RT2872 [RICHTEK]
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| 型号： | RT2872 |
| 厂家： | 
RICHTEK TECHNOLOGY CORPORATION |
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®
RT2872
3A, 36V, Synchronous Step-Down Converter
General Description
Features
z 4.5V to 36V Input Voltage Range
The RT2872 is a high efficiency, current-mode
synchronous step-downDC/DC converter that can deliver
up to 3A output current over a wide input voltage range
from 4.5V to 36V. The device integrates 105mΩ high-side
and 80mΩ low-side MOSFETs to achieve high conversion
efficiency. The current-mode control architecture supports
fast transient response and simple external compensation.
z 3A Output Current
z Internal N-MOSFETs
z Current Mode Control
z Frequency Operation : 300kHz to 1MHz
z Adjustable Output Voltage from 0.8V to 30V
z High Efficiency Up to 95%
z Stable with Low ESR Ceramic Output Capacitors
z Cycle-by-Cycle Current Limit
A cycle-by-cycle current limit function provides protection
against shorted output and an internal soft-start eliminates
input current surge during start-up. The RT2872 provides
complete protection functions such as input under-voltage
lockout, output under-voltage protection, over-current
protection and thermal shutdown.
z Input Under-Voltage Lockout
z Output Under-Voltage Protection
z Thermal Shutdown
z AEC-Q100 Grade 3 Certification
z RoHS Compliant and Halogen Free
The RT2872 is available in the thermal enhanced SOP-8
(Exposed Pad) package.
Applications
z Point of Load Regulator in Distributed Power Systems
Ordering Information
z Digital Set Top Boxes
RT2872
z Broadband Communications
Package Type
SP: SOP-8 (Exposed Pad-Option 2)
z Vehicle Electronics
z AutomotiveAudio,Navigation, and Information Systems
z Enterprise Datacom Platforms Point of Load (POL)
z IndustrialGradeGeneral Purpose Point of Load
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
Richtek products are :
Marking Information
` 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.
RT2872GSP : Product Number
RT2872
YMDNN : Date Code
GSPYMDNN
Simplified Application Circuit
BOOT
RT2872
VIN
V
IN
C
C
B
IN
L
SW
V
OUT
R1
R2
RT
C
OUT
FB
R
T
C
C
R
C
GND
COMP
Copyright 2018 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
DS2872-06 January 2018
www.richtek.com
1
RT2872
Pin Configurations
(TOP VIEW)
8
SW
BOOT
EN
VIN
RT
2
3
4
7
6
5
GND
COMP
FB
9
GND
SOP-8 (Exposed Pad)
Functional Pin Description
Pin No.
Pin Name
Pin Function
1
SW
Switch Node. Connect to external L-C filter.
Bootstrap Supply for the High-Side MOSFET. Connect a 100nF or greater
capacitor between the BOOT and SW pins.
2
3
BOOT
EN
Enable Control Input. A logic-high enables the converter; a logic-low forces the
device into shutdown mode.
4,
Ground. The exposed pad must be soldered to a large PCB and connected to
GND for maximum thermal dissipation.
GND
FB
9 (Exposed Pad)
Feedback Voltage Input. This pin is used to set the output voltage of the
converter to regulate to the desired value via an resistive divider.
5
6
Compensation Node. COMP is used to compensate the regulation control loop.
Connect a R-C network from the COMP to GND. In some cases, an additional
capacitor from COMP to GND is required.
COMP
Switching Frequency Setting. Connect an external resistor to set the switching
frequency from 300kHz to 1MHz.
7
8
RT
Power Input. The input voltage range is from 4.5V to 36V. Must bypass with a
suitable large ceramic capacitor at this pin.
VIN
Copyright 2018 Richtek Technology Corporation. All rights reserved.
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2
DS2872-06 January 2018
RT2872
Function Block Diagram
VIN
V
CC
Internal
Regulator
Oscillator
Current Sense
Amplifier
R
SENSE
VA
Shutdown
Comparator
V
V
CC
A
Slope Comp
UV
+
-
Foldback
Control
1.2V
+
-
0.4V
+
-
BOOT
Lockout
Comparator
S
Q
Q
UV
5kΩ
Comparator
SW
-
+
EN
+
-
R
1.7V
Current
Comparator
GND
3.6V
0.8V
+
+
-
EA
SS
FB
COMP
RT
Operation
side gate driver.
The RT2872 is a constant frequency, current-mode
synchronous step-down converter. In normal operation,
the high-sideN-MOSFET is turned on when the S-R latch
is set by the oscillator and is turned off when the current
comparator resets the S-R latch. While the high-side
N-MOSFET is turned off, the low-sideN-MOSFET is turned
on to conduct the inductor current until next cycle begins.
Enable
The converter is turned on when the ENpin is higher than
2V. When the ENpin is lower than 0.4V, the converter will
enter shutdown mode and reduce the supply current to
0.5µA.
Soft-Start (SS)
Error Amplifier
An internal current source charges an internal capacitor
to build a soft-start ramp voltage. The FB voltage will track
the internal ramp voltage during soft-start interval. The
typical soft-start time is 2ms.
The error amplifier adjusts its output voltage by comparing
the feedback signal (VFB) with the internal 0.8V reference.
When the load current increases, it causes a drop in the
feedback voltage relative to the reference, and then the
error amplifier's output voltage rises to allow higher inductor
current to match the load current.
UV Comparator
If the feedback voltage is lower than 0.4V, the UV
Comparator will go high to turn off the high-side MOSFET.
The output under voltage protection is designed to operate
in hiccup mode. When the UV condition is removed, the
converter will resume switching.
Oscillator
The oscillator frequency can be set by using an external
resister RT. Oscillator frequency range is from 300kHz to
1MHz.
Thermal Shutdown
1000
1000
66876
=
− 29.405
The over-temperature protection function will shut down
the switching operation when the junction temperature
exceeds 150°C. Once the junction temperature cools
down by approximately 20°C, the converter will
automatically resume switching.
RT kΩ
(
)
−0.22
fS kHz
(
)
Internal Regulator
The regulator provides low voltage power to supply the
internal control circuits and the bootstrap power for high-
Copyright 2018 Richtek Technology Corporation. All rights reserved.
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is a registered trademark of Richtek Technology Corporation.
DS2872-06 January 2018
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3
RT2872
Absolute Maximum Ratings (Note 1)
z Supply Voltage, VIN ------------------------------------------------------------------------------------------------ −0.3V to 40V
z Switch Voltage, SW ------------------------------------------------------------------------------------------------ −0.3V to (VIN + 0.3V)
z BOOT Pin ------------------------------------------------------------------------------------------------------------- −0.3V to 46.3V
z EN Pin (with REN (150kΩ to 600kΩ) to VIN) ----------------------------------------------------------------- −0.3V to 40V
z SW Voltage (t < 10ns) --------------------------------------------------------------------------------------------- −5V to 46.3V
z EN Pin------------------------------------------------------------------------------------------------------------------ −0.3V to 3.6V
z Other Pins------------------------------------------------------------------------------------------------------------- −0.3V to 6V
z Power Dissipation, PD @ TA = 25°C
SOP-8 (Exposed Pad) --------------------------------------------------------------------------------------------- 2.041W
z Package Thermal Resistance (Note 2)
SOP-8 (Exposed Pad), θJA ---------------------------------------------------------------------------------------- 49°C/W
SOP-8 (Exposed Pad), θJC --------------------------------------------------------------------------------------- 8°C/W
z Lead Temperature (Soldering, 10 sec.)------------------------------------------------------------------------- 260°C
z Junction Temperature ----------------------------------------------------------------------------------------------- 150°C
z Storage Temperature Range -------------------------------------------------------------------------------------- −65°C to 150°C
z ESD Susceptibility (Note 3)
HBM (Human Body Model)---------------------------------------------------------------------------------------- 2kV
Recommended Operating Conditions (Note 4)
z Supply Input Voltage, VIN ----------------------------------------------------------------------------------------- 4.5V to 36V
z Junction Temperature Range-------------------------------------------------------------------------------------- −40°C to 125°C
z Ambient Temperature Range-------------------------------------------------------------------------------------- −40°C to 85°C
Electrical Characteristics
(VIN = 12V, CIN = 20µF, TA = −40°C to 85°C, unless otherwise specified)
Parameter
Shutdown Supply Current
Quiescent Current
Symbol
Test Conditions
= 0V
Min
--
Typ
--
Max
10
Unit
µA
V
V
EN
EN
I
= 3V, V = 0.9V
--
1
1.3
mA
V
Q
FB
Feedback Reference Voltage
V
4.5V ≤ V ≤ 36V
0.784
--
0.8
105
80
0.816
190
145
REF
IN
High-Side
Switch
R
DS(ON)1
mΩ
On-Resistance
Low-Side
R
--
DS(ON)2
High-Side Switch Current Limit
Range
U
4.25
5
5.75
A
A
OC
Low-Side Switch Current Limit
From Drain to Source
--
1.7
300
500
--
R = 191kΩ
T
264
440
880
336
560
Oscillation Frequency
f
f
kHz
kHz
R = 113kΩ
T
OSC1
R = 51kΩ
T
1000 1120
Short-Circuit Oscillation
Frequency
V
V
= 0V, R = 113kΩ
--
50
--
OSC2
FB
FB
T
Maximum Duty Cycle
Minimum On-Time
D
MAX
= 0.7V
--
--
95
--
%
t
100
120
ns
ON
Copyright 2018 Richtek Technology Corporation. All rights reserved.
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is a registered trademark of Richtek Technology Corporation.
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4
DS2872-06 January 2018
RT2872
Parameter
Logic-High
Logic-Low
Symbol
VIH
Test Conditions
Min Typ Max Unit
2
--
--
3.3
0.4
EN Input Voltage
V
VIL
--
Input Under-Voltage Lockout
Threshold
VUVLO
VIN Rising
3.7
--
4.2
4.5
--
V
Input Under-Voltage Lockout
Hysteresis
∆VUVLO
250
mV
Thermal Shutdown Threshold
Thermal Shutdown Hysteresis
TSD
--
--
150
25
--
--
°C
°C
∆TSD
COMP to Current Sense
Trans-conductance
GCS
∆ICOMP = ±10µA
--
--
4.1
--
--
A/V
Error Amplifier Trans-conductance GEA
950
µA/V
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. The PCB copper area with exposed pad is 70mm2.
Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
Copyright 2018 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
DS2872-06 January 2018
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5
RT2872
Typical Application Circuit
RT2872
BOOT
8
2
1
V
IN
VIN
4.5V to 36V
C
100nF
B
C
IN
L
10µF x 2
SW
V
OUT
R
EN
3
7
R1
R2
Enable
EN
RT
5
6
C
OUT
FB
R
T
C
C
113k
R
C
4, 9 (Exposed Pad)
COMP
GND
Table 1. Suggested Component Values
VOUT (V)
R1 (kΩ)
47
R2 (kΩ)
3.35
3
RC (kΩ)
47
L (µH)
10
CC (nF)
2.7
COUT (µF)
12
8
22 x 2
22 x 2
22 x 2
22 x 2
22 x 2
22 x 2
27
36
8.2
2.7
5
62
11.8
24
24
6.8
2.7
3.3
2.5
1.2
75
16
4.7
2.7
25.5
30
12
12
3.6
2.7
6.8
60
2.2
2.7
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DS2872-06 January 2018
RT2872
Typical Operating Characteristics
Efficiency vs. Output Current
Reference Voltage vs. Input Voltage
100
0.810
0.808
0.805
0.803
0.800
0.798
0.795
0.793
0.790
90
80
VIN = 5V
VIN = 12V
VIN = 24V
VIN = 30V
VIN = 36V
70
60
50
40
30
20
10
0
VOUT = 3.3V, RT = 113k
2.5
VIN = 4.5V to 36V, IOUT = 0A, RT = 113k
0
0.5
1
1.5
2
3
4
8
12
16
20
24
28
32
36
Input Voltage (V)
Output Current (A)
Reference vs. Temperature
Output Voltage vs. Output Current
0.810
3.300
3.295
3.290
3.285
3.280
3.275
3.270
3.265
3.260
3.255
3.250
0.805
0.800
0.795
0.790
VIN = 5V
VIN = 12V
VIN = 24V
VIN = 30V
VIN = 36V
VIN = 4.5V
VIN = 12V
VIN = 24V
VIN = 36V
VOUT = 3.3V, RT = 113k
VOUT = 3.3V, IOUT = 0A, RT = 113k
-50
-25
0
25
50
75
100
125
0
0.5
1
1.5
2
2.5
3
Temperature (°C)
Output Current (A)
Switching Frequency vs. Input Voltage
Switching Frequency vs. Temperature
520
515
510
505
500
495
490
485
480
600
580
560
540
520
500
480
460
440
420
400
VIN = 4.5V
VIN = 12V
VIN = 24V
VIN = 36V
VOUT = 3.3V, IOUT = 0A, RT = 113k
VOUT = 3.3V, IOUT = 0A, RT = 113k
4
8
12
16
20
24
28
32
36
-50
-25
0
25
50
75
100
125
Input Voltage (V)
Temperature (°C)
Copyright 2018 Richtek Technology Corporation. All rights reserved.
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7
RT2872
Current Limit vs. Temperature
Frequency vs. RT
8
7
6
5
4
3
1200
1100
1000
900
800
700
600
500
400
300
200
VIN = 36V
VIN = 24V
VIN = 12V
VIN = 4.5V
VIN = 12V, IOUT = 0A
50 65 80 95 110 125 140 155 170 185 200
2
-50
-25
0
25
50
75
100
125
R (k
)
Ω
Temperature (°C)
T
Load Transient Response
Load Transient Response
VOUT
VOUT
(200mV/Div)
(200mV/Div)
IOUT
(2A/Div)
IOUT
(2A/Div)
VIN = 12V, VOUT = 3.3V,
IOUT = 3A to 1.5A, RT = 113k
VIN = 12V, VOUT = 3.3V,
IOUT = 0A to 3A, RT = 113k
Time (100µs/Div)
Time (100µs/Div)
Switching
Switching
VOUT
VOUT
(5mV/Div)
(5mV/Div)
VSW
VSW
(5V/Div)
(5V/Div)
IL
IL
(1A/Div)
(2A/Div)
VIN = 12V, VOUT = 3.3V, IOUT = 1.5A, RT = 113k
VIN = 12V, VOUT = 3.3V, IOUT = 3A, RT = 113k
Time (1µs/Div)
Time (1µs/Div)
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DS2872-06 January 2018
RT2872
Power On from EN
Power Off from EN
VEN
VEN
(2V/Div)
(2V/Div)
VOUT
VOUT
(2V/Div)
(2V/Div)
IOUT
(2A/Div)
IOUT
(2A/Div)
VIN = 12V, VOUT = 3.3V, IOUT = 3A, RT = 113k
Time (2.5ms/Div)
VIN = 12V, VOUT = 3.3V, IOUT = 3A, RT = 113k
Time (2.5ms/Div)
Power On from VIN
Power Off from VIN
VIN
VIN
(5V/Div)
(5V/Div)
VOUT
VOUT
(2V/Div)
(2V/Div)
IL
IL
(2A/Div)
(2A/Div)
VIN = 12V, VOUT = 3.3V, IOUT = 3A, RT = 113k
Time (5ms/Div)
VIN = 12V, VOUT = 3.3V, IOUT = 3A, RT = 113k
Time (5ms/Div)
Copyright 2018 Richtek Technology Corporation. All rights reserved.
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RT2872
Application Information
Output Voltage Setting
Chip Enable Operation
The resistive divider allows the FB pin to sense the output
voltage as shown in Figure 1.
The EN pin is the chip enable input. Pulling the EN pin
low (<0.4V) will shutdown the device. During shutdown
mode, the RT2872 quiescent current drops to lower than
3µA. Driving the EN pin high (>2.5V, <3.3V) will turn on
the device again. For external timing control, the EN pin
can also be externally pulled high by adding a REN resistor
and CEN capacitor from the VIN pin (see Figure 3).
V
OUT
R1
FB
RT2872
GND
R2
REN must be chose between 150kΩ to 600kΩ, which is
to avoid huge leak current into chip.
Figure 1. Output Voltage Setting
EN
R
EN
V
IN
EN
The output voltage is set by an external resistive voltage
divider according to the following equation :
RT2872
GND
C
EN
R1
R2
VOUT = VREF 1+
Figure 3. Enable Timing Control
where VREF is the reference voltage (0.8V typ.).
An external MOSFET can be added to implement digital
control on the EN pin when no system voltage above 2.5V
is available, as shown in Figure 4. In this case, a 300kΩ
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.
External Bootstrap Diode
Connect a 0.1µF low ESR ceramic capacitor between the
BOOT and SW pins. This capacitor provides the gate driver
voltage for the high-side MOSFET.
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
RT2872.Note that the external boot voltage must be lower
than 5.5V
R
EN
300k
V
IN
EN
RT2872
GND
Q1
EN
Figure 4. Digital Enable Control Circuit
5V
Under-Voltage Protection
Hiccup Mode
BOOT
The RT2872 provides Hiccup Mode Under-Voltage
Protection (UVP). When the VFB voltage drops below 0.4V,
the UVP function will be triggered to shut down switching
operation. If the UVP condition remains for a period, the
RT2872 will retry automatically. When the UVP condition
is removed, the converter will resume operation. The UVP
is disabled during soft-start period.
100nF
RT2872
SW
Figure 2. External Bootstrap Diode
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DS2872-06 January 2018
RT2872
Hiccup Mode
The inductor's current rating (caused a 40°C temperature
rising from 25°C ambient) should be greater than the
maximum load current and its saturation current should
be greater than the short circuit peak current limit. Please
see Table 2 for the inductor selection reference.
VOUT
(2V/Div)
Table 2. Suggested Inductors for Typical
Application Circuit
ILX
(2A/Div)
Component
Supplier
Dimensions
(mm)
Series
TDK
TDK
VLF10045
SLF12565
10 x 9.7 x 4.5
IOUT = Short
12.5 x 12.5 x 6.5
Time (50ms/Div)
TAIYO
YUDEN
NR8040
8 x 8 x 4
Figure 5. Hiccup Mode Under-Voltage Protection
Over-Temperature Protection
CIN and COUT Selection
The RT2872 features an Over-Temperature Protection
(OTP) circuitry to prevent overheat due to excessive power
dissipation. The OTP will shut down switching operation
when junction temperature exceeds 150°C. Once the
junction temperature cools down by approximately 20°C,
the converter will resume operation. To maintain continuous
operation, the maximum junction temperature should be
lower than 125°C.
The input capacitance, CIN, is needed to filter the
trapezoidal current at the Source of the high-side MOSFET.
To prevent large ripple current, a low ESR input capacitor
sized for the maximum RMS current should be used. The
approximate RMS current equation is given :
V
V
V
IN
V
OUT
OUT
I
= I
−1
RMS
OUT(MAX)
IN
This formula has a maximum at VIN = 2VOUT, where
IRMS = IOUT / 2. This simple worst case condition is
commonly used for design because even significant
deviations do not offer much relief.
Inductor Selection
The inductor value and operating frequency determine the
ripple current according to a specific input and output
voltage. The ripple current ∆IL increases with higher VIN
and decreases with higher inductance.
Choose a capacitor rated at a higher temperature than
required. Several capacitors may also be paralleled to
meet size or height requirements in the design.
V
f ×L
VOUT
V
IN
OUT
∆IL =
× 1−
For the input capacitor, two 10µF low ESR ceramic
capacitors are suggested. For the suggested capacitor,
please refer to Table 3 for more details.
Having a lower ripple current reduces not only the ESR
losses in the output capacitors but also the output voltage
ripple. High frequency with small ripple current can achieve
the highest efficiency operation. However, it requires a
large inductor to achieve this goal.
The selection of COUT is determined by the required ESR
to minimize voltage ripple.
Moreover, the amount of bulk capacitance is also a key
for COUT selection to ensure that the control loop is stable.
Loop stability can be checked by viewing the load transient
response as described in a later section.
For the ripple current selection, the value of ∆IL= 0.24(IMAX
)
will be a reasonable starting point. The largest ripple
current occurs at the highest VIN. To guarantee that the
ripple current stays below the specified maximum, the
inductor value should be chosen according to the following
equation :
The output ripple, ∆VOUT, is determined by :
1
∆VOUT ≤ ∆IL ESR +
8fCOUT
V
f ×∆I
V
OUT
V
IN(MAX)
OUT
L =
× 1−
L(MAX)
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RT2872
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 :
The output ripple will be the 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. 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.
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.
Switching Frequency Setting
As shown in Figure 6, the amount of copper area to which
the SOP-8 (Exposed Pad) is mounted affects thermal
performance. When mounted to the standard
SOP-8 (Exposed Pad) pad (Figure 6.a), θJA is 75°C/W.
Adding copper area of pad under the SOP-8 (Exposed
Pad) (Figure 6.b) reduces the θJA to 64°C/W. Even further,
increasing the copper area of pad to 70mm2 (Figure 6.e)
reduces the θJA to 49°C/W.
The switching frequency can be set by using extra resistor
RT. Switching frequency range is from 300kHz to 1MHz.
Through extra resistor RT connect to RT pin to setting the
switching frequency fS, below offer approximate formula
equation :
1000
1000
66876
=
− 29.405
RT kΩ
(
)
−0.22
fS kHz
(
)
The maximum power dissipation depends on operating
ambient temperature for fixed TJ(MAX) and thermal
resistance θJA. The Figure 7 of derating curves allows the
designer to see the effect of rising ambient temperature
on the maximum power dissipation allowed.
2.2
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 :
Four-Layer PCB
2.0
1.8
Copper Area
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
2
70mm
2
50mm
30mm
2
PD(MAX) = (TJ(MAX) − TA ) / θJA
2
10mm
Min.Layout
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
RT2872, the maximum junction temperature is 125°C. The
junction to ambient thermal resistance θJA is layout
dependent. For SOP-8 (Exposed Pad) package, the
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 7. Derating Curve of Maximum PowerDissipation
Copyright 2018 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
12
DS2872-06 January 2018
RT2872
Layout Considerations
For best performance of the RT2872, the following layout
guidelines must be strictly followed.
` Input capacitor must be placed as close to the IC as
possible.
(a) Copper Area = (2.3 x 2.3) mm2,θJA = 75°C/W
` SW should be connected to inductor by wide and short
trace. Keep sensitive components away from this trace.
` The RT resistor, compensator and feedback components
must be connected as close to the device as possible.
(b) Copper Area = 10mm2,θJA = 64°C/W
(c) Copper Area = 30mm2 , θJA = 54°C/W
(d) Copper Area = 50mm2 ,θJA = 51°C/W
(e) Copper Area = 70mm2 ,θJA = 49°C/W
Figure 6. Thermal Resistance vs. CopperArea Layout
Design
Copyright 2018 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
DS2872-06 January 2018
www.richtek.com
13
RT2872
Input capacitor must be placed
as close to the IC as possible.
V
OUT
V
IN
C
OUT
C
IN
The R resistor must be connected
T
SW should be connected to
as close to the device as possible.
Keep sensitive components away.
inductor by wide and short trace.
Keep sensitive components
C *
S
R *
S
L
away from this trace and C
.
BOOT
R
T
8
7
6
5
SW
BOOT
EN
VIN
RT
C
V
BOOT
2
3
4
R
C
GND
C
C
C
COMP
FB
IN
9
R
EN
GND
P
R1
V
OUT
R2
The R component
EN
must be connected.
GND
The Compensator and feedback
components must be connected as
close to the device as possible.
* : Option
Figure 8. PCB Layout Guide
Table 3. Suggested Capacitors for CIN and COUT
Location
CIN
Component Supplier
Part No.
Capacitance (µF)
Case Size
1206
MURATA
TAIYO YUDEN
MURATA
TDK
GRM32ER71H475K
UMK325BJ475MM-T
GRM31CR61E106K
C3225X5R1E106K
TMK316BJ106ML
GRM31CR60J476M
C3225X5R0J476M
GRM32ER71C226M
C3225X5R1C22M
4.7
4.7
10
10
10
47
47
22
22
CIN
1206
CIN
1206
CIN
1206
CIN
TAIYO YUDEN
MURATA
TDK
1206
COUT
COUT
COUT
COUT
1206
1210
MURATA
TDK
1210
1210
Copyright 2018 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
14
DS2872-06 January 2018
RT2872
Outline Dimension
H
A
Y
M
EXPOSED THERMAL PAD
(Bottom of Package)
J
B
X
F
C
I
D
Dimensions In Millimeters Dimensions In Inches
Symbol
Min
Max
Min
Max
A
B
C
D
F
H
I
4.801
3.810
1.346
0.330
1.194
0.170
0.000
5.791
0.406
2.000
2.000
2.100
3.000
5.004
4.000
1.753
0.510
1.346
0.254
0.152
6.200
1.270
2.300
2.300
2.500
3.500
0.189
0.150
0.053
0.013
0.047
0.007
0.000
0.228
0.016
0.079
0.079
0.083
0.118
0.197
0.157
0.069
0.020
0.053
0.010
0.006
0.244
0.050
0.091
0.091
0.098
0.138
J
M
X
Y
X
Y
Option 1
Option 2
8-Lead SOP (Exposed Pad) Plastic Package
Richtek Technology Corporation
14F, No. 8, Tai Yuen 1st Street, Chupei City
Hsinchu, Taiwan, R.O.C.
Tel: (8863)5526789
Richtek products are sold by description only. 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.
DS2872-06 January 2018
www.richtek.com
15
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