RT6204
that the device will supply more inductor current to
match the load current. The frequency compensation
components, such as the series resistor and capacitor,
and an optional capacitor, are placed between the
COMP pin and ground.
Oscillator
The internal oscillator frequency is set to a typical
350kHz as a fixed frequency for PWM operation.
Slope Compensation
In order to prevent sub-harmonic oscillations that may
occur over all specified load and line conditions when
operating at duty cycle higher than 50%, the RT6204
features an internal slope compensation, which adds a
compensating slope signal to the sensed current signal
to support applications with duty cycle up to 93%.
There is an exclusive condition for the internal slope
compensation. When the loading current is reducing to
make the COMP voltage touch its minimum level, the
internal slope compensation will be disabled to keep a
minimum peak current no matter what duty cycle it is.
Thus a sub-harmonic oscillation may happen if the
operation duty cycle is larger than 50% and it results in
a higher output ripple voltage during such kind of light
load operation.
Internal Regulator
When the VIN is plugged in, the internal regulator will
generate a low voltage to drive internal control circuitry
and to supply the bootstrap power for the high-side
gate driver.
Chip Enable
The RT6204 provides an EN pin, as an external chip
enable control, to enable or disable the device. When
VIN is higher than the input under-voltage lockout
threshold (V
UVLO
) with the EN voltage (V
EN
) higher
than 1.35V, the converter will be turned on. When V
EN
is lower than 0.925V, the converter will enter into
shutdown mode, during which the supply current can
be even reduced to 3A or below.
External Soft-Start
The RT6204 provides external soft-start feature to
Copyright © 2018 Richtek Technology Corporation. All rights reserved.
reduce input inrush current. The soft-start time can be
programmed by selecting the value of the capacitor
C
SS
connected from the SS pin to GND. An internal
current source I
SS
(typically, 6A) charges the external
capacitor C
SS
to build a soft-start ramp voltage. The
feedback voltage V
FB
will be compared with the
soft-start ramp voltage during soft-start time. For the
RT6204, the external capacitor C
SS
is required, and for
soft-start control, the SS pin should never be left
unconnected, and it is not recommended to be
connected to an external voltage source. The soft-start
time depends on RC time constant; for example, a
0.1F capacitor for programming soft-start time will
result in 18.333ms (typ.) soft-start time.
Output Under-Voltage Protection (UVP) with Hiccup
Mode
The RT6204 provides under-voltage protection with
hiccup mode. When the feedback voltage V
FB
drops
below under-voltage protection threshold V
TH-UVP
, half
of the feedback reference voltage V
REF
, the UVP
function will be triggered to turn off the high-side
MOSFET immediately. The converter will attempt
auto-recovery soft-start after under-voltage condition
has occurred for a period of time. Once the
under-voltage condition is removed, the converter will
resume switching and be back to normal operation.
Current Limit Protection
The RT6204 provides cycle-by-cycle current limit
protection against over-load or short-circuited condition.
When the peak inductor current reaches the current
limit, the high-side MOSFET will be turned off
immediately with no violating minimum on-time t
ON_MIN
requirement to prevent the device from operating in an
over-current condition.
Thermal Shutdown
The RT6204 provides over-temperature protection
(OTP) function to prevent the chip from damaging due
to over-heating. The over-temperature protection
function will shut down the switching operation when
the junction temperature exceeds 165C. Once the
over-temperature condition is removed, the converter
will resume switching and be back to normal operation.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
4
DS6204-04
February 2018
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
