NB669, 24V, HIGH CURRENT SYNCHRONOUS BUCK CONVERTER WITH LDO
PIN FUNCTIONS
PIN #
1
2
3
4
5
Name
VIN
PGND
NC
PG
CLK
Description
Supply Voltage. The VIN pin supplies power for internal MOSFET and regulator. The
NB669 operates from a +6.5V to +24V input rail. An input capacitor is needed to
decouple the input rail. Use wide PCB traces and multiple vias to make the
connection.
Power Ground. Use wide PCB traces and multiple vias to make the connection.
Not connected.
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 Vout
≥
95% to PGOOD goes high.
300kHZ CLK output to drive the external charge pump
Internal 5V LDO output. Decouple with a minimum 4.7µF ceramic capacitor as close
to the pin as possible. X7R or X5R grade dielectric ceramic capacitors are
recommended for their stable temperature characteristics.
Once the output voltage of the Buck regulator is ready, it will switch over the LDO
output to save the power loss.
Output voltage sense. For the NB669, the output of the Buck regulator is fixed to 5V.
VOUT pin is used to sense the output voltage of the Buck regulator, connect this pin
to the output capacitor of the regulator directly. This pin also acts as the input of the
5V LDO switch over power input.
Keep the VOUT sensing trace far away from the SW node. Vias should also be
avoided on the VOUT sensing trace.
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.
Bootstrap. A capacitor connected between SW and BST pins is required to form a
floating supply across the high-side switch driver.
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.
100mA LDO and VCC enable pin. ENLDO is internally pulled up to high. Leave this
pin open to enable the LDO. Drive it low to turn off all the regulators.
Buck regulator and charge pump clock enable pin. EN is a digital input that turns the
Buck regulator and CLK on or off. When the power supply of the control circuit is
ready, drive EN high to turn on the Buck regulator and charge pump clock, drive it
low to turn them off.
Analog ground. The internal reference is referred to AGND.
6
LDO
7
VOUT
8, 9
Exposed Pad
15, 16
SW
10
BST
11
VCC
12
ENLDO
13
14
EN
AGND
NB669 Rev. 1.01
7/23/2013
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
5
MPS [ MONOLITHIC POWER SYSTEMS ]
