RT8292A
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DS8292A-03 March 2011 www.richtek.com
Ordering Information
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.
Pin Configurations
(TOP VIEW)
Applications
z Wireless AP/Router
zSet-Top-Box
zIndustrial a nd Commercial Low Power Syste ms
zLCD Monitors and TVs
zGreen Electronics/Applia nces
zPoint of Load Regulation of High-Performa nce DSPs
SOP-8 (Exposed Pad)
2A, 23V, 340kHz Synchronous Step-Down Converter
General Description
The RT8292A 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
RT8292A'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 RT8292A also provides under
voltage protection and thermal shutdown prptection. The
low current (<3μA) shutdown mode provides output
disconnection, enabling easy power management in
battery-powered systems. The RT8292A is available in
a n SOP-8 (Exposed Pad) pa ckage.
Features
zz
zz
z ±±
±±
±1.5% High Accuracy Feedback Voltage
zz
zz
z 4.5V to 23V Input Voltage Range
zz
zz
z 2A Output Current
zz
zz
z Integrated N-MOSFET Switches
zz
zz
z Current Mode Control
zz
zz
z Fixed Frequency Operation : 340kHz
zz
zz
z Output Adjustable from 0.8V to 20V
zz
zz
z Up to 95% Efficiency
zz
zz
z Programmable Soft-Start
zz
zz
z Stable with Low-ESR Ceramic Output Capacitors
zz
zz
z Cycle-by-Cycle Over Current Protection
zz
zz
z Input Under Voltage Lockout
zz
zz
z Output Under Voltage Protection
zz
zz
z Thermal Shutdown Protection
zz
zz
z RoHS Compliant and Halogen Free
BOOT
VIN
SW
GND
SS
EN
FB
COMP
GND
2
3
45
6
7
8
9
Marking Information
RT8292AxGSP : Product Number
x : H or L
YMDNN : Date Code
RT8292AxZSP : Product Number
x : H or L
YMDNN : Date Code
RT8292Ax
GSPYMDNN
RT8292Ax
ZSPYMDNN
RT8292AxGSP RT8292AxZSP
Package Type
SP : SOP-8 (Exposed Pad-Option 1)
RT8292A
Lead Plating System
G : Green (Halogen Free and Pb Free)
Z : ECO (Ecological Element with
Halogen Free and Pb free)
H : UVP Hiccup
L : UVP Latch-Off
RT8292A
2DS8292A-03 March 2011www.richtek.com
Functional Pin Description
Pin No. Pin Name Pin Function
1 BOOT Bootstrap for High Side Gate Driver. Connect a 0.1µF or greater ceramic
capacitor from BOOT to SW pins.
2 VIN Input Supply Voltage, 4.5V to 23V. Must bypass with a suitably large ceramic
capacitor.
3 SW Phase Node. Connect this pin to an external L-C filter.
4,
9 (Exposed Pad) GND Ground. The exposed pad must be soldered to a large PCB and connected to
GND for maximum power dissipation.
5 FB
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.
6 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.
7 EN Enable Input Pin. A logic high enables the converter; a logic low forces the
RT8292A 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.
8 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 13.5ms.
Typical Application Circuit
VOUT (V)
R1 (kΩ)
R2 (kΩ)
RC (kΩ)
CC (nF)
L (µH) COUT (µF)
8 27 3 27 3.3 22 22 x 2
5 62 11.8 20 3.3 15 22 x 2
3.3 75 24 13 3.3 10 22 x 2
2.5 25.5 12 9.1 3.3 6.8 22 x 2
1.5 10.5 12 4.7 3.3 3.6 22 x 2
1.2 12 24 3.6 3.3 3.6 22 x 2
1 3 12 3 3.3 2 22 x 2
VIN
EN
GND
BOOT
FB
SW
7
5
2
3
1L
10µH
100nF
22µF x 2
R1
75k
R2
24k
VOUT
3.3V/2A
10µF
VIN
4.5V to 23V RT8292A
SS
8
CSS
COMP
CC
3.3nF RC
13k
CP
Open
6
4, 9 (Exposed Pad)
CBOOT
CIN
0.1µF
COUT
REN 100k
Table 1. Recommended Component Selection
RT8292A
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Function Block Diagram
VA
+
-
+
-
+
-
UV
Comparator
Oscillator
Foldback
Control
0.4V
Internal
Regulator
+
-
2.7V
Shutdown
Comparator
Current Sense
Amplifier
BOOT
VIN
GND
SW
FB
EN
COMP
3V
5k
VA VCC
6µA
Slope Comp
Current
Comparator
+
-EA
0.8V
S
R
Q
Q
SS
+
-
1.2V
Lockout
Comparator
VCC
+
130m
Ω
130m
Ω
RT8292A
4DS8292A-03 March 2011www.richtek.com
Electrical Characteristics
(VIN = 12V, TA = 25°C, unless otherwise specified)
Absolute Maximum Ratings (Note 1)
lSupply Voltage, VIN ----------------------------------------------------------------------------------------------- −0.3V to 25V
lInput Voltage, SW------------------------------------------------------------------------------------------------- −0.3V to (VIN + 0.3V)
lVBOOT - VSW --------------------------------------------------------------------------------------------------------- −0.3V to 6V
l Other Pin Voltages------------------------------------------------------------------------------------------------ −0.3V to 6V
lPower Dissipation, PD @ TA = 25°C
SOP-8 (Exposed Pad)--------------------------------------------------------------------------------------------1.333W
l Package Thermal Resistance (Note 2)
SOP-8 (Exposed Pad), θJA---------------------------------------------------------------------------------------75°C/W
SOP-8 (Εxposed Pad), θJC --------------------------------------------------------------------------------------15°C/W
lLead Temperature (Soldering, 10 sec.)------------------------------------------------------------------------260°C
lJunction Temperature---------------------------------------------------------------------------------------------150°C
lStorage Temperature Range------------------------------------------------------------------------------------- −65°C to 150°C
lESD Susceptibility (Note 3)
HBM (Human Body Mode)---------------------------------------------------------------------------------------2kV
MM (Machine Mode)----------------------------------------------------------------------------------------------200V
Recommended Operating Conditions (Note 4)
lSupply Voltage, VIN -----------------------------------------------------------------------------------------------4.5V to 23V
lJunction Temperature Range------------------------------------------------------------------------------------ −40°C to 125°C
lAmbient Temperature Range------------------------------------------------------------------------------------ −40°C to 85°C
Parameter Symbol
Test Conditions Min Typ Max
Unit
Shutdown Supply Current VEN = 0V -- 0.5 3 µA
Supply Current VEN = 3 V, VFB = 0.9V -- 0.8 1.2 mA
Feedback Voltage VFB 4.5V ≤ VIN ≤ 23V 0.788
0.8 0.812
V
Error Amplifier
Transconductance GEA ∆IC = ± 10µA -- 940 -- µA/V
High Side Switch
On-Resistance RDS(ON)1
-- 130 -- mΩ
Low Side Switch
On-Resistance RDS(ON)2
-- 130 -- mΩ
High Side Switch Leakage
Current VEN = 0V, VSW = 0V -- 0 10 µA
Upper Switch Current Limit
Min. Duty Cycle, VBOOT−VSW = 4.8V -- 4.3 -- A
Lower Switch Current Limit
From Drain to Source -- 1.3 -- A
COMP to Current Sense
Transconductance GCS -- 4 -- A/V
Oscillation Frequency f
OSC1 300 340 380 kHz
Short Circuit Oscillation
Frequency fOSC2 VFB = 0V -- 100 -- kHz
Maximum Duty Cycle DMAX VFB = 0.7V -- 93 -- %
Minimum On Time t
ON -- 100 -- ns
To be continued
RT8292A
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DS8292A-03 March 2011 www.richtek.com
Parameter Symbol Test Conditions Min Typ Max Unit
Logic-High VIH 2.7 -- 5.5
EN Input Threshold
Voltage Logic-Low VIL -- -- 0.4 V
Input Under Voltage Lockout Threshold
VUVLO VIN Rising 3.8 4.2 4.5 V
Input Under Voltage Lockout Hysteresis
∆VUVLO -- 320 -- mV
Soft-Start Current ISS VSS = 0V -- 6 -- µA
Soft-Start Period tSS CSS = 0.1µF -- 13.5
-- ms
Thermal Shutdown TSD -- 150
-- °C
Note 1. Stresses listed as the above "Absolute Maximum Ratings" may cause permanent damage to the device. These are for
stress ratings. 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 for extended
periods may remain possibility to affect device reliability.
Note 2. θJA is measured in the natural convection at TA = 25°C on a high effective thermal conductivity four -layer test board of
JEDEC 51-7 thermal measurement standard. The measurement case position of θJC is on 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.
RT8292A
6DS8292A-03 March 2011www.richtek.com
Typical Operating Characteristics
Efficiency vs. Output Current
0
10
20
30
40
50
60
70
80
90
100
0 0.25 0.5 0.75 1 1.25 1.5 1.75 2
Output Current (A)
Efficiency (%)
VIN = 4.5V
VIN = 12V
VIN = 23V
VOUT = 3.3V
Reference Voltage vs. Input Voltage
0.780
0.785
0.790
0.795
0.800
0.805
0.810
0.815
0.820
4 6 8 10 12 14 16 18 20 22 24
Input Voltage (V)
Reference Voltage (V)
Reference Voltage vs. Temperature
0.780
0.785
0.790
0.795
0.800
0.805
0.810
0.815
0.820
-50 -25 0 25 50 75 100 125
Temperature (°C)
Reference Voltage (V)
Output Voltage vs. Output Current
3.290
3.293
3.295
3.298
3.300
3.303
3.305
3.308
3.310
0 0.25 0.5 0.75 1 1.25 1.5 1.75 2
Output Current (A)
Output Voltage (V)
VIN = 4.5V
VIN = 12V
VIN = 23V
VOUT = 3.3V
Frequency vs. Input Voltage
300
310
320
330
340
350
360
370
380
4 6 8 10 12 14 16 18 20 22 24
Input Voltage (V)
Frequency (kHz) 1
VOUT = 3.3V, IOUT = 0A
Frequency vs. Temperature
300
310
320
330
340
350
360
370
380
-50 -25 0 25 50 75 100 125
Temperature (°C)
Frequency (kHz)
VIN = 12V, VOUT = 3.3V, IOUT = 0A
RT8292A
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Current Limit vs. Tem perature
3.00
3.25
3.50
3.75
4.00
4.25
4.50
4.75
5.00
5.25
5.50
5.75
6.00
-50-25 0 25 50 75100125
Temprature (°C)
Curr en t Lim it (A)
VIN = 12V, VOUT = 3.3V
Load Transient Response
Time (100μs/Div)
VOUT
(100mV/Div)
IOUT
(1A/Div)
VIN = 12V, VOUT = 3.3V, IOUT = 0A to 2A
Load Transient Response
Time (100μs/Div)
VIN = 12V, VOUT = 3.3V, IOUT = 1A to 2A
IOUT
(1A/Div)
VOUT
(100mV/Div)
Switching
Time (1μs/Div)
VIN = 12V, VOUT = 3.3V, IOUT = 2A
IL
(1A/Div)
VOUT
(10mV/Div)
VSW
(10V/Div)
Power Off from VIN
Time (10ms/Div)
IL
(2A/Div)
VOUT
(2V/Div)
VIN
(5V/Div)
VIN = 12V, VOUT = 3.3V, I OUT = 2A
Power On from VIN
Time (10ms/Div)
VIN = 12V, VOUT = 3.3V, IOUT = 2A
IL
(2A/Div)
VOUT
(2V/Div)
VIN
(5V/Div)
RT8292A
8DS8292A-03 March 2011www.richtek.com
Power On from EN
Time (10ms/Div)
VOUT
(2V/Div)
VEN
(2V/Div)
IL
(1A/Div) VIN = 12V, VOUT = 3.3V, I OUT = 2A
Power Off from EN
Time (10ms/Div)
VIN = 12V, VOUT = 3.3V, I OUT = 2A
VOUT
(2V/Div)
VEN
(2V/Div)
IL
(1A/Div)
RT8292A
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Application Information
The RT8292A 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.
Output Voltage Setting
The resistive voltage divider allows the FB pin to sense
the output voltage as shown in Figure 1.
Figure 1. Output Voltage Setting
The output voltage is set by an external resistive voltage
divider according to the following equation :
+
OUTFB
R1
V = V1
R2
where VFB is the feedback reference voltage (0.8V typ.).
External Bootstrap Diode
Connect a 100nF low ESR ceramic capacitor between
the BOOT pin and SW pin. This capacitor provides the
gate driver voltage for the high side MOSFET.
It is recommended to add an external bootstrap diode
between an external 5V and 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
RT8292A. Note that the external boot voltage must be
lower than 5.5V.
Figure 2. External Bootstrap Diode
Soft-Start
The RT8292A 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 13.5ms(typ.).
Chip Enable Operation
The EN pin is the chip enable input. Pulling the EN pin
low (<0.4V) will shut down the device. During shutdown
mode, the RT8292A 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
REN* resistor and CEN* capacitor from the VIN pin
(see Figure 5).
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.
Figure 3. Enable Control Circuit for Logic Control with
Low Voltage
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.
RT8292A
GND
FB
R1
R2
VOUT
SW
BOOT
5V
RT8292A 100nF
VIN
EN
GND
BOOT
FB
SW
7
5
2
3
1
L
R1
R2
VOUT
Chip Enable
VIN RT8292A
SS
8
CSS COMP CCRC
CP
6
CBOOT
COUT
CIN
REN
Q1
100k
4,
9 (Exposed Pad)
RT8292A
10 DS8292A-03 March 2011www.richtek.com
Having a lower ripple current reduces not only the ESR
losses in the output capacitors but also the output voltage
ripple. High frequency with small ripple current can achieve
highest efficiency operation. However, it requires a large
inductor to achieve this goal.
For the ripple current selection, the value of ∆IL = 0.24(IMAX)
will be a reasonable starting point. The largest ripple
current occurs at the highest VIN. To guarantee that the
OUTOUT
L(MAX)IN(MAX)
VV
L =1
fIV
×−
×∆
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.
Table 2. Suggested Inductors for Typical
Application Circuit
Component
Supplier Series Dimensions
(mm)
TDK VLF10045
10 x 9.7 x 4.5
TDK SLF12565
12.5 x 12.5 x 6.5
TAIYO
YUDEN NR8040 8 x 8 x 4
OUT IN
RMSOUT(MAX) INOUT
V V
I = I1
VV
−
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.
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.
For the input capacitor, one 10µF low ESR ceramic
capacitors are recommended. For the recommended
capacitor, please refer to table 3 for more detail.
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
CIN and COUT Selection
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
RMS current is given by :
OUTOUT
LIN
VV
I =1
fLV
∆×−
×
Hiccup Mode
For the RT8292AH, Hiccup Mode Under Voltage Protection
(UVP) is provided. When the FB voltage drops below half
of the feedback reference voltage, VFB, the UVP function
will be triggered and the RT8292AH will shut down for a
period of time and then recover automatically. The Hiccup
Mode UVP can reduce input current in short-circuit
conditions.
Latch-Off Mode
For the RT8292AL, Latch-Off Mode Under Voltage
Protection (UVP) is provided. When the FB voltage drops
below half of the feedback reference voltage, VFB, UVP
will be triggered and the RT8292AL will shutdown in Latch-
Off Mode. In shutdown condition, the RT8292AL can be
reset via the EN pin or power input VIN.
Inductor Selection
The inductor value and operating frequency determine the
ripple current according to a specific input and output
voltage. The ripple current ∆IL increases with higher VIN
and decreases with higher inductance.
Figure 4. The Resistors can be Selected to Set IC
Lockout Threshold
ripple current stays below the specified maximum, the
inductor value should be chosen according to the following
equation :
VIN
EN
GND
BOOT
FB
SW
7
5
2
3
1
L
R1
R2
VOUT
VIN
RT8292A
SS
8
CSS COMP CCRC
CP
6
CBOOT
COUT
CIN
100k 8V
12V
REN2
REN1 10µF
4,
9 (Exposed Pad)
RT8292A
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OUTL
OUT
1
VIESR 8fC
∆≤∆+
The output ripple will be highest at the maximum input
voltage since ∆IL increases with input voltage. Multiple
capacitors placed in parallel may be needed to meet the
ESR and RMS current handling requirement. Dry tantalum,
special polymer, aluminum electrolytic and ceramic
capacitors are all available in surface mount
packages.Special polymer capacitors offer very low ESR
value. However, it provides lower capacitance density than
other types. Although Tantalum capacitors have the highest
capacitance density, it is important to only use types that
pass the surge test for use in switching power supplies.
Aluminum electrolytic capacitors have significantly higher
ESR. However, it can be used in cost-sensitive applications
for ripple current rating and long term reliability
considerations. Ceramic capacitors have excellent low
ESR characteristics but can have a high voltage coefficient
and audible piezoelectric effects. The high Q of ceramic
capacitors with trace inductance can also lead to significant
ringing.
Higher values, lower cost ceramic capacitors are now
becoming available in smaller case sizes. Their high ripple
current, high voltage rating and low ESR make them ideal
for switching regulator applications. However, care must
be taken when these capacitors are used at input and
output. When a ceramic capacitor is used at the input
and the power is supplied by a wall adapter through long
wires, a load step at the output can induce ringing at the
input, VIN. At best, this ringing can couple to the output
response as described in a later section.
The output ripple, ∆VOUT , is determined by :
and be mistaken as loop instability. At worst, a sudden
inrush of current through the long wires can potentially
cause a voltage spike at VIN large enough to damage the
part.
Checking Transient Response
The regulator loop response can be checked by looking
at the load transient response. Switching regulators take
several cycles to respond to a step in load current. When
a load step occurs, VOUT immediately shifts by an amount
equal to ∆ILOAD (ESR) and COUT also begins to be charged
or discharged COUT 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.
EMI Consideration
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 locking 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
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.
Figure 5. Reference Circuit with Snubber and Enable Timing Control
VIN
EN
GND
BOOT
FB
SW
7
5
2
3
1
L
10µH
100nF
22µFx2
R1
75k
R2
24k
VOUT
3.3V/2A
10µF
Chip Enable
VIN
4.5V to 23V RT8292A
SS
8
CSS
0.1µFCOMP
CC
3.3nF RC
13k
CP
NC
6
4,
9 (Exposed Pad)
CBOOT
COUT
CIN
RBOOT*
RS*
CS*
REN*
CEN*
* : Optional
RT8292A
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Figure 7. Derating Curves for RT8292A Package
(a) Copper Area = (2.3 x 2.3) mm2, θJA = 75°C/W
(b) Copper Area = 10mm2, θJA = 64°C/W
(c) Copper Area = 30mm2 , θJA = 54°C/W
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 :
PD(MAX) = (TJ(MAX) − TA ) / θJA
where TJ(MAX) is the maximum operation junction
temperature , TA is the ambient temperature and the θJA is
the junction to ambient thermal resistance.
For recommended operating conditions specification of
RT8292A, 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 :
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)
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.
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 6a), 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. For RT8292A packages, the derating curves
in Figure 7 allow the designer to see the effect of rising
ambient temperature on the maximum power dissipation
allowed.
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
025 50 75 100 125
Ambient Temperature (°C)
Power Dissipation (W)
Copper Area
70mm2
50mm2
30mm2
10mm2
Min.Layout
Four Layer PCB
RT8292A
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DS8292A-03 March 2011 www.richtek.com
(d) Copper Area = 50mm2 , θJA = 51°C/W (e) Copper Area = 70mm2 , θJA = 49°C/W
Figure 6. Themal Resistance vs. Copper Area Layout Design
Figure 8. PCB Layout Guide
Table 3. Suggested Capacitors for CIN and COUT
Location
Component Supplier
Part No. Capacitance ( µF)
Case Size
CIN MURATA GRM31CR61E106K 10 1206
CIN TDK C3225X5R1E106K 10 1206
CIN TAIYO YUDEN TMK316BJ106ML 10 1206
COUT MURATA GRM31CR60J476M 47 1206
COUT TDK C3225X5R0J476M 47 1210
COUT MURATA GRM32ER71C226M 22 1210
COUT TDK C3225X5R1C22M 22 1210
Layout Considerations
For best performance of the RT8292A, the following layout giidelines must be strictly followed.
}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
VIN
VOUT
GND
GND
CP
CC
RC
SW
VOUT
COUT L1
R1
R2
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.
BOOT
VIN
SW
GND
SS
EN
FB
COMP
GND
2
3
45
6
7
8
9
CSS
RSCS
GND
VIN
REN
CIN
RT8292A
14 DS8292A-03 March 2011www.richtek.com
Richtek Technology Corporation
Headquarter
5F, No. 20, Taiyuen Street, Chupei City
Hsinchu, Taiwan, R.O.C.
Tel: (8863)5526789 Fax: (8863)5526611
Information that is provided by Richtek Technology Corporation is believed to be accurate and reliable. Richtek reserves the right to make any change in circuit
design, specification or other related things if necessary without notice at any time. No third party intellectual property infringement of the applications should be
guaranteed by users when integrating Richtek products into any application. No legal responsibility for any said applications is assumed by Richtek.
Richtek Technology Corporation
Taipei Office (Marketing)
5F, No. 95, Minchiuan Road, Hsintien City
Taipei County, Taiwan, R.O.C.
Tel: (8862)86672399 Fax: (8862)86672377
Email: marketing@richtek.com
Outline Dimension
A
B
J
F
H
M
C
D
I
Y
X
EXPOSED THERMAL PAD
(Bottom of Package)
8-Lead SOP (Exposed Pad) Plastic Package
Symbol Dimensions In Millimeters
Dimensions In Inches
Min Max Min Max
A 4.801 5.004 0.189 0.197
B 3.810 4.000 0.150 0.157
C 1.346 1.753 0.053 0.069
D 0.330 0.510 0.013 0.020
F 1.194 1.346 0.047 0.053
H 0.170 0.254 0.007 0.010
I 0.000 0.152 0.000 0.006
J 5.791 6.200 0.228 0.244
M 0.406 1.270 0.016 0.050
Option 1
X 2.000 2.300 0.079 0.091
Y 2.000 2.300 0.079 0.091
Option 2
X 2.100 2.500 0.083 0.098
Y 3.000 3.500 0.118 0.138
