RT6208
High Efficiency, 36V 100mA Synchronous Step-Down Converter
General Description
The RT6208 is a high-efficiency, monolithic synchronous
step-down DC/DC converter that can deliver up to
100mA output current from a 4.75V to 36V input supply.
It requires only 25A typical supply current at no load
while maintaining output voltage regulation. The RT6208
achieves Boundary Conduction Mode (BCM) operation,
low quiescent current and programmable high-side peak
current limit, providing high efficiency over a wide range
of load currents. It also provides soft-start protection to
eliminate input current surge during start-up. The low
current
(3A)
shutdown
mode
provides
output
Features
Achieves Very High Efficiency in Low Load
Conditions
1%
High Accuracy Feedback Voltage
4.75V to 36V Input Voltage Range
100mA Output Current
Integrated High-Side and Low-Side Switches
No Compensation Required
Low Quiescent Current
Adjustable Peak Current Limit
Cycle-by-Cycle Over Current Protection
Input Under Voltage Lockout
Internal Soft-Start
Thermal Shutdown Protection
disconnect, enabling easy power management in
battery-powered systems. The RT6208 is available in a
SOT-23-6 and SOT-23-8 packages.
Applications
Ordering Information
RT6208
Package Type
E : SOT-23-6
V8 : SOT-23-8
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
Richtek products are :
RoHS compliant and compatible with the current
requirements of IPC/JEDEC J-STD-020.
Suitable for use in SnPb or Pb-free soldering processes
Wireless Charger
Industrial and Commercial Low Power Systems
Green Electronics/Appliances
Point of Load Regulation for High-Performance DSPs
MCU Supply in Wireless LED Lighting
Marking Information
RT6208GE
30=DNN
RT6208GV8
30= : Product Code
DNN : Date Code
0E=DNN
0E= : Product Code
DNN : Date Code
Copyright © 2016 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS6208-02
May 2016
www.richtek.com
1
RT6208
Pin Configurations
(TOP VIEW)
PGOOD
6
3
SW VIN ISET
6
5
4
8
2
3
7
2
FB GND EN
ISET
GND
VIN
SW
SOT-23-6
SOT-23-8
Functional Pin Description
Pin No
SOT-23-6
1
2
SOT-23-8
7
2
Pin Name
Pin Function
Feedback Voltage Input. This pin receives the feedback voltage from
a resistive divider connected across the output.
Power Ground.
Enable Control Input. A voltage on this pin above 1.25V enables the
converter into normal mode; forcing this pin below 0.3V shuts down
the IC, reducing quiescent current to 3A.
An internal 2A current pulls up enable pin for automatic startup.
High-Side Peak Current Set Pin. A resistor from this pin to GND sets
the high-side peak current limit. Leave floating for the maximum
peak current, 225mA. Short this pin to GND for the minimum peak
current, 50mA. A 1A current is sourced out of this pin.
Input Supply Voltage. Must bypass with a suitably large ceramic
capacitor.
Switch Node. Connect The Switching Node To External Inductor.
Power Good Open Drain Output. Asserts low if output voltage is low
due to OTP, UVP, UVLO, EN shutdown or during soft-start.
Analog Ground.
FB
GND
3
8
EN
4
1
ISET
5
6
--
--
3
4
6
5
VIN
SW
PGOOD
AGND
Copyright © 2016 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
2
AGND
5
4
EN
FB
DS6208-02
May 2016
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
RT6208
this architecture, the maximum average output current
is equal to half of the peak current. The hysteresis
nature of this control architecture results in a switching
frequency that is a function of the input voltage, output
voltage and inductor value. This behavior provides
inherent short‑circuit protection. If the output is shorted
to ground, the inductor current will decay very slowly
during a single switching cycle. Since the high-side
switch turns on only when the inductor current is near
zero, the RT6208 inherently switches at a lower
frequency during short-circuit condition.
V
REF
V
FB
V
REF
- V
Hys
High-Side Peak Current (PC)
Inductor Current
Low-Side Zero Current (ZC)
Sleep
Mode
Boundary Conduction
Mode
Sleep
Mode
Stop Switch
Switch between High-Side PC and
Low-Side ZC
Figure 1. Hysteresis Mode
Copyright © 2016 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
4
DS6208-02
May 2016
RT6208
Absolute Maximum Ratings
(Note 1)
Supply Voltage, VIN
---------------------------------------------------------------------------------------------------
0.3V
to 40V
Switch Voltage, SW
----------------------------------------------------------------------------------------------------
0.3V
to (VIN + 0.3V)
<10ns
-----------------------------------------------------------------------------------------------------------------------
5V
to 46.3V
All Other Pins
------------------------------------------------------------------------------------------------------------
0.3V
to 6V
Power Dissipation, P
D
@ T
A
= 25C
SOT-23-6
------------------------------------------------------------------------------------------------------------------
0.48W
SOT-23-8
------------------------------------------------------------------------------------------------------------------
0.53W
Package Thermal Resistance
(Note 2)
SOT-23-6,
JA
-----------------------------------------------------------------------------------------------------------
208.2C/W
SOT-23-6,
JC
-----------------------------------------------------------------------------------------------------------
32C/W
SOT-23-8,
JA
-----------------------------------------------------------------------------------------------------------
186.2C/W
SOT-23-8,
JC
-----------------------------------------------------------------------------------------------------------
47.4C/W
Lead Temperature (Soldering, 10 sec.)
-------------------------------------------------------------------------
260C
Junction Temperature
-------------------------------------------------------------------------------------------------
150C
Storage Temperature Range
---------------------------------------------------------------------------------------
65C
to 150C
ESD Susceptibility
(Note 3)
HBM (Human Body Model)
-----------------------------------------------------------------------------------------
2kV
MM (Machine Model)
-------------------------------------------------------------------------------------------------
200V
Recommended Operating Conditions
(Note 4)
Input Voltage Range
--------------------------------------------------------------------------------------------------
4.75V
to 36V
Ambient Temperature Range
--------------------------------------------------------------------------------------
40C
to 85C
Junction Temperature Range
--------------------------------------------------------------------------------------
40C
to 125C
Electrical Characteristics
(V
IN
= 12V, T
A
= 25C, unless otherwise specified)
Parameter
Active Mode
Supply Current
Sleep Mode
Shutdown Mode
Feedback Comparator Trip Voltage
Feedback Comparator Hysteresis
Feedback Pin Current
High-Side Switch On-Resistance
Low-Side Switch On-Resistance
Enable Threshold Voltage
Enable Hysteresis
Symbol
Test Conditions
Min
--
--
Typ
160
25
3
0.8
5
0
3
1.5
1.2
100
4.2
Max
190
40
6
0.808
7
100
--
--
1.4
--
4.75
Unit
A
A
A
V
mV
nA
V
mV
V
V
EN
= 0V
V
FB
V
FBHYS
I
FB
R
DS(ON)_H
R
DS(ON)_L
Enable Rising
V
FB
Rising
--
0.792
3
100
--
--
1
--
Input Under Voltage Lockout Threshold V
UVLO
Copyright © 2016 Richtek Technology Corporation. All rights reserved.
V
IN
Rising
3.9
is a registered trademark of Richtek Technology Corporation.
DS6208-02
May 2016
www.richtek.com
5
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