RICHTEK RT8284N

®
RT8284N
2A, 23V, 340kHz Synchronous Step-Down Converter
General Description
Features
The RT8284N is a high efficiency, monolithic synchronous
step down DC/DC converter that can deliver up to 2A output
current from a 4.5V to 23V input supply. The RT8284N's
current mode architecture and external compensation
allow the transient response to be optimized over a wide
range of loads and output capacitors. Cycle-by-cycle
current limit provides protection against shorted outputs
and soft-start eliminates input current surge during start
up. The RT8284N also provides under voltage protection
and thermal shutdown protection. The low current (< 3μA)
shutdown mode provides output disconnection, enabling
easy power management in battery-powered systems. The
RT8284N is a available in a SOP-8 and SOP-8
(Exposed Pad) package.
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Ordering Information
`
5
5
1
8
3
2
5-
Richtek products are :
RoHS compliant and compatible with the current require-
75
0
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Pin Configurations
(TOP VIEW)
Suitable for use in SnPb or Pb-free soldering processes.
Marking Information
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RT8284NGS
圳
RT8284NGS : Product Number
RT8284N
GSYMDNN
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5
0
Wireless AP/Router
Set-Top-Box
Industrial and Commercial Low Power Systems
LCD Monitors and TVs
Green Electronics/Appliances
Point of Load Regulation of High-Performance DSPs
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国
ments of IPC/JEDEC J-STD-020.
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1
2
25
Package Type
S : SOP-8
SP: SOP-8 (Exposed Pad-Option 1)
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
0
5
4
Applications
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RT8284N
±1.5% High Accuracy Feedback Voltage
Input Voltage Range : 4.5V to 23V
2A Output Current
Integrated N-MOSFETs
Current Mode Control
340kHz Fixed Frequency Operation
Output Adjustable Voltage Range : 0.923V to 20V
Efficiency Up to 95%
Programmable Soft-Start
Stable with Low ESR Ceramic Output Capacitors
Cycle-by-Cycle Over Current Protection
Input Under Voltage Lockout
Output Under Voltage Protection
Thermal Shutdown Protection
RoHS Compliant and Halogen Free
8
BOOT
7
EN
SW
GND
3
6
COMP
4
5
FB
8
SS
深
YMDNN : Date Code
SOP-8
BOOT
RT8284NGSP
RT8284NGSP : Product Number
RT8284N
GSPYMDNN
SS
VIN
2
YMDNN : Date Code
Copyright © 2012 Richtek Technology Corporation. All rights reserved.
DS8284N-03 May 2012
VIN
2
SW
GND
3
GND
7
EN
6
COMP
5
FB
9
4
SOP-8 (Exposed Pad)
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1
RT8284N
Typical Application Circuit
2
VIN
4.5V to 23V
CIN
10µF
CBOOT
L
10nF 10µH
RT8284N
SW 3
REN 100k
CSS
0.1µF
1
BOOT
VIN
R1
26.1k
7 EN
8 SS
4, 9 (Exposed Pad)
CC
3.3nF
6
COMP
GND
CC (nF)
3.3
3.3
3.3
3.3
3.3
3.3
RC
13k
R2
10k
SOP-8
SOP-8
(Exposed Pad)
1
1
2
2
3
4
38
BOOT
2
5
5
7
0
3
7
8
7
8
厦
Bootstrap for High Side Gate Driver. Connect a 10nF or greater
ceramic capacitor from BOOT to SW pins.
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Ground. The exposed pad must be soldered to a large PCB and
connected to GND for maximum power dissipation.
Feedback Input Pin. 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 internal resistive voltage divider. For an adjustable
output, an external resistive voltage divider is connected to this pin.
COMP
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.
EN
Enable Input pin. A logic high enables the converter; a logic low
forces the RT8284N into shutdown mode reducing the supply current
to less than 3μA. Attach this pin to VIN with a 100kΩ pull up resistor
for automatic startup.
SS
Soft-Start Control Input. SS controls the soft-start period. Connect a
capacitor from SS to GND to set the soft-start period. A 0.1μF
capacitor sets the soft-start period to 15.5ms .
Copyright © 2012 Richtek Technology Corporation. All rights reserved.
www.richtek.com
2
28
Pin Function
Phase Node. Connect this pin to external L-C filter.
FB
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6
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Input Supply Voltage, 4.5V to 23V. Must bypass with a suitably large
ceramic capacitor.
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5
4
1
2
VIN
4,
GND
9 (Exposed Pad)
5
5
5
1
Pin Name
0
5
4
COUT (μF)
22 x 2
22 x 2
22 x 2
22 x 2
22 x 2
22 x 2
25
Functional Pin Description
Pin No.
电
L (μH)
22
15
10
6.8
4.7
3.6
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COUT
22µF x 2
FB 5
CP
Open
Recommended Component Selection
VOUT (V) R1 (kΩ) R2 (kΩ) RC (kΩ)
8
76.8
10
27
5
45.3
10
20
3.3
26.1
10
13
2.5
16.9
10
9.1
1.8
9.53
10
5.6
1.2
3
10
3.6
VOUT
3.3V/2A
is a registered trademark of Richtek Technology Corporation.
DS8284N-03 May 2012
RT8284N
Function Block Diagram
VIN
Internal
Regulator
Oscillator
Slope Comp
Shutdown
VA VCC
Comparator
1.2V
Foldback
Control
+
-
0.5V
Lockout
Comparator
-
5k
EN
2.7V
3V
Current Sense
Amplifier
+
VA
-
+
BOOT
UV
Comparator
S
Q
SW
+
+
130m Ω
Current
Comparator
R
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130m Ω
Q
电
VCC
维
6µA
SS
佳
+
+
Error Amp
0.923V
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FB
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5
5
1
8
3
2
5-
5
7
0
4
1
2
3
8
/
COMP
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0
5
4
GND
室
5
0
28
厦
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Copyright © 2012 Richtek Technology Corporation. All rights reserved.
DS8284N-03 May 2012
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
3
RT8284N
Absolute Maximum Ratings
(Note 1)
Supply Voltage, VIN ----------------------------------------------------------------------------------------------Input Voltage, SW -------------------------------------------------------------------------------------------------<20ns ----------------------------------------------------------------------------------------------------------------VBOOT − VSW --------------------------------------------------------------------------------------------------------Other Pins Voltages ----------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C
SOP-8 ----------------------------------------------------------------------------------------------------------------SOP-8 (Exposed Pad) -------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2)
SOP-8, θJA ----------------------------------------------------------------------------------------------------------SOP-8 (Exposed Pad), θJA --------------------------------------------------------------------------------------SOP-8 (Exposed Pad), θJC -------------------------------------------------------------------------------------Junction Temperature ---------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -----------------------------------------------------------------------Storage Temperature Range ------------------------------------------------------------------------------------ESD Susceptibility (Note 3)
HBM (Human Body Model) ---------------------------------------------------------------------------------------
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Recommended Operating Conditions
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1
2
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1.111W
1.333W
90°C/W
75°C
15°C
150°C
260°C
−65°C to 150°C
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4
3
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−0.3V to 25V
−0.3V to (VIN + 0.3V)
−3V to (VIN + 3V)
−0.3V to 6V
−0.3V to 6V
2kV
室
5
0
(Note 4)
Supply Voltage, VIN ----------------------------------------------------------------------------------------------- 4.5V to 23V
Junction Temperature Range ------------------------------------------------------------------------------------- −40°C to 125°C
Ambient Temperature Range ------------------------------------------------------------------------------------- −40°C to 85°C
5
5
1
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3
2
Electrical Characteristics
5-
5
7
0
Min
Typ
Max
Unit
VEN = 0V
--
0.5
3
μA
VEN = 3 V, VFB = 1V
--
0.8
1.2
mA
0.909
0.923
0.937
V
--
940
--
μA/V
RDS(ON)1
--
130
--
mΩ
RDS(ON)2
--
130
--
mΩ
ICC
Feedback Voltage
VFB
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Low Side Switch-On Resistance
Test Conditions
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Error Amplifier Transconductance GEA
High Side Switch-On Resistance
际
Symbol
Shutdown Supply Current
Supply Current
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(VIN = 12V, TA = 25°C unless otherwise specified)
Parameter
28
4.5V ≤ VIN ≤ 23V
ΔIC = ±10μA
High Side Switch Leakage Current
VEN = 0V, VSW = 0V
--
0
10
μA
Upper Switch Current Limit
Min.Duty Cycle, VBOOT−SW = 4.8V
--
4.3
--
A
Low Switch Current Limit
COMP to Current Sense
Transconductance
Oscillator Frequency
From Drain to Source
--
1.3
--
A
GCS
--
4
--
A/V
fOSC1
300
340
380
kHz
Short Circuit Oscillation
Frequency
fOSC2
--
100
--
kHz
深
VFB = 0V
Copyright © 2012 Richtek Technology Corporation. All rights reserved.
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4
is a registered trademark of Richtek Technology Corporation.
DS8284N-03 May 2012
RT8284N
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
--
93
--
%
ns
Maximum Duty Cycle
DMAX
Minimum On-Time
tON
--
100
--
Logic-High
VIH
2.7
--
5.5
Logic-Low
VIL
--
--
0.4
3.8
4.2
4.5
V
--
320
--
mV
EN Input Threshold
Voltage
VFB = 0.7V
Input Under Voltage Lockout Threshold
VUVLO
Input Under Voltage Lockout Hysteresis
ΔVUVLO
Soft-Start Current
ISS
VSS = 0V
--
6
--
μA
Soft-Start Period
tSS
CSS = 0.1μF
--
15.5
--
ms
--
150
--
°C
Thermal Shutdown
(Note 5)
VIN Rising
V
TSD
子
电
Note 1. Stresses beyond those listed “Absolute Maximum Ratings” may cause permanent damage to the device. These are
0
5
4
stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in
维
the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions may
佳
affect device reliability.
富
4
1
2
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.
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Note 3. Devices are ESD sensitive. Handling precaution is recommended.
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Note 4. The device is not guaranteed to function outside its operating conditions..
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Note 5. Guaranteed by design.
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0
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28
厦
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Copyright © 2012 Richtek Technology Corporation. All rights reserved.
DS8284N-03 May 2012
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
5
RT8284N
Typical Operating Characteristics
Efficiency vs. Output Current
Reference Voltage vs. Input Voltage
100
0.940
90
VIN = 4.5V
VIN = 12V
VIN = 23V
70
0.935
Reference Voltage (V)
Efficiency (%)
80
60
50
40
30
0.930
0.925
0.920
0.915
0.910
20
0.900
0
0.25
0.5
0.75
1
1.25
1.5
1.75
维
2
Output Current (A)
佳
Reference Voltage vs. Temperature
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0.935
深
0.925
0.920
38
0.910
0.905
0.900
-50
-2
55
-25
0
25
50
75
100
际
125
18
20
22
24
室
5
0
3.31
3.30
28
3.29
3.28
VIN = 4.5V
VIN = 12V
VIN = 23V
厦
3.27
VOUT = 3.3V
3.24
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
Output Current (A)
Frequency vs. Temperature
370
Frequency (kHz)1
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340
16
380
圳
350
14
4
4
3.32
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3.33
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50
12
Input Voltage (V)
3.26
诚
Frequency vs. Input Voltage
380
10
3.25
Temperature (°C)
07
8
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5
52
8
1
2
3
3.35
5
1
0.915
6
3.36
3.34
圳
0.930
4
Output Voltage vs. Output Current
Output Voltage (V)
0.940
Reference Voltage (V)
电
VOUT = 3.3V
0
Frequency (kHz)1
子
0.905
10
330
320
360
350
340
330
320
310
310
VOUT = 3.3V, VIN = 12V, IOUT = 0A
VOUT = 3.3V, IOUT = 0A
300
300
4
6
8
10
12
14
16
18
20
22
Input Voltage (V)
Copyright © 2012 Richtek Technology Corporation. All rights reserved.
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6
24
-50
-25
0
25
50
75
100
125
Temperature (°C)
is a registered trademark of Richtek Technology Corporation.
DS8284N-03 May 2012
RT8284N
Current Limit vs. Temperature
Load Transient Response
6.0
Current Limit (A)
5.5
VOUT
(100mV/Div)
5.0
4.5
4.0
IOUT
(1A/Div)
子
3.5
电
VIN = 12V, VOUT = 3.3V
3.0
-50
-25
0
25
50
75
100
维
125
Temprature (°C)
佳
Load Transient Response
IOUT
(1A/Div)
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VOUT
(100mV/Div)
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5
5
1
8
3
2
5
5
Time (100μs/Div)
07
Switching
2
3
8
VOUT
(10mV/Div)
IL
(1A/Div)
VSW
(10V/Div)
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0
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Power On from VIN
0
5
4
Time (100μs/Div)
14
/
5
2
VIN = 12V, VOUT = 3.3V, IOUT = 1A to 2A
VIN = 12V, VOUT = 3.3V, IOUT = 0A to 2A
VIN = 12V, VOUT = 3.3V, IOUT = 2A
Time (1μs/Div)
Power Off from VIN
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VIN
(5V/Div)
VOUT
(2V/Div)
圳
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IL
(1A/Div)
VIN = 12V, VOUT = 3.3V, IOUT = 2A
Time (10ms/Div)
Copyright © 2012 Richtek Technology Corporation. All rights reserved.
DS8284N-03 May 2012
VIN
(5V/Div)
VOUT
(2V/Div)
IL
(1A/Div)
VIN = 12V, VOUT = 3.3V, IOUT = 2A
Time (10ms/Div)
is a registered trademark of Richtek Technology Corporation.
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7
RT8284N
Power On from EN
Power Off from EN
VEN
(2V/Div)
VEN
(2V/Div)
VOUT
(2V/Div)
VOUT
(2V/Div)
IOUT
(2A/Div)
IOUT
(2A/Div)
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VIN = 12V, VOUT = 3.3V, IOUT = 2A
维
Time (10ms/Div)
佳
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5
5
1
5-
5
7
0
4
1
2
25
8
3
2
0
5
4
Time (10ms/Div)
3
8
/
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VIN = 12V, VOUT = 3.3V, IOUT = 2A
室
5
0
28
厦
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Copyright © 2012 Richtek Technology Corporation. All rights reserved.
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8
is a registered trademark of Richtek Technology Corporation.
DS8284N-03 May 2012
RT8284N
Application Information
Soft-Start
The RT8284N is a synchronous high voltage buck converter
that can support the input voltage range from 4.5V to 23V
and the output current can be up to 2A.
The RT8284N contains an external soft-start clamp that
gradually raises the output voltage. The soft-start timing
can be programmed by the external capacitor between
SS pin and GND. The chip provides a 6μA charge current
for the external capacitor. If 0.1μF capacitor is used to
set the soft-start, the period will be 15.5ms (typ.).
Output Voltage Setting
The resistive voltage divider allows the FB pin to sense
the output voltage as shown in Figure 1.
VOUT
Chip Enable Operation
R1
RT8284N
电
R2
GND
维
佳
Figure 1. Output Voltage Setting
富
The output voltage is set by an external resistive voltage
divider according to the following equation :
市
VOUT = VFB ⎛⎜ 1+ R1 ⎞⎟
⎝ R2 ⎠
where VFB is the feedback reference voltage 0.923V (typ.).
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External Bootstrap Diode
5
5
1
8
3
2
5-
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10nF
SW
Figure 2. External Bootstrap Diode
Copyright © 2012 Richtek Technology Corporation. All rights reserved.
DS8284N-03 May 2012
厦
REN
100k
Chip Enable
2
VIN
CIN
BOOT
1
CBOOT
RT8284N
7 EN
VOUT
L
SW 3
R1
Q1
8 SS
CSS
4,
9 (Exposed Pad)
GND
COUT
FB 5
COMP
6
CC
RC
R2
CP
Figure 3. Enable Control Circuit for Logic Control with
Low Voltage
5V
BOOT
RT8284N
室
5
0
28
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3
8
/
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 3. 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.
VIN
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
RT8284N. Note that the external boot voltage must be
lower than 5.5V
0
5
4
4
1
2
25
Connect a 10nF low ESR ceramic capacitor between the
BOOT pin and SW pin. This capacitor provides the gate
driver voltage for the high side MOSFET.
5
7
0
The EN pin is the chip enable input. Pulling the EN pin
low (<0.4V) will shut down the device. During shutdown
mode, the RT8284N quiescent current drops to lower than
3μA. Driving the EN pin high ( > 2.7V, < 5.5V) will turn on
the device again. For external timing control (e.g.RC),
the EN pin can also be externally pulled high by adding a
R EN* resistor and C EN* capacitor from the VIN pin
(see Figure 5).
子
FB
To prevent enabling circuit when VIN is smaller than the
VOUT target value, a resistive voltage divider can be placed
between the input voltage and ground and connected to
the EN pin to adjust IC lockout threshold, as shown in
Figure 4. For example, if an 8V output voltage is regulated
from a 12V input voltage, the resistor, REN2, can be
selected to set input lockout threshold larger than 8V.
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9
RT8284N
2
VIN
12V
REN1
100k
CIN
10µF
BOOT
VIN
1
SW 3
7 EN
R1
REN2
COUT
COMP
GND
6
CC
Series
Dimensions
(mm)
TDK
VLF10045
10 x 9.7 x 4.5
TDK
TAIYO
YUDEN
SLF12565
12.5 x 12.5 x 6.5
NR8040
8x8x4
R2
RC
CP
Figure 4. The Resistors can be Selected to Set IC
Lockout Threshold
CIN and COUT Selection
The input capacitance, C IN, 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
RMS current is given by :
子
Hiccup Mode
电
For the RT8284N, Hiccup Mode Under Voltage Protection
(UVP) is provided. When the FB voltage, VFB, drops below
0.5V, the UVP function will be triggered and the RT8284N
will shut down for a period of time and then recover
automatically. The Hiccup Mode UVP can reduce input
current in short-circuit conditions.
维
佳
富
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圳
Inductor Selection
深
5
5
1
V
V
ΔIL = ⎡⎢ OUT ⎤⎥ × ⎡⎢1− OUT ⎤⎥
VIN ⎦
⎣ f ×L ⎦ ⎣
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.
38
2
5
5
7
0
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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.
Copyright © 2012 Richtek Technology Corporation. All rights reserved.
14
2
3
8
VIN
−1
VOUT
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.
室
5
0
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.
28
厦
For the input capacitor, one 10μF low ESR ceramic
capacitors are recommended. For the recommended
capacitor, please refer to table 3 for more detail.
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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 :
⎡ VOUT ⎤ ⎡
VOUT ⎤
L =⎢
⎥ × ⎢1 − VIN(MAX) ⎥
f
I
×
Δ
L(MAX)
⎣
⎦ ⎣
⎦
0
5
4
V
IRMS = IOUT(MAX) OUT
VIN
/
5
2
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.
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10
Component
Supplier
FB 5
8 SS
CSS
4,
9 (Exposed Pad)
Table 2. Suggested Inductors for Typical
Application Circuit
VOUT
8V
CBOOT
L
RT8284N
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.
The output ripple, ΔVOUT , is determined by :
1
⎤
ΔVOUT ≤ ΔIL ⎡⎢ESR +
8fCOUT ⎥⎦
⎣
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.
is a registered trademark of Richtek Technology Corporation.
DS8284N-03 May 2012
RT8284N
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.
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) and COUT also begins to be charge
or discharged to generate 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.
子
EMI Consideration
电
维
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.
佳
富
市
圳
深
1
8
3
5
7
0
2
VIN
4.5V to 23V
REN*
市
Chip Enable
圳
CEN*
深
诚
VIN
8 SS
GND
室
5
0
28
capability to the high side MOSFET. It is strongly
recommended to reserve the R-C snubber during PCB
layout for EMI improvement. Moreover, reducing the SW
trace area and keeping the main power in a small loop will
be helpful on EMI performance. For detailed PCB layout
guide, please refer to the section Layout Considerations.
厦
际
BOOT
1
RBOOT*
CBOOT
L
10nF 10µH
RT8284N
7 EN
CSS
4,
0.1µF 9 (Exposed Pad)
3
8
/
大
国
鼎
CIN
10µF
0
5
4
4
1
2
25
55
2
5
Since parasitic inductance and capacitance effects in PCB
circuitry would cause a spike voltage on SW pin when
high-side MOSFET is turned-on/off, this spike voltage on
SW may impact on EMI performance in the system. In
order to enhance EMI performance, there are two methods
to suppress the spike voltage. One way is by placing an
R-C snubber between SW and GND and locating them as
close as possible to the SW pin (see Figure 5). Another
method is by adding a resistor in series with the bootstrap
capacitor, CBOOT, but this method will decrease the driving
SW 3
RS*
VOUT
3.3V/2A
R1
26.1k
CS*
COUT
22µFx2
FB 5
COMP
6
CC
3.3nF
RC
13k
R2
10k
CP
NC
* : Optional
Figure 5. Reference Circuit with Snubber and Enable Timing Control
Copyright © 2012 Richtek Technology Corporation. All rights reserved.
DS8284N-03 May 2012
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
11
RT8284N
(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.
Thermal Considerations
For continuous operation, do not exceed absolute
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
junctions to ambient. The maximum power dissipation can
be calculated by following formula :
The maximum power dissipation depends on operating
ambient temperature for fixed T J(MAX) and thermal
resistance θJA. The of de-rating curves in Figure 7 allow
the designer to see the effect of rising ambient temperature
on the maximum power dissipation allowed.
PD(MAX) = (TJ(MAX) − TA) / θJA
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.
2.2
市
圳
5
5
1
P D(MAX) = (125°C − 25°C) / (75°C/W) = 1.33W
(min. copper area PCB layout with SOP-8 Exposed Pad)
8
3
2
5-
5
7
0
1.6
维
1.4
0
5
4
4
1
2
1.2
1.0
0.8
3
8
/
0.6
0.4
25
Four-Layer PCB
电
1.8
佳
富
P D(MAX) = (125°C − 25°C) / (49°C/W) = 2.04W
(70mm2 copper area PCB layout with SOP-8 Exposed
Pad)
Power Dissipation (W)
For recommended operating conditions specification, 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. For SOP-8 package, the thermal
resistance θJA is 90°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 :
深
子
2.0
室
5
0
0.2
0.0
0
25
50
75
Copper Area
70mm2
50mm2
30mm2
10mm2
Min.Layout
SOP-8
100
125
28
Ambient Temperature (°C)
Figure 7. Derating Curve of Maximum Power Dissipation
厦
大
际
国
P D(MAX) = (125°C − 25°C) / (90°C/W) = 1.11W
(min. copper area PCB layout with SOP-8)
诚
鼎
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.
市
(a) Copper Area = (2.3 x 2.3) mm2, θJA = 75°C/W
圳
深
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
Copyright © 2012 Richtek Technology Corporation. All rights reserved.
www.richtek.com
12
(b) Copper Area = 10mm2, θJA = 64°C/W
is a registered trademark of Richtek Technology Corporation.
DS8284N-03 May 2012
RT8284N
Layout Considerations
For best performance of the RT8284N, the following layout
guidelines must be strictly followed.
(c) Copper Area = 30mm2 , θJA = 54°C/W
`
Input capacitor must be placed as close to the IC as
possible.
`
SW should be connected to inductor by wide and short
trace. Keep sensitive components away from this trace.
`
The feedback components must be connected as close
to the device as possible
子
The feedback components
must be connected as close
to the device as possible.
Input capacitor must be placed
as close to the IC as possible.
电
维
(d) Copper Area = 50mm2 , θJA = 51°C/W
市
圳
5/
1
8
3
Figure 6. Themal Resistance vs. Copper Area Layout
Design
Table 3. Suggested Capacitors for CIN and COUT
CIN
CIN
75
GND
4
GND
6
COMP
5
FB
9
REN VIN
CP
室
5
0
Figure 8. PCB Layout Guide
28
厦
大
际
10
1206
C3225X5R1E106K
10
1206
TMK316BJ106ML
10
1206
圳
GRM31CR60J476M
47
1206
TDK
C3225X5R0J476M
47
1210
MURATA
GRM32ER71C226M
22
1210
TDK
C3225X5R1C22M
22
1210
鼎
市
COUT
MURATA
深
COUT
Part No.
GRM31CR61E106K
TDK
Copyright © 2012 Richtek Technology Corporation. All rights reserved.
DS8284N-03 May 2012
VOUT
GND
诚
MURATA
RC
R1
R2
Case Size
TAIYO YUDEN
COUT
3
EN
Capacitance (μF)
CIN
COUT
SW
SS
7
国
Component Supplier
0
2
CC
8
L1
SW should be connected to inductor by
wide and short trace. Keep sensitive
components away from this trace.
2
5
5
(e) Copper Area = 70mm2 , θJA = 49°C/W
4
1
2
VIN
83
COUT
0
5
4
CSS
BOOT
RS CS
VOUT
深
Location
CIN
佳
富
2
5
SW GND
VIN
GND
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
13
RT8284N
Outline Dimension
H
A
M
J
B
F
子
电
C
I
维
佳
D
富
Max
4.801
5.004
3
8
/
3.988
0.150
1.753
0.053
圳
深
A
B
D
0.330
5-
H
5
7
0
M
0.400
鼎
市
0.007
0.010
0.254
0.002
0.010
6.200
0.228
0.244
1.270
0.016
0.050
大
际
国
诚
0.069
0.053
0.254
5.791
0.157
0.047
0.170
J
厦
0.197
0.020
1.346
0.050
28
Max
0.013
1.194
I
0.189
0.508
23
室
5
0
Min
25
81
1.346
Dimensions In Inches
55
3.810
C
F
4
1
2
Min
市
Dimensions In Millimeters
Symbol
0
5
4
8-Lead SOP Plastic Package
圳
深
Copyright © 2012 Richtek Technology Corporation. All rights reserved.
www.richtek.com
14
is a registered trademark of Richtek Technology Corporation.
DS8284N-03 May 2012
RT8284N
H
A
M
EXPOSED THERMAL PAD
(Bottom of Package)
Y
J
B
X
F
子
电
维
I
佳
富
市
Symbol
圳
A
深
B
5
5
1
D
0.330
8
3
2
H
J
室
5
0
4.000
0.150
1.753
0.053
0.510
0.013
1.194
1.346
0.170
0.254
0.000
28
厦
0.197
0.157
0.069
0.020
0.010
0.152
0.000
0.006
6.200
0.228
0.244
0.406
1.270
0.016
0.050
2.000
2.300
0.079
0.091
2.000
2.300
0.079
0.091
X
2.100
2.500
0.083
0.098
Y
3.000
3.500
0.118
0.138
5.791
X
市
大
际
国
诚
鼎
Y
深
0.189
0.007
Option 1
圳
Max
0.053
M
Option 2
Min
0.047
5
5
I
83
Max
5.004
3.810
1.346
Dimensions In Inches
/
5
2
4.801
C
F
07
Min
4
1
2
D
Dimensions In Millimeters
0
5
4
C
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.
DS8284N-03 May 2012
www.richtek.com
15