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PDF RT8237B Data sheet ( Hoja de datos )
| Número de pieza | RT8237B | |
| Descripción | (RT8237A/B) High Efficiency Single Synchronous Buck PWM Controller | |
| Fabricantes | RICHTEK | |
| Logotipo |  |
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RT8237A/B
High Efficiency Single Synchronous Buck PWM Controller
General Description
The RT8237A/B 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 RT8237A/B 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 and enter diode emulation mode at
light load condition. The buck conversion allows this device
to directly step down high voltage batteries at the highest
possible efficiency. The pre-set frequency selections
minimize design effort required for new designs. The
RT8237A/B is intended for CPU core, chipset, DRAM, or
other low voltage supplies as low as 0.7V. The RT8237A
is available in a WDFN-10L 3x3 package, The RT8237B is
available in a WQFN-12L 2x2 package.
Ordering Information
RT8237 -
Package Type
QW : WDFN-10L 3x3 (W-Type)
QW : WQFN-12L 2x2 (W-Type)
Lead Plating System
G : Green (Halogen Free and Pb Free)
Z : ECO (Ecological Element with
Halogen Free and Pb free)
A : WDFN-10L 3x3
B : WQFN-12L 2x2
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.
Copyright ©2012 Richtek Technology Corporation. All rights reserved.
DS8237A/B-05 March 2012
Features
z Wide Input Voltage Range : 4.5V to 26V
z Output Voltage Range : 0.7V to 3.3V
z Built-in 0.5% 0.7V Reference Voltage
z Quick Load-Step Response within 100ns
z 4700ppm/°C Programmable Current Limit by Low
Side RDS(ON) Sensing
z 4 Selectable Frequency Setting
z Soft-Start Control
z Drives Large Synchronous-Rectifier FETs
z Integrated Boot Switch
z Built-in OVP/OCP/UVP
z Thermal Shutdown
z Power Good Indicator
z RoHS Compliant and Halogen Free
Applications
z Notebook Computers
z CPU Core Supply
z Chipset/RAM Supply as Low as 0.7V
z Generic DC/DC Power Regulator
Pin Configurations
(TOP VIEW)
PGOOD 1
CS 2
EN 3
FB 4
RF 5
10 BOOT
9 UGATE
8 PHASE
7 VCC
11 6 LGATE
WDFN-10L 3x3
RT8237A
12 11 10
LGATE 1
VCC 2
PHASE 3
GND
13
456
9 FB
8 EN
7 CS
WQFN-12L 2x2
RT8237B
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1
Free Datasheet http://www.datasheet4u.com/
1 page  
RT8237A/B
Absolute Maximum Ratings (Note 1)
z VCC, FB, PGOOD, EN, CS, RF to GND ---------------------------------------------------------------------------- −0.3V to 6V
z PHASE to GND
DC ----------------------------------------------------------------------------------------------------------------------------- −0.3V to 32V
<20ns ------------------------------------------------------------------------------------------------------------------------ −8V to 38V
z BOOT to PHASE ---------------------------------------------------------------------------------------------------------- −0.3V to 6V
z UGATE to PHASE -------------------------------------------------------------------------------------------------------- −0.3V to 6V
DC ----------------------------------------------------------------------------------------------------------------------------- −0.3V to 6V
<20ns ------------------------------------------------------------------------------------------------------------------------ −5V to 7.5V
z LGATE to GND ------------------------------------------------------------------------------------------------------------- −0.3V to 6V
DC ----------------------------------------------------------------------------------------------------------------------------- −0.3V to 6V
<20ns ------------------------------------------------------------------------------------------------------------------------ −2.5V to 7.5V
z Power Dissipation, PD @ TA = 25°C
WDFN-10L 3x3 ------------------------------------------------------------------------------------------------------------- 0.952W
WQFN-12L 2x2 ------------------------------------------------------------------------------------------------------------ 0.606W
z Package Thermal Resistance (Note 2)
WDFN-10L 3x3, θJA ------------------------------------------------------------------------------------------------------- 105°C/W
WDFN-10L 3x3, θJC ------------------------------------------------------------------------------------------------------- 8.2°C/W
WQFN-12L 2x2, θJA ------------------------------------------------------------------------------------------------------- 165°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 Control Voltage, VCC ------------------------------------------------------------------------------------------------------ 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
(VCC = 5V, TA = 25°C, unless otherwise specified)
Parameter
Symbol
Test Conditions
Input Power Supply
VCC Quiescent Supply
Current
VCC Shutdown Current
CS Shutdown Current
IQ
ISHDN
FB forced above the regulation
point, EN = 5V,
VCC Current, EN = 0V
CS pull to GND
FB Error Comparator
Threshold
VREF
DEM
DEM, TA = −40 to 85°C (Note 5)
Min
--
--
--
0.7005
0.697
Typ
500
--
--
0.704
0.704
Max
1250
1
1
0.7075
0.711
Unit
μA
μA
μA
V
Copyright ©2012 Richtek Technology Corporation. All rights reserved.
DS8237A/B-05 March 2012
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
5
Free Datasheet http://www.datasheet4u.com/
5 Page 
RT8237A/B
Application Information
The RT8237A/B 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. Richtek 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
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 block diagram, the synchronous UGATE driver
is turned on at the beginning of each cycle. After the
internal one-shot timer expires, the UGATE driver will be
turned off. The pulse width of this one shot is determined
by the converter's input voltage and the output voltage 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/MODE)
The on-time one-shot comparator has two inputs. One
input monitors the output voltage from the PHASE pin,
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 output
voltage and inversely proportional to input voltage.
The on-time is given by :
tON = (VOUT / VIN) / fSW
Copyright ©2012 Richtek Technology Corporation. All rights reserved.
DS8237A/B-05 March 2012
Table 1. RF Connection and Switching Frequency
RRF (kΩ)
470kΩ
200kΩ
100kΩ
39kΩ
Switching Frequency (kHz)
290
340
380
430
Note : For DEM, connect RRF to GND; for CCM, connect RRF
to PGOOD.
Enable and Disable
The EN pin allows for power sequencing between the
controller bias voltage and another voltage rail. The
RT8237A/B remains in shutdown if the EN pin is lower
than 500mV. When the EN pin rises above the VEN trip
point, the RT8237A/B will begin a new initialization and
soft-start cycle.
POR, UVLO and Soft-Start
Power On Reset (POR) occurs when VCC rises above
approximately 4.1V, in which the RT8237A/B resets the
fault latch and prepares the PWM for operation. Below
3.7V (min), the VCC Under Voltage Lockout (UVLO)
circuitry inhibits switching by keeping UGATE and LGATE
low. A built-in soft-start is used to prevent the power supply
input from surge currents after PWM is enabled. A ramping
up current limit threshold eliminates the VOUT folded-back
current during the soft-start duration.
Mode Selection (RF) Operation
To select the operation mode, connect a resistor from the
RF pin to either GND or PGOOD. When the resistor is
connected to GND, the controller operates in diode
emulation mode. When the resistor is connected to
PGOOD, the controller operates in CCM mode.
Diode-Emulation Mode (RRF Connected to GND)
In diode-emulation mode, the RT8237A/B automatically
reduces switching frequency at light load conditions to
maintain high efficiency. This reduction of frequency is
achieved smoothly without increasing VOUT ripple or load
regulation. As the output current decreases from heavy
load condition, the inductor current is reduced and
eventually comes to the point where its valley touches
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
11
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| Páginas | Total 18 Páginas | |
| PDF Descargar | [ Datasheet RT8237B.PDF ] | |
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