RT6200 - Richtek

®
RT6200
0.6A, 36V, 1.2MHz Step-Down Converter
General Description
Features
The RT6200 is a high voltage Buck converter that can
support the input voltage range from 4.5V to 36V and the
output current can be up to 0.6A. Current mode operation
provides fast transient response and eases loop
stabilization.

Wide Operating Input Voltage Range : 4.5V to 36V

Adjustable Output Voltage Range : 0.8V to 15V
0.6A Output Current
0.35Ω
Ω Internal Power MOSFET Switch
High Efficiency up to 95%
1.2MHz Fixed Switching Frequency (Duty <90%)
Support duty up to 95%
Stable with Low ESR Output Ceramic Capacitors
Thermal Shutdown
Cycle-By-Cycle Over-Current Protection
The chip also provides protection functions such as cycleby-cycle current limit and thermal shutdown protection.
The RT6200 is available in the SOT-23-6 package.
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Ordering Information
RT6200
Applications
Package Type
E : SOT-23-6
Lead Plating System
G : Green (Halogen Free and Pb Free)




Note :
Richtek products are :

RoHS compliant and compatible with the current require-
Distributed Power Systems
Battery Chargers
Pre-Regulator for Linear Regulators
WLED Drivers
Pin Configurations
(TOP VIEW)
ments of IPC/JEDEC J-STD-020.

Suitable for use in SnPb or Pb-free soldering processes.
PHASE VIN EN
6
5
4
2
3
Marking Information
0Q= : Product Code
0Q=DNN
BOOT GND FB
DNN : Date Code
SOT-23-6
Simplified Application Circuit
VIN
BOOT
VIN
C1
RT6200
VOUT
CB
L1
PHASE
D1
Enable
EN
R1
FB
Open =
Automatic Startup
GND
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DS6200-04 August 2015
C2
R2
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RT6200
Functional Pin Description
Pin No.
Pin Name
Pin Function
BOOT
Bootstrap Supply for High-Side Gate Driver. A capacitor is connected between the
PHASE and BOOT pins to form a floating supply across the power switch driver.
This capacitor is needed to drive the power switch’s gate above the supply voltage.
2
GND
Ground. This pin is the voltage reference for the regulated output voltage. For this
reason, care must be taken in its layout. This node should be placed outside of the
D1 to C1 ground path to prevent switching current spikes from inducing voltage
noise into the part.
3
FB
Feedback Voltage Input. An external resistor divider from the output to GND tapped
to the FB pin sets the output voltage. The value of the divider resistors also set loop
bandwidth.
4
EN
Enable Control Input (Active High). If the EN pin is open, it will be pulled to high by
internal circuit. If using pull high resistor connected to VIN, the recommended value
is larger than 250k.
5
VIN
Supply Voltage Input. Bypass VIN to GND with a suitable large capacitor to prevent
large voltage spikes from appearing at the input.
6
PHASE
Switch Node.
1
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RT6200
Function Block Diagram
VIN
-
X20
1µA
Current Sense Amp
EN
3V
FB
1.1V
45mΩ
Ramp
Generator
Regulator
10k
+
BOOT
-
Oscillator
1.2MHz
+
Shutdown Reference
Comparator
S
Q
+
EA
-
400k
30pF
+
Driver
R
PWM
Comparator
PHASE
Bootstrap
Control
OC Limit Clamp
GND
2pF
Operation
The RT6200 is a constant frequency, current mode
asynchronous step-down converter. In normal operation,
the high side N-MOSFET is turned on when the S-R latch
is set by the oscillator and is turned off when the current
comparator resets the S-R latch. While the N-MOSFET
is turned off, the inductor current conducts through the
external diode.
Error Amplifier
The error amplifier adjusts its output voltage by comparing
the feedback signal (VFB) with the internal 0.8V reference.
When the load current increases, it causes a drop in the
feedback voltage relative to the reference, the error
amplifier's output voltage then rises to allow higher inductor
current to match the load current.
Internal Regulator
The regulator provides low voltage power to supply the
internal control circuits and the bootstrap power for highside gate driver.
Enable
The converter is turned on when the EN pin is higher than
1.2V and turned off when the EN pin is lower than 0.94V.
When the EN pin is open, it will be pulled up to logic-high
by 1μA current internally.
Soft-Start (SS)
An internal current source charges an internal capacitor
to build a soft-start ramp voltage. The FB voltage will track
the internal ramp voltage during soft-start interval. The
typical soft-start time is 700μs.
Oscillator
The internal oscillator runs at fixed frequency 1.2MHz.
The RT6200 can support duty up to 95% by decreasing
switching frequency to 600kHz. In short circuit condition,
the frequency is reduced for low power consumption.
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DS6200-04 August 2015
Thermal Shutdown
The over temperature protection function will shut down
the switching operation when the junction temperature
exceeds 150°C. Once the junction temperature cools
down by approximately 20°C, the converter will
automatically resume switching.
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RT6200
Absolute Maximum Ratings
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

(Note 1)
Supply Voltage, VIN -------------------------------------------------------------------------------------------------PHASE Voltage ------------------------------------------------------------------------------------------------------BOOT Voltage --------------------------------------------------------------------------------------------------------Other Pins -------------------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C
SOT-23-6 --------------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2)
SOT-23-6, θJA ---------------------------------------------------------------------------------------------------------Junction Temperature -----------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -------------------------------------------------------------------------Storage Temperature Range --------------------------------------------------------------------------------------ESD Susceptibility (Note 3)
HBM (Human Body Model) ----------------------------------------------------------------------------------------MM (Machine Model) ------------------------------------------------------------------------------------------------
Recommended Operating Conditions





40V
−0.3V to (VIN + 0.3V)
VPHASE + 6V
0.3V to 6V
0.48W
208.2°C/W
150°C
260°C
−65°C to 150°C
2kV
200V
(Note 4)
Supply Voltage, VIN -------------------------------------------------------------------------------------------------Output Voltage, VOUT -----------------------------------------------------------------------------------------------EN Voltage, VEN -----------------------------------------------------------------------------------------------------Junction Temperature Range --------------------------------------------------------------------------------------Ambient Temperature Range ---------------------------------------------------------------------------------------
4.5V to 36V
0.8V to 15V
0V to 5.5V
−40°C to 125°C
−40°C to 85°C
Electrical Characteristics
(VIN = 12V, TA = 25°C unless otherwise specified)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
0.784
0.8
0.816
V
--
0.1
0.3
A
Feedback Reference Voltage
VFB
4.5V  VIN  36V
Feedback Current
IFB
VFB = 0.8V
Switch On Resistance
RDS(ON) VBOOT  VPHASE = 4.8V
--
0.35
--

VEN = 0V, VPHASE = 0V
--
--
10
A
Switch Leakage
Current Limit
ILIM
VBOOT  VPHASE = 4.8V, duty = 90%
--
1.2
--
A
Oscillator Frequency
f SW
Duty < 90%
1
1.2
1.4
MHz
--
95
--
%
--
80
--
ns
3.9
4.2
4.5
V
--
200
--
mV
Maximum Duty Cycle
Minimum On-Time
tON
Under-Voltage Lockout
Threshold
Rising
Under-Voltage Lockout
Threshold Hysteresis
EN Input Voltage
Logic-High
VIH
0.98
1.08
1.2
Logic-Low
VIL
0.94
1
1.06
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V
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DS6200-04 August 2015
RT6200
Parameter
Symbol
EN Pull-Up Current
Test Conditions
Min
Typ
Max
Unit
VEN = 0V
--
1
--
A
Shutdown Current
ISHDN
VEN = 0V
--
20
--
A
Quiescent Current
IQ
VEN = 2V, VFB = 1V (Not Switching)
--
0.55
0.8
mA
Thermal Shutdown
TSD
--
150
--
°C
Note 1. Stresses beyond those listed “Absolute Maximum Ratings” may cause permanent damage to the device. These are
stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the
operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions may affect
device reliability.
Note 2. θJA is measured at TA = 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7.
Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
DS6200-04 August 2015
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RT6200
Typical Application Circuit
VIN
5
C1
4.7µF
Enable
Open =
Automatic Startup
BOOT
VIN
RT6200
PHASE 6
CB
10nF
L1
15µH
D1
B250A
4 EN
VOUT
5V
R1
91k
FB 3
GND
2
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1
C2
10µF
R2
17.4k
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RT6200
Typical Operating Characteristics
Efficiency vs. Output Current
Output Voltage vs. Input Voltage
100
5.10
90
5.05
Output Voltage (V)
Efficiency (%)
80
VIN = 7V
VIN = 12V
VIN = 17V
70
60
50
40
30
20
5.00
IOUT = 0.6A
IOUT = 0.1A
IOUT = 0A
4.95
4.90
4.85
10
VOUT = 5V
VOUT = 5V
0
4.80
0
0.1
0.2
0.3
0.4
0.5
0.6
6
11
16
Output Current (A)
Reference Voltage vs. Temperature
31
36
Output Voltage vs. Output Current
5.20
5.15
0.83
5.10
0.82
Output Voltage (V)
Reference Voltage (V)
26
Input Voltage (V)
0.84
0.81
0.80
0.79
0.78
5.05
5.00
4.95
VIN = 7V
VIN = 12V
VIN = 17V
4.90
4.85
4.80
4.75
4.70
0.77
4.65
VIN = 12V, IOUT = 0.1A
0.76
VOUT = 5V
4.60
-50
-25
0
25
50
75
100
125
0
0.1
0.2
0.3
0.4
0.5
0.6
Output Current (A)
Temperature (°C)
Frequency vs. Temperature
Frequency vs. Input Voltage
1600
1600
1500
1500
1400
1400
Frequency (kHz)a
Frequency (kHz) A
21
1300
1200
1100
1000
1300
1200
1100
1000
900
900
VOUT = 3.3V, IOUT = 0A
VIN = 12V, VOUT = 3.3V
800
800
4
8
12
16
20
24
28
32
Input Voltage (V)
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36
-50
-25
0
25
50
75
100
125
Temperature (°C)
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RT6200
Load Transient Response
Load Transient Response
VOUT
(50mV/Div)
VOUT
(50mV/Div)
VIN = 12V, VOUT = 5V,
IOUT = 50mA to 0.6A, L = 15μH
IOUT
(200mA/Div)
VOUT
(10mV/Div)
VIN = 12V, VOUT = 5V,
IOUT = 0.25A to 0.6A, L = 15μH
IOUT
(200mA/Div)
Time (50μs/Div)
Time (50μs/Div)
Output Ripple Voltage
Output Ripple Voltage
VIN = 12V, VOUT = 5V, IOUT = 0.1A, L = 15μH
VIN = 12V, VOUT = 5V, IOUT = 0.6A, L = 15μH
VOUT
(10mV/Div)
VPHASE
(10V/Div)
VPHASE
(10V/Div)
I PHASE
(200mA/Div)
I PHASE
(200mA/Div)
Time (1μs/Div)
Time (1μs/Div)
Power On from EN
Power Off from EN
VIN = 12V, VOUT = 5V, IOUT = 0.6A
VIN = 12V, VOUT = 5V, IOUT = 0.6A
VOUT
(5V/Div)
VOUT
(5V/Div)
VEN
(2V/Div)
VEN
(2V/Div)
VPHASE
(10V/Div)
VPHASE
(10V/Div)
I PHASE
(500mA/Div)
I PHASE
(500mA/Div)
Time (200μs/Div)
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Time (200μs/Div)
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RT6200
Application Information
The RT6200 is a high voltage buck converter that can
support the input voltage range from 4.5V to 36V and the
output current can be up to 0.6A.
Output Voltage Setting
The resistive voltage divider allows the FB pin to sense a
fraction of the output voltage as shown in Figure 1.
VOUT
R1
FB
RT6200
R2
GND
Figure 1. Output Voltage Setting
For adjustable voltage mode, the output voltage is set by
an external resistive voltage divider according to the
following equation :
VOUT = VFB  1 R1 
 R2 
Where VFB is the feedback reference voltage (0.8V typ.).
External Bootstrap Diode
Connect a 10nF low ESR ceramic capacitor between the
BOOT pin and PHASE pin. This capacitor provides the
gate driver voltage for the high side MOSFET.
It is recommended to add an external bootstrap diode
between an external 5V and the BOOT pin for efficiency
improvement when input voltage is lower than 5.5V or duty
ratio is higher than 65%. The bootstrap diode can be a
low cost one such as 1N4148 or BAT54.
The external 5V can be a 5V fixed input from system or a
5V output of the RT6200.
5V
BOOT
RT6200
10nF
PHASE
Figure 2. External Bootstrap Diode
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DS6200-04 August 2015
Inductor Selection
The inductor value and operating frequency determine the
ripple current according to a specific input and output
voltage. The ripple current ΔIL increases with higher VIN
and decreases with higher inductance.
V
V
IL =  OUT   1 OUT 
f

L
VIN 

 
Having a lower ripple current reduces not only the ESR
losses in the output capacitors but also the output voltage
ripple. High frequency with small ripple current can achieve
highest efficiency operation. However, it requires a large
inductor to achieve this goal.
For the ripple current selection, the value of ΔIL = 0.4(IMAX)
will be a reasonable starting point. The largest ripple
current occurs at the highest VIN. To guarantee that the
ripple current stays below the specified maximum, the
inductor value should be chosen according to the following
equation :
 VOUT  
VOUT 
L =
 1 


 f  IL(MAX)   VIN(MAX) 
Inductor Core Selection
The inductor type must be selected once the value for L
is known. Generally speaking, high efficiency converters
can not afford the core loss found in low cost powdered
iron cores. So, the more expensive ferrite or
mollypermalloy cores will be a better choice.
The selected inductance rather than the core size for a
fixed inductor value is the key for actual core loss. As the
inductance increases, core losses decrease. Unfortunately,
increase of the inductance requires more turns of wire
and therefore the copper losses will increase.
Ferrite designs are preferred at high switching frequency
due to the characteristics of very low core losses. So,
design goals can focus on the reduction of copper loss
and the saturation prevention.
Ferrite core material saturates “hard”, which means that
inductance collapses abruptly when the peak design
current is exceeded. The previous situation results in an
abrupt increase in inductor ripple current and consequent
output voltage ripple.
Do not allow the core to saturate!
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RT6200
Different core materials and shapes will change the size/
current and price/current relationship of an inductor.
Toroid or shielded pot cores in ferrite or permalloy materials
are small and do not radiate energy. However, they are
usually more expensive than the similar powdered iron
inductors. The rule for inductor choice mainly depends
on the price vs. size requirement and any radiated field/
EMI requirements.
Diode Selection
When the power switch turns off, the path for the current
is through the diode connected between the switch output
and ground. This forward biased diode must have a
minimum voltage drop and recovery times. Schottky diode
is recommended and it should be able to handle those
current. The reverse voltage rating of the diode should be
greater than the maximum input voltage, and current rating
should be greater than the maximum load current.
CIN and COUT Selection
The input capacitance, C IN, is needed to filter the
trapezoidal current at the source of the top MOSFET. To
prevent large ripple current, a low ESR input capacitor
sized for the maximum RMS current should be used. The
RMS current is given by :
V
IRMS = IOUT(MAX) OUT
VIN
VIN
1
VOUT
This formula has a maximum at VIN = 2VOUT, where
I RMS = I OUT/2. This simple worst-case condition is
commonly used for design because even significant
deviations do not offer much relief.
Choose a capacitor rated at a higher temperature than
required. Several capacitors may also be paralleled to
meet size or height requirements in the design.
The selection of COUT is determined by the required Effective
Series Resistance (ESR) to minimize voltage ripple.
Moreover, the amount of bulk capacitance is also a key
for COUT selection to ensure that the control loop is stable.
Loop stability can be checked by viewing the load transient
response as described in a later section.
The output ripple, ΔVOUT , is determined by :
1

VOUT  IL ESR 

8fC
OUT

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The output ripple will be highest at the maximum input
voltage since ΔIL increases with input voltage. Multiple
capacitors placed in parallel may be needed to meet the
ESR and RMS current handling requirement. Dry tantalum,
special polymer, aluminum electrolytic and ceramic
capacitors are all available in surface mount packages.
Special polymer capacitors offer very low ESR value.
However, it provides lower capacitance density than other
types. Although Tantalum capacitors have the highest
capacitance density, it is important to only use types that
pass the surge test for use in switching power supplies.
Aluminum electrolytic capacitors have significantly higher
ESR. However, it can be used in cost-sensitive applications
for ripple current rating and long term reliability
considerations. Ceramic capacitors have excellent low
ESR characteristics but can have a high voltage coefficient
and audible piezoelectric effects. The high Q of ceramic
capacitors with trace inductance can also lead to significant
ringing.
Higher values, lower cost ceramic capacitors are now
becoming available in smaller case sizes. Their high ripple
current, high voltage rating and low ESR make them ideal
for switching regulator applications. However, care must
be taken when these capacitors are used at input and
output. When a ceramic capacitor is used at the input
and the power is supplied by a wall adapter through long
wires, a load step at the output can induce ringing at the
input, VIN. At best, this ringing can couple to the output
and be mistaken as loop instability. At worst, a sudden
inrush of current through the long wires can potentially
cause a voltage spike at VIN large enough to damage the
part.
Checking Transient Response
The regulator loop response can be checked by looking
at the load transient response. Switching regulators take
several cycles to respond to a step in load current. When
a load step occurs, VOUT immediately shifts by an amount
equal to ΔILOAD (ESR) also begins to charge or discharge
COUT generating a feedback error signal for the regulator
to return VOUT to its steady-state value. During this recovery
time, VOUT can be monitored for overshoot or ringing that
would indicate a stability problem.
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DS6200-04 August 2015
RT6200
Thermal Considerations
Layout Consideration
For continuous operation, do not exceed the maximum
operation junction temperature 125°C. The maximum
power dissipation depends on the thermal resistance of
IC package, PCB layout, the rate of surroundings airflow
and temperature difference between junction to ambient.
Follow the PCB layout guidelines for optimal performance
of RT6200.
The maximum power dissipation can be calculated by
following formula :
PD(MAX) = (TJ(MAX) − TA) / θJA

Keep the traces of the main current paths as short and
wide as possible.

Put the input capacitor as close as possible to the device
pins (VIN and GND).

PHASE node is with high frequency voltage swing and
should be kept at small area. Keep sensitive
components away from the PHASE node to prevent
stray capacitive noise pick-up.

Place the feedback components to the FB pin as close
as possible.

Connect GND to a ground plane for noise reduction and
thermal dissipation.
where T J(MAX) is the maximum operation junction
temperature, TA is the ambient temperature and the θJA is
the junction to ambient thermal resistance.
For recommended operating conditions specifications, the
maximum junction temperature of the die is 125°C. The
junction to ambient thermal resistance θJA is layout
dependent. For SOT-23-6 package, the thermal resistance
θJA is 208.2°C/W on standard JEDEC 51-7 four-layers
C OUT
V OUT
thermal test board. The maximum power dissipation at TA
= 25°C can be calculated by following formula :
L1
CB
D1
PD(MAX) = (125°C − 25°C) / (208.2°C/W) = 0.48W for
SOT-23-6 packages
BOOT
1
6
PHASE
GND
2
5
VIN
FB
3
4
EN
C IN
The maximum power dissipation depends on operating
ambient temperature for fixed T J(MAX) and thermal
resistance θJA. The derating curves in Figure 3 allows
the designer to see the effect of rising ambient temperature
on the maximum power dissipation.
R2
V OUT
R1
GND
Figure 4. PCB Layout Guide
Maximum Power Dissipation (W)1
1.0
Four-Layer PCB
0.8
0.6
0.4
0.2
0.0
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 3. Derating Curves of Maximum Power
Dissipation
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RT6200
Outline Dimension
H
D
L
C
B
b
A
A1
e
Dimensions In Millimeters
Dimensions In Inches
Symbol
Min
Max
Min
Max
A
0.889
1.295
0.031
0.051
A1
0.000
0.152
0.000
0.006
B
1.397
1.803
0.055
0.071
b
0.250
0.560
0.010
0.022
C
2.591
2.997
0.102
0.118
D
2.692
3.099
0.106
0.122
e
0.838
1.041
0.033
0.041
H
0.080
0.254
0.003
0.010
L
0.300
0.610
0.012
0.024
SOT-23-6 Surface Mount Package
Richtek Technology Corporation
14F, No. 8, Tai Yuen 1st Street, Chupei City
Hsinchu, Taiwan, R.O.C.
Tel: (8863)5526789
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obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. Richtek cannot
assume responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek product. Information furnished by Richtek is believed to be
accurate and reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringements of patents or other rights of third
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DS6200-04 August 2015