RT6204
Functional Block Diagram
VIN
EN
HV
Protection
1.2V
1μA
-
Thermal
Shutdown
UVLO
Internal
Regulator
+
Shutdown
Comparator
Current
Sense
BOOT
UVLO
BOOT
0.4V
+
UV
Comparator
-
Logic &
Clamp
Control
Gate Driver
with Dead
Time Control
HS
SW
LS
FB
0.8V
-
+ EA
+
HS Switch
Current
Comparator
LS Switch
Current
Comparator
Oscillator
Current
Sense
6μA
SS
Slope
Compensation
GND
COMP
Operation
The RT6204 is a synchronous step-down converter,
integrated with both high-side (HS) and low-side (LS)
MOSFETs to reduce external component count and a
gate driver with dead-time control logic to prevent
shoot-through condition from happening. The RT6204
also features constant frequency and peak
current-mode control with slope compensation. During
PWM operation, output voltage is regulated down, and
is sensed from the FB pin to be compared with an
internal 0.8V reference voltage V
REF
. In normal
operation, the high-side N-MOSFET is turned on when
an S-R latch is set by the rising edge of an internal
oscillator output as the PWM clock, and is turned off
when the S-R latch is reset by the output of a (high-side)
current comparator, which compares the high-side
sensed current signal with the current signal related to
the COMP voltage. While the high-side N-MOSFET is
turned off, the low-side N-MOSFET will be turned on. If
the output voltage is not established, the high-side
power switch will be turned on again and another cycle
begins.
Pulse Skipping Operation
At very light-load condition, the RT6204 provides pulse
skipping technique to decrease switching loss for better
efficiency. When load current decreases, the FB
voltage V
FB
will increase slightly. With V
FB
1% higher
than V
REF
, the COMP voltage will be clamped at a
minimum value and the converter will enter into pulse
skipping mode. When the converter operates in pulse
skipping mode, the internal oscillator will be stopped,
which makes the switching period being extended. In
pulse skipping mode, as the load current decreases,
V
FB
will be discharged more slowly, which in turn will
extend the switching period even more.
Error Amplifier
The RT6204 adopts a transconductance amplifier as
the error amplifier. The error amplifier of a typical
970A/V transconductance (gm) compares the
feedback voltage V
FB
with the lower one of the
soft-start voltage or the internal reference voltage V
REF
,
0.8V. As V
FB
drops due to the load current increase,
the output voltage of the error amplifier will go up so
is a registered trademark of Richtek Technology Corporation.
Copyright © 2018 Richtek Technology Corporation. All rights reserved.
DS6204-04
February 2018
www.richtek.com
3
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