RT6214A/B
18V, 3A, ACOTTM Step-Down Converter in 6 and 8 Pin TSOT-23
General Description
Features
The RT6214A/B is a simple, easy-to-use, 3A
synchronous step-down DC-DC converter with an input
supply voltage range of 4.5V to 18V. The device
integrates low RDS(ON) power MOSFETs to achieve
high efficiency in a SOT-23 package and build-in
accurate reference voltage (0.765V or 0.8V by product
options).
The RT6214A/B adopts Advanced Constant On-Time
(ACOTTM) control architecture to provide an ultrafast
transient response with few external components and
to operate in nearly constant switching frequency over
the line, load, and output voltage range. The RT6214A
operates in automatic PSM that maintains high
efficiency during light load operation. RT6214B
operates in Forced PWM that helps meet tight voltage
regulation accuracy requirements.
The RT6214A/B senses both FETs current for a robust
over-current
protection. The
device features
cycle-by-cycle current limit protection and prevent the
device from the catastrophic damage in output short
circuit, over current or inductor saturation. The
RT6214A/B SOT-23-6 series built-in soft-start function
prevents inrush current during start-up and the
SOT-23-8 series offers programmable start-up by
connecting a capacitor at external SS pin. The device
also includes input under-voltage lockout, output
under-voltage protection, and over-temperature
protection (thermal shutdown) to provide safe and
smooth operation in all operating conditions. The
RT6214A/B are offered in TSOT-23-6 (FC) and
TSOT-23-8 (FC) package.
Copyright © 2017 Richtek Technology Corporation. All rights reserved.
DS6214A/B-04
August 2017
Input Supply Voltage Range : 4.5V to 18V
3A Converter With Built-in 100m/50m Low
RDS(ON) Power FETs
Advanced Constant On-Time (ACOT TM) Control
for Ultrafast Transient Response
Fixed Switching Frequency : 500kHz (SOT23-6)
or 650kHz (SOT23-8)
Optional for Operation Modes :
Automatically
(RT6214A)
Power
Saving
Forced PWM Mode (RT6214B)
Mode
(PSM)
Optimized for Low-ESR Ceramic Output
Capacitors
1.5% High-Accuracy Feedback Reference
Voltage
Output Voltage Range : up to 6.5V
Internal fixed Soft-Start (typ. 1ms) for SOT-23-6
Externally Adjustable Soft-Start for SOT-23-8
Monotonic Start-Up for Pre-biased Outputs
Both HS/LS FETs Protection for Robust Over
Current Protection
Input Under-Voltage Lockout (UVLO)
Output Under-Voltage Protection (UVP) with
Hiccup Mode
Over-Temperature Protection (OTP) (Thermal
Shutdown)
Enable Control
Power Good Indication for SOT-23-8
RoHS Compliant and Halogen Free
Available in TSOT-23-6 or TSOT-23-8 Package
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1
RT6214A/B
Ordering Information
RT6214A/B
(
Marking Information
RT6214AHRGJ6F
)
Package Type
J6F : TSOT-23-6 (FC)
J8F : TSOT-23-8 (FC)
2Y=DNN
2Y= : Product Code
DNN : Date Code
RT6214BHRGJ6F
Lead Plating System
G : Green (Halogen Free and Pb Free)
2X=DNN
Reference Voltage
None : VREF = 0.8V (Only for TSOT-23-6 (FC))
R : VREF = 0.765V
RT6214AHGJ6F
UVP Option
H : Hiccup
1G=DNN
PWM Operation Mode
A : Automatic PSM
B : Forced PWM
2X= : Product Code
DNN : Date Code
1G= : Product Code
DNN : Date Code
RT6214BHGJ6F
1F=DNN
1F= : Product Code
DNN : Date Code
Note :
RT6214AHRGJ8F
Richtek products are :
RoHS compliant and compatible with the current
24=DNN
24= : Product Code
DNN : Date Code
requirements of IPC/JEDEC J-STD-020.
Suitable for use in SnPb or Pb-free soldering processes.
RT6214BHRGJ8F
23=DNN
23= : Product Code
DNN : Date Code
Applications
Set-Top Boxes
LCD TVs
Home Networking Devices
Surveillance
General Purpose
Pin Configuration
FB
SS
8
7
6
5
2
3
4
VIN
PGOOD
4
2
3
GND LX VIN
TSOT-23-6 (FC)
Copyright © 2017 Richtek Technology Corporation. All rights reserved.
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2
EN
5
LX
6
FB
GND
BOOT EN
BOOT
(TOP VIEW)
TSOT-23-8 (FC)
is a registered trademark of Richtek Technology Corporation.
DS6214A/B-04
August 2017
RT6214A/B
Functional Pin Description
Pin No.
Pin Name
Pin Function
TSOT-23-6
(FC)
TSOT-23-8
(FC)
1
1
GND
Power ground. This pin, connected to analog ground, must be
soldered to a large PCB copper area for maximum power dissipation.
2
2
LX
Switch node between the internal switch and the synchronous
rectifier. Connect this pin to the inductor and bootstrap capacitor.
3
3
VIN
Power input. The input voltage range is from 4.5V to 18V. Connect a
suitable input capacitor between this pin and GND, with a typical
capacitance of 22F.
--
4
PGOOD
Open-drain power-good indication output. Once being started-up,
PGOOD will be pulled low to GND if any internal protection is
triggered.
--
5
SS
Soft-start capacitor connection node. Connect an external capacitor
between this pin and ground to set the soft-start time. Do not leave
this pin unconnected. A capacitor of 8.2nF is suggested.
4
6
FB
Feedback voltage input. Connect this pin to the midpoint of the
external feedback resistive divider to set the output voltage of the
converter to the desired regulation level. The device regulates the FB
voltage at Feedback Threshold Voltage, typically 0.765V/0.8V.
5
7
EN
Enable control input. Floating this pin or connecting this pin to GND
can disable the device and connecting this pin to logic high can enable
the device.
6
8
BOOT
Bootstrap capacitor connection node to supply the high-side gate
driver. Connect a 0.1F ceramic capacitor between this pin and LX
pin.
Copyright © 2017 Richtek Technology Corporation. All rights reserved.
DS6214A/B-04
August 2017
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
3
RT6214A/B
Functional Block Diagram
For TSOT-23-6 (FC)
VIN
LX
6.5K
-
EN
3V
UVLO
+
VEN_
REF
Shutdown
Comparator
VCC
Internal
Regulator
PVCC
OnTime
BOOT
OC
UGATE
UV
Protection
VCC
Control
Ripple
Gen.
+
+
-
FB
Power
Stage &
Dead-time
Control
LX
LGATE
MIN OFF
Comparator
VCC
VIBIAS
GND
VRef
For TSOT-23-8 (FC)
VIN
LX
6.5K
-
EN
3V
UVLO
+
VEN_
REF
Shutdown
Comparator
VCC
Internal
Regulator
PVCC
OnTime
BOOT
OC
UGATE
UV
Protection
VCC
6µA
Control
Ripple
Gen.
+
+
-
SS
FB
-
LX
LGATE
MIN OFF
Comparator
GND
VCC
+
0.9VREF
Power
Stage &
Dead-time
Control
PGOOD
Comparator
VIBIAS
VRef
PGOOD
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is a registered trademark of Richtek Technology Corporation.
DS6214A/B-04
August 2017
RT6214A/B
Operation
The RT6214A/B is a high-efficiency, synchronous
step-down DC-DC converter that can deliver up to 3A
output current from a 4.5V to 18V input supply. The
RT6214A/B adopts ACOTTM control mode, which can
reduce the output capacitance and provide ultrafast
transient responses, and allow minimal component
sizes without any additional external compensation
network.
Output Under-Voltage Protection
The RT6214A/B includes output under-voltage
protection (UVP) against over-load or short-circuited
condition by constantly monitoring the feedback
voltage VFB. If VFB drops below the under-voltage
protection trip threshold, the UV comparator will go
high to turn off both the internal high-side and low-side
MOSFET switches.
Enable Control
The RT6214A/B provides an EN pin, as an external
chip enable control, to enable or disable the device. If
VEN is held below a logic-low threshold voltage
(VENHVEN) of the enable input (EN), the converter
will enter into shutdown mode, that is, the converter is
disabled and switching is inhibited even if the VIN
voltage is above VIN under-voltage lockout threshold
(VUVLO). During shutdown mode, the supply current
can be reduced to ISHDN (5A or below). If the EN
voltage rises above the logic-high threshold voltage
(VENH) while the VIN voltage is higher than UVLO
threshold (VUVLO), the device will be turned on, that is,
switching being enabled and soft-start sequence being
initiated.
Low-Side Current Limit Protection
The RT6214A/B features a cycle-by-cycle valley-type
current limit protection, measuring the inductor current
through the synchronous rectifier (low-side switch). The
inductor current level is determined by measuring the
low-side switch voltage between the LX pin and GND,
which is proportional to the switch current, during the
low-side on-time. For greater accuracy, temperature
compensation is added to the voltage sensing. Once
the current rises above the low-side switch valley
Copyright © 2017 Richtek Technology Corporation. All rights reserved.
DS6214A/B-04
August 2017
current limit (ILIM), the on-time one-shot will be inhibited
until the inductor current ramps down to the current
limit level (ILIM), that is, another on-time can only be
triggered when the inductor current goes below the
low-side current limit. This function can prevent the
average output current from greatly exceeding the
guaranteed low-side current limit value.
If the output load current exceeds the available inductor
current (clamped by the above-mentioned low-side
current limit), the output capacitor needs to supply the
extra current such that the output voltage will begin to
drop. If it drops below the output under-voltage
protection trip threshold, the IC will stop switching to
avoid excessive heat.
High-Side Current Limit Protection
The RT6214A/B also includes a cycle-by-cycle
peak-type current limit protection against the condition
that the inductor current increasing abnormally, even
over the inductor saturation current rating. To ensure
the low-side current limit protection can still function
properly, the inductor current through the high-side
switch will only be measured after a certain amount of
delay when the high-side switch being turned on. If an
over-current condition occurs, the converter will
immediately turn off the high-side switch and turn on
the low-side switch to prevent the inductor current
exceeding the high-side switch peak-current limit.
Hiccup Mode
If the output under-voltage condition continues for a
period of time, the RT6214A/B will enter output
under-voltage protection with hiccup mode. During
hiccup mode, the device remains shut down. After a
period of time, a soft-start sequence for auto-recovery
will be initiated. Upon completion of the soft-start
sequence, if the fault condition is removed, the
converter will resume normal operation; otherwise,
such cycle for auto-recovery will be repeated until the
fault condition is cleared. Hiccup mode allows the
circuit to operate safely with low input current and
power dissipation, and then resume normal operation
as soon as the over-load or short-circuit condition is
removed.
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RT6214A/B
External Bootstrap Capacitor
Connect a 0.1F low-ESR ceramic capacitor between
the BOOT and LX pins. This bootstrap capacitor
supplies for the gate driver of the high-side N-channel
MOSFET switch.
after this ramp voltage is greater than the feedback
voltage VFB to ensure the converters have a smooth
start-up. For soft-start control, the SS pin should never
be left unconnected.
Power Good Indication
Over-Temperature Protection (Thermal Shutdown)
(For RT6214A/BHRGJ8F)
The RT6214A/B includes an over-temperature
protection (OTP) circuitry to prevent overheating due to
excessive power dissipation. The OTP will shut down
switching operation when junction temperature
exceeds a thermal shutdown threshold TSD. Once the
junction temperature cools down by a thermal
The PGOOD pin is an open-drain output and is
connected to an external pull-up resistor. It is controlled
by a comparator, which the feedback signal VFB is fed
to. If VFB is above 90% of the internal reference voltage
after soft-start finished, the PGOOD pin will be in high
impedance and VPGOOD will be held high. Otherwise,
shutdown hysteresis (TSD), the IC will resume normal
operation with a complete soft-start.
the PGOOD output will be pulled low.
Soft-Start (SS)
(For RT6214A/BHRGJ6F)
The soft-start function is used to prevent large inrush
currents while the converter is being powered up. The
RT6214A/B provides an internal soft-start feature for
inrush control. During the start-up sequence, the
internal capacitor is charged by an internal current
source ISS to generate a soft-start ramp voltage as a
reference voltage to the PWM comparator. The device
will initiate switching and the output voltage will
smoothly ramp up to its targeted regulation voltage only
after this ramp voltage is greater than the feedback
voltage VFB to ensure the converters have a smooth
start-up. The typical soft-start time is 1ms.
Soft-Start (SS)
(For RT6214A/BHRGJ8F)
The soft-start function is used to prevent large inrush
currents while the converter is being powered up. The
RT6214A/B provides a soft-start feature for inrush
control. It provides an SS pin so that the soft-start time
can be programmed by selecting the value of the
external capacitor CSS connected from the SS pin to
GND. During the start-up sequence, the external
capacitor is charged by an internal current source ISS
(typically, 6A) to generate a soft-start ramp voltage as
a reference voltage to the PWM comparator. The
device will initiate switching and the output voltage will
smoothly ramp up to its targeted regulation voltage only
Copyright © 2017 Richtek Technology Corporation. All rights reserved.
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is a registered trademark of Richtek Technology Corporation.
DS6214A/B-04
August 2017
RT6214A/B
Absolute Maximum Ratings
(Note 1)
Supply Input Voltage --------------------------------------------------------------------------------- 0.3V to 20V
Switch Node Voltage, LX ---------------------------------------------------------------------------- 0.3V to (VIN + 0.3V)
< 50ns ---------------------------------------------------------------------------------------------------- 5V to 25V
BOOT Pin Voltage ------------------------------------------------------------------------------------ (VLX – 0.3V) to (VIN + 6.3V)
BOOT to LX, VBOOT VLX -------------------------------------------------------------------------- –0.3V to 6V
Other Pins ----------------------------------------------------------------------------------------------- 0.3V to 6V
Power Dissipation, PD @ TA = 25C
TSOT-23-6 (FC) --------------------------------------------------------------------------------------- 1.667W
TSOT-23-8 (FC) --------------------------------------------------------------------------------------- 1.667W
Package Thermal Resistance
(Note 2)
TSOT-23-6 (FC), JA --------------------------------------------------------------------------------- 60C/W
TSOT-23-6 (FC), JC --------------------------------------------------------------------------------- 8C/W
TSOT-23-8 (FC), JA --------------------------------------------------------------------------------- 60C/W
TSOT-23-8 (FC), JC --------------------------------------------------------------------------------- 8C/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
Recommended Operating Conditions
(Note 4)
Supply Input Voltage --------------------------------------------------------------------------------- 4.5V to 18V
Ambient Temperature Range----------------------------------------------------------------------- 40C to 85C
Junction Temperature Range ---------------------------------------------------------------------- 40C to 125C
Electrical Characteristics
(VIN = 12V, TA = 25C, unless otherwise specified)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
4.5
--
18
V
RT6214A/BHGJ6F
3.6
3.9
4.2
RT6214A/BHRGJ6F
3.45
3.75
4.05
--
340
--
mV
Supply Voltage
VIN Supply Input Operating
Voltage
VIN
Under-Voltage Lockout
Threshold
VUVLO
Under-Voltage Lockout
Threshold Hysteresis
VUVLO
V
Supply Current
Supply Current (Shutdown)
ISHDN
VEN = 0V
--
--
5
A
Supply Current (Quiescent)
IQ
VEN = 2V, VFB = 0.85V
--
0.5
--
mA
Copyright © 2017 Richtek Technology Corporation. All rights reserved.
DS6214A/B-04
August 2017
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
7
RT6214A/B
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
--
1000
--
s
VEN rising, RT6214A/BHGJ6F
1.38
1.5
1.62
VEN rising, RT6214A/BRHGJ6/8F
1.32
1.43
1.55
--
0.18
--
4.5V VIN 18V,
RT6214A/BHGJ6F
0.788
0.8
0.812
4.5V VIN 18V,
RT6214A/BHRGJ6/8F
0.753
0.765
0.777
--
100
--
--
50
--
4
4.5
--
A
420
500
--
kHz
Soft-Start
Soft-Start Time
tSS
RT6214A/BHGJ6F,
RT6214A/BHRGJ6F
Enable Voltage
Enable Voltage Threshold
VEN_R
Enable Voltage Hysteresis
V
V
Feedback Voltage
Feedback Reference Voltage
VREF
V
Internal MOSFET
High-Side On-Resistance
RDS(ON)_H
Low-Side On-Resistance
RDS(ON)_L
VBOOT VLX = 4.8V
m
Current Limit
Current Limit
ILIM
Valley current
Switching Frequency
Switching Frequency
f SW
On-Time Timer Control
Minimum On-Time
tON_MIN
--
60
--
Minimum Off-Time
tOFF_MIN
--
240
--
UVP detect
45
50
55
Hysteresis
--
10
--
ns
Output Under-Voltage Protections
UVP Trip Threshold
%
Thermal Shutdown
Thermal Shutdown Threshold
TSD
--
150
--
°C
Thermal Shutdown Hysteresis
TSD
--
20
--
°C
RT6214A/BHRGJ8F (TSOT-23-8)
Supply Voltage
Under-Voltage Lockout
Threshold
VUVLO
--
3.7
--
V
Under-Voltage Lockout
Threshold Hysteresis
VUVLO
--
300
--
mV
Soft-Start
Soft-Start Internal Charging
Current
Current Limit
ISS
--
6
--
A
Current Limit
ILIM
3.5
4.2
6.3
A
Valley current
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is a registered trademark of Richtek Technology Corporation.
DS6214A/B-04
August 2017
RT6214A/B
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
--
650
--
kHz
UVP detect
57.5
62.5
67.5
Hysteresis
--
10
--
FB rising
--
90
--
FB falling
--
85
--
Switching Frequency
Switching Frequency
f SW
Output Under-Voltage Protections
UVP Trip Threshold
%
Power Good
Power Good Threshold
VPGOOD
%
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. JA is measured under natural convection (still air) at TA = 25C with the component mounted on a high
effective-thermal-conductivity four-layer test board on a JEDEC 51-7 thermal measurement standard. The first layer is
filled with copper. JA is measured at the lead of the package.
Note 3. Devices are ESD sensitive. Handling precaution recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
Copyright © 2017 Richtek Technology Corporation. All rights reserved.
DS6214A/B-04
August 2017
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
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RT6214A/B
Typical Application Circuit
For TSOT-23-6 (FC)
RT6214A/B
3
VIN
CIN
22μF
VIN
BOOT
LX
5
Enable
6
2
CBOOT
0.1μF
VOUT
L
EN
CFF
Open
R1
FB
GND
1
COUT
44μF
4
RT*
10k
R2
For TSOT-23-8 (FC)
RT6214A/B
VIN
3
CIN
22μF
BOOT
LX
7
Enable
VPGOOD
VIN
RPGOOD 4
5
8
2
CBOOT
0.1μF
VOUT
L
EN
CFF
Open
R1
PGOOD
FB
SS
CSS
COUT
44μF
6
RT*
10k
GND
1
R2
* Note : When CFF is added, it is necessary to add RT = 10k between feedback network and chip FB pin.
Part Options for fSW Mode and Package
Product No.
PSM/PWM
VREF (V)
f SW (Hz)
Package
RT6214AHGJ6F
PSM
0.8
500k
TSOT-23-6
RT6214BHGJ6F
PWM
0.8
500k
TSOT-23-6
RT6214AHRGJ6F
PSM
0.765
500k
TSOT-23-6
RT6214BHRGJ6F
PWM
0.765
500k
TSOT-23-6
RT6214AHRGJ8F
PSM
0.765
650k
TSOT-23-8
RT6214BHRGJ8F
PWM
0.765
650k
TSOT-23-8
Table 1. Suggested Component Values (VIN = 12V, RT6214A/BHGJ6F)
VOUT (V)
R1 (k)
R2 (k)
L (H)
COUT (F)
CFF (pF)
1.05
10
32.4
2.2
44
--
1.2
20.5
41.2
2.2
44
--
1.8
40.2
32.4
3.6
44
--
2.5
40.2
19.1
3.6
44
22 to 68
3.3
40.2
13
4.7
44
22 to 68
5
40.2
7.68
4.7
44
22 to 68
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is a registered trademark of Richtek Technology Corporation.
DS6214A/B-04
August 2017
RT6214A/B
Table 2. Suggested Component Values (VIN = 12V, RT6214A/BHRGJ6F)
VOUT (V)
R1 (k)
R2 (k)
L (H)
COUT (F)
CFF (pF)
1.05
10
27
2.2
44
--
1.2
20.5
36
2.2
44
--
1.8
40.2
30
3.6
44
--
2.5
40.2
18
3.6
44
22 to 68
3.3
40.2
12.1
4.7
44
22 to 68
5
40.2
7.32
4.7
44
22 to 68
Table 3. Suggested Component Values (VIN = 12V, RT6214A/BHRGJ8F)
VOUT (V)
R1 (k)
R2 (k)
L (H)
COUT (F)
CFF (pF)
1.05
10
27
1.5
44
--
1.2
20.5
36
1.5
44
--
1.8
40.2
30
2.2
44
--
2.5
40.2
18
2.2
44
22 to 68
3.3
40.2
12.1
3.6
44
22 to 68
5
40.2
7.32
3.6
44
22 to 68
Note 1 : All the input and output capacitances are the suggested values, which refer to the effective
capacitances, and are subject to any de-rating effect, like a DC bias.
Note 2 : For lower output voltage applications, load transient responses can also be improved by
adding a feedforward capacitor (CFF, 22pF to 68pF).
Copyright © 2017 Richtek Technology Corporation. All rights reserved.
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August 2017
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RT6214A/B
Typical Operating Characteristics
Efficiency vs. Output Current
Efficiency vs. Output Current
100
100
90
90
80
70
VOUT = 3.3V
60
VOUT = 1.8V
Efficiency (%)
Efficiency (%)
80
VOUT = 1.05V
50
40
30
70
VOUT = 5V
60
VOUT = 3.3V
50
VOUT = 1.8V
40
VOUT = 1.05V
30
20
20
10
10
RT6214A, VIN = 5V
0
0.001
0.01
0.1
1
RT6214A, VIN = 12V
0
0.001
10
0.01
0.1
10
Output Current (A)
Output Current (A)
Efficiency vs. Output Current
Efficiency vs. Output Current
100
100
90
90
80
80
70
VOUT = 3.3V
60
VOUT = 1.8V
50
VOUT = 1.05V
Efficiency (%)
Efficiency (%)
1
40
30
70
VOUT = 5V
60
VOUT = 3.3V
50
VOUT = 1.8V
40
VOUT = 1.05V
30
20
20
10
10
RT6214B, VIN = 5V
0
0.001
0.01
0.1
1
RT6214B, VIN = 12V
0
0.001
10
0.01
0.1
1
10
Output Current (A)
Output Current (A)
Output Voltage vs. Output Current
Output Voltage vs. Temperature
1.40
1.220
RT6214A
1.210
Output Voltage (V)
Output Voltage (V)
1.35
1.30
1.25
1.20
VIN = 18V
1.15
1.200
1.190
VIN = 12V
VIN = 18V
1.180
1.170
VIN = 12V
VOUT = 1.2V
VOUT = 1.2V, IOUT = 1A
1.10
1.160
0
0.5
1
1.5
2
2.5
Output Current (A)
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12
3
-50
-25
0
25
50
75
100
125
Temperature (°C)
is a registered trademark of Richtek Technology Corporation.
DS6214A/B-04
August 2017
RT6214A/B
Reference Voltage vs. Temperature
Reference Voltage vs. Temperature
0.820
0.780
RT6214A/BHRGJ6F
RT6214A/BHRGJ8F
0.775
Reference Voltage(V)
Reference Voltage (V)
0.815
0.810
0.805
0.800
0.795
0.790
VIN = 12V, IOUT = 1A,
RT6214A/BHGJ6F
0.785
0.770
0.765
0.760
0.755
VIN = 12V, IOUT = 1A
0.750
0.780
-50
-25
0
25
50
75
100
-50
125
-25
0
25
50
EN Threshold vs. Temperature
100
125
Enable Threshold vs. Temperature
1.6
1.6
RT6214A/BHRGJ6F
RT6214A/BHRGJ8F
Rising
1.5
Enable Threshold (V)
1.5
EN Threshold (V)
75
Temperature (°C)
Temperature (°C)
1.4
1.3
Falling
1.2
Rising
1.4
1.3
1.2
Falling
1.1
VOUT = 1.2V, IOUT = 0A,
RT6214A/BHGJ6
VOUT = 1V, IOUT = 0A
1.1
1.0
-50
VOUT
(50mV/Div)
-25
0
25
50
75
100
125
-50
-25
0
25
50
Temperature (°C)
Temperature (°C)
Load Transient
Load Transient
VIN = 12V, VOUT = 1.2V,
IOUT = 0A to 3A , L = 2.2H
75
100
125
VOUT
(50mV/Div)
IOUT
(1A/Div)
VIN = 12V, VOUT = 1.2V,
IOUT = 1.5A to 3A , L = 2.2H
IOUT
(1A/Div)
Time (100s/Div)
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DS6214A/B-04
August 2017
Time (100s/Div)
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13
RT6214A/B
Power On then Short
Output Ripple Voltage
VIN
(5V/Div)
VOUT
(2V/Div)
VSW
(6V/Div)
VIN = 12V, VOUT = 5V
VIN = 12V, VOUT = 1.2V,
IOUT = 3A , L = 2.2H
VOUT
(20mV/Div)
IOUT
(2A/Div)
For TSOT-23-6 (FC)
Time (1s/Div)
Time (4ms/Div)
Power On from EN
Power Off from EN
VIN = 12V, VOUT = 5V, IOUT = 3A
VIN
(10V/Div)
VOUT
(2V/Div)
VEN
(2V/Div)
VLX
(10V/Div)
VEN
(5V/Div)
VOUT
(5V/Div)
VIN = 12V, VOUT = 5V, IOUT = 3A
IOUT
(2A/Div)
IOUT
(2A/Div)
For TSOT-23-6 (FC)
Time (1ms/Div)
Time (20s/Div)
Power On from VIN
Power Off from VIN
VIN
(10V/Div)
For TSOT-23-6 (FC)
VOUT
(2V/Div)
VIN
(10V/Div)
VLX
(2V/Div)
VIN = 12V, VOUT = 5V,
IOUT = 3A
Time (1ms/Div)
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For TSOT-23-6 (FC)
VIN = 12V, VOUT = 5V,
IOUT = 3A
VEN
(5V/Div)
VEN
(5V/Div)
IOUT
(2A/Div)
For TSOT-23-6 (FC)
IOUT
(2A/Div)
Time (20s/Div)
is a registered trademark of Richtek Technology Corporation.
DS6214A/B-04
August 2017
RT6214A/B
Power Off from EN
Power On from EN
VEN
(2V/Div)
VOUT
(2V/Div)
VIN = 12V, VOUT = 5V, IOUT = 3A,
CSS = 8.2nF
VIN = 12V, VOUT = 5V, IOUT = 3A,
CSS = 8.2nF
VOUT
(2V/Div)
For TSOT-23-8 (FC)
SS
(2V/Div)
SS
(2V/Div)
PGOOD
(5V/Div)
PGOOD
(5V/Div)
For TSOT-23-8 (FC)
Time (5ms/Div)
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DS6214A/B-04
VEN
(2V/Div)
August 2017
Time (20s/Div)
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RT6214A/B
Application Information
Inductor Selection
Selecting an inductor involves specifying its inductance
and also its required peak current. The exact inductor
value is generally flexible and is ultimately chosen to
obtain the best mix of cost, physical size, and circuit
efficiency. Lower inductor values benefit from reduced
size and cost and they can improve the circuit's
transient response, but they increase the inductor
ripple current and output voltage ripple and reduce the
inductor current (and the output current) while ensuring
that IL(PEAK) does not exceed the upper current limit
level.
For best efficiency, choose an inductor with a low DC
resistance that meets the cost and size requirements.
For low inductor core losses some type of ferrite core is
usually best and a shielded core type, although
possibly larger or more expensive, will probably give
fewer EMI and other noise problems.
efficiency due to the resulting higher peak currents.
Conversely, higher inductor values increase efficiency,
Considering the Typical Operating Circuit for 1.2V
output at 3A and an input voltage of 12V, using an
but the inductor will either be physically larger or have
higher resistance since more turns of wire are required
and transient response will be slower since more time
is required to change current (up or down) in the
inductor. A good compromise between size, efficiency,
and transient response is to use a ripple current (IL)
inductor ripple of 0.9A (30%), the calculated inductance
value is :
about 20% to 50% of the desired full output load
current. Calculate the approximate inductor value by
selecting the input and output voltages, the switching
frequency (f SW ), the maximum output current
(IOUT(MAX)) and estimating a IL as some percentage of
that current.
L=
VOUT VIN VOUT
VIN fSW IL
L
1.2 12 1.2
2.4μH
12 500kHz 0.9A
The ripple current was selected at 0.9A and, as long as
we use the calculated 2.4H inductance, that should be
the actual ripple current amount. The ripple current and
required peak current as below :
IL =
1.2 12 1.2
= 0.9A
12 500kHz 2.4μH
and IL(PEAK) = 3A 0.9A = 3.45A
2
Once an inductor value is chosen, the ripple current
For the 2.4H value, the inductor's saturation and
thermal rating should exceed 3.45A. Since the actual
(IL) is calculated to determine the required peak
inductor current.
value used was 2.4H and the ripple current exactly
0.9A, the required peak current is 3.45A.
IL =
VOUT VIN VOUT
I
and IL(PEAK) = IOUT(MAX) L
VIN fSW L
2
To guarantee the required output current, the inductor
needs a saturation current rating and a thermal rating
that exceeds IL(PEAK). These are minimum requirements.
To maintain control of inductor current in overload and
short circuit conditions, some applications may desire
current ratings up to the current limit value. However,
the IC's output under-voltage shutdown feature make
this unnecessary for most applications.
IL(PEAK) should not exceed the minimum value of IC's
upper current limit level or the IC may not be able to
meet the desired output current. If needed, reduce the
inductor ripple current (IL) to increase the average
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16
Input Capacitor Selection
Input capacitors are needed to smooth out the RMS
ripple current (IRMS) imposed by the switching currents
and drawn from the input power source, by reducing
the ripple voltage amplitude seen at the input of the
converters. The voltage rating of the input filter
capacitors must be greater than the maximum input
voltage. It’s also important to consider the ripple current
capabilities of capacitors.
The RMS ripple current (IRMS) of the regulator can be
determined by the input voltage (VIN), output voltage
(VOUT), and rated output current (IOUT) as the following
equation :
is a registered trademark of Richtek Technology Corporation.
DS6214A/B-04
August 2017
RT6214A/B
IRMS = IOUT
VOUT
VIN
1
VIN
VOUT
From the above, the maximum RMS input ripple
current occurs at maximum output load, which will be
used as the requirements to consider the current
capabilities of the input capacitors. Furthermore, for a
single phase buck converter, the duty cycle is
approximately the ratio of output voltage to input
voltage. The maximum ripple voltage usually occurs at
50% duty cycle, that is, VIN = 2 x VOUT. The maximum
IRMS, as IRMS (Max), can be approximated as 0.5 x
IOUT_MAX, where IOUT_MAX is the maximum rated
output current. Besides, the variation of the
capacitance value with temperature, DC bias voltage,
switching frequency, and allowable peal-to-peak ripple
voltage that reflects back to the input, also need to be
taken into consideration. For example, the capacitance
value of a capacitor decreases as the DC bias across
the capacitor increases; also, higher switching
frequency allows the use of input capacitors of smaller
capacitance values.
Ceramic capacitors are most commonly used to be
placed right at the input of the converter to reduce
ripple voltage amplitude because only ceramic
capacitors have extremely low ESR which is required
to reduce the ripple voltage. Note that the capacitors
need to be placed as close as to the input pins as
possible for highest effectiveness. Ceramic capacitors
are preferred also due to their low cost, small size, high
RMS current ratings, robust inrush surge current
capabilities, and low parasitic inductance, which helps
reduce the high-frequency ringing on the input supply.
However, care must be taken when ceramic capacitors
are used at the input, and the input power is supplied
by a wall adapter, connected through a long and thin
wire. When a load step occurs at the output, a sudden
inrush current will surge through the long inductive wire,
which can induce ringing at the device’s power input
and potentially cause a very large voltage spike at the
VIN pin to damage the device. For applications where
the input power is located far from the device input, it
may be required that the low-ESR ceramic input
capacitors be placed in parallel with a bulk capacitor of
other types, such as tantalum, electrolytic, or polymer,
to dampen the voltage ringing and overshoot at the
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DS6214A/B-04
August 2017
input, caused by the long input power path and input
ceramic capacitor.
It is suggested to choose capacitors with higher
temperature ratings than required. Several ceramic
capacitors may be parallel to meet application
requirements, such as the RMS current, size, and
height. The Typical Application Circuit can use one
22F, or two 10F and one high-frequencynoise-filtering 0.1uF low-ESR ceramic capacitors at the
input.
Output Capacitor Selection
Output capacitance affects the output voltage of the
converter, the response time of the output feedback
loop, and the requirements for output voltage sag and
soar. The sag occurs after a sudden load step current
applied, and the soar occurs after a sudden load
removal. Increasing the output capacitance reduces
the output voltage ripple and output sag and soar, while
it increases the response time that the output voltage
feedback loop takes to respond to step loads,
Therefore, there is a tradeoff between output
capacitance and output response. It is recommended
to choose a minimum output capacitance to meet the
output voltage requirements of the converter, and have
a quick transient response to step loads.
The ESR of the output capacitor affects the damping of
the output filter and the transient response. In general,
low-ESR capacitors are good choices due to their
excellent capability in energy storage and transient
performance. The RT6214A/B, therefore, is specially
optimized for ceramic capacitors. Consider also DC
bias and aging effects while selecting the output
capacitor.
Output Ripple
Output ripple at the switching frequency is caused by
the inductor current ripple and its effect on the output
capacitor's ESR and stored charge. These two ripple
components are called ESR ripple and capacitive ripple.
Since ceramic capacitors have extremely low ESR and
relatively little capacitance, both components are
similar in amplitude and both should be considered if
ripple is critical.
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RT6214A/B
VRIPPLE = VRIPPLE(ESR) VRIPPLE(C)
VOUT
VRIPPLE(ESR) = IL RESR
VRIPPLE(C) =
IL
8 COUT fSW
For the Typical Operating Circuit for 1.2V output and an
inductor ripple of 0.4A, with 2 x 22F output capacitance
each with about 5m ESR including PCB trace
R1
CFF
FB
RT6214A/B
R2
GND
resistance, the output voltage ripple components are :
Figure 1. CFF Capacitor Setting
VRIPPLE(ESR) = 0.9A 5m = 4.5mV
0.9A
= 5.11mV
8 44μF 500kHz
VRIPPLE = 4.5mV 5.11mV = 9.61mV
VRIPPLE(C) =
Feed-Forward Capacitor (CFF)
The RT6214A/B is optimized for ceramic output
capacitors and for low duty-cycle applications. This
optimization makes circuit stability easy to achieve with
reasonable output capacitors, but it also narrows the
optimization of transient responses of the converter.
For high output voltage (that is, high duty-cycle)
applications, the FB voltage is highly attenuated from
the output, the circuit's response becomes
under-damped and transient response is slowed. A
small feedforward capacitor (CFF) can be introduced
into the feedback network to speed up the transient
response of high output voltage circuits. The
feedforward capacitor is added across the upper FB
divider resistor (as seen in Figure 1) to speed up the
transient response without affecting the steady-state
stability of the circuit.
To optimize transient response, a CFF value is chosen
so that the gain and phase boost of the feedback
network increases the bandwidth of the converter,
while still maintaining an acceptable phase margin.
Generally, larger CFF values provide higher bandwidth,
but may result in an unacceptable phase margin or
instability. Suitable feedforward capacitor values can
be chosen from the table of Suggested Component
Values.
Enable Operation (EN)
For automatic start-up the EN pin can be connected to
VIN, through a 100k resistor. Its large hysteresis
band makes EN useful for simple delay and timing
circuits. EN can be externally pulled to VIN by adding a
resistor-capacitor delay (REN and CEN in Figure 2).
Calculate the delay time using EN's internal threshold
where switching operation begins.
An external MOSFET can be added to implement
digital control of EN when no system voltage above 2V
is available (Figure 3). In this case, a 100k pull-up
resistor, REN, is connected between VIN and the EN
pin. MOSFET Q1 will be under logic control to pull
down the EN pin. To prevent enabling circuit when VIN
is smaller than the VOUT target value or some other
desired voltage level, a resistive voltage divider can be
placed between the input voltage and ground and
connected to EN to create an additional input under
voltage lockout threshold (Figure 4).
EN
VIN
REN
EN
RT6214A/B
CEN
GND
Figure 2. External Timing Control
VIN
Enable
REN
100k
EN
Q1
RT6214A/B
GND
Figure 3. Digital Enable Control Circuit
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18
is a registered trademark of Richtek Technology Corporation.
DS6214A/B-04
August 2017
RT6214A/B
VIN
voltage VBOOT must be lower than 5.5V.
REN1
EN
REN2
5V
RT6214A/B
DBOOT
GND
BOOT
Figure 4. Resistor Divider for Lockout Threshold
Setting
CBOOT
0.1μF
RT6214A/B
LX
Output Voltage Setting
Set the desired output voltage using a resistive divider
from the output to ground with the midpoint connected
to FB. The output voltage is set according to the
following equation :
VOUT = 0.8V x (1 + R1 / R2), RT6214A/BHGJ6F
VOUT = 0.765V x (1 + R1 / R2), RT6214A/BHRGJ6/8F
VOUT
R1
FB
RT6214A/B
R2
GND
Figure 5. Output Voltage Setting
Place the FB resistors within 5mm of the FB pin.
Choose R2 between 10k and 100k to minimize
power consumption without excessive noise pick-up
and calculate R1 as follows :
R1
R2 (VOUT VREF )
VREF
For output voltage accuracy, use divider resistors with
1% or better tolerance.
External BOOT Bootstrap Diode
Figure 6. External Bootstrap Diode
Resistor at BOOT Pin
The gate driver of an internal power MOSFET, utilized
as a high-side switch, is optimized for turning on the
switch not only fast enough for reducing switching
power loss, but also slow enough for minimizing EMI.
The EMI issue is worse when the switch is turned on
rapidly due to high di/dt noises induced. When the
high-side switch is being turned off, the LX node will be
discharged relatively slowly by the inductor current due
to the presence of the dead time when both the
high-side and low-side switches are turned off.
In some cases, it is desirable to reduce EMI further,
even at the expense of some additional power
dissipation. The turn-on rate of the high-side switch can
be slowed by placing a small (< 47) resistor between
the BOOT pin and the external bootstrap capacitor.
This will slow down the rates of the high-side switch
turn-on and the rise of VLX. The recommended
application circuit is shown in Figure 7, which includes
an external bootstrap diode for charging the bootstrap
capacitor and a bootstrap resistor RBOOT being placed
between the BOOT pin and the capacitor/diode
connection.
5V
A bootstrap capacitor of 0.1F low-ESR ceramic
capacitor is connected between the BOOT and LX pins
to supply the high-side gate driver. It is recommended
to add an external bootstrap diode between an external
5V voltage supply and the BOOT pin to improve
enhancement of the internal MOSFET switch and
improve efficiency when the input voltage is below 5.5V.
The bootstrap diode can be a low-cost one, such as
1N4148 or BAT54. The external 5V can be a fixed 5V
voltage supply from the system, or a 5V output voltage
generated by the RT6214A/B. Note that the BOOT
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DS6214A/B-04
August 2017
DBOOT
RBOOT
BOOT
RT6214A/B
CBOOT
0.1μF
SW
Figure 7. External Bootstrap Diode and Resistor at the
BOOT Pin
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RT6214A/B
Soft-Start
PD(MAX) = (TJ(MAX) TA) / JA
(For RT6214A/BHRGJ8F)
where TJ(MAX) is the maximum junction temperature,
TA is the ambient temperature, and JA is the
calculated as follows :
Soft-Start time tSS = CSS x 0.7 / 11A + CSS x VFB / 6A
Power-Good Output
(For RT6214A/BHRGJ8F)
The PGOOD pin is an open-drain power-good
indication output and is to be connected to an external
voltage source through a pull-up resistor. The
power-good function is activated after soft-start is
finished and is controlled by the feedback signal VFB.
During soft-start, PGOOD is actively held low and only
allowed to transition high after soft-start is over. If VFB
rises above a power-good threshold (VTH_PGLH)
(typically 90% of the target value), the PGOOD pin will
be in high impedance and VPGOOD will be held high
after a certain delay elapsed. Once being started-up, if
any internal protection is triggered, PGOOD will be
pulled low to GND.
Thermal Considerations
The junction temperature should never exceed the
absolute maximum junction temperature TJ(MAX), listed
under Absolute Maximum Ratings, to avoid permanent
damage to the device. The maximum allowable power
dissipation depends on the thermal resistance of the IC
package, the PCB layout, the rate of surrounding
airflow, and the difference between the junction and
ambient temperatures. The maximum power
dissipation can be calculated using the following
formula :
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20
junction-to-ambient thermal resistance.
For continuous operation, the maximum operating
junction temperature indicated under Recommended
Operating
Conditions
is
125C.
The
junction-to-ambient thermal resistance,JA, is highly
package dependent. For a TSOT-23-6 (FC) package,
the thermal resistance, JA, is 60C/W on a standard
JEDEC 51-7 high effective-thermal-conductivity
four-layer test board. For a TSOT-23-8 (FC) package,
the thermal resistance, JA, is 60C/W on a standard
JEDEC 51-7 high effective-thermal-conductivity
four-layer test board. The maximum power dissipation
at TA = 25C can be calculated as below :
PD(MAX) = (125C 25C) / (60C/W) = 1.667W for a
TSOT-23-6 (FC) package.
PD(MAX) = (125C 25C) / (60C/W) = 1.667W for a
TSOT-23-8 (FC) package.
The maximum power dissipation depends on the
operating ambient temperature for the fixed TJ(MAX) and
the thermal resistance, JA. The derating curves in
Figure 8 allows the designer to see the effect of rising
ambient temperature on the maximum power
dissipation.
2.0
Maximum Power Dissipation (W)1
The RT6214A/B provides adjustable soft-start function.
When the EN pin becomes high, the SS charge current
(ISS) begins charging the capacitor which is connected
from the SS pin to GND (CSS).The soft-start function is
used to prevent large inrush current while converter is
being powered-up. The soft-start timing can be
programmed by the external capacitor CSS between SS
and GND. An internal current source ISS (6A) charges
an external capacitor to build a soft-start ramp voltage.
The VFB voltage will track the internal ramp voltage
during soft-start interval. The typical soft-start time is
Four-Layer PCB
1.8
1.6
1.4
TSOT-23-6 (FC)
TSOT-23-8 (FC)
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 8. Derating Curve of Maximum Power
Dissipation
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DS6214A/B-04
August 2017
RT6214A/B
Layout Considerations
Follow the PCB layout
performance of the device.
guidelines
for
optimal
Keep the traces of the main current paths as short
and wide as possible.
Put the input capacitor as close as possible to VIN
pin.
components away from the LX node to prevent stray
capacitive noise pickup.
Connect feedback network behind the output
capacitors. Keep the loop area small. Place the
feedback components near the device.
An example of RT6214A/B PCB layout guide is
shown in Figure 9 and Figure 10 for references.
LX node is with high frequency voltage swing and
should be kept at small area. Keep analog
L
GND
CB
VOUT
COUT
RBOOT
COUT
CEN
VIA
GND
CIN CIN
REN2
6
BOOT
LX
2
5
EN
VIN
3
4
FB
RT
CFF
REN1
R1
R2
EN
VIN
VOUT
GND
Figure 9. PCB Layout Guide for TSOT-23-6 package
L
GND
CB
VOUT
COUT
RBOOT
COUT
CEN
REN2
4
FB
5
3
PGOOD
EN
6
VIN
BOOT
7
2
LX
CIN CIN
8
GND
SS
RT
CFF
VIN
CSS
REN1
RPGOOD
R2
EN VOUT
VOUT
R1
GND
Figure 10. PCB Layout Guide for TSOT-23-8 package
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August 2017
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21
RT6214A/B
Outline Dimension
Symbol
Dimensions In Millimeters
Dimensions In Inches
Min.
Max.
Min.
Max.
A
0.700
1.000
0.028
0.039
A1
0.000
0.100
0.000
0.004
B
1.397
1.803
0.055
0.071
b
0.300
0.559
0.012
0.022
C
2.591
3.000
0.102
0.118
D
2.692
3.099
0.106
0.122
e
0.950
0.037
H
0.080
0.254
0.003
0.010
L
0.300
0.610
0.012
0.024
TSOT-23-6 (FC) Surface Mount Package
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is a registered trademark of Richtek Technology Corporation.
DS6214A/B-04
August 2017
RT6214A/B
Dimensions In Millimeters
Symbol
Dimensions In Inches
Min.
Max.
Min.
Max.
A
0.700
1.000
0.028
0.039
A1
0.000
0.100
0.000
0.004
B
1.397
1.803
0.055
0.071
b
0.220
0.380
0.009
0.015
C
2.591
3.000
0.102
0.118
D
2.692
3.099
0.106
0.122
e
0.585
0.715
0.023
0.028
H
0.080
0.254
0.003
0.010
L
0.300
0.610
0.012
0.024
TSOT-23-8 (FC) Surface Mount Package
Richtek Technology Corporation
14F, No. 8, Tai Yuen 1st Street, Chupei City
Hsinchu, Taiwan, R.O.C.
Tel: (8863)5526789
Richtek products are sold by description only. Customers should 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.
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