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PDF RT8020 Data sheet ( Hoja de datos )
| Número de pieza | RT8020 | |
| Descripción | Dual High-Efficiency PWM Step-Down DC-DC Converter | |
| Fabricantes | Richtek | |
| Logotipo |  |
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RT8020
Dual High-Efficiency PWM Step-Down DC-DC Converter
General Description
The RT8020 is a dual high-efficiency Pulse-Width-
Modulated (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 RT8020 is ideally
suited for portable electronic devices that are powered
www.DataSfhroeemt41U-.cceolml Li-ion battery or from other power sources within
the range such as cellular phones, PDAs and other hand-
held devices.
Two operational modes are available : PWM/Low-Dropout
auto-switch and shutdown modes. Internal synchronous
rectifier with low RDS(ON) dramatically reduces conduction
loss at PWM mode. No external Schottky diode is
required in practical application.
The RT8020 enters Low-Dropout mode when normal PWM
cannot provide regulated output voltage by continuously
turning on the upper PMOS. The RT8020 enter shutdown
mode and consumes less than 0.1µA when 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 small
WDFN-12L 3x3 package provides 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
(TOP VIEW)
VIN2
LX2
GND
FB1
NC1
EN1
1
2
3
4
5
6
GND
13
12 EN2
11 NC2
10 FB2
9 GND
8 LX1
7 VIN1
WDFN-12L 3x3
Marking Information
For marking information, contact our sales representative
directly or through a Richtek distributor located in your
area, otherwise visit our website for detail.
Features
l +2.5V to +5.5V Input Range
l Adjustable Output From 0.6V to VIN
l 1.2V, 1.3V, 1.8V, 2.5V and 3.3V Fixed/ Adjustable
Output Voltage
l 1A Output Current
l 95% Efficiency
l No Schottky Diode Required
l 50uA Quiescent Current per Channel
l 1.5MHz Fixed-Frequency PWM Operation
l Small 12-Lead WDFN Package
l RoHS Compliant and 100% Lead (Pb)-Free
Applications
l Mobile Phones
l Personal Information Appliances
l Wireless and DSL Modems
l MP3 Players
l Portable Instruments
Ordering Information
RT8020
Package Type
QW : WDFN-12L 3x3 (W-Type)
Operating Temperature Range
P : Pb Free with Commercial Standard
G : Green (Halogen Free with Commer-
cial Standard)
Output Voltage : VOUT1/VOUT2
Default : Adjustable
A : 3.3V/1.8V
B : 3.3V/1.3V
C : 3.3V/1.2V
D : 2.5V/1.8V
Note :
Richtek Pb-free and Green products are :
}RoHS compliant and compatible with the current require-
ments of IPC/JEDEC J-STD-020.
}Suitable for use in SnPb or Pb-free soldering processes.
}100% matte tin (Sn) plating.
DS8020-03 August 2007
www.richtek.com
1
1 page  
RT8020
Parameter
Symbol
Test Conditions
Min
Output Voltage
Accuracy
Adjustable ∆VOUT
VIN = VOUT + ∆V to 5.5V
0A < IOUT < 1A
(Note 5) −3
FB Input Current
RDS(ON) of P-MOSFET
RDS(ON) of N-MOSFET
www.DataSheet4U.com
P-Channel Current Limit
EN High-Level Input Voltage
EN Low-Level Input Voltage
Oscillator Frequency
Thermal Shutdown Temperature
Maximum Duty Cycle
IFB VFB = VIN
RDS(ON)_P IOUT = 200mA
VIN = 2.5V
VIN = 3.6V
RDS(ON)_N IOUT = 200mA
VIN = 2.5V
VIN = 3.6V
ILIM_P
VIN = 2.5V to 5.5 V
VEN_H
VIN = 2.5V to 5.5V
VEN_L
VIN = 2.5V to 5.5V
fOSC
VIN = 3.6V, IOUT = 100mA
TSD
−50
--
--
--
--
1.4
1.5
--
1.2
--
100
LX Leakage Current
ILX VIN = 3.6V, VLX = 0V or VLX = 3.6V −1
Typ
--
--
0.38
0.28
0.35
0.25
1.5
--
--
1.5
160
--
--
Max Units
+3 %
50 nA
--
Ω
--
--
Ω
--
2A
VIN
V
0.4
1.8 MHz
-- °C
-- %
1 µA
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. Devices are ESD sensitive. Handling precaution recommended.
Note 3. The device is not guaranteed to function outside its operating conditions.
Note 4. θJA is measured in the natural convection at TA = 25°C on a high effective four layers thermal conductivity test board of
JEDEC 51-7 thermal measurement standard.
Note 5. ∆V = IOUT x PRDS(ON)
Note 6. Guarantee by design.
DS8020-03 August 2007
www.richtek.com
5
5 Page 
RT8020
The output ripple is highest at 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 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
www.DataShueseet4tUyp.ceosmthat 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 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 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.
Output Voltage Programming
The resistive divider allows the FB pin to sense a fraction
of the output voltage as shown in Figure 3.
VOUT
FB
RT8020
GND
R1
R2
Figure 3. Setting the Output Voltage
DS8020-03 August 2007
For adjustable voltage mode, the output voltage is set by
an external resistive divider according to the following
equation :
VOUT = VREF x (1+ R1/R2)
Where VREF is the internal reference voltage (0.6V typical)
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
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 VIN quiescent current oppears 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 ∆Q moves from VIN
to ground.
The resulting ∆Q/∆t 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
www.richtek.com
11
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet RT8020.PDF ] | |
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