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SS6620/21/2

SS6622

PIN 1: FB-

Connect to OUT for +3.3V output.

Use a resistor network to set the out-

put voltage from +1.8V to +4.0V.

PIN 2: LBI-

Low-Battery comparator input. Inter-

nally set to trip at +1.23V.

PIN 3: LBO- Open-drain low battery comparator

output. Output is low when VLBI is

<1.23V. LBO is high impedance dur-

ing shutdown.

PIN 4:

CLSEL-

Current-limit selects

input. CLSEL= OUT sets the current

limit to 0.8A. CLSEL=GND sets the

current limit to 0.45A.

PIN 5: REF-

1.23V reference voltage. Bypass

with a 0.1

µF capacitor.

PIN 6: SHDN- Shutdown input. High=operating,

low=shutdown.

PIN 7: BATT- Battery input and damping switch

connection. If damping switch is

unused, leave BATT unconnected.

PIN 8: GND-

Ground.

PIN 9: LX-

N-channel and P-channel power

MOSFET drain.

PIN 10: OUT-

Power output. OUT provides boot-

strap power to the IC.

Overview

The SS6620/21/22 series are high efficiency,

step-up DC/DC converters, designed to feature a

built-in synchronous rectifier, which reduces size and

cost by eliminating the need for an external Schottky

diode. The start-up voltage is as low as 0.8V and they

can operate with an input voltage down to 0.7V. Qui-

escent supply current is only 20

µA. In addition, the

SS6622 feature a circuit that eliminates inductor-

ringing to reduce noise. The internal P-MOSFET on-

resistance is typically 0.3

Ω to improve overall effi-

ciency by minimizing AC losses. The current limit of

the SS6620 and SS6621 is 0.8A and 0.45A

respectively. The SS6622 offers a selectable current

-

limit (0.45A or 0.8A). The lower current limit allows

the use of a physically smaller inductor in space-

sensitive applications.

PFM Control Scheme

The key feature of the SS6620 series is a unique

minimum-off-time, current-limited, pulse-frequency-

modulation (PFM) control scheme (see BLOCK

DIAGRAM) with ultra-low quiescent current. A con-

stant-peak-current limit in the switching allows the in-

ductor current to vary between this peak limit and

some lesser value. The peak current of the internal N-

MOSFET power switch can be fixed at 0.8A, 0.45A or

is selectable. The ripple voltage does not exceed the

product of the peak current limit and the filter capaci-

tor equivalent-series-resistance (ESR). The switch

frequency depends on the loading condition and input

voltage, and can range up to 500KHz. The switching

frequency is governed by a pair of one-shots that set

a minimum off-time (1

µs) and a maximum on-time

(4

µs).

Rev.2.01 6/06/2003