NB650/NB650H – 6A, 28V, FAST-TRANSIENT, SYNCHRONOUS STEP-DOWN CONVERTERS
PIN FUNCTIONS
QFN17
Pin #
Name Description
1,2
SW
Switch Output. Connect using wide PCB traces.
Bootstrap. Requires a capacitor between SW and BST to form a floating supply across
the high-side switch driver.
3
BST
Power Good. Output is an open drain and is high if the output voltage exceeds 90% of
the nominal voltage. There is a delay from FB≥90%×Vref to PG goes high.
4
5
PG
EN
EN=1 to enable. For automatic start-up, connect to VIN with a 100kꢀ resistor.
VID inputs. Control signals for the output-voltage scaling. Acts as the control signals for
the internal VID switches. Usually uses an external resistor in parallel with the low-side
FB resistor. Changing the VID ON/OFF state changes the FB divider scaling and result
in different output voltages.
VID1
VID2
6,7
Internal LDO output. The power supply of the internal control circuits. Decouple with 1μF
capacitor.
8
VCC
GND
IN
System Ground. The reference ground of the regulated output voltage. Layout requires
extra care.
9,10
Supply Voltage. Operates from a 4.5V-to-28V input rail. Requires C1 to decouple the
input rail. Connect using wide PCB traces.
11
12
13
AGND Analog Ground.
Feedback. Connect to the tap of an external resistor divider from the output to GND to
FB
set the output voltage.
Drain of the internal VID switches. Typically uses an external resistor in parallel with the
RFB2 low-side FB resistor along with the internal VID switch to change the ON/OFF state of
RFB1 the VID switching to change the FB divider scaling and result in different output
voltages.
14,15
Soft-Start. Connect an external capacitor to program the soft-start time for the switch-
mode regulator.
16
17
SS
Frequency Set during CCM. The input voltage and the frequency-set resistor between
FREQ the IN and FREQ pin determines the ON period. For best results, use an ON period
longer than 200ns. Decouple with a 1nF capacitor.
NB650/NB650H Rev. 1.12
10/11/2012
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