18V, 2A Synchronous DC-DC Buck Converter
Figure 2. Pin Configuration of AP3512E (Top View)
Bootstrap pin. A bootstrap capacitor is connected between the
BS pin and SW pin. The voltage across the bootstrap
capacitor drives the internal high-side NMOS switch.
Supply input pin. A capacitor should be connected between
the IN pin and GND pin to keep the DC input voltage
Power switch output pin. This pin is connected to the inductor
and bootstrap capacitor.
Feedback pin. This pin is connected to an external resistor
divider to program the system output voltage. When the FB
pin voltage exceeds 1.1V, the over voltage protection is
triggered. When the FB pin voltage is below 0.3V, the
oscillator frequency is lowered to realize short circuit
Compensation pin. This pin is the output of the
transconductance error amplifier and the input to the current
comparator. This pin is used to compensate the control loop.
Connect a series RC network from this pin to GND pin. In
some cases, an additional capacitor from this pin to GND pin
Enable Input. EN is a digital input that turns the regulator on
or off. Drive EN high to turn on the regulator, drive it low to
turn off. Pull up with 100kΩ resistor for automatic startup.
Soft-start control input pin. SS controls the soft start period.
Connect a capacitor from SS to GND to set the soft-start
period. A 0.1µF capacitor sets the soft-start period to 15ms.
To disable the soft-start feature, leave SS unconnected.
Exposed pad. It should be connected to GND in PCB layout
Dec. 2012 Rev. 1. 1
BCD Semiconductor Manufacturing Limited