SS6611GOTR datasheet(11/16 Pages) SSC

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SS6610/11G

4/21/2006 Rev.3.01

PIN DESCRIPTIONS

PIN 1: FB

Connect to pin 8:OUT to get +3.3V

output, connect to pin 6:GND to get

+5.0V output, or use a resistor

network to set the output voltage

between +1.8V and +5.5V.

PIN 2: LBI

Low-battery comparator input.

Internally set at +1.23V to trip.

PIN 3: LBO

Open-drain low-battery comparator

output. Output is low when VLBI is

<1.23V. LBO is high-impedance

during shutdown.

PIN 4: REF

1.23V reference voltage. Bypass

with a 0.1

µF capacitor.

PIN 5: SHDN Shutdown input. High = operating,

low = shutdown.

PIN 6: GND

Ground

PIN 7: LX

N-channel and P-channel power

MOSFET drain.

PIN 8: OUT

Power output. OUT provides the

bootstrap power to the IC.

APPLICATION INFORMATION

Overview

The SS6610/11 series are high-efficiency, step-up DC/DC

converters, featuring a built-in synchronous

rectifier, which reduces size and cost by eliminating

the need for an external Schottky diode. The start-up

voltage of the SS6610 and SS6611 is as low as

0.8V and they operate with an input voltage down

to 0.7V. Quiescent supply current is only 20

µA.

The internal P-MOSFET on-resistance is typically

0.3

Ω to improve overall efficiency by minimizing AC

losses. The output voltage can be easily set using

two external resistors for 1.8V to 5.5V; connecting

FB to OUT to get 3.3V; or connecting to GND to get

5.0V. The peak current of the internal switch is fixed

at 1.0A (SS6610) or 0.65A (SS6611) for design

flexibility. The current limits of the SS6610 and SS6611

are 1.0A and 0.65A respectively. The lower current

limit allows the use of a physically smaller inductor in

space-sensitive applications.

PFM Control Scheme

A key feature of the SS6610 series is a unique

minimum-off-time, constant-on-time, current-limited,

pulse-frequency-modulation (PFM) control scheme

(see BLOCK DIAGRAM) with ultra-low quiescent

current. The peak current of the internal N-MOSFET

power switch can be fixed at 1.0A (SS6610) or

0.65A (SS6611). The switch frequency depends on

either loading conditions or input voltage, and can

range up to 500KHz. It is governed by a pair of one-

shots that set a minimum off-time (1

µs) and a

maximum on-time (4

µs).

Synchronous Rectification

Using the internal synchronous rectifier eliminates

the need for an external Schottky diode, reducing

the cost and board space. During the cycle of off-

time, the P-MOSFET turns on and shuts the N-

MOSFET off. Due to the low turn-on resistance

of the MOSFET, the synchronous rectifier signif-

cantly improves efficiency without an additional ex-

ternal Schottky diode. Thus, the conversion effi-

ciency can be as high as 93%.

Reference Voltage

The reference voltage (REF) is nominally 1.23V for

excellent T.C. performance. In addition, the REF pin can

source up to 100

µA to an external circuit with good load

regulation (<10mV). A bypass capacitor of 0.1

µF is

required for proper operation and good performance.

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