DS8020E 03

®
RT8020E
Dual High-Efficiency PWM Step-Down DC/DC Converter
General Description
Features
The RT8020E is a dual high-efficiency Pulse-WidthModulated (PWM) step-down DC/DC converter. It is
capable of delivering 1A output current over a wide input
voltage range from 2.5V to 5.5V. The RT8020E is ideally
suited for portable electronic devices that are powered by
1-cell Li-ion battery or other power sources within the range
such as cellular phones, PDAs and other hand-held
devices.

2.5V to 5.5V Input Range

1.2V and 1.8V Fixed Output Voltage
1A Output Current
95% Efficiency
No Schottky Diode Required
50μ
μA Quiescent Current per Channel
1.5MHz Fixed Frequency PWM Operation
Small 12-Lead WDFN Package
RoHS Compliant and Halogen Free
Two operational modes are available : PWM/Low-Dropout
auto-switch mode and shutdown mode. Internal
synchronous rectifier with low R DS(ON) dramatically
reduces conduction loss at PWM mode. No external
Schottky diode is required in practical application.
The RT8020E enters Low-Dropout mode when normal
PWM cannot provide regulated output voltage by
continuously turning on the upper PMOS. The RT8020E
enters shutdown mode and consumes less than 0.1μA
when the EN pin is pulled low.
The switching ripple is easily smoothed-out by small
package filtering elements due to a fixed operation
frequency of 1.5MHz. This, along with a small
WDFN-12L 3x3 package, provides an ideal solution for
small PCB area application. Other features include soft
start, lower internal reference voltage with 2% accuracy,
over temperature protection, and over current protection.
Pin Configurations
1
2
3
4
5
6
GND
13






Applications






Digital Still Cameras
Mobile Phones
Personal Information Appliances
Wireless and DSL Modems
MP3 Players
Portable Instruments
Ordering Information
RT8020E
Package Type
QW : WDFN-12L 3x3 (W-Type)
(Exposed Pad-Option 1)
Lead Plating System
P : Pb Free
G : Green (Halogen Free and Pb Free)
Fixed Output Voltage : VOUT1/VOUT2
1.2V/1.8V
Note :
(TOP VIEW)
VIN2
LX2
GND
FB1
NC1
EN1

12
11
10
9
8
7
EN2
NC2
FB2
GND
LX1
VIN1
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.
WDFN-12L 3x3
Marking Information
JS= : Product Code
JS=YM
DNN
YMDNN : Date code
Copyright © 2014 Richtek Technology Corporation. All rights reserved.
DS8020E-03 August 2014
is a registered trademark of Richtek Technology Corporation.
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1
RT8020E
Typical Application Circuit
L2
4.7µH
VIN2
VOUT2
1.8V
RT8020E
CIN2
4.7µF
1 VIN2
EN2 12
2
NC2 11
3, 13 (Exposed Pad)
4
LX2
COUT2
10µF
FB2 10
GND
FB1
GND
5 NC1
LX1
6 EN1
VIN1
9
8
7
CIN1
4.7µF
VIN1
L1
4.7µH
VOUT1
1.2V
COUT1
10µF
Functional Pin Description
Pin No.
Pin Name
1
VIN2
2
LX2
3, 9,
13 (Exposed Pad)
4
GND
Pin Function
Power Input of Channel 2.
Pin for Switching of Channel 2.
Ground. The exposed pad must be soldered to a large PCB and connected to
GND for maximum power dissipation.
FB1
Feedback of Channel 1.
NC1, NC2
No Internal Connection or Connect to VIN.
6
EN1
Chip Enable of Channel 1 (Active High). VEN1 ≦ VIN1.
7
VIN1
Power Input of Channel 1.
5, 11
8
LX1
Pin for Switching of Channel 1.
10
FB2
Feedback of Channel 2.
12
EN2
Chip Enable of Channel 2 (Active High). VEN2 ≦ VIN2.
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DS8020E-03 August 2014
RT8020E
Function Block Diagram
ENx
VINx
RS1
OSC and
Shutdown
Control
Current Limit
Detector
Slope
Compensation
Current
Sense
PWM
Comparator
FBx
Driver
LXx
Error
Amplifier
RC
UVLO and
Power Good
Detector
COMP
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DS8020E-03 August 2014
Control
Logic
RS2
VREF
GND
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3
RT8020E
Absolute Maximum Ratings








(Note 1)
Supply Input Voltage, VIN1, VIN2 ----------------------------------------------------------------------------------- −0.3V to 6.5V
EN1, FB1, LX1, EN2, FB2 and LX2 Pin Voltage --------------------------------------------------------------- −0.3V to VIN + 0.3V
Power Dissipation, PD @ TA = 25°C
WDFN-12L 3x3 --------------------------------------------------------------------------------------------------------- 1.667W
Package Thermal Resistance (Note 2)
WDFN-12L 3x3, θJA --------------------------------------------------------------------------------------------------- 60°C/W
WDFN-12L 3x3, θJC --------------------------------------------------------------------------------------------------- 8.2°C/W
Lead Temperature (Soldering, 10 sec.) --------------------------------------------------------------------------- 260°C
Junction Temperature ------------------------------------------------------------------------------------------------- 150°C
Storage Temperature Range ---------------------------------------------------------------------------------------- −65°C to 150°C
ESD Susceptibility (Note 3)
HBM (Human Body Mode) ------------------------------------------------------------------------------------------ 2kV
MM (Machine Mode) -------------------------------------------------------------------------------------------------- 200V
Recommended Operating Conditions



(Note 4)
Supply Input Voltage, VIN1, VIN2 ----------------------------------------------------------------------------------- 2.5V to 5.5V
Junction Temperature Range ---------------------------------------------------------------------------------------- −40°C to 125°C
Ambient Temperature Range ---------------------------------------------------------------------------------------- −40°C to 85°C
Electrical Characteristics
(VIN = 3.6V, VOUT = 1.8V, L = 4.7μH, CIN = 4.7μF, COUT = 10μF, IMAX= 1A, TA = 25°C, unless otherwise specified)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
--
1.8
--
V
--
0.1
--
V
Channel 1 and Channel 2
Under Voltage Lock Out
threshold
VUVLO
Hysteresis
Quiescent Current
IQ
IOUT = 0mA, VFB = VREF + 5%
--
50
70
A
Shutdown Current
I SHDN
EN = GND
--
0.1
1
A
VOUT1
VIN1 = 2.5V to 5.5V, VOUT1 = 1.2V
0A < IOUT1 < 1A
2
--
2
%
VOUT2
2
--
2
%
50
--
50
nA
VIN = 2.5V
--
0.38
--
VIN = 3.6V
--
0.28
--
VIN = 2.5V
--
0.35
--
VIN = 3.6V
--
0.25
--
Output Voltage Accuracy
FB Input Current
I FB
VIN2 = 2.5 to 5.5V, VOUT2 = 1.8V
0A < IOUT2 < 1A
VFB = VIN
RDS(ON) of P-MOSFET
RDS(ON)_P
IOUT = 200mA
RDS(ON) of N-MOSFET
RDS(ON)_N
IOUT = 200mA
P-Channel Current Limit
I LIM_P
VIN = 2.5V to 5.5 V
1.4
1.5
2
Logic-High
EN Input
Threshold Voltage Logic-Low
VIH
VIN = 2.5V to 5.5V
1.5
--
VIN
VIL
VIN = 2.5V to 5.5V
--
--
0.4
Oscillator Frequency
f OSC
VIN = 3.6V, IOUT = 100mA
1.2
1.5
1.8
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

A
V
MHz
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DS8020E-03 August 2014
RT8020E
Parameter
Symbol
Thermal Shutdown Temperature
TSD
Maximum Duty Cycle
DMAX
LX Leakage Current
ILX
Test Conditions
VIN = 3.6V, VLX = 0V or VLX = 3.6V
Min
Typ
Max
Unit
--
160
--
C
100
--
--
%
1
--
1
A
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 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 recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
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RT8020E
Typical Operating Characteristics
CH1 Efficiency vs. Output Current
CH2 Efficiency vs. Output Current
100
100
90
90
80
VIN
VIN
VIN
VIN
VIN
VIN
VIN
VIN
70
60
50
40
30
=
=
=
=
=
=
=
=
2.4V
2.7V
3V
3.3V
3.6V
3.9V
4.2V
4.5V
Efficiency (%)
Efficiency (%)
80
20
VIN
VIN
VIN
VIN
VIN
VIN
VIN
VIN
70
60
50
40
30
=
=
=
=
=
=
=
=
2.4V
2.7V
3V
3.3V
3.6V
3.9V
4.2V
4.5V
20
10
10
VOUT = 1.2V, L = 4.7μH, COUT = 10μF
0
0
0.2
0.4
0.6
0.8
VOUT = 1.8V, L = 4.7μH, COUT = 10μF
0
1
0
0.2
0.4
Output Current (A)
1
1.86
VIN
VIN
VIN
VIN
1.21
=
=
=
=
1.84
3V
3.6V
4.2V
5V
Output Voltage (V)
1.22
Output Voltage (V)
0.8
CH2 Output Voltage vs. Output Current
CH1 Output Voltage vs. Output Current
1.23
1.20
1.19
1.82
1.80
VIN
VIN
VIN
VIN
1.78
VOUT = 1.2V, L = 4.7μH, COUT = 10μF
=
=
=
=
3V
3.6V
4.2V
5V
VOUT = 1.8V, L = 4.7μH, COUT = 10μF
1.18
1.76
0
0.2
0.4
0.6
0.8
0
1
0.2
Output Current (A)
0.4
0.6
0.8
1
Output Current (A)
CH2 Output Voltage vs. Input Voltage
CH1 Output Voltage vs. Input Voltage
1.83
1.23
1.22
1.82
IOUT = 0mA
IOUT = 300mA
IOUT = 600mA
1.21
Output Voltage (V)
Output Voltage (V)
0.6
Output Current (A)
1.20
IOUT = 0mA
IOUT = 300mA
IOUT = 600mA
1.81
1.80
1.79
1.19
VOUT = 1.8V, L = 4.7μH, COUT = 10μF
VOUT = 1.2V, L = 4.7μH, COUT = 10μF
1.78
1.18
2.5
3.0
3.5
4.0
4.5
Input Voltage (V)
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5.0
2.5
3.0
3.5
4.0
4.5
5.0
Input Voltage (V)
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DS8020E-03 August 2014
RT8020E
EN Pin Threshold vs. Temperature
2.0
1.8
1.8
1.6
1.6
EN Pin Threshold (V)
EN Pin Threshold (V)
EN Pin Threshold vs. Input Voltage
2.0
1.4
1.2
Rising
1.0
0.8
Falling
0.6
0.4
VOUT = 1.2V, L = 4.7μH,
COUT = 10μF, IOUT = 0A
0.2
1.4
1.2
Rising
1.0
0.8
Falling
0.6
0.4
VOUT = 1.2V, L = 4.7μH,
COUT = 10μF, IOUT = 0A
0.2
0.0
0.0
2.5
3.0
3.5
4.0
4.5
5.0
-50
5.5
-25
0
Switching Frequency vs. Input Voltage
75
100
125
Switching Frequency vs. Temperature
1600
1600
Switching Frequency (kHz)1
Switching Frequency (kHz)1
50
Temperature (°C)
Input Voltage (V)
1550
1500
1450
1400
1350
VOUT = 1.8V, L = 4.7μH,
COUT = 10μF, IOUT = 300mA
1550
1500
1450
1400
1350
VIN = 3.7V, VOUT = 1.8V, L = 4.7μH,
COUT = 10μF, IOUT = 300mA
1300
1300
2.5
3
3.5
4
4.5
-50
5
-25
0
1.83
1.21
1.82
Output Voltage (V)
1.20
1.19
VIN = 2.5V
VIN = 3.7V
VIN = 4.5V
1.17
1.16
VOUT = 1.2V, L = 4.7μH,
COUT = 10μF, IOUT = 300mA
1.15
50
75
100
125
CH2 Output Voltage vs. Temperature
CH1 Output Voltage vs. Temperature
1.22
1.18
25
Temperature (°C)
Input Voltage (V)
Output Voltage (V)
25
1.14
1.81
1.80
1.79
VIN = 2.5V
VIN = 3.7V
VIN = 4.5V
1.78
1.77
1.76
VOUT = 1.8V, L = 4.7μH,
COUT = 10μF, IOUT = 300mA
1.75
1.74
-50
-25
0
25
50
75
100
Temperature (°C)
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125
-50
-25
0
25
50
75
100
125
Temperature (°C)
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RT8020E
Output Current Limit vs. Temperature
Output Current Limit vs. Input Voltage
2.4
2.6
VOUT = 1.2V, L = 4.7μH, COUT = 10μF
Output Current Limit (A)
Output Current Limit (A)
VOUT = 1.2V, L = 4.7μH, COUT = 10μF
2.4
2.2
2.0
1.8
1.6
1.4
1.2
2.2
VIN = 5V
2.0
VIN = 3.6V
1.8
1.6
1.4
VIN = 2.5V
1.2
1.0
1.0
2.5
3.0
3.5
4.0
4.5
-50
5.0
0
25
50
75
Input Voltage (V)
Temperature (°C)
CH1 Power On from EN
CH1 Power Off from EN
I IN
(500mA/Div)
I IN
(500mA/Div)
VEN
(2V/Div)
VEN
(2V/Div)
VOUT
(1V/Div)
VOUT
(1V/Div)
Time (100μs/Div)
Time (100μs/Div)
CH1 Power On from EN
CH1 Power Off from EN
VIN = 3.6V, VOUT = 1.2V, IOUT = 1A
I IN
(1A/Div)
100
125
VIN = 3.6V, VOUT = 1.2V, IOUT = 10mA
VIN = 3.6V, VOUT = 1.2V, IOUT = 10mA
VIN = 3.6V, VOUT = 1.2V, IOUT = 1A
I IN
(1A/Div)
VEN
(2V/Div)
VEN
(2V/Div)
VOUT
(1V/Div)
VOUT
(1V/Div)
Time (500μs/Div)
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RT8020E
CH2 Power On from EN
CH2 Power Off from EN
VIN = 3.6V, VOUT = 1.8V, IOUT = 10mA
VIN = 3.6V, VOUT = 1.8V, IOUT = 10mA
I IN
(500mA/Div)
I IN
(500mA/Div)
VEN
(2V/Div)
VEN
(2V/Div)
VOUT
(1V/Div)
VOUT
(1V/Div)
Time (100μs/Div)
Time (100μs/Div)
CH2 Power On from EN
CH2 Power Off from EN
VIN = 3.6V, VOUT = 1.8V, IOUT = 1A
VIN = 3.6V, VOUT = 1.8V, IOUT = 1A
I IN
(1A/Div)
I IN
(1A/Div)
VEN
(2V/Div)
VEN
(2V/Div)
VOUT
(1V/Div)
VOUT
(1V/Div)
Time (500μs/Div)
Time (500μs/Div)
Power On from VIN
Power Off from VIN
VIN = 3.6V, VOUT = 1.2V, IOUT = 10mA
VIN = 3.6V, VOUT = 1.2V, IOUT = 10mA
I IN
(500mA/Div)
I IN
(500mA/Div)
VIN
(2V/Div)
VIN
(2V/Div)
VOUT
(1V/Div)
VOUT
(1V/Div)
Time (250μs/Div)
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Time (1ms/Div)
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RT8020E
Output Voltage Ripple
Output Voltage Ripple
VIN = 3.6V, VOUT = 1.2V, IOUT = 1A
VIN = 5V, VOUT = 1.2V, IOUT = 1A
VLX
(2V/Div)
VLX
(2V/Div)
VOUT
(5mV/Div)
VOUT
(5mV/Div)
Time (500ns/Div)
Time (500ns/Div)
Load Transient Response
Load Transient Response
VIN = 3.6V, VOUT = 1.2V, IOUT = 50mA to 500mA
VIN = 3.6V, VOUT = 1.2V, IOUT = 50mA to 1A
IOUT
(500mA/Div)
IOUT
(500mA/Div)
VOUT
(20mV/Div)
VOUT
(20mV/Div)
Time (1ms/Div)
Time (1ms/Div)
Load Transient Response
Load Transient Response
VIN = 5V, VOUT = 1.2V, IOUT = 50mA to 1A
VIN = 5V, VOUT = 1.2V, IOUT = 50mA to 500mA
IOUT
(500mA/Div)
IOUT
(500mA/Div)
VOUT
(20mV/Div)
VOUT
(20mV/Div)
Time (1ms/Div)
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RT8020E
Applications Information
The basic RT8020E application circuit is shown in Typical
Application Circuit. External component selection is
determined by the maximum load current and begins with
the selection of the inductor value and operating frequency
followed by CIN and COUT.
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

∆IL   OUT   1  OUT 
f
L

V
IN 

 
Having a lower ripple current reduces the ESR losses in
the output capacitors and the output voltage ripple. Highest
efficiency operation is achieved at low frequency with small
ripple current. This, however, requires a large inductor.
A reasonable starting point for selecting the ripple current
is ΔIL = 0.4(IMAX). 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  V
f
I


L(MAX)  
IN(MAX) 

Inductor Core Selection
Once the value for L is known, the type of inductor can be
selected. High efficiency converters generally cannot afford
the core loss found in low cost powdered iron cores, thus,
limiting the use to more expensive ferrite or permalloy
cores. Actual core loss is independent of core size for a
fixed inductor value, but it is very dependent on the
inductance selected. As the inductance increases, core
losses decrease. However, increased inductance requires
more turns of wire and therefore higher copper losses.
Ferrite designs have very low core losses and are preferred
at high switching frequencies, thus allowing design goals
to concentrate on copper loss and saturation prevention.
Ferrite core material saturates “hard”, which means that
inductance collapses abruptly when the peak design
current is exceeded.
Copyright © 2014 Richtek Technology Corporation. All rights reserved.
DS8020E-03 August 2014
This results in an abrupt increase in inductor ripple current
and consequent output voltage ripple.
Do not allow the core to saturate!
Different core materials and shapes will change the size/
current and price/current relationship of an inductor. Toroid
or shielded pot cores in ferrite or permalloy materials are
small and don't radiate energy but generally cost more
than powdered iron core inductors with similar
characteristics. The choice of which type of inductor to
use mainly depends on the price vs. size requirements
and any radiated field/EMI requirements.
CIN and COUT Selection
The input capacitance, C IN, is needed to filter the
trapezoidal current at the source of the top MOSFET. To
prevent large ripple voltage, a low ESR input capacitor
sized for the maximum RMS current should be used. RMS
current is given by :
IRMS  IOUT(MAX)
VOUT
VIN
VIN
1
VOUT
This formula has a maximum at VIN = 2VOUT, where
I RMS = I OUT/2. This simple worst-case condition is
commonly used for design because even significant
deviations do not result in much difference. Note that ripple
current ratings from capacitor manufacturers are often
based on a life time of only 2000 hours, which makes it
advisable to further de-rate the capacitor or choose a
capacitor rated at a higher temperature than required.
Several capacitors may also be paralleled to meet the
size or height requirements in the design.
The selection of COUT is determined by the effective series
resistance (ESR) that is required to minimize voltage ripple
and load step transients, as well as by the amount of bulk
capacitance that is necessary to ensure that the control
loop is stable. Loop stability can be checked by viewing
the load transient response as described in a later section.
The output ripple, ΔVOUT, is determined by :

1 
∆VOUT  ∆IL ESR 

8fC
OUT 

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RT8020E
The output ripple is highest at maximum input voltage
since ΔIL increases with input voltage. Multiple capacitors
placed in parallel may be needed to meet the ESR and
RMS current handling requirements. Dry tantalum, special
polymer, aluminum electrolytic and ceramic capacitors are
all available in surface mount packages. Special polymer
capacitors offer very low ESR, but have lower capacitance
density than other types. Tantalum capacitors have the
highest capacitance density, but it is important to only
use types that have been surge tested for use in switching
power supplies. Aluminum electrolytic capacitors have
significantly higher ESR, but can be used in cost-sensitive
applications provided that consideration is given to ripple
current ratings and long-term reliability. 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.
Using Ceramic Input and Output Capacitors
Higher value, 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 the 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.
Efficiency Considerations
The efficiency of a switching regulator is equal to the output
power divided by the input power times 100%. It is often
useful to analyze individual losses to determine what is
limiting the efficiency and which change would produce
the most improvement. Efficiency can be expressed as :
Efficiency = 100% − (L1+ L2+ L3+...)
where L1, L2, etc. are the individual losses as a percentage
of input power. Although all dissipative elements in the
circuit produce losses, two main sources usually account
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12
for most of the losses : VIN quiescent current and I2R
losses.
The VIN quiescent current loss dominates the efficiency
loss at very low load currents whereas the I2R loss
dominates the efficiency loss at medium to high load
currents. In a typical efficiency plot, the efficiency curve
at very low load currents can be misleading since the
actual power lost is of no consequence.
1.The V IN quiescent current appears due to two
components : the DC bias current and the gate charge
currents. The gate charge current results from switching
the gate capacitance of the internal power MOSFET
switches. Each time the gate is switched from high to
low to high again, a packet of charge ΔQ moves from VIN
to ground.
The resulting ΔQ/Δt is the current out of VIN that is typically
larger than the DC bias current. In continuous mode,
IGATECHG = f(QT + QB)
where QT and QB are the gate charges of the internal top
and bottom switches. Both the DC bias and gate charge
losses are proportional to VIN and thus their effects will
be more pronounced at higher supply voltages.
2. I2R losses are calculated from the resistances of the
internal switches, RSW and external inductor, RL. In
continuous mode the average output current flowing
through inductor L is “chopped” between the main switch
and the synchronous switch. Thus, the series resistance
looking into the LX pin is a function of both top and bottom
MOSFET RDS(ON) as well as the duty cycle (DC). The
equation is shown below :
RSW = RDS(ON)TOP x DC + RDS(ON)BOT x (1 − DC)
The RDS(ON) for both the top and bottom MOSFETs can be
obtained from the Typical Performance Characteristics
curves. Thus, to obtain I2R losses, simply add RSW to RL
and multiply the result by the square of the average output
current. Other losses including C IN and C OUT ESR
dissipative losses and inductor core losses generally
account for less than 2% of the total loss.
Checking Transient Response
The regulator loop response can be checked by looking
at the load transient response. Switching regulators take
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DS8020E-03 August 2014
RT8020E
several cycles to respond to a step in load current. When
a load step occurs, VOUT immediately shifts by an amount
equal to ΔILOAD (ESR), where ESR is the effective series
resistance of COUT. ΔILOAD also begins to charge or
discharge COUT, generating a feedback error signal used
by the regulator to return VOUT to its steady-state value.
During this recovery time, VOUT can be monitored for
overshoot or ringing which would indicate a stability
problem.
Maximum Power Dissipation (W)
1.8
Thermal Considerations
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
conditions specification of the RT8020E DC/DC converter,
TJ(MAX) is the maximum junction temperature of the die
and TA is the ambient temperature. The junction to ambient
thermal resistance θJA is layout dependent. For WDFN12L 3x3 packages, 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-12L 3x3 package
The maximum power dissipation depends on the operating
ambient temperature for fixed T J(MAX) and thermal
resistance, θJA. For the RT8020E package, the derating
curves in Figure 1 allows the designer to see the effect of
rising ambient temperature on the maximum power
dissipation.
Copyright © 2014 Richtek Technology Corporation. All rights reserved.
DS8020E-03 August 2014
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0
The maximum power dissipation depends on the thermal
resistance of 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
1.6
25
50
75
100
125
Ambient Temperature (°C)
Figure 1. Derating Curve for RT8020E Package
Layout Considerations
Follow the PCB layout guidelines for optimal performance
of the RT8020E.

For the main current paths, keep their traces short and
wide.

Place the input capacitor as close as possible to the
device pins (VIN and GND).

LX node experiences high frequency voltage swing and
should be kept in a small area. Keep analog components
away from LX node to prevent stray capacitive noise
pick-up.

Connect feedback network behind the output capacitors.
Keep the loop area small. Place the feedback
components near the RT8020E.

Connect all analog grounds to a command node and
then connect the command node to the power ground
behind the output capacitors.
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13
RT8020E
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.
Symbol
D2
Dimensions In Millimeters
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
0.150
0.250
0.006
0.010
D
2.950
3.050
0.116
0.120
Option1
2.300
2.650
0.091
0.104
Option2
1.970
2.070
0.078
0.081
2.950
3.050
0.116
0.120
Option1
1.400
1.750
0.055
0.069
Option2
1.160
1.260
0.046
0.050
E
E2
Dimensions In Inches
e
L
0.450
0.350
0.018
0.450
0.014
0.018
W-Type 12L DFN 3x3 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. 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.
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14
DS8020E-03 August 2014