NB671, 24V, HIGH CURRENT SYNCHRONOUS STEP-DOWN CONVERTER
PIN FUNCTIONS
PIN #
Name
Description
Supply Voltage. The IN pin supplies power for internal MOSFET and regulator. The
NB671 operate from a +5V to +22V input rail. An input capacitor is needed to
decouple the input rail. Use wide PCB traces and multiple vias to make the
connection.
1
VIN
2
4
PGND
PG
Power Ground. Use wide PCB traces and multiple vias to make the connection
Power good output, the output of this pin is an open drain signal and is high if the
output voltage is higher than 95% of the nominal voltage. There is a delay from FB ≥
95% to PGOOD goes high.
3, 5, 6
7
NC
VOUT pin is used to sense the output voltage of the Buck regulator, connect this pin
to the output capacitor of the regulator directly.
VOUT
Switch Output. Connect this pin to the inductor and bootstrap capacitor. This pin is
driven up to the VIN voltage by the high-side switch during the on-time of the PWM
duty cycle. The inductor current drives the SW pin negative during the off-time. The
on-resistance of the low-side switch and the internal diode fixes the negative
voltage. Use wide and short PCB traces to make the connection. Try to minimize the
area of the SW pattern.
8,9
Exposed
Pad 15, 16
SW
Bootstrap. A capacitor connected between SW and BS pins is required to form a
floating supply across the high-side switch driver.
10
11
BST
VCC
Internal 5V LDO output. The driver and control circuits are powered from this
voltage. Decouple with a minimum 1µF ceramic capacitor as close to the pin as
possible. X7R or X5R grade dielectric ceramic capacitors are recommended for their
stable temperature characteristics.
Feedback. An external resistor divider from the output to GND, tapped to the FB pin,
sets the output voltage. It is recommended to place the resistor divider as close to
FB pin as possible. Vias should be avoided on the FB traces. It is recommended to
set the current through FB resistors around 10uA.
12
FB
Enable pin. 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 it off. Connect EN with VIN through a pull-up
resistor or a resistive voltage divider for automatic startup. Do not float this pin.
13
14
EN
Analog ground. The internal reference is referred to AGND. Connect the GND of the
FB divider resistor to AGND for better load regulation.
AGND
NB671 Rev. 1.0
1/14/2013
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5
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