nx2114 Microsemi Corporation, nx2114 Datasheet - Page 15

• Manufacturer Part Number: nx2114
• Description: 300khz & 600khz Synchronous Pwm Controller
• Manufacturer: Microsemi Corporation

the feedback voltage will be lower than 0.4V and com-
parator will change the state. After certain internal delay,
both high side and low side driver will be turned off. The
output will be latched. The normal operation should be
achieved by removing the short and recycle the VCC.
dition.
short.
to zero by the synchronous FET. FB voltage starts in-
crease from zero when digital start block operates. Be-
fore half of the start up time, the Feedback Under Volt-
Rev. 4.0
06/20/06
During the normal operation, if the output is short,
Figure 16 - Operation waveform with start up at
During the start up, the output voltage is discharged
Figure 15 - Operation waveforms during short con-
CH3-bus voltage
5V/DIV
CH2-Vcc voltage
CH4-output current
CH1-Fb voltage
0.5V/DIV
5V/DIV
10A/DIV
age Lock Out comparator is disabled. After half of start
up time, the Feedback UVLO comparator is enabled.
The FB UVLO threshold is set to be half of voltage at the
positive input of error amplifier. With this set up, if the
output is short before soft start, the Feedback UVLO
comparator can catch it and turn off the driver. The short
circuit operation waveform during normal operation and
during the soft start are shown as follows.
will take the role. But during the soft start, due to the
input voltage dropping, UVLO Vcc will take the role,
hiccup happens.
tection under certain conditions. However, since feed-
back does not have accurate information of current, this
protection only provides certain level of over current pro-
tection. MOSFET should design such that it can survive
with high pulse current for a short period of time.
Layout Considerations
frequency switching converters. Layout will affect noise
pickup and can cause a good design to perform with
less than expected results.
the layout which are power components and small sig-
nal components. Power components usually consist of
input capacitors, high-side MOSFET, low-side MOSFET,
inductor and output capacitors. A noisy environment is
generated by the power components due to the switch-
ing power. Small signal components are connected to
sensitive pins or nodes. A multilayer layout which in-
cludes power plane, ground plane and signal plane is
recommended .
layer connected by wide, copper filled areas. The input
capacitor, inductor, output capacitor and the MOSFETs
should be close to each other as possible. This helps to
reduce the EMI radiated by the power loop due to the
high switching currents through them.
ripple current and a high frequency decoupling ceramic
The Feedback UVLO can provide short circuit pro-
The layout is very important when designing high
There are two sets of components considered in
Layout guidelines:
1. First put all the power components in the top
2. Low ESR capacitor which can handle input RMS
During the normal operation, Feedback UVLO
NX2114/2114A
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