NB650/NB650H – 6A, 28V, FAST-TRANSIENT, SYNCHRONOUS STEP-DOWN CONVERTERS
on the output and triggers OCP immediately. This
UVLO Protection
is short circuit protection (SCP).
The NB650/NB650H has under-voltage lockout
(UVLO) protection. When VIN exceeds the UVLO-
rising threshold voltage, the NB650/NB650H
powers up. It shuts off when VIN falls below the
UVLO-falling threshold voltage. This is non-latch
protection.
Under OCP/SCP condition, NB650 will latch off.
The converter needs power cycle to restart.
NB650H will try to recover from OCP/SCP fault
with hiccup mode. That means in OCP/SCP
protection, the NB650H will disable the output
power stage, discharge soft-start capacitor and
then automatically try to start again. If the over-
current condition still holds after soft-start ends,
the NB650H repeats this operation cycle till over-
current fault is removed and output rises back to
regulation level.
Thermal Shutdown
The NB650/NB650H employs thermal shutdown
by internally monitoring the temperature of the
junction. If the junction temperature exceeds the
threshold value (typically 150°C), the converter
shuts off. This is non-latch protection. There is
about 25°C hysteresis. Once the junction
temperature drops to around 125°C, it initiates a
soft-start.
Over/Under-Voltage Protection
The NB650/NB650H monitors the output voltage
through the FB voltage to detect overvoltage and
under voltage on the output. When the FB
voltage exceeds 0.8V, the over-voltage
protection (OVP) triggers. Once OVP triggers,
the LS-FET is always on while the HS-FET is
always off. The device needs to power cycle to
power up again. Under-voltage protection (UVP)
triggers when the FB voltage is below 0.4V.
Usually, UVP accompanies hitting the current
limit, which results in SCP.
NB650/NB650H Rev. 1.12
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13
10/11/2012
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