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PDF RT8204L Data sheet ( Hoja de datos )
| Número de pieza | RT8204L | |
| Descripción | Single Synchronous Buck Controller | |
| Fabricantes | Richtek | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de RT8204L (archivo pdf) en la parte inferior de esta página. Total 18 Páginas | ||
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RT8204L
Single Synchronous Buck Controller
General Description
The RT8204L PWM controller provides high efficiency,
excellent transient response, and high DC output accuracy
needed for stepping down high voltage batteries to
generate low voltage CPU core, I/O, and chipset RAM
supplies in notebook computers.
The constant-on-time PWM control scheme handles wide
input/output voltage ratios with ease and provides 100ns
“instant-on” response to load transients while maintaining
a relatively constant switching frequency.
The RT8204L achieves high efficiency at a reduced cost
by eliminating the current sense resistor found in
traditional current mode PWMs. Efficiency is further
enhanced by its ability to drive very large synchronous
rectifier MOSFETs. The buck conversion allows this device
to directly step down high voltage batteries for the highest
possible efficiency. The RT8204L is intended for CPU core,
chipset, DRAM, or other low voltage supplies as low as
0.75V. The RT8204L is available in a WQFN-16L 3x3
package.
A built in LDO controller can drive an external N-MOSFET
to provide a second output voltage from PWM output or
other power source. The RT8204L can provide adjustable
voltage down to 0.75V and maximum output voltage is
dependen on the selected MOSFET. The internal 0.75V
reference voltage with ±1.5% accuracy provides tight
regulation of the output voltage. Other features such as
independent enable control, open drain power good
indicator, under voltage protection, and soft start make
the RT8204L a system friendly power management solution
for various applications.
Features
z PWM Controller
` Ultra High Efficiency
` Resistor Programmable Current Limit by Low Side
RDS(ON) Sense (Lossless Limit)
` 4700ppm/°C RDS(ON) Current Sensing
` Quick Load Step Response within 100ns
` 1% VFB Accuracy Over Line and Load
` Adjustable 0.75V to 3.3V Output Range
` 4.5V to 26V Battery Input Range
` Resistor Programmable Frequency
` Integrated Bootstrap Switch
` Over/Under Voltage Protection
` Voltage Ramp Soft-Start
` Power Good Indicator
z LDO Controller
` 1.5% accuracy Over Line and Load
` Independent Enable and Power Good Indicator
` Drive N-MOSFETs within Rail to Rail Controller
Voltage
` MLCC and POSCAP Stable
z RoHS Compliant and Halogen Free
Applications
z Notebook Computers
z CPU Core Supply
z Chipset/RAM Supply as Low as 0.75V
Ordering Information
RT8204L
Package Type
QW : WQFN-16L 3x3 (W-Type)
Lead Plating System
G : Green (Halogen Free and Pb Free)
Z : ECO (Ecological Element with
Halogen Free and Pb free)
Note :
Richtek 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.
DS8204L-04 April 2011
www.richtek.com
1
1 page  
RT8204L
Absolute Maximum Ratings (Note 1)
z Input Voltage, TON to GND ------------------------------------------------------------------------------------------------ –0.3V to 32V
z BOOT to PHASE ------------------------------------------------------------------------------------------------------------ –0.3V to 6V
z UGATE to PHASE
DC ------------------------------------------------------------------------------------------------------------------------------- –0.3V to 6V
< 20ns ------------------------------------------------------------------------------------------------------------------------- −5V to 7.5V
z LGATE to GND
DC ------------------------------------------------------------------------------------------------------------------------------- –0.3V to 6V
< 20ns ------------------------------------------------------------------------------------------------------------------------- −2.5V to 7.5V
z PHASE to GND
DC ------------------------------------------------------------------------------------------------------------------------------- –0.3V to 32V
< 20ns ------------------------------------------------------------------------------------------------------------------------- −8V to 38V
z VDD, VDDP, VOUT, EN/DEM, LEN, LFB, FB, PGOOD, LPGOOD, LDRV to GND ------------------------- –0.3V to 6V
z OC to GND -------------------------------------------------------------------------------------------------------------------- –0.3V to 28V
z Power Dissipation, PD @ TA = 25°C
WQFN-16L 3x3 -------------------------------------------------------------------------------------------------------------- 1.471W
z Package Thermal Resistance (Note 2)
WQFN-16L 3x3, θJA --------------------------------------------------------------------------------------------------------- 68°C/W
WQFN-16L 3x3, θJC -------------------------------------------------------------------------------------------------------- 7.5°C/W
z Lead Temperature (Soldering, 10 sec.) --------------------------------------------------------------------------------- 260°C
z Junction Temperature ------------------------------------------------------------------------------------------------------- 150°C
z Storage Temperature Range ---------------------------------------------------------------------------------------------- –65°C to 150°C
z ESD Susceptibility (Note 3)
HBM (Human Body Mode) ------------------------------------------------------------------------------------------------ 2kV
MM (Machine Mode) -------------------------------------------------------------------------------------------------------- 200V
Recommended Operating Conditions (Note 4)
z Input Voltage, VIN ------------------------------------------------------------------------------------------------------------ 4.5V to 26V
z Supply Voltage, VDD, VDDP ------------------------------------------------------------------------------------------------ 4.5V to 5.5V
z Junction Temperature Range --------------------------------------------------------------------------------------------- −40°C to 125°C
z Ambient Temperature Range --------------------------------------------------------------------------------------------- −40°C to 85°C
Electrical Characteristics
(VDD = VDDP = 5V, VIN = 15V, VEN/DEM = VDD, RTON = 1MΩ, TA = 25°C, unless otherwise specified)
Parameter
Symbol
Test Conditions
Min
PWM Controller
Quiescent Current
TON Operating Current
IQ
Shutdown Current
ISHDN
FB Reference Voltage
VFB
VDD + VDDP, VFB = 0.8V, forced above
the regulation point
VDD + VDDP
TON
VEN/DEM = 0V
VDD = 4.5V to 5.5V
--
--
--
--
−10
0.742
Typ
--
15
1
1
−1
0.75
Max
1250
--
10
5
--
0.758
Unit
μA
μA
μA
V
DS8204L-04 April 2011
To be continued
www.richtek.com
5
5 Page 
Applications Information
The RT8204L PWM controller provides the high efficiency,
excellent transient response, and high DC output accuracy
needed for stepping down high voltage batteries to
generate low voltage CPU core, I/O, and chipset RAM
supplies in notebook computers. RichTek's Mach
ResponseTM technology is specifically designed for
providing 100ns “instant-on” response to load steps while
maintaining a relatively constant operating frequency and
inductor operating point over a wide range of input voltages.
The topology circumvents the poor load transient timing
problems of fixed frequency current mode PWMs while
also avoiding the problems caused by widely varying
switching frequencies in conventional constant-on-time and
constant- off-time PWM schemes. The DRVTM mode PWM
modulator is specifically designed to have better noise
immunity for such a single output application.
PWM Operation
The Mach ResponseTM, DRVTM mode controller relies on
the output filter capacitor's effective series resistance
(ESR) to act as a current-sense resistor, so the output
ripple voltage provides the PWM ramp signal. Referring to
the function diagrams of the RT8204L, the synchronous
high side MOSFET is turned on at the beginning of each
cycle. After the internal one shot timer expires, the
MOSFET is turned off. The pulse width of this one shot is
determined by the converter’s input and output voltages
to keep the frequency fairly constant over the input voltage
range. Another one-shot sets a minimum off-time (400ns
typ.).
On-Time Control (TON)
The on-time one-shot comparator has two inputs. One
input looks at the output voltage, while the other input
samples the input voltage and converts it to a current.
This input voltage proportional current is used to charge
an internal on-time capacitor. The on-time is the time
required for the voltage on this capacitor to charge from
zero volts to VOUT, thereby making the on-time of the high
side switch directly proportional to the output voltage and
inversely proportional to the input voltage. The
implementation results in a nearly constant switching
frequency without the need of a clock generator.
RT8204L
tON
=
3.85p x RTON x VOUT
(VIN − 0.5)
And then the switching frequency is :
Frequency =
VOUT
(VIN x tON )
RTON is a resistor connected from the input supply (VIN)
to the TON pin.
Mode Selection (EN/DEM) Operation
The EN/DEM pin enables the supply. When EN/DEM is
tied to VDD, the controller is enabled and operates in
diode-emulation mode. When the EN/DEM pin is floating,
the RT8204L will operate in forced-CCM mode.
Diode-Emulation Mode (EN/DEM = High)
In diode-emulation mode, the RT8204L automatically
reduces switching frequency at light load conditions to
maintain high efficiency. This reduction of frequency is
achieved smoothly and without increasing VOUT ripple or
load regulation. As the output current decreases from
heavy-load condition, the inductor current is also reduced,
and eventually comes to the point when its valley touches
zero current, which is the boundary between continuous
conduction and discontinuous conduction modes. By
emulating the behavior of diodes, the low side MOSFET
allows only partial negative current when the inductor
freewheeling current becomes negative. As the load current
is further decreased, it takes longer and longer to discharge
the output capacitor to the level that requires the next
“ON” cycle. The on-time is kept the same as that in the
heavy-load condition. In reverse, when the output current
increases from light load to heavy load, the switching
frequency increases to the preset value as the inductor
current reaches the continuous condition. The transition
load point to the light load operation can be calculated as
follows (Figure 1) :
ILOAD
≈
(VIN − VOUT )
2L
x tON
where tON is the On-time.
DS8204L-04 April 2011
www.richtek.com
11
11 Page | ||
| Páginas | Total 18 Páginas | |
| PDF Descargar | [ Datasheet RT8204L.PDF ] | |
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