ncp3155a ON Semiconductor, ncp3155a Datasheet - Page 2

• Manufacturer Part Number: ncp3155a
• Description: Ncp3155a, Ncp3155b 3 A Synchronous Buck Regulator
• Manufacturer: ON Semiconductor

PIN FUNCTION DESCRIPTION
Pin
1
2
3
4
5
6
7
8
COMP
Pin Name
COMP
PGND
AGND
FB
ISET
V
BST
V
FB
SW
IN
OSCILLATOR
The PGND pin is the high current ground pin for the lower MOSFET and drivers which should be soldered to a
large copper area to reduce thermal resistance.
The V
is also connected to the internal power NMOS switch. It is also used in conjunction with the V
current in the high side MOSFET. The V
to the pin of the device.
Supply rail for the floating top gate driver. Connect a capacitor (CBST) between this pin and the V
ical values for CBST range from 1 nF to 10 nF.
Compensation pin. The comp pin is the output of the transconductance amplifier and the non−inverting input of
the PWM comparator. The comp pin in conjunction with the FB pin are used to compensate the voltage−control
feedback loop.
Inverting input to the Operational Transconductance Amplifier (OTA). The FB pin in conjunction with the extern-
al compensation serves to stabilize and achieve the desired output voltage with voltage mode compensation.
The AGND pin serves as small−signal ground. All small−signal ground paths should connect to the AGND pin
at a single point to avoid any high current ground returns.
Bottom gate MOSFET driver pin and the internal current set pin. Place a resistor to ground to set the current
limit of the converter.
The V
V
transitions.
IN
VIN
REF
when the high side switch is on to small negative voltages when the low side switch is on with high dV/dt
IN
SW
pin powers the internal control circuitry and is monitored by an undervoltage comparator. The V
pin is the connection of the drain and source of the internal N MOSFETS. The V
DMAX/
START
RAMP
SOFT
CLK/
INTERNAL BIAS
POR/STARTUP
Figure 2. NCP3155 Block Diagram
THERMAL SD
AGND
+
+
−
−
1.5 V
+
−
http://onsemi.com
OOV
OUV
DRIVE
LOGIC
IN
GATE
2
pin has high dI/dt edges and must be decoupled to PGND pin close
Description
LEVEL
CURRENT
SHIFT
VIN
LIMIT
VC
VC
ISET
ACTIVE
BOOST
BST
LSDRV
SAMPLE &
HOLD
HSDRV
VIN
SW
pin swings from
SW
VSW
PGND
ISET
pin to sense
SW
pin. Typ-
IN
pin