Richtek GRM31CR60J476M 4a, 21v 500khz synchronous step-down converter Datasheet

®
RT8287A
4A, 21V 500kHz Synchronous Step-Down Converter
General Description
Features
The RT8287A 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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Adjustable 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
Small 14-Lead WDFN Package
RoHS Compliant and Halogen Free
Fault condition protection includes cycle-by-cycle current
limiting and thermal shutdown. An adjustable soft-start
reduces the stress on the input source at startup.
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The RT8287A requires a minimal number of readily
available external components, providing a compact
solution.
Ordering Information
RT8287A
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Applications
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Package Type
QW : WDFN-14L 4x3 (W-Type)
Lead Plating System
Z : ECO (Ecological Element with
Halogen Free and Pb free)
Note :
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Distributive Power Systems
Battery Charger
DSL Modems
Pre-Regulator for Linear Regulators
Pin Configurations
Richtek products are :
`
RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020.
`
Suitable for use in SnPb or Pb-free soldering processes.
Marking Information
01 : Product Code
01 YM
DNN
(TOP VIEW)
VIN
SW
SW
SW
SW
BOOT
EN
14
13
1
2
3
4
5
6
7
GND
15
12
11
10
9
8
AGND
GND
GND
VCC
SS
PGOOD
FB
WDFN-14L 4x3
YMDNN : Date Code
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DS8287A-03 June 2012
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1
RT8287A
Typical Application Circuit
1
VIN
BOOT
VIN
CIN
22µF
RT8287A
SW
6
CBOOT
0.1µF
2, 3, 4, 5
L
VOUT
1.2V/4A
9 PGOOD
PGOOD
R3
100k
11
VCC
CC
0.1µF
SS 10
R1
RT
FB 8
COUT
CSS
47nF
R2
7 EN
ON/OFF
AGND GND
14
12, 13, 15 (Exposed Pad)
Table 1. Recommended Components Selection
VOUT (V)
5
3.3
2.5
1.8
1.5
1.2
1.05
R1 (kΩ)
75
75
75
5
5
5
5
R2 (kΩ)
14.46
24.32
35.82
4.07
5.84
10.31
16.69
RT (kΩ)
0
0
0
30
39
47
47
L (μH)
4.7
3.6
3.6
2
2
2
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
Pin Function
1
VIN
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.
2, 3, 4, 5
SW
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.
6
BOOT
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.
7
EN
8
FB
9
PGOOD
10
SS
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.
Power Good Output. The output of this pin is open-drain. Power good threshold is
90% low to high and 70% high to low of regulation value.
Soft-Start Control Input. SS controls the soft-start period. Connect a capacitor from
SS to GND to set the soft-start period.
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DS8287A-03 June 2012
RT8287A
Pin No.
Pin Name
11
Pin Function
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.
VCC
12, 13
GND
15 (Exposed Pad)
14
AGND
Analog Ground. Connect this pin to the system ground in PCB layout.
Function Block Diagram
VIN
1.2V
EN
Shutdown
Comparator
+
Regulator
-
Current Sense
Amplifier
-
Ramp
Generator
+
VA
VA
5k
VC
-
1µA
3V
+
Oscillator
500kHz
BOOT
S
Lockout
Comparator
Q
+
1.7V
Driver
R
PWM
Comparator
VCC
PGOOD
+
SW
Reference
Error
+ Amplifier
+
-
-
FB
VC
30pF
GND
400k
10µA
SS
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DS8287A-03 June 2012
1pF
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RT8287A
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
WDFN-14L 4x3 -----------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2)
WDFN-14L 4x3, θJA -----------------------------------------------------------------------------------------WDFN-14L 4x3, θJC -----------------------------------------------------------------------------------------Junction Temperature ---------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -----------------------------------------------------------------Storage Temperature Range ------------------------------------------------------------------------------ESD Susceptibility (Note 3)
HBM (Human Body Model) ---------------------------------------------------------------------------------
Recommended Operating Conditions
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−0.3V to 26V
−0.3V to (VIN + 0.3V)
(SW − 0.3V) to (SW + 6V)
−0.3V to 6V
1.667W
60°C/W
7°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
R DS(ON)1
--
120
--
mΩ
Lower Switch On Resistance
R DS(ON)2
--
40
--
mΩ
Switch Leakage
ILEAK
VEN = 0V, VSW = 0V or 12V
--
0
10
μA
Current Limit
ILIMIT
VBOOT − VSW = 4.8V
6.2
7
--
A
Oscillator Frequency
fSW
VFB = 0.75V
425
500
575
kHz
VFB = 0V
--
150
--
kHz
VFB = 0.8V
--
90
--
%
--
100
--
ns
0.82
V
nA
Short Circuit Frequency
Maximum Duty Cycle
D MAX
Minimum On Time
tON
Feedback Voltage
VFB
Feedback Current
IFB
--
10
50
Logic-High
VIH
2
--
5.5
Logic-Low
VIL
--
--
0.4
VEN = 2V
--
1
--
VEN = 0V
--
0
--
EN Threshold
Voltage
Enable Current
4.5V ≤ VIN ≤ 21V
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0.796 0.808
V
μA
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RT8287A
Parameter
Symbol
Min
Typ
Max
Unit
Power Good Rising Threshold
--
90
--
%
Power Good Falling Threshold
--
70
--
%
Power Good Delay
--
20
--
μs
--
--
0.4
V
--
10
--
nA
3.8
4
4.2
V
--
400
--
mV
--
5
--
V
ICC = 5mA
--
5
--
%
CSS = 47nF
--
4.7
--
ms
Power Good Sink Current
Capability
Test Conditions
Sink 4mA
Power Good Leakage Current
Under Voltage Lockout
Threshold
Under Voltage Lockout
Threshold Hysteresis
VUVLO
VIN Rising
ΔVUVLO
VCC Regulator
VCC Load Regulation
Soft-Start Period
tSS
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.
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.
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5
RT8287A
Typical Operating Characteristics
Efficiency vs. Output Current
Reference Voltage vs. Input Voltage
100
0.830
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
0.790
0
0.5
1
1.5
2
2.5
3
3.5
4
4
6
8
10
Output Current (A)
14
16
18
20
22
Input Voltage (V)
Reference Voltage vs. Temperature
Output Voltage vs. Output Current
0.84
1.226
0.83
1.224
0.82
1.222
Output Voltage (V)
Reference Voltage (V)
12
0.81
0.80
0.79
0.78
1.220
1.218
1.216
1.214
0.77
1.212
0.76
1.210
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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DS8287A-03 June 2012
RT8287A
Current Limit vs. Input Voltage
Current Limit vs. Temperature
12
11
10
Current Limit (A)
Current Limit (A)
10
8
6
4
9
8
7
6
5
2
4
VIN = 12V, VOUT = 1.22V
0
3
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)
VLX
(10V/Div)
VLX
(10V/Div)
IL
(2A/Div)
IL
(2A/Div)
VIN = 12V, IOUT = 1A
Time (1μs/Div)
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125
VIN = 12V, IOUT = 4A
Time (1μs/Div)
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RT8287A
Power Off from VIN
Power On from VIN
VIN
(10V/Div)
VIN
(10V/Div)
VOUT
(1V/Div)
VOUT
(1V/Div)
VPGOOD
(5V/Div)
IL
(5A/Div)
VPGOOD
(5V/Div)
IL
(5A/Div)
VIN = 12V, VOUT = 1.22V, IOUT = 4A
Time (5ms/Div)
Time (50ms/Div)
Power On from EN
Power Off from EN
VEN
(5V/Div)
VEN
(5V/Div)
VOUT
(1V/Div)
VOUT
(1V/Div)
VPGOOD
(5V/Div)
IL
(5A/Div)
VPGOOD
(5V/Div)
IL
(5A/Div)
VIN = 12V, VOUT = 1.22V, IOUT = 4A
Time (2.5ms/Div)
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VIN = 12V, VOUT = 1.22V, IOUT = 4A
VIN = 12V, VOUT = 1.22V, IOUT = 4A
Time (50μs/Div)
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RT8287A
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.
Soft-Start
The output voltage is set by an external resistive divider
according to the following equation :
The IC contains an external soft-start clamp that gradually
raises the output voltage. The soft-start timing is
programmed by the external capacitor between SS pin
and GND. The chip provides an internal 10μA charge current
for the external capacitor. If 47nF capacitor is used to set
the soft-start, the period will be 4.7ms (typ.).
VOUT = VFB ⎛⎜ 1+ R1 ⎞⎟
⎝ R2 ⎠
Under Voltage Lockout Threshold
Output Voltage Setting
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
RT8287A
R2
GND
Figure 1. Output Voltage Setting
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
RT8287A
100nF
SW
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.
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 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.
Figure 2. External Bootstrap Diode
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RT8287A
1
VIN
BOOT
VIN
CIN
REN
100k
Chip Enable
CBOOT
RT8287A
SW
7 EN
6
2, 3, 4, 5
L
VOUT
Q1
COUT
R1
9
PGOOD
R3
100k
11
CC
RT
FB 8
PGOOD
SS
VCC
10
CSS
47nF
R2
AGND GND
14
12, 13, 15 (Exposed Pad)
Figure 3. Enable Control Circuit for Logic Control with Low Voltage
1
VIN
REN
100k
BOOT
VIN
CIN
CBOOT
RT8287A
7 EN
6
SW
2, 3, 4, 5
L
VOUT
REN2
R1
9
PGOOD
R3
100k
CC
11
PGOOD
VCC
FB 8
SS
COUT
RT
10
CSS
47nF
R2
AGND GND
14
12, 13, 15 (Exposed Pad)
Figure 4. The Resistors can be Selected to Set IC Lockout Threshold
Power Good Output
The power good output is an open-drain output and requires
a pull up resistor. When the output voltage is 70% below
its set voltage, PGOOD will be pulled low. It is held low
until the output voltage returns to within the allowed
tolerances once more. During soft-start, PGOOD is actively
held low and only allowed to transition high after soft-start
is over and the output voltage has reached 90% of its set
voltage.
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
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ripple current ΔIL increases with higher VIN and decreases
with higher inductance.
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. 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 :
⎡ 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
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DS8287A-03 June 2012
RT8287A
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.
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 :
Table 2. Suggested Inductors for Typical
Application Circuit
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.
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
V
IRMS = IOUT(MAX) OUT
VIN
VIN
−1
VOUT
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.
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.
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 :
ΔVOUT
1
⎤
≤ ΔIL ⎡⎢ESR +
8fCOUT ⎥⎦
⎣
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
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DS8287A-03 June 2012
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.
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 whole chip
is shutdown. The chip is automatically re-enable when
the junction temperature cools down by approximately
30 degrees.
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
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RT8287A
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
1
VIN
REN*
BOOT
VIN
CIN
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.
CBOOT
RT8287A
7 EN
6
SW
L
2, 3, 4, 5
VOUT
CS*
CEN*
COUT
RS*
9
PGOOD
R3
100k
CC
11
R1
RT
PGOOD
FB 8
VCC
SS 10
CSS
47nF
R2
AGND GND
14
12, 13, 15 (Exposed Pad)
* : Optional
Figure 5. Reference Circuit with Snubber and Enable Timing Control
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
thermal resistance.
For recommended operating condition specifications, the
maximum junction temperature is 125°C. The junction to
ambient thermal resistance, θJA, is layout dependent. For
WDFN-14L 4x3 package, the thermal resistance, θJA, is
60°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) / (60°C/W) = 1.667W for
WDFN-14L 4x3 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.
Maximum Power Dissipation (W)1
Thermal Considerations
1.80
Four-Layer PCB
1.65
1.50
1.35
1.20
1.05
0.90
0.75
0.60
0.45
0.30
0.15
0.00
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 6. Derating Curve of Maximum Power Dissipation
Copyright © 2012 Richtek Technology Corporation. All rights reserved.
www.richtek.com
12
is a registered trademark of Richtek Technology Corporation.
DS8287A-03 June 2012
RT8287A
Layout Considerations
`
Connect feedback network behind the output capacitors.
Keep the loop area small. Place the feedback
components near the IC.
`
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.
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.
Place the input and output
capacitors as close to the
IC as possible.
GND
CIN
SW should be
VIN
connected to
SW
inductor by wide
SW
and short trace and
SW
CBOOT SW
keep sensitive
components away
BOOT
EN
from this trace.
L
VOUT
1
14
2
13
3
4
5
6
7
12
GND
15
11
10
9
8
AGND
GND CSS
GND
VCC
SS
PGOOD
FB
RT
R2
R1
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.
DS8287A-03 June 2012
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
13
RT8287A
Outline Dimension
2
1
2
1
DETAIL A
Pin #1 ID and Tie Bar Mark Options
Note : The configuration of the Pin #1 identifier is optional,
but must be located within the zone indicated.
Dimensions In Millimeters
Dimensions In Inches
Symbol
Min
Max
Min
Max
A
0.700
0.800
0.028
0.031
A1
0.000
0.050
0.000
0.002
A3
0.175
0.250
0.007
0.010
b
0.180
0.300
0.007
0.012
D
3.900
4.100
0.154
0.161
D2
3.250
3.350
0.128
0.132
E
2.900
3.100
0.114
0.122
E2
1.650
1.750
0.065
0.069
e
L
0.500
0.350
0.020
0.450
0.014
0.018
W-Type 14L DFN 4x3 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
DS8287A-03 June 2012
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