absolute Maximum Ratings.

To determine if a heatsink is required, the power dissipated

by the regulator, P

The figure below shows the voltages and currents which are

present in the circuit, as welI as the formula for calcuIating

the power dissipated in the regulator:

Error Output Timing Diagram

DS011962-29

external supply. To avoid this invalid response, pull-up to regulator output.

Power Dissipation Diagram

DS011962-30

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