NB621EV-LF-P Datasheet, PDF (10/14 Pages) MPS Industries, Inc. – 8A, 25V, 600kHz Synchronous Step-Down Converter with Integrated LDO

NB621 – 8A, 25V, 600kHz SYNCHRONOUS STEP-DOWN CONVERTER WITH INTEGRATED LDO
BLOCK DIAGRAM
Figure 1—Function Block Diagram
OPERATION
The NB621 is a high frequency synchronous
rectified step-down switch mode converter with a
built in internal high side power MOSFET. It
offers a very compact solution to achieve 8A
continuous output current over a wide input
supply range with excellent load and line
regulation.
The NB621 operates in a fixed frequency, peak
current control mode to regulate the output
voltage. A PWM cycle is initiated by the internal
clock. The integrated high-side power MOSFET
is turned on and remains on until its current
reaches the value set by the COMP voltage.
When the power switch is off, it remains off until
the next clock cycle starts. If, in 90% of one PWM
period, the current in the power MOSFET does
not reach the COMP set current value, the power
MOSFET will be forced to turn off.
Error Amplifier
The error amplifier compares the FB pin voltage
with the internal 0.8V reference (REF) and
outputs a current proportional to the difference
between the two. This output current is then used
to charge or discharge the internal compensation
network to form the COMP voltage, which is used
to control the power MOSFET current. The
optimized internal compensation network
minimizes the external component counts and
simplifies the control loop design.
Internal Regulator
Most of the internal circuitries are powered from
the 5V internal regulator. This regulator takes the
VIN input and operates in the full VIN range.
When VIN is greater than 5.0V, the output of the
NB621 Rev. 0.9
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10
12/10/2013
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