RT6365
delay elapsed. When VFB falls below power-good low
threshold (VTH_PGHL2) (92% of the reference voltage,
typically) or exceeds VTH_PGHL1 (109% of the reference
voltage, typically), the PGOODpin will be pulled low. For
VFB higher than VTH_PGHL1, VPGOOD can be pulled high
again if VFB drops back by a power-good high threshold
(VTH_PGLH2) (106% of the reference voltage, typically).
Once being started-up, if any internal protection is
triggered, PGOODwill be pulled low toGND. The internal
open-drain pull-down device (45Ω, typically) will pull the
PGOODpin low. The power good indication profile is shown
in Figure 2.
certain amount of delay when the high-side MOSFET
being turned on. If an over-current condition occurs, the
converter will immediately turn off the high-side MOSFET
to prevent the inductor current exceeding the high-side
MOSFET peak current limit (ILIM).
Output Under-Voltage Protection
The RT6365 includes output under-voltage protection
(UVP) against over-load or short-circuited condition by
constantly monitoring the feedback voltage VFB. If VFB
drops below the under-voltage protection trip threshold
(50% of the internal reference voltage, typically), the UV
comparator will go high to turn off the internal high-side
switch. If the output under-voltage condition continues for
a period of time, the RT6365 enters output under-voltage
protection with hiccup mode and discharges the CSS/TR
by an internal discharging current source ISS_DIS (0.5μA,
typically). During hiccup mode, the device remains
shutdown. After the SS pin voltage is discharged to less
than 54mV (typically), the RT6365 attempts to re-start up
again, and the internal charging current source ISS (1.7μA,
typically) gradually increases the voltage on CSS/TR. The
high-side MOSFET will start switching when voltage
difference between SS pin and FB pin is larger than 42mV
( i.e. VSS − VFB > 42mV, typically). If the output under-
voltage condition is not removed, the high-side MOSFET
stops switching when the voltage difference between SS
pin and FB pin is 1.2V ( i.e. VSS − VFB = 1.2V, typically)
and then the ISS_DIS discharging current source begins to
discharge CSS/TR. Upon completion of the soft-start
sequence, if the output under-voltage condition is removed,
the converter will resume normal operation; otherwise, such
cycle for auto-recovery will be repeated until the output
under-voltage condition is cleared. Hiccup mode allows
the circuit to operate safely with low input current and
power dissipation, and then resume normal operation as
soon as the over-load or short-circuit condition is removed.
V
TH_PGHL1
V
TH_PGLH2
V
TH_PGLH1
V
TH_PGHL2
V
FB
V
PGOOD
Figure 2. The Logic of PGOOD for RT6365GQW
Input Under-Voltage Lockout
In addition to the EN pin, the RT6365 also provides enable
control through the VIN pin. If VEN rises above VTH_EN first,
the switching will be inhibited until the VIN voltage rises
above VUVLOH. It is to ensure that the internal regulator is
ready so that operation with not-fully-enhanced internal
high-side MOSFET can be prevented. After the device is
powered up, if the input voltage VIN goes below the UVLO
falling threshold voltage (VUVLOL), this switching will be
inhibited; if VIN rises above the UVLO rising threshold
(VUVLOH), the device will resume switching. Note that VIN
= 4V is only design for input voltage momentarily falls
down to the UVLO threshold voltage requirement, and
normal input voltage should be larger than the VUVLOH
.
Since the CSS/TR will be discharged to 54mV when the
RT6365 enters output under-voltage protection, the first
discharging time (tSS_DIS1) can be calculated as below :
High-Side MOSFET Peak Current Limit Protection
The RT6365 includes a cycle-by-cycle high-side MOSFET
peak current-limit protection against the condition that
the inductor current increasing abnormally, even over the
inductor saturation current rating. The inductor current
through the high-side MOSFET will be measured after a
V
0.054
SS
t
= C
SS_DIS1
SS
I
SS_DIS
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is a registered trademark of Richtek Technology Corporation.
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8
DS6365-01 October 2019
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
