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PDF RT9232B Data sheet ( Hoja de datos )
| Número de pieza | RT9232B | |
| Descripción | Programmable Frequency Synchronous Buck PWM Controller | |
| Fabricantes | Richtek | |
| Logotipo |  |
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RT9232B
Programmable Frequency Synchronous Buck PWM Controller
General Description
www.datasheet4u.com
The RT9232B is a single-phase synchronous buck PWM
DC-DC converter controller designed to drive two
N- MOSFETs. It provides a highly accurate, programmable
output voltage precisely regulated to low voltage
requirement with an internal 0.8V ± 1% reference.
The RT9232B uses an external compensated, single
feedback loop voltage mode PWM control for fast transient
response. An oscillator with Programmable frequency
(50kHz to 800kHz) reduces the external inductor and
capacitor component size for saving PCB board area.
The RT9232B provides fast transient response to satisfy
high current output applications (up to 25A) while
minimizing external components. It is suitable for high-
performance graphic processors, DDR and VTT power.
The RT9232B integrates complete protect functions such
as Soft Start, Output Enable, UVLO(under-voltage lockout)
and OCP into a small 14-pin package.
Applications
System (Graphic, MB) with 12V Power.
Graphic Cards (AGP 8X, 4X, PCI Express*16) :
`High-Current for High-Performance Graphic Processors
(GPU, VPU)
`Middle Current for High-Performance Graphic Memory
Power (DDR, DDR II)
`Low Current with Sink Capacity for High-Performance
Graphic Memory Power (DDR/VTT)
3.3V to 12V Input DC-DC Regulators
Low Voltage Distributed Power Supplies
Pin Configurations
(TOP VIEW)
RT
OCSET
SS
COMP
FB
EN
GND
2
3
4
5
6
7
14 VCC
13 PVCC
12 LGATE
11 PGND
10 BOOT
9 UGATE
8 PHASE
SOP-14
Features
Single IC Supply Voltage : 12V
Single phase DC/DC Buck Converter with
`High Output Current (up to 25A )
`Low Output Voltage (down to 0.8V )
`High Input Voltage (up to 12V )
Operate from 12V, 5V or 3.3V Input
0.8V ± 1% Internal Reference
Adaptive Non-Overlapping Gate Drivers
Integrated High-Current, HV Gate Drivers
External Programmable Soft Start
External Programmable Frequency
(Range : 50kHz to 800kHz, 200kHz Free Run )
Provide Over Current Protection by Sensing
MOSFET RDS(ON)
On/Off Control by Enable Pin
Drives Two N-MOSFET
Full 0 to 100% Duty Cycle
Fast Transient Response
Voltage Mode PWM Control with External
Feedback Loop Compensation
RoHS Compliant and 100% Lead (Pb)-Free
Ordering Information
RT9232B
Package Type
S : SOP-14
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.
DS9232B-03 March 2007
www.richtek.com
1
1 page  
RT9232B
Absolute Maximum Ratings (Note 1)
Supply Input Voltage, VCC, PVCC --------------------------------------------------------------------------- 15V
PHASE to GND
www.dDaCtas-h--e-e-t-4-u--.c--o-m------------------------------------------------------------------------------------------------------- −5V to 15V
< 200ns ------------------------------------------------------------------------------------------------------------ −10V to 30V
BOOT to PHASE ------------------------------------------------------------------------------------------------ 15V
BOOT to GND
DC ------------------------------------------------------------------------------------------------------------------- −0.3V to VCC+15V
< 200ns ------------------------------------------------------------------------------------------------------------ −0.3V to 42V
SS, FB, COMP, RT --------------------------------------------------------------------------------------------- 6V
Input, Output or I/O Voltage ----------------------------------------------------------------------------------- GND−0.3V to VCC+ 0.3V
Package Thermal Resistance (Note 4)
SOP-14, θJA ----------------------------------------------------------------------------------------------------- 100°C/W
Lead Temperature (Soldering, 10 sec.) -------------------------------------------------------------------- 260°C
Junction Temperature ------------------------------------------------------------------------------------------ 150°C
Storage Temperature Range ---------------------------------------------------------------------------------- −65°C to 150°C
ESD Susceptibility (Note 2)
HBM (Human Body Mode) ----------------------------------------------------------------------------------- 2kV
MM (Machine Mode) ------------------------------------------------------------------------------------------- 150V
Recommended Operating Conditions (Note 3)
Supply Input Voltage, VCC ------------------------------------------------------------------------------------ 12V ±10%
Supply Voltage to Drain of Upper MOSFETs, VIN ------------------------------------------------------- 3.3V, 5V to 12V ±10%
Ambient Temperature Range --------------------------------------------------------------------------------- −40°C to 85°C
Junction Temperature Range --------------------------------------------------------------------------------- −40°C to 125°C
Electrical Characteristics
(VCC = 12V, TA = 25°C, Unless otherwise specified.)
Parameter
VCC Supply Current
Nominal Supply Current
Power-On Reset (POR)
Symbol
Test Conditions
Min
ICC EN = VCC, UGATE, LGATE open --
VCC Rising Threshold
VCC_ON VOCSET = 4.5V
Power On Reset Hysteresis
VOCSET = 4.5V
OCSET Rising Threshold for start up VOCSET_ON
Enable Input Threshold (ON)
VEN_ON VOCSET = 4.5V
Enable Input Threshold (OFF)
VEN,_OFF VOCSET = 4.5V
Oscillator
8.4
0.3
--
--
0.8
RT9232B
Free Running Frequency
Variation
fOSC
6k < (RT to GND) < 200k
170
−20
Ramp Amplitude
ΔVOSC
--
Typ. Max Units
3 -- mA
-- 10.4
0.7 --
1.5 2
-- 2
-- --
V
V
V
V
V
200 230 kHz
-- 20 %
1.5 -- VP-P
To be continued
DS9232B-03 March 2007
www.richtek.com
5
5 Page 
RT9232B
Switching Frequency Setting
The default switching frequency is 200kHz when RT pin
left open. A resistor connected (RRT) from RT pin to ground
increases the switching frequency as Equation (3).
www.datasheet4u.com
fOSC
=
200kHz
+
2.9 ×106
RRT (Ω)
kHz
(3)
(RRT to GND)
Conversely, connecting a pull-up resistor (RRT) from RT pin
reduces the switching frequency according to Equation (4)
fOSC
=
200kHz
−
33 ×106
RRT (Ω)
kHz
(4)
(RRT to VCC = 12V)
Under Voltage Protection
The under voltage protection is enabled when the RT9232B
is activated and SS voltage is higher than 4V. The UVP
function is specified for protecting the converter from an
instant output short circuit during normal operation. The
RT9232B continuously monitors the output voltage by
detecting the voltage on FB pin. The UVP function is
triggered and initiates the hiccup cycles when output
voltage lower than 75% of designated voltage with a 30us
delay.
Hiccup cycle turns off both upper and lower MOSFET first.
An internal 10uA current sink discharges the softstart
capacitor CSS. SS pin voltage ramps down linearly. When
SS pin voltage touches 0V, hiccup cycle releases and
normal softstart cycle takes over. When SS voltage is
higher than 4V, the UVP function is enabled again. The
hiccup cycle restarts if the output short event still remains.
The converter is shutdown permanently after 3 times hiccup
and only restarting supply voltages can enable the
converter.
Note that triggering the POR function or EN will reset the
hiccup counter. Make sure that VCC, EN and OCSET pin
voltages are higher than their respective trip level when
output short circuit occurs or the UVP function may not
latch up the converter causing permanent damage to the
converter.
Component Selection
Components should be appropriately selected to ensure
stable operation, fast transient response, high efficiency,
minimum BOM cost and maximum reliability.
Output Inductor Selection
The selection of output inductor is based on the
considerations of efficiency, output power and operating
frequency. For a synchronous buck converter, the ripple
current of inductor (ΔIL) can be calculated as follows :
ΔIL
= (VIN
− VOUT ) ×
VOUT
VIN × fOSC
×L
(5)
Generally, an inductor that limits the ripple current between
20% and 50% of output current is appropriate. Make sure
that the output inductor could handle the maximum output
current and would not saturate over the operation
temperature range.
Output Capacitor Selection
The output capacitors determine the output ripple voltage
(ΔVOUT) and the initial voltage drop after a high slew-rate
load transient. The selection of output capacitor depends
on the output ripple requirement. The output ripple voltage
is described as Equation (6).
ΔVOUT
=
ΔIL
× ESR +
1×
8
VOUT
fO2 SC × L × COUT
(1− D)
(6)
For electrolytic capacitor application, typically 90~95%
of the output voltage ripple is contributed by the ESR of
output capacitors. Paralleling lower ESR ceramic capacitor
with the bulk capacitors could dramatically reduce the
equivalent ESR and consequently the ripple voltage.
Input Capacitor Selection
Use mixed types of input bypass capacitors to control
the input voltage ripple and switching voltage spike across
the MOSFETs. The buck converter draws pulsewise
current from the input capacitor during the on time of upper
MOSFET. The RMS value of ripple current flowing through
the input capacitor is described as :
IIN(RMS) = IOUT × D × (1− D)
(7)
The input bulk capacitor must be cable of handling this
ripple current. Sometime, for higher efficiency the low ESR
capacitor is necessarily. Appropriate high frequency
ceramic capacitors physically near the MOSFETs
effectively reduce the switching voltage spikes.
DS9232B-03 March 2007
www.richtek.com
11
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet RT9232B.PDF ] | |
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