RT6207A/B
Function Block Diagram
PVCC
V
IN
Reg
VIBIAS
BOOT
PVCC
Min.
Off
V
REF
Control
Driver
LGATE
PVCC
UGATE
SW
GND
VIN
OC
UV & OV
PVCC
6µA
SS
FB
V
IN
SW
On-Time
GND SW
SW
Ripple
Gen.
+
-
-
Comparator
Comparator
0.9 V
REF
FB
+
-
PGOOD
EN
EN
Detailed Description
The RT6207A/B is a high-performance 650kHz 5A step-
down regulators with internal power switches and
synchronous rectifiers. It features an Advanced Constant
On-Time (ACOT
TM
) control architecture that provides
stable operation with ceramic output capacitors without
complicated external compensation, among other benefits.
The ACOT
TM
control mode also provide fast transient
response, especially for low output voltages and low duty
cycles.
The input voltage range is from 4.5V to 18V and the output
is adjustable from 0.7V to 8V. The proprietary ACOT
TM
control scheme improves upon other constant on-time
architectures, achieving nearly constant switching
frequency over line, load, and output voltage ranges. The
RT6207A/B are optimized for ceramic output capacitors.
Since there is no internal clock, response to transients is
nearly instantaneous and inductor current can ramp quickly
to maintain output regulation without large bulk output
capacitance.
Constant On-Time (COT) Control
The heart of any COT architecture is the on-time one shot.
Each on-time is a pre-determined
“fixed”
period that is
triggered by a feedback comparator. This robust
Copyright
©
2015 Richtek Technology Corporation. All rights reserved.
arrangement has high noise immunity and is ideal for low
duty cycle applications. After the on-time one-shot period,
there is a minimum off-time period before any further
regulation decisions can be considered. This arrangement
avoids the need to make any decisions during the noisy
time periods just after switching events, when the
switching node (SW) rises or falls. Because there is no
fixed clock, the high-side switch can turn on almost
immediately after load transients and further switching
pulses can ramp the inductor current higher to meet load
requirements with minimal delays.
Traditional current mode or voltage mode control schemes
typically must monitor the feedback voltage, current
signals (also for current limit), and internal ramps and
compensation signals, to determine when to turn off the
high-side switch and turn on the synchronous rectifier.
Weighing these small signals in a switching environment
is difficult to do just after switching large currents, making
those architectures problematic at low duty cycles and in
less than ideal board layouts.
Because no switching decisions are made during noisy
time periods, COT architectures are preferable in low duty
cycle and noisy applications. However, traditional COT
is a registered trademark of Richtek Technology Corporation.
DS6207A/B-02
December 2015
www.richtek.com
3
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
