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SS6612 View Datasheet(PDF) - Silicon Standard Corp.

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SS6612 Datasheet PDF : 16 Pages
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SS6612
PIN DESCRIPTIONS
PIN 1: FB- Connected to OUT to get +3.3V
output, connected to GND to get
+5.0V output, or using a resistor
network to set output voltage rang-
ing from +1.8V to +5.5V.
PIN 2: LBI- Low-battery comparator input inter-
nally 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:CLSEL-Current-limit select input. CLSEL=
OUT sets the current limit to 1.0A.
CLSEL=GND sets the current limit
to 0.65A.
APPLICATION INFORMATION
Overview
The SS6612 is a high-efficiency, step-up DC/DC
converter, 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 SS6612 is as low as 0.8V and it operates
with an input voltage down to 0.7V. Quiescent supply
current is only 20µA. In addition, the SS6612 features a
circuit that eliminates inductor ringing to reduce
noise. The internal P-MOSFET on-resistance is typi-
cally 0.3to improve overall efficiency by minimizing
AC losses. The output voltage can be easily set; by
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 CLSEL pin offers a selectable current
limit (1.0A or 0.65A). The lower current limit allows
the use of a physically smaller inductor in space-
sensitive applications.
PFM Control Scheme
A key feature of the SS6612 is a unique minimum-
off-time, constant-on-time, current-limited, pulse-
frequency-modulation (PFM) control scheme (see
PIN 5: REF- 1.23V reference voltage. Bypass
with a 0.1µF 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
bootstrap power to the IC.
BLOCK DIAGRAM) with ultra-low quiescent current.
The peak current of the internal N-MOSFET power
switch is selectable. 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 (1µs ) and a
maximum on-time (4µs ).
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 signifi-
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 100µA to an external circuit with good load
Rev.2.02 12/06/2003
www.SiliconStandard.com
11 of 16
 

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