RICHTEK RT8288A

®
RT8288A
4A, 21V 500kHz Synchronous Step-Down Converter
General Description
Features
The RT8288A is a synchronous step-down regulator with
an internal power MOSFET. It achieves 4A of continuous
output current over a wide input supply range with excellent
load and line regulation. Current mode operation provides
fast transient response and eases loop stabilization.
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4A Output Current
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Internal Soft-Start
120mΩ
Ω/40mΩ
Ω Internal Power MOSFET Switch
Internal Compensation Minimizes External Parts
Count
Fixed 500kHz Frequency
Thermal Shutdown Protection
Cycle-by-Cycle Over Current Protection
Wide 4.5V to 21V Operating Input Range
Adjustable Output from 0.808V to 15V
Available in an SOP-8 (Exposed Pad) Package
RoHS Compliant and Halogen Free
Fault condition protection includes cycle-by-cycle current
limiting and thermal shutdown. An internal soft-start
minimizes external parts count and internal compensation
circuitry.
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The RT8288A requires a minimal number of readily
available external components, providing a compact
solution.
Ordering Information
RT8288A
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Applications
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Package Type
SP : SOP-8 (Exposed Pad-Option 2)
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Lead Plating System
Z : ECO (Ecological Element with
Halogen Free and Pb free)
Distributive Power Systems
Battery Charger
DSL Modems
Pre-Regulator for Linear Regulators
Pin Configurations
Note :
(TOP VIEW)
Richtek products are :
`
`
RoHS compliant and compatible with the current require-
VIN
ments of IPC/JEDEC J-STD-020.
SW
2
SW
3
BOOT
4
Suitable for use in SnPb or Pb-free soldering processes.
Marking Information
8
GND
GND
7
VCC
6
FB
5
EN
9
SOP-8 (Exposed Pad)
RT8288AZSP : Product Number
RT8288A
ZSPYMDNN
YMDNN : Date Code
Copyright © 2012 Richtek Technology Corporation. All rights reserved.
DS8288A-03 June 2012
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1
RT8288A
Typical Application Circuit
1
VIN
CIN
22µF
Chip Enable
4
RT8288A
SW
5 EN
8, 9 (Exposed Pad)
VOUT (V)
5
3.3
2.5
1.8
1.5
1.2
1.05
BOOT
VIN
GND
2, 3
CBOOT
100nF
L
VOUT
6
FB
RT
VCC 7
R2
R1
COUT
CC
0.1µF
Table 1. Recommended Components Selection
R1 (kΩ)
R2 (kΩ)
RT (kΩ)
L (μH)
75
14.46
0
4.7
75
24.32
0
3.6
75
35.82
0
3.6
5
4.07
30
2
5
5.84
39
2
5
10.31
47
2
5
16.69
47
1.5
COUT (μF)
22 x 2
22 x 2
22 x 2
22 x 2
22 x 2
22 x 2
22 x 2
Function Pin Description
Pin No.
Pin Name
1
VIN
2, 3
SW
4
BOOT
5
EN
6
FB
7
VCC
8,
GND
9 (Exposed Pad)
Pin Function
Supply Input. VIN supplies the power to the IC, as well as the step-down converter
switches. Drive VIN with a 4.5V to 21V power source. Bypass VIN to GND with a
suitably large capacitor to eliminate noise on the input to the IC.
Switch Node. SW is the switching node that supplies power to the output. Connect
the output LC filter from SW to the output load. Note that a capacitor is required
from SW to BOOT to power the high side switch.
High Side Gate Drive Boost Input. BOOT supplies the drive for the high side
N-MOSFET switch. Connect a 100nF or greater capacitor from SW to BOOT to
power the high side switch.
Chip Enable (Active High). For automatic start-up, connect the EN pin to VIN with a
100kΩ resistor.
Feedback Input. FB senses the output voltage to regulate said voltage. Drive FB
with a resistive voltage divider from the output voltage. The feedback threshold is
0.808V.
Bias Supply. Decouple with 0.1μF to 0.22μF capacitor. The capacitance should be
no more than 0.22μF.
Ground. The exposed pad must be soldered to a large PCB and connected to
GND for maximum power dissipation.
Copyright © 2012 Richtek Technology Corporation. All rights reserved.
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is a registered trademark of Richtek Technology Corporation.
DS8288A-03 June 2012
RT8288A
Function Block Diagram
VIN
1.2V
Shutdown
Comparator
+
-
5k
1µA
3V
+
Regulator
BOOT
-
EN
Current Sense
Amplifier
-
Ramp
Generator
Oscillator
500kHz
+
Lockout
Comparator
S
Q
+
1.7V
PWM
Comparator
VCC
Reference
FB
Error
+ Amplifier
Driver
R
SW
GND
-
30pF
400k
1pF
Copyright © 2012 Richtek Technology Corporation. All rights reserved.
DS8288A-03 June 2012
is a registered trademark of Richtek Technology Corporation.
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3
RT8288A
Absolute Maximum Ratings
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(Note 1)
Supply Input Voltage, VIN ---------------------------------------------------------------------------------Switch Voltage, SW ----------------------------------------------------------------------------------------Boot Voltage, BOOT ----------------------------------------------------------------------------------------Other Pins -----------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C
SOP-8 (Exposed Pad) -------------------------------------------------------------------------------------Package Thermal Resistance (Note 2)
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) ---------------------------------------------------------------------------------
Recommended Operating Conditions
z
z
z
−0.3V to 26V
−0.3V to (VIN + 0.3V)
(SW − 0.3V) to (SW + 6V)
−0.3V to 6V
1.333W
75°C/W
15°C/W
150°C
260°C
−65°C to 150°C
2kV
(Note 4)
Supply Input Voltage, VIN ---------------------------------------------------------------------------------- 4.5V to 21V
Junction Temperature Range ------------------------------------------------------------------------------- −40°C to 125°C
Ambient Temperature Range ------------------------------------------------------------------------------- −40°C to 85°C
Electrical Characteristics
(VIN = 12V, TA = 25°C unless otherwise specified)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
Shutdown Current
ISHDN
VEN = 0
--
0
1
μA
Quiescent Current
IQ
VEN = 2V, VFB = 1V
--
0.7
--
mA
Upper Switch On Resistance
RDS(ON)1
--
120
--
mΩ
Lower Switch On Resistance
Switch Leakage
RDS(ON)2
ILEAK
---
40
0
-10
mΩ
μA
Current Limit
Oscillator Frequency
Short Circuit Frequency
ILIMIT
fSW
VBOOT − VSW = 4.8V
VFB = 0.75V
VFB = 0V
5.9
425
--
7
500
150
-575
--
A
kHz
kHz
Maximum Duty Cycle
DMAX
VFB = 0.8V
--
90
--
%
Minimum On Time
tON
--
100
--
ns
Feedback Voltage
VFB
0.82
V
Feedback Current
IFB
--
10
50
nA
Logic-High VIH
2
--
5.5
Logic-Low VIL
--
--
0.4
VEN = 2V
--
1
--
VEN = 0V
--
0
--
EN Input Threshold
Voltage
Enable Current
VEN = 0V, VSW = 0V or 12V
4.5V ≤ V IN ≤ 21V
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4
0.796 0.808
V
μA
is a registered trademark of Richtek Technology Corporation.
DS8288A-03 June 2012
RT8288A
Parameter
Symbol
Under Voltage Lockout
Threshold
VUVLO
Under Voltage Lockout
Threshold Hysteresis
ΔVUVLO
Test Conditions
VIN Rising
VCC Regulator
VCC Load Regulation
ICC = 5mA
Min
Typ
Max
Unit
3.8
4
4.2
V
--
400
--
mV
--
5
--
V
--
5
--
%
Soft-Start Period
tSS
--
2
--
ms
Thermal Shutdown
TSD
--
150
--
°C
Thermal Shutdown Hysteresis
ΔTSD
--
30
--
°C
Note 1. Stresses beyond those listed “Absolute Maximum Ratings” may cause permanent damage to the device. These are
stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in
the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions may
affect device reliability.bsolute maximum rating conditions for extended periods may remain possibility to 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.
Copyright © 2012 Richtek Technology Corporation. All rights reserved.
DS8288A-03 June 2012
is a registered trademark of Richtek Technology Corporation.
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5
RT8288A
Typical Operating Characteristics
Reference Voltage vs. Input Voltage
Efficiency vs. Output Current
0.830
100
90
VIN = 12V
0.825
Reference Voltage (V)
Efficiency (%)
80
VIN = 21V
70
60
50
40
30
20
0.820
0.815
0.810
0.805
0.800
0.795
10
VOUT = 1.22V, IOUT = 0A to 4A
0.790
0
0
0.5
1
1.5
2
2.5
3
3.5
4
4
6
8
10
14
16
18
20
22
Input Voltage (V)
Output Current (A)
Reference Voltage vs. Temperature
Output Voltage vs. Output Current
0.84
1.240
0.83
1.235
0.82
1.230
Output Voltage (V)
Reference Voltage (V)
12
0.81
0.80
0.79
0.78
1.225
1.220
1.215
1.210
0.77
1.205
0.76
1.200
VIN = 12V, VOUT = 1.22V, IOUT = 0A to 4A
-50
-25
0
25
50
75
100
0
125
0.5
1
1.5
Temperature (°C)
Switching Frequency vs. Input Voltage
2.5
3
3.5
4
Switching Frequency vs. Temperature
550
550
525
525
Switching Frequency (kHz)1
Switching Frequency (kHz)1
2
Output Current (A)
500
475
450
425
400
375
500
475
450
425
400
375
VOUT = 1.22V, IOUT = 0.8A
VIN = 12V, VOUT = 1.22V, IOUT = 1A
350
350
4
6
8
10
12
14
16
18
20
Input Voltage (V)
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22
-50
-25
0
25
50
75
100
125
Temperature (°C)
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DS8288A-03 June 2012
RT8288A
Current Limit vs. Temperature
Current Limit vs. Input Voltage
11
12
10
Current Limit (A)
Current Limit (A)
10
8
6
4
9
8
7
6
5
2
4
VIN = 12V, VOUT = 1.22V
3
0
4
6
8
10
12
14
16
18
20
22
-50
-25
0
25
50
75
100
Input Voltage (V)
Temperature (°C)
Load Transient Response
Load Transient Response
VOUT
(200mV/Div)
VOUT
(200mV/Div)
IOUT
(2A/Div)
IOUT
(2A/Div)
VIN = 12V, VOUT = 1.22V, IOUT = 1A to 4A
VIN = 12V, VOUT = 1.22V, IOUT = 0A to 4A
Time (100μs/Div)
Time (100μs/Div)
Output Voltage Ripple
Output Voltage Ripple
VOUT
(50mV/Div)
VOUT
(50mV/Div)
VSW
(10V/Div)
VSW
(10V/Div)
IL
(2A/Div)
IL
(2A/Div)
VIN = 12V, IOUT = 1A
Time (1μs/Div)
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DS8288A-03 June 2012
125
VIN = 12V, IOUT = 4A
Time (1μs/Div)
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RT8288A
Power Off from VIN
Power On from VIN
VIN
(10V/Div)
VIN
(10V/Div)
VOUT
(1V/Div)
VOUT
(1V/Div)
IL
(5A/Div)
IL
(5A/Div)
VIN = 12V, VOUT = 1.22V, IOUT = 4A
VIN = 12V, VOUT = 1.22V, IOUT = 4A
Time (5ms/Div)
Time (50ms/Div)
Power On from EN
Power Off from EN
VEN
(5V/Div)
IL
(5A/Div)
VEN
(5V/Div)
IL
(5A/Div)
VSW
(10V/Div)
VSW
(10V/Div)
VOUT
(1V/Div)
VOUT
(1V/Div)
VIN = 12V, VOUT = 1.22V, IOUT = 4A
Time (2.5ms/Div)
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VIN = 12V, VOUT = 1.22V, IOUT = 4A
Time (50μs/Div)
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DS8288A-03 June 2012
RT8288A
Application Information
The IC is a synchronous high voltage buck converter that
can support the input voltage range from 4.5V to 21V and
the output current can be up to 4A.
Output Voltage Setting
The output voltage is set by an external resistive divider
according to the following equation :
VOUT = VFB ⎛⎜ 1+ R1 ⎞⎟
⎝ R2 ⎠
where VFB is the feedback reference voltage 0.808V
(typical).
The resistive divider allows the FB pin to sense a fraction
of the output voltage as shown in Figure 1.
VOUT
R1
FB
RT8288A
R2
GND
the converter starts up. Soft-Start automatically begins
once the chip is enabled. During soft-start, the internal
soft-start capacitor becomes charged and generates a
linear ramping up voltage across the capacitor. This voltage
clamps the voltage at the internal reference, causing the
duty pulse width to increase slowly and in turn reduce the
output surge current. Finally, the internal 1V reference
takes over the loop control once the internal ramping-up
voltage becomes higher than 1V. The typical soft-start
time for this IC is set at 2ms.
Under Voltage Lockout Threshold
The IC includes an input Under Voltage Lockout Protection
(UVLO). If the input voltage exceeds the UVLO rising
threshold voltage (4.2V), the converter resets and prepares
the PWM for operation. If the input voltage falls below the
UVLO falling threshold voltage (3.8V) during normal
operation, the device stops switching. The UVLO rising
and falling threshold voltage includes a hysteresis to
prevent noise caused reset.
Figure 1. Output Voltage Setting
Chip Enable Operation
External Bootstrap Diode
Connect a 100nF low ESR ceramic capacitor between
the BOOT pin and SW pin as shown in Figure 2. 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
IC. Note that the external boot voltage must be lower than
5.5V.
5V
BOOT
RT8288A
100nF
SW
Figure 2. External Bootstrap Diode
Soft-Start
The IC contains an internal soft-start function to prevent
large inrush current and output voltage overshoot when
Copyright © 2012 Richtek Technology Corporation. All rights reserved.
DS8288A-03 June 2012
The EN pin is the chip enable input. Pulling the EN pin
low (<0.4V) will shut down the device. During shutdown
mode, the IC quiescent current drops to lower than 1μA.
Driving the EN pin high (>2V, <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, as can be seen from
the Figure 5.
An external MOSFET can be added to implement digital
control on the EN pin when front age system voltage below
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.
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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RT8288A
1
VIN
REN
100k
BOOT
VIN
CIN
RT8288A
SW
5 EN
Chip Enable
4
CBOOT
L
2, 3
VOUT
Q1
R1
7
RT
FB 6
VCC
CC
GND
COUT
8, 9 (Exposed Pad)
R2
Figure 3. Enable Control Circuit for Logic Control with Low Voltage
1
VIN
REN
100k
BOOT
VIN
CIN
RT8288A
5 EN
SW
4
CBOOT
L
2, 3
VOUT
REN2
R1
7
FB 6
RT
VCC
CC
GND
COUT
8, 9 (Exposed Pad)
R2
Figure 4. The Resistors can be Selected to Set IC Lockout Threshold
Under Output Voltage Protection-Hiccup Mode
For the IC, Hiccup Mode of 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 IC will shut down for a period of time and
then recover automatically. The Hiccup Mode of UVP can
reduce input current in short circuit conditions.
Inductor Selection
For a given input and output voltage, the inductor value
and operating frequency determine the ripple current. The
ripple current ΔIL increases with higher VIN and decreases
with higher inductance.
V
V
ΔIL = ⎡⎢ OUT ⎤⎥ × ⎡⎢1− OUT ⎤⎥
f
×
L
VIN ⎦
⎣
⎦ ⎣
Having a lower ripple current reduces not only the ESR
losses in the output capacitors but also the output voltage
ripple. Highest efficiency operation is achieved by reducing
ripple current at low frequency, but it requires a large
inductor to attain this goal.
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 a specified maximum, the
inductor value should be chosen according to the following
equation :
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⎡ VOUT ⎤ ⎡
VOUT ⎤
L =⎢
⎥ × ⎢1 − VIN(MAX) ⎥
f
I
×
Δ
L(MAX)
⎣
⎦ ⎣
⎦
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 and it is
highly recommended to keep inductor value as close as
possible to the recommended inductor values for each
VOUT as shown in Table 1.
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
8x8x4
Input and Output Capacitors 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 :
V
IRMS = IOUT(MAX) OUT
VIN
VIN
−1
VOUT
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DS8288A-03 June 2012
RT8288A
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 22μF low ESR ceramic
capacitors are recommended. For the recommended
capacitor, please refer to Table 3 for more detail.
Table 3. Suggested Capacitors for CIN and COUT
Location
Component Supplier
Part No.
Capacitance (μF)
Case Size
CIN
MURATA
GRM32ER71C226M
22
1210
CIN
TDK
C3225X5R1C226M
22
1210
COUT
MURATA
GRM31CR60J476M
47
1206
COUT
TDK
C3225X5R0J476M
47
1210
COUT
MURATA
GRM32ER71C226M
22
1210
COUT
TDK
C3225X5R1C226M
22
1210
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.
The output ripple, ΔVOUT, is determined by :
1
⎤
ΔVOUT ≤ ΔIL ⎡⎢ESR +
8fC
OUT ⎥⎦
⎣
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.
Copyright © 2012 Richtek Technology Corporation. All rights reserved.
DS8288A-03 June 2012
Thermal Shutdown
Thermal shutdown is implemented to prevent the chip from
operating at excessively high temperatures. When the
junction temperature is higher than 150°C, the chip will
shut down the switching operation. The chip will
automatically resume switching, once the junction
temperature cools down by approximately 30°C.
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 (RS*, CS*) between SW and GND and locating
them as close as possible to the SW pin, as shown in
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.
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RT8288A
1
VIN
REN*
CIN
4
BOOT
VIN
CBOOT
RT8288A
5 EN
L
2, 3
SW
CEN*
COUT
RS*
7
* : Optional
VOUT
CS*
VCC
CC
RT
FB 6
GND
R1
R2
8, 9 (Exposed Pad)
Figure 5. Reference Circuit with Snubber and Enable Timing Control
Thermal Considerations
Maximum Power Dissipation (W)1
1.4
For continuous operation, do not exceed absolute
maximum junction temperature. The maximum power
dissipation depends on the thermal resistance of the IC
package, PCB layout, rate of surrounding airflow, and
difference between junction and ambient temperature. The
maximum power dissipation can be calculated by the
following formula :
PD(MAX) = (TJ(MAX) − TA) / θJA
where TJ(MAX) is the maximum junction temperature, TA is
the ambient temperature, and θJA is the junction to ambient
Four-Layer PCB
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0
25
50
75
100
125
Ambient Temperature (°C)
thermal resistance.
Figure 6. Derating Curve of Maximum Power Dissipation
For recommended operating condition specifications, 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 a standard JEDEC 51-7 four-layer
thermal test board. The maximum power dissipation at TA
= 25°C can be calculated by the following formula :
PD(MAX) = (125°C − 25°C) / (75°C/W) = 1.333W for
Layout Considerations
Follow the PCB layout guidelines for optimal performance
of the IC.
`
Keep the traces of the main current paths as short and
wide as possible.
`
Put the input capacitor as close as possible to the device
pins (VIN and GND).
`
SW node is with high frequency voltage swing and
should be kept at small area. Keep analog components
away from the SW 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 IC.
SOP-8 (Exposed Pad) package
The maximum power dissipation depends on the operating
ambient temperature for fixed T J(MAX) and thermal
resistance, θJA. The derating curve in Figure 6 allows the
designer to see the effect of rising ambient temperature
on the maximum power dissipation.
Copyright © 2012 Richtek Technology Corporation. All rights reserved.
www.richtek.com
12
is a registered trademark of Richtek Technology Corporation.
DS8288A-03 June 2012
RT8288A
`
Connect all analog grounds to a common node and then
connect the common node to the power ground behind
the output capacitors.
`
An example of PCB layout guide is shown in Figure 7
for reference.
Place the input and
output capacitors
as close to the IC
as possible.
GND
CIN
SW should be connected
to inductor by wide and
short trace and keep
sensitive components
away from this trace.
L
VIN
8
SW
2
SW
3
BOOT
4
GND
GND
7
VCC
6
FB
5
EN
9
RT
R1
CBOOT
VOUT
R2
Place the feedback
as close to the IC as
possible.
VOUT
COUT
GND
Figure 7. PCB Layout Guide
Copyright © 2012 Richtek Technology Corporation. All rights reserved.
DS8288A-03 June 2012
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
13
RT8288A
Outline Dimension
H
A
M
EXPOSED THERMAL PAD
(Bottom of Package)
Y
J
X
B
F
C
I
D
Dimensions In Millimeters
Dimensions In Inches
Symbol
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
X
2.000
2.300
0.079
0.091
Y
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
Option 1
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
DS8288A-03 June 2012