LM25005 datasheet(3/21 Pages) NSC

3 / 21 page

Pin Descriptions

Pin(S)

Name

Description

Application Information

VCC

Output of the bias regulator

Vcc tracks Vin up to 9V. Beyond 9V, Vcc is regulated to

7 Volts. A 0.1uF to 1uF ceramic decoupling capacitor is

required. An external voltage (7.5V – 14V) can be

applied to this pin to reduce internal power dissipation.

Shutdown or UVLO input

If the SD pin voltage is below 0.7V the regulator will be in

a low power state. If the SD pin voltage is between 0.7V

and 1.225V the regulator will be in standby mode. If the

SD pin voltage is above 1.225V the regulator will be

operational. An external voltage divider can be used to

set a line undervoltage shutdown threshold. If the SD pin

is left open circuit, a 5µA pull-up current source

configures the regulator fully operational.

3, 4

Vin

Input supply voltage

Nominal operating range: 7V to 42V

SYNC

Oscillator synchronization input or

output

The internal oscillator can be synchronized to an external

clock with an external pull-down device. Multiple

LM25005 devices can be synchronized together by

connection of their SYNC pins.

COMP

Output of the internal error amplifier

The loop compensation network should be connected

between this pin and the FB pin.

Feedback signal from the regulated

output

This pin is connected to the inverting input of the internal

error amplifier. The regulation threshold is 1.225V.

Internal oscillator frequency set input

The internal oscillator is set with a single resistor,

connected between this pin and the AGND pin. The

recommended frequency range is 50KHz to 500KHz.

RAMP

Ramp control signal

An external capacitor connected between this pin and the

AGND pin sets the ramp slope used for current mode

control. Recommended capacitor range 50pF to 2000pF.

AGND

Analog ground

Internal reference for the regulator control functions

Soft-start

An external capacitor and an internal 10µA current

source set the time constant for the rise of the error amp

reference. The SS pin is held low during standby, Vcc

UVLO and thermal shutdown.

OUT

Output voltage connection

Connect directly to the regulated output voltage.

13, 14

PGND

Power ground

Low side reference for the PRE switch and the IS sense

resistor.

15, 16

Current sense

Current measurement connection for the re-circulating

diode. An internal sense resistor and a sample/hold

circuit sense the diode current near the conclusion of the

off-time. This current measurement provides the DC level

of the emulated current ramp.

17, 18

Switching node

The source terminal of the internal buck switch. The SW

pin should be connected to the external Schottky diode

and to the buck inductor.

PRE

Pre-charge assist for the bootstrap

capacitor

This open drain output can be connected to SW pin to

aid charging the bootstrap capacitor during very light load

conditions or in applications where the output may be

pre-charged before the LM25005 is enabled. An internal

pre-charge MOSFET is turned on for 250ns each cycle

just prior to the on-time interval of the buck switch.

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