RT6208
Function Block Diagram
VIN
ISET
2V
2μA
EN
5k
6V
FB
1μA
V
CC
UVLO
Internal
Regulator
HS Switch
Current
Comparator
-
Current
Sense
1.21
+
Shutdown
Comparator
0.8V
-
+
+
Logic &
Deadtime
Control
SW
1ms Ramp
AGND
PGOOD
FB
Comparator
LS Switch
Current
Comparator
Current
Sense
GND
PGOOD
Generator
Operation
The RT6208 is a step-down DC/DC converter with
internal power switches that uses Hysteresis Mode
control, combining low quiescent current, which results
in high efficiency across a wide range of load currents.
Hysteresis
Mode
operation
functions
by
using
comparators are disabled, reducing the VIN pin supply
current to only 25A. As the load current discharges
the output capacitor, the voltage on the V
FB
pin
decreases. When this voltage falls 5mV below the
800mV reference, the feedback comparator trips and
enables BCM. At the beginning of the BCM, the internal
high-side power switch (P-channel MOSFET) is turned
on and the inductor current begins to ramp up. The
inductor current increases until either the current
exceeds the peak current comparator threshold, or the
ON time of the high-side MOSFET exceeds 5μs during
the time V
FB
is higher than 800mV, at which the
high-side power switch is turned off, and the Low-side
power switch is turned on. The inductor current ramps
down until the reverse current is close to zero. If the
voltage on the V
FB
pin is still less than the 800mV
reference, the high-side power switch is turned on
again and another cycle commences which keep the
inductor current operated in a boundary conduction
mode. The average current during the BCM will
normally be greater than the average load current. For
is a registered trademark of Richtek Technology Corporation.
Boundary Conduction Mode (BCM) to ramp the
inductor current through the internal power switches,
followed by a sleep cycle where the power switches are
off and the load current is supplied by the output
capacitor. During the sleep cycle, the RT6208 draws
only 25A of supply current. At light loads, the BCM
cycles are a small percentage of the total cycle time
which minimizes the average supply current, greatly
improving efficiency.
Scheme of Hysteresis Mode
The feedback comparator monitors the voltage on the
V
FB
pin and compares it to an internal 800mV
reference, as shown in Figure 1. If this voltage is
greater than the reference, the comparator activates a
sleep mode in which the power switches and current
Copyright © 2016 Richtek Technology Corporation. All rights reserved.
DS6208-02
May 2016
www.richtek.com
3
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
