UMK325BJ475MM- [RICHTEK]
3A, 36V, 500kHz Synchronous Step-Down Converter; 3A ， 36V ， 500kHz的同步降压型转换器
| 型号： | UMK325BJ475MM- |
| 厂家： | 
RICHTEK TECHNOLOGY CORPORATION |
| 描述： | 3A, 36V, 500kHz Synchronous Step-Down Converter |
| 文件： | 总14页 (文件大小：255K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
®
RT7272A
3A, 36V, 500kHz Synchronous Step-Down Converter
General Description
Features
z 4.5V to 36V Input Voltage Range
The RT7272A is a high efficiency, current mode
synchronous step-downDC/DC converter that can deliver
up to 3A output current over a wide input voltage range
from 4.5V to 36V. The device integrates a 150mΩ high
side and a 80mΩ low side MOSFET to achieve high
conversion efficiency up to 95%. The current mode control
architecture supports fast transient response and simple
compensation circuit.
z 3A Output Current
z Internal N-MOSFETs
z Current Mode Control
z Fixed Frequency Operation : 500kHz
z Adjustable Output Voltage from 0.8V to 30V
z High Efficiency Up to 95%
z Stable with Low ESR Ceramic Output Capacitors
z Cycle-by-Cycle Current Limit
z Input Under Voltage Lockout
z Output Under Voltage Protection
z Thermal Shutdown Protection
z Adjustable Current Limit
A cycle-by-cycle current limit function provides protection
against shorted output and an internal soft-start eliminates
input current surge during start-up. The RT7272A provides
complete protection functions such as input under voltage
lockout, output under voltage protection, over current
protection and thermal shutdown.
z RoHS Compliant and Halogen Free
The RT7272Ais available in the thermal enhanced SOP-8
(Exposed Pad) package.
Applications
z Distributed Power Systems
z Pre-Regulator for Linear Regulators
z Notebook Computers
Ordering Information
RT7272A
z Point of Load Regulator in Distributed Power System
z Digital Set-top Boxes
Package Type
SP : SOP-8 (Exposed Pad-Option 2)
z PersonalDigital Recorders
z Broadband Communications
z Flat Panel TVs and Monitors
z Vehicle Electronics
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
Richtek products are :
` RoHS compliant and compatible with the current require-
ments of IPC/JEDEC J-STD-020.
` Suitable for use in SnPb or Pb-free soldering processes.
Simplified Application Circuit
V
BOOT
RT7272A
VIN
IN
C
IN
C
B
L
SW
V
OUT
R1
R2
RLIM
GND
C
OUT
FB
R
C
C
L
R
C
COMP
Copyright 2013 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
DS7272A-01 January 2013
www.richtek.com
1
RT7272A
Pin Configurations
Marking Information
RT7272AGSP : Product Number
(TOP VIEW)
RT7272A
GSPYMDNN
YMDNN : Date Code
8
7
6
5
SW
BOOT
EN
VIN
2
3
4
RLIM
COMP
FB
GND
9
GND
SOP-8 (Exposed Pad)
Functional Pin Description
Pin No.
Pin Name
Pin Function
1
SW
Switch Node Connect to external L-C filter.
Bootstrap Supply for High Side Gate Drive. A 100nF or greater capacitor is
recommended to connect from BOOT pin to SW pin.
2
3
BOOT
EN
Enable Control Input. A logic-high enables the converter; a logic-low forces the
device into shutdown mode.
4,
Ground. The exposed pad must be soldered to a large PCB and connected to
GND for maximum thermal dissipation.
GND
9 (Exposed Pad)
Feedback Input. This pin is connected to the converter output. It is used to set
the output of the converter to regulate to the desired value via an resistive
divider.
Compensation Node. COMP is used to compensate the regulation control loop.
Connect a series RC network from COMP to GND. In some cases, an additional
capacitor from COMP to GND is required.
5
6
FB
COMP
7
8
RLIM
VIN
Current Limit Setting. Connect to a resistor to determine current limit.
Power Input. The input voltage range is from 4.5V to 36V. Must bypass with a
suitable large ceramic capacitor.
Function Block Diagram
VIN
V
CC
Internal
Regulator
Oscillator
Current Sense
Amplifier
Shutdown
Comparator
V
V
CC
A
Slope Comp
+
V
A
Foldback
Control
R
SENSE
-
1.2V
+
-
0.4V
+
BOOT
SW
UV
Lockout
Comparator
-
S
R
Q
Q
150mΩ
80mΩ
UV
5kΩ
Comparator
-
EN
+
-
+
1.7V
Current
Comparator
GND
V
CC
+
0.8V
EA
SS
+
-
RLIM
FB
COMP
Copyright 2013 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
2
DS7272A-01 January 2013
RT7272A
Operation
The RT7272A is a constant frequency, current mode
synchronous step-down converter. In normal operation,
the high sideN-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 high side
N-MOSFET is turned off, the low sideN-MOSFET is turned
on to conduct the inductor current until next cycle begins.
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 2ms.
Current Setting
The current limit of high side MOSFET is adjustable by
an external resistor connected to the RLIM pin. The current
limit range is from 2A to 6A. When the inductor current
reaches the current limit threshold, the COMP voltage
will be clamped to limit the inductor current.
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.
UV Comparator
If the feedback voltage (VFB) is lower than 0.4V, the UV
Comparator will go high to turn off the high side MOSFET.
The output under voltage protection is designed to operate
in Hiccup mode. When the UV condition is removed, the
converter will resume switching.
Oscillator
The internal oscillator runs at fixed frequency 500kHz. In
short circuit condition, the frequency is reduced to 75kHz
for low power consumption.
Thermal shutdown
Internal Regulator
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.
The regulator provides low voltage power to supply the
internal control circuits and the bootstrap power for high
side gate driver.
Enable
The converter is turned on when the ENpin is higher than
2V. When the ENpin is lower than 0.4V, the converter will
enter shutdown mode and reduce the supply current to
0.5μA.
Copyright 2013 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
DS7272A-01 January 2013
www.richtek.com
3
RT7272A
Absolute Maximum Ratings (Note 1)
z Supply Input Voltage, VIN ----------------------------------------------------------------------------------------- −0.3V to 40V
z Switch Voltage, SW ------------------------------------------------------------------------------------------------ −0.3V to (VIN + 0.3V)
z VBOOT − VSW ---------------------------------------------------------------------------------------------------------- −0.3V to 6V
z Other Pins Voltage -------------------------------------------------------------------------------------------------- −0.3V to 40V
z Power Dissipation, PD @ TA = 25°C
SOP-8 (Exposed Pad) --------------------------------------------------------------------------------------------- 2.041W
z Package Thermal Resistance (Note 2)
SOP-8 (Exposed Pad), θJA ---------------------------------------------------------------------------------------- 49°C/W
SOP-8 (Exposed Pad), θJC --------------------------------------------------------------------------------------- 15°C/W
z Lead Temperature (Soldering, 10 sec.)------------------------------------------------------------------------- 260°C
z Junction Temperature ----------------------------------------------------------------------------------------------- 150°C
z Storage Temperature Range -------------------------------------------------------------------------------------- −65°C to 150°C
z ESD Susceptibility (Note 3)
HBM (Human Body Model)---------------------------------------------------------------------------------------- 2kV
Recommended Operating Conditions (Note 4)
z Supply Input Voltage, VIN ----------------------------------------------------------------------------------------- 4.5V to 36V
z Junction Temperature Range-------------------------------------------------------------------------------------- −40°C to 125°C
z Ambient Temperature Range-------------------------------------------------------------------------------------- −40°C to 85°C
Electrical Characteristics
(VIN = 12V, CIN = 20μF, TA = 25°C, unless otherwise specified)
Parameter
Shutdown Supply Current
Quiescent Current
Symbol
Test Conditions
Min
--
Typ
0.5
0.9
Max
3
Unit
μA
V
V
= 0V
EN
I
= 3V, V = 0.9V
--
1.2
mA
Q
EN
FB
Feedback Reference
Voltage
V
4.5V ≤ V ≤ 36V
0.788
0.8
150
80
0
0.812
--
V
REF
IN
High Side Switch
On-Resistance
R
R
--
--
--
2
mΩ
mΩ
μA
A
DS(ON)1
DS(ON)2
Low Side Switch
On-Resistance
--
High Side Switch Leakage
Current
V
EN
= 0V, V
= 0V
10
SW
Upper Switch Current Limit
Range
U
U
--
6.3
OC
Min. Duty Cycle, R
Min. Duty Cycle, R
Min. Duty Cycle, R
= 57.6kΩ
= 84.5kΩ
= 137kΩ
1.9
2.7
4.5
--
2.5
3.5
5.5
1.5
3.1
4.2
6.5
--
LIM
LIM
LIM
OC
Upper Switch Current Limit
Lower Switch Current Limit
A
A
(Note 5)
From Drain to Source
Copyright 2013 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
4
DS7272A-01 January 2013
RT7272A
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
Oscillation Frequency
f
f
450
500
550
kHz
OSC1
OSC2
Short Circuit Oscillation
Frequency
V
FB
= 0V
--
75
--
kHz
Maximum Duty Cycle
Minimum On-Time
D
V
FB
= 0.7V
--
--
2
90
100
--
--
--
%
MAX
t
ns
ON
Logic-High
Logic-Low
V
V
--
IH
EN Input Voltage
V
--
--
0.4
IL
Input Under Voltage Lockout
Threshold
Input Under Voltage Lockout
Hysteresis
V
V
IN
Rising
3.9
--
4.1
4.3
--
V
UVLO
ΔV
250
mV
UVLO
Thermal Shutdown
T
--
--
150
20
--
--
°C
°C
SD
Thermal Shutdown Hysteresis
ΔT
SD
COMP to Current Sense
Transconductance
G
ΔI
= ±10μA
COMP
--
--
4.7
--
A/V
CS
Error Amplifier Transconductance
1000
--
μA/V
G
EA
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. θJC is
measured at the exposed pad of the package.
Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
Note 5. RLIM (kΩ) = [UOC x 24.14 x (1 + 0.024 x (UOC − 3.5)) − 1.3], where UOC is desired upper switch peak current limit
value.
Copyright 2013 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
DS7272A-01 January 2013
www.richtek.com
5
RT7272A
Typical Application Circuit
RT7272A
BOOT
V
2
1
IN
8
VIN
4.5V to 36V
C
C
B
100nF
IN
10µF x 2
L
3
7
SW
V
OUT
Enable
RLIM
EN
R1
R2
RLIM
5
6
C
OUT
FB
R
179k
L
C
C
R
C
4, 9 (Exposed Pad)
COMP
GND
Table 1. Suggested Component Values
VOUT (V)
R1 (kΩ)
47
R2 (kΩ)
3.35
3
RC (kΩ)
47
L (μH)
10
CC (nF)
2.7
COUT (μF)
22 x 2
12
8
27
36
8.2
2.7
22 x 2
5
62
11.8
24
6.8
2.7
22 x 2
3.3
2.5
1.2
75
25.5
30
24
12
60
16
12
4.7
3.6
2.2
2.7
2.7
2.7
22 x 2
22 x 2
22 x 2
6.8
Copyright 2013 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
6
DS7272A-01 January 2013
RT7272A
Typical Operating Characteristics
Efficiency vs. Output Current
Reference Voltage vs. Input Voltage
100
0.810
0.808
0.805
0.803
0.800
0.798
0.795
0.793
0.790
90
80
VIN = 4.5V
VIN = 12V
70
VIN = 24V
60
50
40
30
20
10
0
VIN = 36V
VOUT = 3.3V
2.5
VIN = 4.5V to 36V, IOUT = 0A
0
0.5
1
1.5
2
3
2
6.75 11.5 16.25 21 25.75 30.5 35.25 40
Input Voltage (V)
Output Current (A)
Reference Voltage vs. Temperature
Output Voltage vs. Output Current
0.810
0.805
0.800
0.795
0.790
3.320
3.315
3.310
3.305
3.300
3.295
3.290
VIN = 12V
V
V
IN = 24V
IN = 30V
VIN = 4.5V
VIN = 12V
VIN = 24V
VIN = 36V
VOUT = 3.3V, IOUT = 0A
50 75 100 125
VOUT = 3.3V
2.5 3
-50
-25
0
25
0
0.5
1
1.5
2
Temperature (°C)
Output Current (A)
Switching Frequency vs. Input Voltage
Switching Frequency vs. Temperature
500
490
480
470
460
450
500
490
480
470
460
450
440
VIN = 36V
VIN = 24V
VIN = 12V
VIN = 4.5V
VOUT = 3.3V, IOUT = 0A
VOUT = 3.3V, IOUT = 0A
4
8
12
16
20
24
28
32
36
-50
-25
0
25
50
75
100
125
Input Voltage (V)
Temperature (°C)
Copyright 2013 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
DS7272A-01 January 2013
www.richtek.com
7
RT7272A
Current Limit vs. Temperature
Load Transient Response
8
7
6
5
4
3
2
VOUT
(200mV/Div)
IOUT
(2A/Div)
VIN = 12V
100 125
VIN = 12V, VOUT = 3.3V, IOUT = 1.5A to 3A
-50
-25
0
25
50
75
Time (100μs/Div)
Temperature (°C)
Load Transient Response
Switching
VOUT
(5mV/Div)
VOUT
(200mV/Div)
VSW
(5V/Div)
IOUT
(2A/Div)
IL
(2A/Div)
VIN = 12V, VOUT = 3.3V, IOUT = 0 to 3A
VIN = 12V, VOUT = 3.3V, IOUT = 3A
Time (100μs/Div)
Time (1μs/Div)
Power On from EN
Power Off from EN
VEN
VIN
(5V/Div)
(5V/Div)
VOUT
VOUT
(2V/Div)
(2V/Div)
IOUT
IOUT
(2A/Div)
(2A/Div)
VIN = 12V, VOUT = 3.3V, IOUT = 3A
Time (2.5ms/Div)
VIN = 12V, VOUT = 3.3V, IOUT = 3A
Time (2.5ms/Div)
Copyright 2013 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
8
DS7272A-01 January 2013
RT7272A
Application Information
Output Voltage Setting
Chip Enable Operation
The resistive divider allows the FB pin to sense the output
voltage as shown in Figure 1.
The EN pin is the chip enable input. Pulling the EN pin
low (<0.4V) will shutdown the device. During shutdown
mode, the RT7272A quiescent current drops to lower than
3μA. Driving the EN pin high (>2.5V, < 18V) will turn on
the device again. For external timing control, the EN pin
can also be externally pulled high by adding a REN resistor
and CEN capacitor from the VIN pin (see Figure 3).
V
OUT
R1
FB
RT7272A
GND
R2
EN
R
EN
V
IN
EN
RT7272A
Figure 1. Output Voltage Setting
C
EN
GND
The output voltage is set by an external resistive voltage
divider according to the following equation :
Figure 3. Enable Timing Control
R1
R2
⎛
⎝
⎞
⎟
⎠
VOUT = VREF 1+
⎜
An external MOSFET can be added to implement digital
control on the EN pin when no system voltage above 2.5V
is available, as shown in Figure 4. In this case, a 100kΩ
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.
Where VREF is the reference voltage (0.8V typ.).
External Bootstrap Diode
Connect a 0.1μF low ESR ceramic capacitor between the
BOOT and SW pins. This capacitor provides the gate driver
voltage for the high side MOSFET.
R
EN
100k
V
It is recommended to add an external bootstrap diode
between an external 5V and 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 IN4148 or BAT54. The external 5V
can be a 5V fixed input from system or a 5V output of the
RT7272A. Note that the external boot voltage must be
lower than 5.5V
EN
RT7272A
GND
IN
Q1
EN
Figure 4. Digital Enable Control Circuit
Under Voltage Protection
5V
Hiccup Mode
The RT7272A provides Hiccup Mode Under Voltage
Protection (UVP). When the VFB voltage drops below 0.4V,
the UVP function will be triggered to shut down switching
operation. If the UVP condition remains for a period, the
RT7272Awill retry automatically. When the UVP condition
is removed, the converter will resume operation. The UVP
is disabled during soft-start period.
BOOT
100nF
RT7272A
SW
Figure 2. External Bootstrap Diode
Copyright 2013 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
DS7272A-01 January 2013
www.richtek.com
9
RT7272A
Hiccup Mode
The inductor's current rating (caused a 40°C temperature
rising from 25°C ambient) should be greater than the
maximum load current and its saturation current should
be greater than the short circuit peak current limit. Please
see Table 2 for the inductor selection reference.
VOUT
(2V/Div)
Table 2. Suggested Inductors for Typical
Application Circuit
ILX
(2A/Div)
Component
Supplier
Dimensions
(mm)
Series
TDK
TDK
VLF10045
SLF12565
10 x 9.7 x 4.5
IOUT = Short
12.5 x 12.5 x 6.5
Time (50ms/Div)
TAIYO
YUDEN
NR8040
8 x 8 x 4
Figure 5. Hiccup Mode Under Voltage Protection
Over Temperature Protection
CIN and COUT Selection
The RT7272A features an Over Temperature Protection
(OTP) circuitry to prevent from overheating due to
excessive power dissipation. The OTP will shut down
switching operation when junction temperature exceeds
150°C. Once the junction temperature cools down by
approximately 20°C, the converter will resume operation.
To maintain continuous operation, the maximum junction
temperature should be lower than 125°C.
The input capacitance, CIN, is needed to filter the
trapezoidal current at the Source of the high side MOSFET.
To prevent large ripple current, a low ESR input capacitor
sized for the maximum RMS current should be used. The
approximate RMS current equation is given :
V
V
V
IN
V
OUT
OUT
I
= I
−1
RMS
OUT(MAX)
IN
This formula has a maximum at VIN = 2VOUT, where
IRMS = IOUT / 2. This simple worst case condition is
commonly used for design because even significant
deviations do not offer much relief.
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.
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.
V
f ×L
V
OUT
V
IN
⎡
⎤ ⎡
⎦ ⎣
⎤
OUT
ΔI =
L
× 1−
⎥ ⎢
⎢
⎣
⎥
⎦
For the input capacitor, two 10μF low ESR ceramic
capacitors are suggested. For the suggested capacitor,
please refer to Table 3 for more details.
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
the highest efficiency operation. However, it requires a
large inductor to achieve this goal.
The selection of COUT is determined by the required 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.
For the ripple current selection, the value of ΔIL= 0.24(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 :
The output ripple, ΔVOUT , is determined by :
1
⎡
⎤
ΔVOUT ≤ ΔIL ESR +
⎢
⎣
⎥
⎦
8fCOUT
⎡
⎤ ⎡
⎤
V
f × ΔI
V
OUT
V
IN(MAX)
OUT
L =
× 1−
⎢
⎥ ⎢
⎥
L(MAX)
⎣
⎦ ⎣
⎦
Copyright 2013 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
10
DS7272A-01 January 2013
RT7272A
The thermal resistance θJA of SOP-8 (Exposed Pad) is
determined by the package architecture design and the
PCB layout design. However, the package architecture
design had been designed. If possible, it's useful to
increase thermal performance by the PCB layout copper
design. The thermal resistance θJA can be decreased by
adding copper area under the exposed pad of SOP-8
(Exposed Pad) package.
The output ripple will be the 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. 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.
As shown in Figure 6, the amount of copper area to which
the SOP-8 (Exposed Pad) is mounted affects thermal
performance. When mounted to the standard
SOP-8 (Exposed Pad) pad (Figure 6.a), θJA is 75°C/W.
Adding copper area of pad under the SOP-8 (Exposed
Pad) (Figure 6.b) reduces the θJA to 64°C/W. Even further,
increasing the copper area of pad to 70mm2 (Figure 6.e)
reduces the θJA to 49°C/W.
The maximum power dissipation depends on operating
ambient temperature for fixed TJ(MAX) and thermal
resistance θJA. The Figure 7 of derating curves allows the
designer to see the effect of rising ambient temperature
on the maximum power dissipation allowed.
Thermal Considerations
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.
The maximum power dissipation can be calculated by
following formula :
2.2
Four-Layer PCB
2.0
1.8
Copper Area
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
2
70mm
PD(MAX) = (TJ(MAX) − TA ) / θJA
2
50mm
30mm
2
Where TJ(MAX) is the maximum operation junction
temperature , TA is the ambient temperature and the θJA is
the junction to ambient thermal resistance.
2
10mm
Min.Layout
For recommended operating conditions specification of
RT7272A, the maximum junction temperature is 125°C.
The junction to ambient thermal resistance θJA is layout
dependent. For SOP-8 (Exposed Pad) package, the
thermal resistance θJA is 75°C/W on the standard JEDEC
51-7 four-layers thermal test board. The maximum power
dissipation at TA = 25°C can be calculated by following
formula :
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 7.Derating Curve of Maximum PowerDissipation
PD(MAX) = (125°C − 25°C) / (75°C/W) = 1.333W
(min.copper area PCB layout)
PD(MAX) = (125°C − 25°C) / (49°C/W) = 2.04W
(70mm2copper area PCB layout)
Copyright 2013 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
DS7272A-01 January 2013
www.richtek.com
11
RT7272A
Layout Considerations
For best performance of the RT7272A, the following layout
guidelines must be strictly followed.
` Input capacitor must be placed as close to the IC as
possible.
(a) Copper Area = (2.3 x 2.3) mm2,θJA = 75°C/W
` SW should be connected to inductor by wide and short
trace. Keep sensitive components away from this trace.
` The RL resistor, compensator and feedback components
must be connected as close to the device as possible.
(b) Copper Area = 10mm2,θJA = 64°C/W
(c) Copper Area = 30mm2 ,θJA = 54°C/W
(d) Copper Area = 50mm2 ,θJA = 51°C/W
(e) Copper Area = 70mm2 ,θJA = 49°C/W
Figure 6. Thermal Resistance vs. CopperArea Layout
Design
Copyright 2013 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
12
DS7272A-01 January 2013
RT7272A
Input capacitor must be placed
as close to the IC as possible.
V
V
OUT
IN
C
OUT
C
IN
The R resistor must be connected
as close to the device as possible.
Keep sensitive components away.
L
SW should be connected to
inductor by wide and short trace.
Keep sensitive components
C *
S
R *
S
L
away from this trace and C
.
BOOT
R
L
8
7
6
5
SW
BOOT
EN
VIN
C
V
BOOT
2
3
4
RLIM
COMP
FB
R
C
GND
C
C
C
IN
9
R
EN
GND
P
R1
V
OUT
R2
The R component
EN
must be connected.
GND
The Compensator and feedback
components must be connected as
close to the device as possible.
* : Option
Figure 8. PCB Layout Guide
Table 3. Suggested Capacitors for CIN and COUT
Location
Component Supplier
Part No.
Capacitance (μF)
Case Size
1206
C
IN
C
IN
C
IN
C
IN
C
IN
MURATA
TAIYO YUDEN
MURATA
TDK
GRM32ER71H475K
UMK325BJ475MM-T
GRM31CR61E106K
C3225X5R1E106K
TMK316BJ106ML
GRM31CR60J476M
C3225X5R0J476M
GRM32ER71C226M
C3225X5R1C22M
4.7
4.7
10
10
10
47
47
22
22
1206
1206
1206
TAIYO YUDEN
MURATA
TDK
1206
C
C
C
C
1206
OUT
OUT
OUT
OUT
1210
MURATA
TDK
1210
1210
Copyright 2013 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
DS7272A-01 January 2013
www.richtek.com
13
RT7272A
Outline Dimension
H
A
Y
M
EXPOSED THERMAL PAD
(Bottom of Package)
J
B
X
F
C
I
D
Dimensions In Millimeters Dimensions In Inches
Symbol
Min
Max
Min
Max
A
B
C
D
F
H
I
4.801
3.810
1.346
0.330
1.194
0.170
0.000
5.791
0.406
2.000
2.000
2.100
3.000
5.004
4.000
1.753
0.510
1.346
0.254
0.152
6.200
1.270
2.300
2.300
2.500
3.500
0.189
0.150
0.053
0.013
0.047
0.007
0.000
0.228
0.016
0.079
0.079
0.083
0.118
0.197
0.157
0.069
0.020
0.053
0.010
0.006
0.244
0.050
0.091
0.091
0.098
0.138
J
M
X
Option 1
Y
X
Y
Option 2
8-Lead SOP (Exposed Pad) Plastic Package
Richtek Technology Corporation
5F, No. 20, Taiyuen Street, Chupei City
Hsinchu, Taiwan, R.O.C.
Tel: (8863)5526789
Richtek products are sold by description only. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. 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. 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
parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Richtek or its subsidiaries.
www.richtek.com
14
DS7272A-01 January 2013
相关型号：
UMK325F475KH-T
Ceramic Capacitor, Multilayer, Ceramic, 50V, 10% +Tol, 10% -Tol, Y5V, -82/+22% TC, 4.7uF, Surface Mount, 1210, CHIP
TAIYO YUDEN
UMK325F475ZH-B
CAPACITOR, CERAMIC, MULTILAYER, 50V, Y5V, 4.7uF, SURFACE MOUNT, 1210, CHIP
TAIYO YUDEN
©2020 ICPDF网 联系我们和版权申明