Functional Pin Descriptions
GND (Bottom Pad)
Signal common of the IC. Unless otherwise stated, signals
are referenced to the GND pin, not the PGND pin.
VIN (Pin 1)
The VIN pin measures the converter input voltage which is a
required input to the R3 PWM modulator. Connect across
the drain of the high-side MOSFET to the GND pin.
VCC (Pin 2)
The VCC pin is the input bias voltage for the IC. Connect
+5V from the VCC pin to the GND pin. Decouple with at least
1µF of a MLCC capacitor from the VCC pin to the GND pin.
FCCM (Pin 3)
The FCCM pin configures the controller to operate in forced-
continuous-conduction-mode (FCCM) or diode-emulation-
mode (DEM.) DEM is disabled when the FCCM pin is pulled
above the rising threshold voltage VFCCMTHR, conversely
DEM is enabled when the FCCM pin is pulled below the
falling threshold voltage VFCCMTHF.
EN (Pin 4)
The EN pin is the on/off switch of the IC. The soft-start
sequence begins when the EN pin is pulled above the rising
threshold voltage VENTHR and VCC is above the power-on
reset (POR) rising threshold voltage VVCC_THR. When the
EN pin is pulled below the falling threshold voltage VENTHF
PWM immediately stops.
COMP (Pin 5)
The COMP pin is the output of the control-loop error
amplifier. Compensation components for the control-loop
connect across the COMP and FB pins.
FB (Pin 6)
The FB pin is the inverting input of the control-loop error
amplifier. The converter output voltage regulates to 600mV
from the FB pin to the GND pin. Program the desired output
voltage with a resistor network connected across the VO,
FB, and GND pins. Select the resistor values such that FB to
GND is 600mV when the converter output voltage is at the
programmed regulation value.
FSET (Pin 7)
The FSET pin programs the PWM switching frequency.
Program the desired PWM frequency with a resistor and a
capacitor connected across the FSET and GND pins.
VO (Pin 8)
The VO pin measures the converter output voltage and is
used exclusively as an input to the R3 PWM modulator.
Connect at the physical location where the best output
voltage regulation is desired.
ISEN (Pin 9)
The ISEN pin programs the threshold of the OCP
overcurrent fault protection. Program the desired OCP
threshold with a resistor connected across the ISEN and
PHASE pins. The OCP threshold is programmed to detect
the peak current of the output inductor. The peak current is
the sum of the DC and AC components of the inductor
PGND (Pin 10)
The PGND pin conducts the turn-off transient current
through the LG gate driver. The PGND pin must be
connected to complete the pulldown circuit of the LG gate
driver. The PGND pin should be connected to the source of
the low-side MOSFET through a low impedance path,
preferably in parallel with the trace connecting the LG pin to
the gate of the low-side MOSFET. The adaptive shoot-
through protection circuit, measures the low-side MOSFET
gate-source voltage from the LG pin to the PGND pin.
LG (Pin 11)
The LG pin is the output of the low-side MOSFET gate
driver. Connect to the gate of the low-side MOSFET.
PVCC (Pin 12)
The PVCC pin is the input voltage bias for the LG low-side
MOSFET gate driver. Connect +5V from the PVCC pin to the
PGND pin. Decouple with at least 1µF of an MLCC capacitor
across the PVCC and PGND pins.
BOOT (Pin 13)
The BOOT pin stores the input voltage for the UG high-side
MOSFET gate driver. Connect an MLCC capacitor across
the BOOT and PHASE pins. The boot capacitor is charged
through an internal boot diode connected from the PVCC pin
to the BOOT pin, each time the PHASE pin drops below
PVCC minus the voltage dropped across the internal boot
UG (Pin 14)
The UG pin is the output of the high-side MOSFET gate
driver. Connect to the gate of the high-side MOSFET.
PHASE (Pin 15)
The PHASE pin detects the voltage polarity of the PHASE
node and is also the current return path for the UG high-side
MOSFET gate driver. Connect the PHASE pin to the node
consisting of the high-side MOSFET source, the low-side
MOSFET drain, and the output inductor.
PGOOD (Pin 16)
The PGOOD pin is an open-drain output that indicates when
the converter is able to supply regulated voltage. Connect
the PGOOD pin to +5V through a pull-up resistor.
August 7, 2006