RT6214A/B
Resume normal
operation
Abnormal case
detected (UV)
t
= 1.6ms
HICCUP_ON
VIN = 12V
Fault condition
removed
= 4.8ms
HICCUP_OFF
VOUT
t
VIN
EN
t
t
1ms
0.25ms
1ms
LX
VOUT
External Bootstrap Capacitor
Connect a 0.1F low-ESR ceramic capacitor between
the BOOT and LX pins. This bootstrap capacitor
supplies for the gate driver of the high-side N-channel
MOSFET switch.
Soft-Start
(For RT6214A/BHRGJ8F)
The RT6214A/B provides adjustable soft-start function.
When the EN pin becomes high, the SS charge current
(ISS) begins charging the capacitor which is connected
from the SS pin to GND (CSS).The soft-start function is
used to prevent large inrush current while converter is
being powered-up. The soft-start timing can be
programmed by the external capacitor CSS between SS
and GND. An internal current source ISS (6A) charges
an external capacitor to build a soft-start ramp voltage.
The VFB voltage will track the internal ramp voltage
during soft-start interval. The typical soft-start time is
calculated as follows :
Over-Temperature Protection (Thermal Shutdown)
The RT6214A/B includes an over-temperature
protection (OTP) circuitry to prevent overheating due to
excessive power dissipation. The OTP will shut down
switching operation when junction temperature
exceeds a thermal shutdown threshold TSD. Once the
junction temperature cools down by a thermal
shutdown hysteresis (TSD), the IC will resume normal
operation with a complete soft-start.
Soft-Start (SS)
Soft-Start time tSS = CSS x 0.7 / 11A + CSS x VFB / ISS
(For RT6214A/BHRGJ6F)
tSS = SS rising to FB settled (T2 + T3)
The RT6214A/B provides an internal soft-start feature
for inrush control. At power up, the internal capacitor is
charged by an internal current source ISS to generate a
soft-start ramp voltage as a reference voltage to the
PWM comparator. The device will initiate switching and
the output voltage will smoothly ramp up to its targeted
regulation voltage only after this ramp voltage is
greater than the feedback voltage VFB to ensure the
converters have a smooth start-up. The output voltage
starts to rise in 0.25ms from EN rising, and the
soft-start ramp-up time (VFB from 0V to VREF) is 1ms.
EN
SS
SS = 2.1V
V1
FB
T1
T2
T3
PG
T1 : EN delay, from EN go high to SS start rising, T1 = 55μs;
T2 : speed up SS, from SS rising to FB start rising, T2 = C x 0.7/11μA;
SS
T3 : normal SS, from FB rising to settled, T3 = C x V /I
;
SS
V1 : offset voltage between SS and FB, V1 = 700mV;
PG go high after SSOK (SS = 2.1V)
FB SS
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is a registered trademark of Richtek Technology Corporation.
www.richtek.com
6
DS6214A/B-09 August 2018
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
