LM5088

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SNVS600G – DECEMBER 2008 – REVISED MARCH 2011

PIN DESCRIPTIONS

Pin(s)

Name

Description

Application Information

1

VIN

Input supply voltage

IC supply voltage. The operating range is 4.5V to 75V

2

EN

Enable input

If the EN pin voltage is below 0.4V the regulator will be in a low power state. If

the EN pin voltage is between 0.4V and 1.2V the controller will be in standby

mode. If the EN pin voltage is above 1.2V the controller will be operational. An

external voltage divider can be used to set a line under voltage shutdown

threshold. If the EN pin is left open, a 5µA pull-up current forces the pin to the

high state and enables the controller.

3

SS

Soft-start

When SS is below the internal 1.2V reference, the SS voltage will control the

error amplifier. An internal 11 µA current source charges an external capacitor to

set the start-up rate of the controller. The SS pin is held low in the standby, VCC

UV and thermal shutdown states. The SS pin can be used for voltage tracking by

connecting this pin to a master voltage supply less than 1.2V. The applied voltage

will act as the reference for the error amplifier.

4

RAMP

Ramp control signal

An external capacitor connected between this pin and the GND pin sets the ramp

slope used for emulated current mode control. Recommended capacitor range

100 pF to 2000 pF. See the Applications section for selection of capacitor value.

5

RT/SYNC

Internal oscillator frequency

The internal oscillator is programmed with a single resistor between this pin and

set input and synchronization the GND pin. The recommended frequency range is 50 kHz to 1 MHz. An

input

external synchronization signal, which is higher in frequency than the

programmed frequency, can be applied to this pin through a small coupling

capacitor. The RT resistor to ground is required even when using external

synchronization.

6

GND

Ground

Ground return.

7

COMP

Output of the internal error

The loop compensation network should be connected between this pin and the

amplifier

FB pin.

8

FB

Feedback signal from the

This pin is connected to the inverting input of the internal error amplifier. The

regulated output

regulation threshold is 1.205V.

9

OUT

Output voltage connection

Connect directly to the regulated output voltage.

10

DITH

Frequency Dithering (

A capacitor connected between DITH pin and GND is charged and discharged by

LM5088-1 Only)

27 µA current sources. As the voltage on the DITH pin ramps up and down, the

oscillator frequency is modulated between -5% to +5% of the nominal frequency

set by the RT resistor. Grounding the DITH pin will disable the frequency

dithering mode.

10

RES

Hiccup Mode Restart (

The RES pin is normally connected to an external capacitor that sets the timing

LM5088-2 Only)

for hiccup mode current limiting. In normal operation, a 25µA current source

discharges the RES pin capacitor to ground. If cycle-by-cycle current limit

threshold is exceeded during any PWM cycle, the current sink is disabled and

RES capacitor is charged by an internal 50 µA current. If the RES voltage

reaches 1.2V, the HG pin gate drive signal will be disabled and the RES pin

capacitor will be discharged by a 1 µA current sink. Normal operation will resume

when the RES pin falls below 0.2V.

11

CSG

Current Sense Ground

Low side reference for the current sense resistor.

12

CS

Current sense

Current measurement connection for the re-circulating diode. An external sense

resistor and an internal sample/hold circuit sense the diode current at the

conclusion of the buck switch off-time. This current measurement provides the

DC offset level for the emulated current ramp.

13

SW

Switching node

Connect to the source terminal of the external MOSFET switch.

14

HG

High Gate

Connect to the gate terminal of the external MOSFET switch.

15

BOOT

Input for bootstrap capacitor

An external capacitor is required between the BOOT and the SW pins to provide

bias to the MOSFET gate driver. The capacitor is charged from VCC via an

internal diode during the off-time of the buck switch.

16

VCC

Output of the bias regulator

VCC tracks VIN up to the regulation level (7.8V Typ). A 0.1 µF to 10 µF ceramic

decoupling capacitor is required. An external voltage between 8.3V and 13V can

be applied to this pin to reduce internal power dissipation.

These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam

during storage or handling to prevent electrostatic damage to the MOS gates.

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