AIC1620/AIC1621/AIC1622
Synchronous Rectification
Using the internal synchronous rectifier eliminates the
need for an external Schottky diode. Therefore, the
cost and board space is reduced. During the cycle of
off-time, the P-MOSFET turns on and shunts the N-
MOSFET.
Due
to
the
low
turn-on
resistance of MOSFET, the synchronous rectifier sig-
nificantly improves efficiency without the addition of
an external component. Thus, the conversion efficien-
cy can be as high as 93%.
BATT/Damping Switch
The AIC1622 is designed with an internal damping
switch (Fig. 15) to reduce ringing at LX. The damping
switch supply a path to quickly dissipate the energy
stored in inductor and reduces the ringing at LX.
Damping LX ringing dose not reduce V
OUT
ripple, but
dose reduce EMI. R1=200Ω works well for most a
p-
plication while reducing efficiency by only 1%. Larger
R1 value provide less damping, but less impact on ef-
ficiency. In principle, lower value of R1 is needed to
fully damp LX when the V
OUT
/V
IN
ratio is high.
Reference Voltage
The reference voltage (REF) is nominally 1.23V for
excellent T.C. performance. In addition, REF pin can
source up to 100µA to external circuit with good load
regulation (<10mV). A bypass capacitor of 0.1µF is
required for proper operation and good performance
Selecting the Output Voltage
V
OUT
can be simply set to 3.3V by connecting the FB
pin to OUT due to internal resistor divider (Fig. 16). In
order to adjust the output voltage, a resistor divider is
connected to V
OUT
, FB, GND (Fig. 17). Use the fol-
lowing equation to calculate:
Shutdown
The whole circuit is shutdown when
V
SHDN
is low.
During shutdown mode, the current can flow from the
battery to the output due to body diode of the P-
MOSFET. V
OUT
falls to approximately Vin-0.6V and
LX remains high impedance. The capacitance and
load at OUT determine the rate at which V
OUT
decays.
Shutdown can be pulled as high as 6V. Regardless of
the voltage at OUT.
R5=R6 [(V
OUT
/ V
REF
)-1]
Where V
REF
=1.23V and V
OUT
may range from 1.8V to
4V.
Low-Battery Detection
The AIC1620 series contain 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.
Current Limit Select Pin
The AIC1622 series allows a selectable inductor cur-
rent limit of either 0.45A or 0.8A. This allows flexibility
in designing for higher current or smaller applications.
CLSEL draws 1.4µA when connected to OUT.
9
AIC [ ANALOG INTERGRATIONS CORPORATION ]
