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PDF RT8805 Data sheet ( Hoja de datos )
| Número de pieza | RT8805 | |
| Descripción | Two Phase General Purpose PWM Controller | |
| Fabricantes | Richtek Technology | |
| Logotipo |  |
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Preliminary
RT8805
Two Phase General Purpose PWM Controller
General Description
The RT8805 is the most compact dual-phase synchronous
buck controller in the industry specifically designed for
high power density applications. This part is capable of
delivering up to 60A output current due to its embedded
bootstrapped drivers that support 12V + 12V driving
www.DataShceaept4aUb.icliotym.
The phase currents are sensed by innovative time sharing
RDS(ON) current sensing technique for current balance and
over current balance. Using one common GM amplifier to
sense two phase currents eliminates offset and
nonlinearity of the GM amplifier and yields good current
balance. Other features include adjustable operation
frequency from 50kHz to 1MHz, adjustable soft-start,
PGOOD, external compensation, enable/shutdown for
various application and performance consideration.
The RT8805 comes to a tiny footprint package of
VQFN-16L 3x3 package that is capable of dissipating up
to 1.47W heat.
Ordering Information
RT8805
Package Type
QV : VQFN-16L 3x3 (V-Type)
Operating Temperature Range
P : Pb Free with Commercial Standard
Features
z 12V Power Supply Voltage
z 2 Phase Power Conversion
z Embedded 12V Boot Strapped Driver
z Precise Core Voltage Regulation
z Low Side MOSFET RDS(ON) Current Sensing for
Power Stage Current Balance
z External Compensation
z Adjustable Soft-Start
z Adjustable Frequency and Typical at 300kHz Per
Phase
z Power Good Indication
z Adjustable Over Current Protection
z Small 16-Lead VQFN Package
z RoHS Compliant and 100% Lead (Pb)-Free
Applications
z Middle-High End GPU Core Power
z High End Desktop PC Memory Core Power
z Low Output Voltage, High Power Density DC-DC
Converters
z Voltage Regulator Modules
Pin Configurations
(TOP VIEW)
Note :
RichTek Pb-free 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.
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.
16 15 14 13
UGATE1
BOOT1
AGND
IMAX
1
2
3
4
GND
12 PHASE2
11 UGATE2
10 BOOT2
9 PGOOD
5678
VQFN-16L 3x3
DS8805-01 November 2005
www.richtek.com
1
1 page  
Preliminary
RT8805
Parameter
Reference Voltage
Feedback Voltage
Error Amplifier
DC Gain
Symbol
Test Conditions
VFB VFB = 0.8V
Gain-Bandwidth Product
Trans-conductance
MAX Current (Source & Sink)
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Current Sense GM Amplifier
OC
Gate Driver
Maximum Upper Drive Source
Upper Drive Sink
Maximum Lower Drive Source
Lower Drive Sink
Protection
Under Voltage Protection
GBW
GM
ICOMP
CLOAD = 5pF
RLOAD = 20kΩ
VCOMP = 2.5V
VPHASE
RIMAX = 33kΩ
IUGATE(MAX) BOOT − PHASE = 12V
RUGATE
VUGATE = 1V
ILGATE(MAX) PVCC = 12V
RLGATE
VLGATE = 1V
Power Sequence
Power Good Threshold
Power Good Sink Capability (4mA)
Min Typ Max Units
0.784 0.8 0.816 V
60 70
6 10
600 660
300 360
-- dB
-- MHz
-- μA/V
-- μA
-- -220 -- mV
1 -- --
-- 3.5 7
1 -- --
-- 2 4
A
Ω
A
Ω
0.55 0.6 0.65 V
3.4 3.7
4
-- 0.05 0.2
V
V
Note 1. Stresses listed as the above "Absolute Maximum Ratings" may cause permanent damage to the device. These are for
stress ratings. Functional operation of the device at these or any other conditions beyond those indicated in the
operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended
periods may remain possibility to affect device reliability.
Note 2. Devices are ESD sensitive. Handling precaution recommended.
Note 3. The device is not guaranteed to function outside its operating conditions.
Note 4. θJA is measured in the natural convection at TA = 25°C on a low effective thermal conductivity test board of
JEDEC 51-3 thermal measurement standard.
DS8805-01 November 2005
www.richtek.com
5
5 Page 
Preliminary
RT8805
80 80
Loop Gain
60
40 40
20
Compensation
Gain
00
Modulator
-20 Gain
-40-40
-60-60
www.DataSheet4U.com110H0zvdb(vo) vdb(comp2)11000vHd0zb(lo)
11.0kKHz 110K0Hzk
FrequFreequnenccyy (Hz)
11000K0Hzk
Figure 8. Type 2 Bode Plot
1.01MHMz
There is another type of compensation called Type 3
compensation that adds a pole-zero pair to the Type 2
network. It's used to compensate output capacitor whose
ESR value is much lower (pure MLCC or OSCON
Capacitors).
As shown in Figure 9, to insert a network between VOUT
and FB in the original Type 2 compensation network can
result in Type 3 compensation. Figure 10 shows the
difference of their AC response. Type 3 compensation has
an additional pole-zero pair that causes a gain boost at
the flat gain region. But the gain boosted is limited by the
ratio (R1+R4)/R4; if R3 << R4.
VOUT
C3 R3
R1 FB +GM
-
C2
VCOMP
C1
R4 R2
Figure 9. Additional Network of Type 3 Compensation
(Add between VOUT and FB)
FP3
Add Type 3 compensation
FP1
Pole
FP2
FZ1 FZ2
Original Type 3 compensation
Figure 10. AC Response Curves of Type 2 and 3
DS8805-01 November 2005
Type 3 will induce three poles and two zeros.
Zeros :
FZ1
=
2π
1
×R2× C2
FZ2
=
2π
1
× (R1+ R3)× C3
Poles :
FP1
=
2π
1
×
R2
×
⎜⎝⎛
C1×
C1+
C2
C2
⎟⎠⎞
FP2
=
2π
1
×R3 × C3
FP3
=
2π
1
× ⎜⎝⎛ R1R×1R+3R×3C1⎟⎠⎞
;
which is in the origin.
We recommend FZ1 placed in 0.5 x FP(LC); FZ2 placed in
FP(LC); FP1 placed in FESR and FP2 placed in 0.5 x FSW.
Figure 11 shows Type 3 Bode Plot.
60
40
20
0
-20
-40
-60
-80
2
Loop Gain
Compensation Gain
Gain
Modulator Gain
3456
Log Frequency
7
Figure 11. Type 3 Bode Plot
Protection
OCP
The RT8805 uses “ Cycle by Cycle” current comparison.
The over current level is set by IMAX pin. When OC
function occurs and SS > 3.7V, a constant current of 10μA
starts to discharge the capacitor connected to SS pin
right away. When OC occurs, UGATE and LGATE will be
off.
www.richtek.com
11
11 Page | ||
| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet RT8805.PDF ] | |
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