RT6228A/B/C
Operation
Overall
The RT6228A/B/C is an advanced constant on-time
(ACOT
TM
) mode synchronous buck converter. The main
control loop of the RT6228A/B/C using an ACOT
TM
Output Over-Voltage Protection (OVP) and Under-
Voltage Protection (UVP)
The RT6228A/B/C includes output over-voltage protection
(OVP) and output under-voltage protection (UVP). If the
output voltage rises above OVP threshold or drops below
UVP threshold for longer than 20μs (typical), the OVP or
UVP function is triggered.
Power Good
The power good output is an open drain output that requires
a pull-up resistor. PGOOD will be pulled high after soft-
start is over and the output reaches 90% of its set voltage.
There is a 10μs delay built into PGOOD circuitry to prevent
false transition.
CLK Generator (RT6228C)
Provide a 300kHz VCLK signal to drive external charge
pump circuit.
mode
control which provides a very fast transient response.
Internal VCC Regulator
The RT6228A/B/C includes a 5V linear regulator (VCC).
The VCC regulator steps down input voltage to supply
both internal circuitry and gate drivers. Do not connect
the VCC pin to external loads.
VCC Bypass Function (RT6228A/B)
When PGOOD is pulled high and BYP pin of RT6228A/B
voltage is above 4.7V, an internal 3Ω P-MOSFET switch
connects VCC to the BYP pin while the VCC linear
regulator is simultaneously turned off.
LDO (RT6228C)
The RT6228C includes a 3.3V 100mA linear regulators
(LDO). When VOUT is higher than the switch over
threshold 4.7V (RT6228C), an automatic circuit will change
the power source of linear regulator from VIN path to VOUT
path.
Soft-Start
The RT6228A/B/C provides an internal soft-start function
to prevent large inrush current and output voltage
overshoot. The typical soft-start duration is around 0.6ms.
Over-Current Limit
The RT6228A/B/C current limit is fixed 9A (RT6228C) or
adjustable (8A, 10A, 12A) by ILMT pin (RT6228A/B) and
it is a cycle-by-cycle
“valley”
type, measuring the
inductor current through the synchronous rectifier during
the off-time while the inductor current ramps down. If output
voltage drops below the output under-voltage protection
level, the RT6228A/B/C will stop switching to avoid
excessive heat.
Copyright
©
2018 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS6228A/B/C-02
September 2018
www.richtek.com
5
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
