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PDF RT9218 Data sheet ( Hoja de datos )
| Número de pieza | RT9218 | |
| Descripción | 5V/12V Synchronous Buck PWM DC/DC and Linear Power Controller | |
| Fabricantes | RichTek | |
| Logotipo |  |
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RT9218
5V/12V Synchronous Buck PWM DC/DC and Linear Power
Controller
General Description
The RT9218 is a dual output with one synchronous buck
PWM and one linear controller. The part is proposed to
generate logic-supply voltages for PC based systems. The
high-performance device includes internal soft-start,
frequency-compensation networks, power good signaling
with specific sequence, and it comes all of the logic control,
output adjustment, power monitoring and protection
functions into a small footprint package. The part is
operated at fixed 300kHz frequeny providing an optimum
compromise between efficiency, external component size,
and cost. The linear controller is implemented to drive an
external MOSFET for regulation and it's adjustable by
setting external resistors. Moreover the specific internal
PGOOD sequence and indicator is also implemented to
conform to Intel®new platform requirement on FSB_VTT
power plane. An adjustable over-current protection (OCP)
is proposed to monitor the voltage drop across the RDS(ON)
of the lower MOSFET for synchronous buck PWM DC/
DC controller.
Ordering Information
RT9218
Package Type
S : SOP-14
Lead Plating System
P : Pb Free
G : Green (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.
Features
z Operating with 5V or 12V Supply Voltage
z Drives All Low Cost N-MOSFETs
z Voltage Mode PWM Control
z 300kHz Fixed Frequency Oscillator
z Fast Transient Response :
`High-Speed GM Amplifier
`Full 0 to 100% Duty Ration
z Internal Soft-Start
z Power Good Indicator
z Adaptive Non-Overlapping Gate Driver
z Over Current Fault Monitor on MOSFET, No Current
Sense Resistor Required
z Specific Power Good Indicator for Intel®
Grantsdale FSB_VTT Power Sequence
z RoHS Compliant and 100% Lead (Pb)-Free
Applications
z Graphic Card
z Motherboard, Desktop Servers
z IA Equipments
z Telecomm Equipments
z High Power DC-DC Regulators
Pin Configurations
(TOP VIEW)
BOOT
UGATE
GND
LGATE
DRV
NC
NC
2
3
4
5
6
7
14 PHASE
13 OPS
12 FB
11 VCC
10 PGOOD
9 FBL
8 NC
SOP-14
DS9218-09 April 2011
www.richtek.com
1
1 page  
RT9218
Absolute Maximum Ratings (Note 1)
z Supply Voltage, VCC ------------------------------------------------------------------------------------ 16V
z BOOT, VBOOT - VPHASE ---------------------------------------------------------------------------------- 16V
z PHASE to GND
DC ----------------------------------------------------------------------------------------------------------- −5V to 15V
< 200ns ---------------------------------------------------------------------------------------------------- −10V to 30V
z BOOT to PHASE ---------------------------------------------------------------------------------------- 15V
z BOOT to GND
DC ----------------------------------------------------------------------------------------------------------- −0.3V to VCC+15V
< 200ns ---------------------------------------------------------------------------------------------------- −0.3V to 42V
z UGATE ----------------------------------------------------------------------------------------------------- VPHASE − 0.3V to VBOOT + 0.3V
z LGATE ----------------------------------------------------------------------------------------------------- GND − 0.3V to VVCC + 0.3V
z Input, Output or I/O Voltage --------------------------------------------------------------------------- GND − 0.3V to 7V
z Package Thermal Resistance (Note 2)
SOP-14, θJA ----------------------------------------------------------------------------------------------- 127.67°C/W
z Junction Temperature ----------------------------------------------------------------------------------- 150°C
z Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------- 260°C
z Storage Temperature Range --------------------------------------------------------------------------- −40°C to 150°C
z ESD Susceptibility (Note 3)
HBM (Human Body Mode) ----------------------------------------------------------------------------- 2kV
MM (Machine Mode) ------------------------------------------------------------------------------------ 200V
Recommended Operating Conditions (Note 4)
z Supply Voltage, VCC ------------------------------------------------------------------------------------ 5V ± 5%,12V ± 10%
z Junction Temperature Range -------------------------------------------------------------------------- −40°C to 125°C
z Ambient Temperature Range -------------------------------------------------------------------------- −40°C to 85°C
Electrical Characteristics
(VCC = 5V/12V, TA = 25°C, unless otherwise specified)
Parameter
Symbol
Test Conditions
VCC Supply Current
Nominal Supply Current
Power-On Reset
POR Threshold
Hysteresis
Switcher Reference
Reference Voltage
Oscillator
Free Running Frequency
Ramp Amplitude
ICC UGATE and LGATE Open
VCCRTH
VCCHYS
VCC Rising
VREF
VCC = 12V
fOSC
ΔVOSC
VCC = 12V
Min Typ Max Unit
-- 6 15 mA
-- 4.1
0.35 0.5
4.5
--
V
V
0.784 0.8 0.816 V
250 300 350 kHz
-- 1.5 -- VP-P
DS9218-09 April 2011
To be continued
www.richtek.com
5
5 Page 
The AC impedance of output capacitor at operating
frequency is quite smaller than the load impedance, so
the ripple current (ΔIL) of the inductor current flows mainly
through output capacitor. The output ripple voltage is
described as :
ΔVOUT = ΔVOR + ΔVOC
ΔVOUT
=
ΔIL
× rc
+
1
CO
∫ t2
t1
ic
dt
ΔVOUT
=
ΔIL
× ΔIL
× rc +
1
8
VOUT
COL
(1− D)T 2
S
(2)
(3)
(4)
where ΔVOR is caused by ESR and ΔVOC by capacitance.
For electrolytic capacitor application, typically 90 to 95%
of the output voltage ripple is contributed by the ESR of
output capacitor. So Equation (4) could be simplified as :
ΔVOUT = ΔIL x rc
(5)
Users could connect capacitors in parallel to get calculated
ESR.
Input Capacitor
The selection of input capacitor is mainly based on its
maximum ripple current capability. The buck converter
draws pulsewise current from the input capacitor during
the on time of S1 as shown in Figure 1. The RMS value of
ripple current flowing through the input capacitor is
described as :
Irms = IOUT D(1− D) (A)
(6)
The input capacitor must be cable of handling this ripple
current. Sometime, for higher efficiency the low ESR
capacitor is necessarily.
PWM Loop Stability
RT9218 is a voltage mode buck converter using the high
gain error amplifier with transconductance (OTA,
Operational Transconductance Amplifier).
The transconductance :
GM
=
dIOUT
dVm
The mid-frequency gain :
dVOUT = dIOUTZOUT = GMdVINZOUT
G=
dVOUT
dVIN
= GMZOUT
DS9218-09 April 2011
RT9218
ZOUT is the shut impedance at the output node to ground
(see Figure 3 and Figure 4),
GM VOUT
C1
C2
R1
Figure 3. A Type 2 error-amplifier with shut network to
ground
EA+ +
EA- - GM
+ RO
VOUT
Figure 4. Equivalent circuit
Pole and Zero :
FP
=
2π
1
× R1C2
;
FZ
=
2π
1
× R1C1
We can see the open loop gain and the Figure 3 whole
loop gain in Figure 5.
Open Loop, Unloaded Gain
A Closed Loop, Unloaded Gain
FZ FP
Gain = GMR1
B
100 1000 10k 100k
Frequency (Hz)
Figure 5. Gain with the Figure 2 circuit
RT9218 internal compensation loop :
GM = 0.2ms, R1 = 75kΩ, C1 = 2.5nF, C2 = 10pF
www.richtek.com
11
11 Page | ||
| Páginas | Total 18 Páginas | |
| PDF Descargar | [ Datasheet RT9218.PDF ] | |
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