RT6238A/B
will be triggered to shut down switching operation. If the
UVP condition remains for a period, the RT6238 will retry
automatically. When the UVP condition is removed, the
converter will resume operation. The UVP is disabled
during soft-start period. During hiccup mode, the shutdown
time is determined by the capacitor at SS. A 2μA current
source discharges V
SS
from its starting voltage (normally
VPVCC). The IC remains shut down until V
SS
reaches
0.2V, about 10ms for a 3.9nF capacitor. At that point the
IC begins to charge the SS capacitor at 6μA, and a normal
start-up occurs. If the fault remains, UVP protection will
be enabled when V
SS
reaches 2.2V (typical). The IC will
then shut down and discharge the SS capacitor from the
2.2V level, taking about 4ms for a 3.9nF SS capacitor.
Latch Mode
For the RT6238AL/RT6238BL, it provides Latch-Off Mode
Under Voltage Protection (UVP). When the FB voltage
drops below 60% of the feedback reference voltage, the
output voltage drops below the UVP trip threshold for longer
than 270μs (typical) then IC's UVP is triggered. UVP
function will be triggered to shut down switching operation.
In shutdown condition, the RT6238 can be reset by EN
pin or power input VIN.
Output Over-Voltage Protection
If the output voltage VOUT rises above the regulation level
and lower 1.2 times regulation level, the high-side switch
naturally remains off and the synchronous rectifier turns
on. For RT6238BL, if the output voltage remains high, the
synchronous rectifier remains on until the inductor current
reaches the low side current limit. If the output voltage
still remains high, then IC's switches remain that the
synchronous rectifier turns on and high-side MOS keeps
off to operate at typical 500kHz switching protection, again
if inductor current reaches low side current limit, the
synchronous rectifier will turn off until next protection
clock. If the output voltage exceeds the OVP trip threshold
(1.2 times regulation level) for longer than 10μs (typical),
then IC's output Over-Voltage Protection (OVP) is
triggered. RT6238BL chip enters latch mode.
For RT6238AL, if the output voltage VOUT rises above
the regulation level and lower 1.2 times regulation level,
the high-side switch naturally remains off and the
Copyright
©
2017 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
synchronous rectifier turns on until the inductor current
reaches zero current. If the output voltage remains high,
then IC's switches remain off. If the output voltage exceeds
the OVP trip threshold (1.2 times regulation level) for
longer than 10μs (typical), the IC's OVP is triggered.
RT6238AL chip enters latch mode.
For RT6238BH, if the output voltage remains high, the
synchronous rectifier remains on until the inductor current
reaches the low side current limit. If the output voltage
still remains high, the synchronous rectifier turns on and
high-side MOSFET keeps off to operate at typical 500kHz
switching protection, again if inductor current reaches low
side current limit, the synchronous rectifier will turn off
until next protection clock. RT6238BH is without OVP
latch function and recover when OV condition release.
For RT6238AH, if the output voltage remains high, the
synchronous rectifier remains on until the inductor current
reaches zero current. If the output voltage still remains
high, then IC's switches remain off. RT6238AH is without
OVP latch function and recover when OV condition release.
Latch-Off Mode
The RT6238AL/BL uses latch-off mode OVP and UVP.
When the protection function is triggered, the IC will shut
down in Latch-Off Mode. The IC stops switching, leaving
both switches open, and is latched off. To restart operation,
toggle EN or power the IC off and then on again.
Shut-Down, Start-Up and Enable (EN)
The enable input (EN) has a shutdown level of 0.4V. When
V
EN
is below this level the IC enters shutdown mode and
supply current drops to less than 10μA. When V
EN
exceeds
its logic-high level of 1.2V the IC is fully operational.
Between these 2 levels there are 2 thresholds (1V typical
and 1.2V typical). Switching operation begins when V
EN
exceeds the upper threshold, and then switching
operation stops when V
EN
decreases to the lower
threshold. Since EN is a low voltage input, it must be
connected to VIN (up to 18V) with a 100kΩ pull-up resistor
for automatic start-up.
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DS6238A/B-08 July 2017
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
