SS6612 Ver la hoja de datos (PDF) - Silicon Standard Corp.
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SS6612
Silicon Standard Corp.
SS6612 Datasheet PDF : 16 Pages
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SS6612
regulation (<10mV). A bypass capacitor of 0.1µF is
required for proper operation and good performance.
Shutdown
The whole circuit is shutdown when VSHDN is low. In
shutdown mode, the current can flow from the battery
to the output due to the body diode of the P-MOSFET.
VOUT falls to approximately (Vin - 0.6V) and LX remains
high impedance. The capacitance and load at OUT de-
termine the rate at which VOUT decays. Shutdown
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 1.4µA 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.
Damping LX ringing does not reduce VOUT ripple,
but does reduce EMI. R1=200Ω 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
needed to fully damp LX when VOUT /VIN ratio is high.
Selecting the Output Voltage
VOUT can be simply set to 3.3V/5.0V by connecting the
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
to VOUT, FB, GND (Fig.36). Vout can be calculated
by the following equation:
R5 = R6 [(VOUT / VREF )-1] .....................................(1)
where V REF =1.23V and VOUT ranges from 1.8V to
5.5V. The recommended R6 is 240kΩ.
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 22µH performs well in most
applications. The SS6612 also works with
inductors in the 10µH to 47µH range. An inductor
with higher peak inductor current creates a higher
output voltage ripple (IPEAK×output filter capaci-
tor ESR). The inductor’s DC resistance signifi-
cantly affects efficiency. We can calculate the
maximum output current as follows:
IOUT(MAX)
=
VIN
VOUT
ILIM
−
t OFF
VOUT − VIN
2×L
η
........................................................................ (2)
where IOUT(MAX)=maximum output current in
amps
VIN=input voltage
L=inductor value in µH
η=efficiency (typically 0.9)
tOFF=LX switch’ off-time in µs
ILIM=1.0A or 0.65A
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 100µF/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.
Rev.2.02 12/06/2003
www.SiliconStandard.com
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