|
|
PDF RT8004 Data sheet ( Hoja de datos )
| Número de pieza | RT8004 | |
| Descripción | Synchronous Step-Down Regulator | |
| Fabricantes | Richtek Technology | |
| Logotipo |  |
|
Hay una vista previa y un enlace de descarga de RT8004 (archivo pdf) en la parte inferior de esta página. Total 16 Páginas | ||
|
No Preview Available !
RT8004
3A, 4MHz, Synchronous Step-Down Regulator
General Description
The RT8004 is a high efficiency synchronous, step-down
DC/DC converter. Its input voltage range is from 2.65V 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 power switch with 75mΩ on-resistance
increases efficiency and eliminates the need for an external
Schottky diode. Switching frequency is set by an external
www.DataSheet4U.com
resistor or can be synchronized to an external clock. 100%
duty cycle provides low dropout operation extending
battery life in portable systems. External compensation
allows the transient response to be optimized over a wide
range of loads and output capacitors.
The RT8004 operates in Forced Continuous Mode which
reduces noise and RF interference. 100% duty cycle in
Low Dropout Operation further maximize battery life.
Ordering Information
RT8004
Package Type
S : SOP-16
CP : TSSOP-16 (Exposed Pad)
QV : VQFN-16L 4x4 (V-Type)
Operating Temperature Range
P : Pb Free with Commercial Standard
G : Green (Halogen Free with Commer-
cial 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.
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
High Efficiency : Up to 95%
Low Quiescent Current : 100μA
Low RDS(ON) Internal Switches : 75mΩ
Programmable Frequency : 300kHz to 4MHz
No Schottky Diode Required
0.8V Reference Allows Low Output Voltage
Low Dropout Operation : 100% Duty Cycle
Synchronizable Switching Frequency
Power Good Output Voltage Monitor
Over Temperature Protection
Thermally Enhanced SOP-16, TSSOP-16 (Exposed
Pad) and 16-Lead VQFN 4x4 Packages
RoHS Compliant and 100% Lead (Pb)-Free
Applications
Portable Instruments
Battery-Powered Equipment
Notebook Computers
Distributed Power Systems
IP Phones
Digital Cameras
Pin Configurations
(TOP VIEW)
16 15 14 13
COMP 1
12 LX
FB 2
RT 3
SYNC 4
GND
17
11 PGND
10 PGND
9 LX
5678
VQFN-16L 4x4
DS8004-03 September 2007
www.richtek.com
1
1 page  
RT8004
Dropout Operation
When the input supply voltage decreases toward the output voltage, the duty cycle increases toward the maximum on-
time. Further reduction of the supply voltage forces the main switch to remain on for more than one cycle eventually
reaching 100% duty cycle. The output voltage will then be determined by the input voltage minus the voltage drop across
the internal P-Channel MOSFET and the inductor.
Low Supply Operation
The RT8004 is designed to operate down to an input supply voltage of 2.65V. One important consideration at low input
supply voltages is that the RDS(ON) of the P-Channel and N-Channel power switches increases. The user should calculate
the power dissipation when the RT8004 is used at 100% duty cycle with low input voltages to ensure that thermal limits
are not exceeded.
www.DataSheet4U.com
Slope Compensation and Inductor Peak Current
Slope compensation provides stability in constant frequency architectures by preventing subharmonic oscillations at
duty cycles greater than 50%. It is accomplished internally by adding a compensating ramp to the inductor current
signal. Normally, the maximum inductor peak current is reduced when slope compensation is added. In the RT8004,
however, separated inductor current signals are used to monitor over current condition and minimum peak current. This
keeps the maximum output current and minimum peak current relatively constant regardless of duty cycle.
Short-Circuit Protection
When the output is shorted to ground, the inductor current decays very slowly during a single switching cycle. A current
runaway detector is used to monitor inductor current. As current increasing beyond the control of current loop, switching
cycles will be skipped to prevent current runaway from occurring.
DS8004-03 September 2007
www.richtek.com
5
5 Page 
RT8004
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
www.DataShereet4sUis.ctaonmce (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
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 = 0.8V(1+ RR21)
The resistive divider allows the VFB pin to sense a fraction
of the output voltage as shown in Figure 1.
VOUT
VFB
RT8004
GND
R2
R1
Figure 1. Setting the Output Voltage
Frequency Synchronization
The RT8004’ s internal oscillator can be synchronized to
an external clock signal. During synchronization, the top
MOSFET turn-on is locked to the falling edge of the
external frequency source. The synchronization frequency
range is 300kHz to 4MHz. Synchronization only occurs if
the external frequency is greater than the frequency set
by the external resistor. Because slope compensation is
generated by the oscillator’ s RC circuit, the external
frequency should be set 25% higher than the frequency
set by the external resistor to ensure that adequate slope
compensation is present.
Soft-Start
The EN/SS pin provides a means to shut down the RT8004
as well as a timer for soft-start. Pulling the EN/SS pin
below 0.5V places the RT8004 in a low quiescent current
shutdown state (IQ < 1μA).
DS8004-03 September 2007
www.richtek.com
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet RT8004.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| RT8003 | High-Efficiency Synchronous Buck PWM Converter |  Richtek |
| RT8004 | Synchronous Step-Down Regulator | Richtek Technology |
| RT8005 | High-Efficiency Synchronous Buck PWM Converter | Richtek |
| RT8008 | High Efficiency PWM Step-Down DC/DC Converter | Richtek |
| Número de pieza | Descripción | Fabricantes |
| SLA6805M | High Voltage 3 phase Motor Driver IC. |
 Sanken |
| SDC1742 | 12- and 14-Bit Hybrid Synchro / Resolver-to-Digital Converters. |
 Analog Devices |
|
DataSheet.es es una pagina web que funciona como un repositorio de manuales o hoja de datos de muchos de los productos más populares, |
| DataSheet.es | 2020 | Privacy Policy | Contacto | Buscar |