AIC3415 Datasheet, PDF (8/11 Pages) Analog Intergrations Corporation – 1.2MHz Synchronous Step-Up Converter

AIC3415
 APPLICATION INFORMATION
The AIC3415 is a synchronous step-up DC-DC con-
verter. It is based on a slope compensated current
mode PWM control topology. It operates at a fixed
frequency of 1.2MHz. At the beginning of each clock
cycle, the main switch (NMOS) is turned on and the
inductor current starts to ramp. After the maximum
duty cycle or the sense current signal equals the error
amplifier (EA) output, the main switch is turned off and
the synchronous switch (PMOS) is turned on. The de-
vice can operate with an input voltage below 1V; the
typical start-up voltage is 0.9V.
Current Limit
The over current protection is to limit the switch current.
The output Voltage will be dropped when over current
is happened. The current limit amplifier will shut the
N-MOS switch off once the current exceeds its thresh-
old. The current amplifier delay to output is about 100
nS.
Anti-Ringing Control
An anti-ringing circuitry is included to remove the high
frequency ringing that appears on the SW pin when the
inductor current goes to zero. In this case, a ringing on
the SW pin is induced due to remaining energy stored
in parasitic components of switch and inductor. The
anti-ringing circuitry clamps the voltage internally to the
battery voltage and therefore dampens this ringing.
Zero Current Comparator
The zero current comparator monitors the inductor
current to the output and shuts off the synchronous
rectifier once the current is below 20 mA, This prevents
the inductor current from reversing in polarity improv-
ing efficiency at light loads.
Device Shutdown
When SHDN is set logic high, the AIC3415 is put into
active mode operation. If SHDN is set logic low, the
device is put into shutdown mode and consumes less
than 1μA of current. At the shutdown mode, the syn-
chronous switch will turn off and the output voltage of
AIC3415 step-up converter will reduce to 0V.After
start-up, the internal circuitry is supplied by VOUT,
however, if shutdown mode is enabled, the internal
circuitry will be supplied by the input source again.
Adjustable Output Voltage
An external resistor divider is used to set the output
voltage. The output voltage of the switching regulator
(V_OUT) is determined by the following equation:
V_OUT

V_FB
 _{}1
R₁
R₂

Where V_FB is 1.2V reference voltage.
Input Inductor Selection
The inductor value determines the ripple current. The
approximate ripple current and inductance value are
measured by the following equations:
ΔI _L
=
V_IND
L × F_SW
Where _ΔIL = inductor ripple current
F_SW = switch frequency
D = duty cycle, (V_OUT- V_IN)/ V_OUT
Where _ΔIL is inductor ripple current, F_SW is switch
frequency and D is the duty cycle. Increasing the value
of inductance will reduce the output ripple current and
ripple voltage.
Input Capacitor Selection
Surfaces mount 4.7μF or greater, X5R or X7R, ceramic
8