APS2415 is a monolithic switching mode Step-Down
DC-DC converter. It utilizes internal MOSFETs to
achieve high efficiency and can generate very low
output voltage by using internal reference at 0.6V. It
operates at a fixed switching frequency, and uses the
slope compensated current mode architecture. This
Step-Down DC-DC Converter supplies 1500mA output
current at Vout = 1.8V with input voltage range from
2.5V to 6.5V.
Current Mode PWM Control
Slope compensated current mode PWM control provides
stable switching and cycle-by-cycle current limit for
excellent load and line responses and protection of the
internal main switch (P-Ch MOSFET) and synchronous
rectifier (N-CH MOSFET). During normal operation,
the internal P-Ch MOSFET is turned on for a certain
time to ramp the inductor current at each rising edge of
the internal oscillator, and switched off when the peak
inductor current is above the error voltage. The current
comparator, ICOMP, limits the peak inductor current.
When the main switch is off, the synchronous rectifier
will be turned on immediately and stay on until either
the inductor current starts to reverse, as indicated by the
current reversal comparator, IZERO, or the beginning of
the next clock cycle. The OVDET comparator controls
output transient overshoots by turning the main switch
off and keeping it off until the fault is no longer present.
converter decreases. Caution must be exercised to
ensure the heat dissipated not to exceed the maximum
junction temperature of the IC.
Note 5: The duty cycle D of a step-down converter is
≈ V OUT
Where TON is the main switch on time and fOSC is the
oscillator frequency (1.2MHz).
Maximum Load Current
The APS2415 will operate with input supply voltage as
low as 2.5V, however, the maximum load current
decreases at lower input due to large IR drop on the
main switch and synchronous rectifier. The slope
compensation signal reduces the peak inductor current
as a function of the duty cycle to prevent sub-harmonic
oscillations at duty cycles greater than 50%.
Conversely the current limit increases as the duty cycle
When laying out the PCB board, the following
suggestions should be taken to ensure proper operation
of the APS2415. These items are also illustrated
graphically in Figure 4 & Figure 5.
Idle Mode Operation
At very light loads, the APS2415 automatically enters
pulse skipping Mode. In the pulse skipping Mode, the
inductor current may reach zero or reverse on each pulse.
The PWM control loop will automatically skip pulses to
maintain output regulation. The bottom MOSFET is
turned off by the current reversal comparator, IZERO, and
the switch voltage will ring. This is discontinuous
mode operation, and is normal behavior for the
When the input voltage decreases toward the value of
the output voltage, the APS2415 allows the main switch
to remain on for more than one switching cycle and
increases the duty cycle (Note 5) until it reaches 100%.
The output voltage then is the input voltage minus the
voltage drop across the main switch and the inductor.
At low input supply voltage, the RDS(ON) of the
P-Channel MOSFET increases, and the efficiency of the
1. The power traces, including the GND trace, the SW
trace and the VIN trace should be kept short, direct
2. The VFB pin should be connected directly to the
feedback resistor. The resistive divider R1/R2 must
be connected between the (+) plate of Cout and
3. Connect the (+) plate of C1 to the VIN pin as
closely as possible. This capacitor provides the AC
current to internal power MOSFET.
4. Keep the switching node, SW, away from the
sensitive VFB node.
5. Keep the (-) plates of C1 and C3 as close as
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