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PDF RT8015 Data sheet ( Hoja de datos )
| Número de pieza | RT8015 | |
| Descripción | Synchronous Step-Down Regulator | |
| Fabricantes | Richtek Technology | |
| Logotipo |  |
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Conceptual
RT8015www.DataSheet4U.com
2A, 4MHz, Synchronous Step-Down Regulator
General Description
The RT8015 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 2A of output current.
The internal synchronous low on-resistance power
switches increase efficiency and eliminate the need for
an external Schottky diode. Switching frequency is set
by an external resistor or can be synchronized to an
external clock. 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.
RT8015 operation in forced continuous PWM Mode which
minimizes ripple voltage and reduces the noise and RF
interference. 100% duty cycle in Low Dropout Operation
further maximize battery life.
Ordering Information
RT8015
Package Type
SP : SOP-8 (Exposed Pad)
Operating Temperature Range
P : Pb Free with Commercial Standard
G : Green (Halogen Free with Comme-
rcial Standard)
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.
Features
z High Efficiency : Up to 95%
z Low RDS(ON) Internal Switches : 110mΩ
z Programmable Frequency : 300kHz to 4MHz
z No Schottky Diode Required
z 0.8V Reference Allows Low Output Voltage
z Forced Continuous Mode Operation
z Low Dropout Operation : 100% Duty Cycle
z RoHS Compliant and 100% Lead (Pb)-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
GND
LX
PGND
8
27
GND
36
45
COMP
FB
VDD
PVDD
SOP-8 (Exposed Pad)
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.
DS8015-03C February 2007
www.richtek.com
1
1 page  
Conceptual
RT8015www.DataSheet4U.com
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)
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
SOP-8 (Exposed Pad) ------------------------------------------------------------------------------------------ 1.33W
z Package Thermal Resistance (Note 4)
SOP-8 (Exposed Pad), θJA -------------------------------------------------------------------------------------- 75°C/W
SOP-8 (Exposed Pad), θJC ------------------------------------------------------------------------------------- 15°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 Voltage
DC Bias Current
VDD 2.6
VFB 0.784
Active , VFB = 0.78V, Not Switching --
Shutdown
--
Output Voltage Line Regulation
VIN = 2.7V to 5.5V
--
Output Voltage Load Regulation
0A < ILOAD < 2A
--
Error Amplifier
Transconductance
gm
--
Current Sense Transresistance
Power Good Range
Power Good Pull-Down
Resistance
RT
Switching Frequency
ROSC = 332k
Switching Frequency
--
--
--
0.8
0.3
Sync Frequency Range
0.3
Typ
--
0.8
460
--
0.04
0.25
800
0.4
±12.5
--
1
--
--
Max Units
5.5
0.816
--
1
V
V
μA
μA
-- %/V
-- %
-- μs
-- Ω
±15 %
120 Ω
1.2 MHz
4 MHz
4 MHz
To be continued
DS8015-03C February 2007
www.richtek.com
5
5 Page 
Conceptual
RT8015www.DataSheet4U.com
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 style inductor to use
mainly depends on the price vs. size requirements and
any radiated field/EMI requirements.
CIN and COUT Selection
The input capacitance, CIN, 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
IRMS = IOUT/2. This simple worst-case condition is
commonly used for design because even significant
deviations do not offer much relief. Note that ripple current
ratings from capacitor manufacturers are often based on
only 2000 hours of life which makes it advisable to further
derate the capacitor, or 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.
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 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 :
ΔVOUT
≤
ΔIL ⎢⎣⎡ESR +
1
8fCOUT
⎤
⎥⎦
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
DS8015-03C February 2007
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 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 output voltage is set by an external resistive divider
according to the following equation :
VOUT
=
VREF
× ⎜⎝⎛1+
R1
R2
⎟⎠⎞
where VREF equals to 0.8V typical.
The resistive divider allows the FB pin to sense a fraction
of the output voltage as shown in Figure 2.
FB
RT8015
GND
VOUT
R1
R2
Figure 2. Setting the Output Voltage
www.richtek.com
11
11 Page | ||
| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet RT8015.PDF ] | |
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