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Rev.2.02 12/06/2003

SS6612

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

µF is

required for proper operation and good performance.

Shutdown

The whole circuit is shutdown when

SHDN

V

is low. In

shutdown mode, the current can flow from the battery

to the output due to the body diode of the P-MOSFET.

high impedance. The capacitance and load at OUT de-

can be pulled as high as 6V, regardless of the volt-

age at OUT.

Current Limit Select Pin

The SS6612 allows a selectable inductor current limit

of either 1.0A or 0.65A, allowing the flexibility to design

for higher current or smaller applications. CLSEL

draws 1.4

µA when connecting to OUT.

BATT/Damping Switch

The SS6612 is designed with an internal damping

switch (Fig.33) to reduce ringing at LX. The damping

switch supplies a path to quickly dissipate the energy

stored in the inductor and reduces the ringing at LX.

but does reduce EMI. R1=200

Ω works well for most

applications while reducing efficiency by only 1%.

Larger R1 values provide less damping, but less im-

pact on efficiency. In principle, a lower value of R1 is

Selecting the Output Voltage

FB pin to OUT/GND due to the use of an internal resis-

tor divider in the IC (Fig.34 and Fig.35). In order to

adjust the output voltage, a resistor divider is connected

by the following equation:

5.5V. The recommended R6 is 240k

Ω.

Low-Battery Detection

The SS6612 contains an on-chip comparator with 50mV

internal hysteresis (REF, REF+50mV) for low battery

detection. If the voltage at LBI falls below the internal

reference voltage, LBO (an open-drain output) sinks

current to GND.

Component Selection

1. Inductor Selection

An inductor value of 22

µH performs well in most

applications. The SS6612 also works with

inductors in the 10

µH to 47µH range. An inductor

with higher peak inductor current creates a higher

tor ESR). The inductor’s DC resistance signifi-

cantly affects efficiency. We can calculate the

maximum output current as follows:

η

























×

−

−

=

L

2

V

V

t

I

V

V

I

IN

OUT

OFF

LIM

OUT

IN

)

MAX

(

OUT

........................................................................ (2)

amps

L=inductor value in

µH

η=efficiency (typically 0.9)

2. Capacitor Selection

The output ripple voltage is related to the peak

inductor current and the output capacitor ESR.

Besides output ripple voltage, the output ripple

current may also be of concern. A filter capacitor

with low ESR is helpful to the efficiency and the

steady state output current of the SS6612.

Therefore a NIPPON MCM series tantalum

capacitor of 100

µF/6V is recommended. A smaller

capacitor (down to 47µF with higher ESR) is ac-

ceptable for light loads or in applications that can

tolerate higher output ripple.