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PDF RT8015B Data sheet ( Hoja de datos )
| Número de pieza | RT8015B | |
| Descripción | Synchronous Step-Down Converter | |
| Fabricantes | Richtek Technology | |
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RT8015B
3A, 2MHz, Synchronous Step-Down Converter
General Description
The RT8015B is a high efficiency synchronous, step-down
DC/DC converter. Its input voltage range is from 2.6V to
5.5V and provides an adjustable regulated output voltage
from 0.8V to 5V while delivering up to 3A of output current.
The internal synchronous low on-resistance power
switches increase efficiency and eliminate the need for
an external Schottky diode. The switching frequency is
set by an external resistor. The 100% duty cycle provides
low dropout operation extending battery life in portable
systems. Current mode operation with external
compensation allows the transient response to be
optimized over a wide range of loads and output capacitors.
The RT8015B is operated in forced continuous PWM Mode
which minimizes ripple voltage and reduces the noise and
RF interference.
The 100% duty cycle in Low Dropout Operation further
maximize battery life.
The RT8015B is available in the WDFN-10L 3x3 package.
Ordering Information
RT8015B
Package Type
QW : WDFN-10L 3x3
Operating Temperature Range
G : Green (Halogen Free with Commer-
rcial Standard)
Note :
Richtek 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.
Features
z High Efficiency : Up to 95%
z Low RDS(ON) Internal Switches : 110mΩ
z Programmable Frequency : 300kHz to 2MHz
z No Schottky Diode Required
z 0.8V Reference Allows for Low Output Voltage
z Forced Continuous Mode Operation
z Low Dropout Operation : 100% Duty Cycle
z Power Good Output Voltage Indicator
z RoHS Compliant and Halogen Free
Applications
z Portable Instruments
z Battery-Powered Equipment
z Notebook Computers
z Distributed Power Systems
z IP Phones
z Digital Cameras
Pin Configurations
(TOP VIEW)
SHDN/RT 1
GND 2
LX 3
LX 4
PGND 5
10 COMP
9 FB
8 PGOOD
7 VDD
11 PVDD
WDFN-10L 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.
DS8015B-01 September 2009
www.richtek.com
1
1 page  
RT8015B
Absolute Maximum Ratings (Note 1)
z Supply Input Voltage, VDD, PVDD ---------------------------------------------------------------------------- −0.3V to 6V
z LX Pin Switch Voltage -------------------------------------------------------------------------------------------- −0.3V to (PVDD + 0.3V)
<200ns --------------------------------------------------------------------------------------------------------------- −5V to 7.5V
z Other I/O Pin Voltages ------------------------------------------------------------------------------------------- −0.3V to (VDD + 0.3V)
z LX Pin Switch Current -------------------------------------------------------------------------------------------- 4A
z Power Dissipation, PD @ TA = 25°C
WDFN-10L 3x3 ----------------------------------------------------------------------------------------------------- 1.429W
z Package Thermal Resistance (Note 4)
WDFN-10L 3x3, θJA ----------------------------------------------------------------------------------------------- 70°C/W
WDFN-10L 3x3, θJC ----------------------------------------------------------------------------------------------- 7.8°C/W
z Junction Temperature --------------------------------------------------------------------------------------------- 150°C
z Lead Temperature (Soldering, 10 sec.) ----------------------------------------------------------------------- 260°C
z Storage Temperature Range ------------------------------------------------------------------------------------ −65°C to 150°C
z ESD Susceptibility (Note 2)
HBM (Human Body Mode) -------------------------------------------------------------------------------------- 2kV
MM (Machine Mode) ---------------------------------------------------------------------------------------------- 200V
Recommended Operating Conditions (Note 3)
z Supply Input Voltage ---------------------------------------------------------------------------------------------- 2.6V to 5.5V
z Junction Temperature Range ------------------------------------------------------------------------------------ −40°C to 125°C
z Ambient Temperature Range ------------------------------------------------------------------------------------ −40°C to 85°C
Electrical Characteristics
(VDD = 3.3V, TA = 25°C, unless otherwise specified)
Parameter
Symbol
Test Conditions
Min
Input Voltage Range
Feedback Reference Voltage
Feedback Leakage Current
DC Bias Current
VDD
VREF
IFB
2.6
0.784
--
Active , VFB = 0.78V, Not Switching --
Shutdown
--
Output Voltage Line Regulation
Output Voltage Load Regulation
Error Amplifier
Transconductance
gm
VIN = 2.7V to 5.5V
Measured in Servo Loop,
VCOMP = 0.2V to 0.7V (Note 5)
--
−0.2
--
Current Sense Transresistance RT
Switching Leakage Current
SHDN/RT = VIN = 5.5V
--
--
Switching Frequency
ROSC = 332k
Switching Frequency
0.8
0.3
Switch On Resistance, High
Switch On Resistance, Low
RPMOS ISW = 0.5A
RNMOS ISW = 0.5A
--
--
Typ
--
0.8
0.1
460
--
0.03
±0.02
800
0.4
--
1
--
110
110
DS8015B-01 September 2009
Max
5.5
0.816
0.4
--
1
--
Units
V
V
μA
μA
μA
%/V
0.2 %
-- μs
-- Ω
1 μA
1.2 MHz
2 MHz
160 mΩ
170 mΩ
To be continued
www.richtek.com
5
5 Page 
RT8015B
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.
Checking Transient Response
The regulator loop response can be checked by looking
at the load transient response. Switching regulators take
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 that would indicate a stability problem.
The COMP pin external components and output capacitor
shown in Typical Application Circuit will provide adequate
compensation for most applications.
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: VDD quiescent current and I2R losses.
The VDD 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 VDD quiescent current is due to two components :
the DC bias current as given in the electrical characteristics
and the internal main switch and synchronous switch 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 VDD to ground. The resulting ΔQ/Δt is the current out
of VDD 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 VDD 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) and the duty cycle (D) as follows :
RSW = RDS(ON)TOP x D + RDS(ON)BOT x (1"D) 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 CIN and COUT ESR dissipative
losses and inductor core losses generally account for less
than 2% of the total loss.
DS8015B-01 September 2009
www.richtek.com
11
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| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet RT8015B.PDF ] | |
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