SS6610 ETC-unknow, SS6610 Datasheet - Page 11

• Manufacturer Part Number: SS6610
• Description: High Efficiency Syncronous Step-up Dc/dc Converter
• Manufacturer: ETC-unknow

Rev.2.01 11/06/2003
PIN DESCRIPTIONS
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 it operates with an input voltage down
to 0.7V. Quiescent supply current is only 20 P A.
The internal P-MOSFET on-resistance is typically
0.3 : to 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 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
PIN 1: FB-
PIN 2: LBI-
PIN 3: LBO- Open-drain low battery comparator
Connecting to OUT to get +3.3V
output, connecting to GND to get
+5.0V output, or using a resistor
network to set the output voltage
from +1.8V to +5.5V.
Low-battery comparator input. In-
ternally set at +1.23V to trip.
output. Output is low when V
<1.23V. LBO is high impedance
during shutdown.
www.SiliconStandard.com
LBI
is
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 Ps ) and a
maximum on-time (4 P s).
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 P A to external circuit with good load
regulation (<10mV). A bypass capacitor of 0.1 P F is
required for proper operation and good performance.
PIN 4: REF-
PIN 5: SHDN- Shutdown input. High=operating,
PIN 6: GND- Ground
PIN 7: LX-
PIN 8: OUT-
1.23V reference voltage. Bypass
with a 0.1 P F capacitor.
low=shutdown.
N-channel and P-channel power
MOSFET drain.
Power output. OUT provides boot-
strap power to the IC.
SS6610/11
11 of 16