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PDF RT8800A Data sheet ( Hoja de datos )
| Número de pieza | RT8800A | |
| Descripción | General Purpose 3-Phase PWM Controller | |
| Fabricantes | Richtek Technology | |
| Logotipo |  |
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RT8800A
General Purpose 3-Phase PWM Controller for High-Density
Power Supply
General Description
Features
The RT8800A is a general-purposed multi-phase
synchronous buck controller dedicating for high power
density applications. The RT8800A operates with 2 or 3
synchronous buck switching stages in interleaved phase
set automatically. The multiphase architecture provides
high output current while maintaining low power dissipation
www.DataSohenetp4Uow.coemr devices and low stress on input and output
capacitors.
The output voltage is precisely regulated to the external
reference voltage at PI pin. The RT8800A can provide Intel®
VRD10.x or AMD® K8 compliant output voltage when
companioned with DAC generator RT9401A/B.
The RT8800A adopts innovative time-sharing DCR current
sensing technique for channel current balance, droop
tuning, and over current protection. Using one common
GM amplifier for current sensing eliminates offset errors
and linearity variation between GMs. As sub-milli-ohm-
grade inductors are widely used in modern mother boards,
slight mismatch of GM amplifiers offset and linearity results
in considerable current shift between phases. The time-
sharing DCR current sensing technique is extremely
important to guarantee phase current balance at mass
production.
Other features include overvoltage protection, undervoltage
protection and internal softstart. The RT8800A comes to
a VQFN-16L 3x3 package.
Ordering Information
RT8800A
Package Type
QV : VQFN-16L 3x3 (V-Type)
Operating Temperature Range
P : Pb Free with Commercial Standard
G : Green (Halogen Free with Commer-
cial Standard)
z 5V Power Supply Voltage
z 2/3-Phase Power Conversion with Automatic Phase
Selection
z Output Voltage Controlled by External Reference
Voltage
z Precise Core Voltage Regulation
z Power Stage Thermal Balance by DCR Current
Sensing
z Extreme Low-Cost, Lossless Time Sharing Current
Sensing
z Internal Soft-Start
z Hiccup Mode Over-Current Protection
z Over-Voltage Protection
z Adjustable Operating Frequency and Typical at
300kHz Per Phase
z Power Good Indication
z Small 16-Lead VQFN Package
z RoHS Compliant and 100% Lead (Pb)-Free
Applications
z Desktop CPU Core Power
z Low Output Voltage, High Power Density DC-DC
Converters
z Voltage Regulator Modules
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.
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.
All brand name or trademark belong to their owner respectively
DS8800A-04 August 2007
www.richtek.com
1
1 page  
RT8800A
Absolute Maximum Ratings (Note 1)
z Supply Voltage, VDD ------------------------------------------------------------------------------------------- 7V
z Input, Output or I/O Voltage ---------------------------------------------------------------------------------- GND − 0.3V to VDD+ 0.3V
z Power Dissipation, PD @ TA = 25°C
VQFN-16L 3x3 -------------------------------------------------------------------------------------------------- 1.47W
z Package Thermal Resistance (Note 4)
VQFN-16L 3x3, θJA --------------------------------------------------------------------------------------------- 68°C/W
z Junction Temperature ------------------------------------------------------------------------------------------ 150°C
z Lead Temperature (Soldering, 10 sec.) -------------------------------------------------------------------- 260°C
www.DataShzeSett4oUr.acgome Temperature Range --------------------------------------------------------------------------------- −65°C to 150°C
z ESD Susceptibility (Note 2)
HBM (Human Body Mode) ----------------------------------------------------------------------------------- 2kV
MM (Machine Mode) ------------------------------------------------------------------------------------------- 200V
Recommended Operating Conditions (Note 3)
z Supply Voltage, VDD ------------------------------------------------------------------------------------------- 5V ± 10%
z Ambient Temperature Range --------------------------------------------------------------------------------- 0°C to 70°C
z Junction Temperature Range --------------------------------------------------------------------------------- 0°C to 125°C
Electrical Characteristics
(VDD = 5V, TA = 25°C, unless otherwise specified)
Parameter
Symbol
VDD Supply Current
Nominal Supply Current
Power-On Reset
VDD Threshold
Rising
Hysteresis
DVD Rising Threshold
IDD
DVD Hysteresis
Oscillator
Free Running Frequency
Frequency Adjustable Range
Ramp Amplitude
Ramp Valley
Maximum On-Time of Each Channel
fOSC
fOSC_ADJ
ΔVOSC
VRV
RT Pin Voltage
Reference Voltage
IMAX Reference Voltage
VID125 Reference Voltage
VRT
VIMAX
VVID125
Test Conditions
PWM 1,2,3 Open
RRT = 16kΩ
RRT = 16kΩ
RRT = 16kΩ
RIMAX = 16kΩ
RVID125 = 16kΩ
Min
--
4.0
0.2
0.75
--
170
50
--
--
62
0.77
0.75
0.75
All brand name or trademark belong to their owner respectively
DS8800A-04 August 2007
Typ Max Units
5 -- mA
4.2 4.5
V
0.5 --
V
0.8 0.85 V
65 -- mV
200
--
1.7
1.0
66
0.82
230
400
--
--
75
0.87
kHz
kHz
V
V
%
V
0.8 0.85
0.8 0.85
V
V
To be continued
www.richtek.com
5
5 Page 
RT8800A
COMP VRAMP_Valley
Cross-over
SS_Internal
VCORE
www.DataSheet4U.com
SSE_Internal
S/H CKT
+
-
IX
T1
T3
LX RLX ILX
RX CX
+ VX -
VOUT
Figure 2
Time-Sharing DCR Current Sensing
RT8800A adopts an innovative time-sharing DCR current
sensing technique to sense the phase currents for phase
current balance (phase thermal balance), over current
protection and load line regulation as shown in Figure 3.
The current sensing amplifier GM samples and holds
voltages VX across the current sensing capacitor CX by
turns in a switching cycle. According to the Basic Circuit
Theory, if
LX
RLX
= RX ×CX
then VX
= ILX × RLX
Consequently, the sensing current IX is proportional to
inductor current ILX and is expressed as
IX
=
ILX ×RLX
RCOMM
The sensed current IX is used for current balance, over
current protection, and droop tuning as described as
followed. Since all phases share one common GM, GM
offset and linearity variation effect are eliminated in
practical applications. As sub-milli-ohmgrade inductors are
widely used in modern motherboards, slight mismatch of
GM amplifiers offset and linearity results in considerable
current shift between phases. The time sharing DCR current
sensing technical is extremely important to guarantee
phase current balance at mass production.
T2
Figure 3
RCOMM
Figure 4 and 5 show the linearity of GM amplifier and its
test circuit respectively. A voltage source is applied to
ISPx while other ISPx pins are short to VOUT. The voltage
VADJ across resistor RADJ is measured. It is observed from
Figure 5 shows that all ISPx share the same
transconductance linearity and voltage offset.
70
60
50
40
30
20
10
0
0
GM
GM1
GM3
GM2
20 40 60 80
VXC (mV)
Figure 4. The Linearity of GMx
100
All brand name or trademark belong to their owner respectively
DS8800A-04 August 2007
www.richtek.com
11
11 Page | ||
| Páginas | Total 21 Páginas | |
| PDF Descargar | [ Datasheet RT8800A.PDF ] | |
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