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PDF RT9248A Data sheet ( Hoja de datos )
| Número de pieza | RT9248A | |
| Descripción | Multi-Phase PWM Controller | |
| Fabricantes | Richtek Technology | |
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Preliminary
RT9248A
Multi-Phase PWM Controller for CPU Core Power Supply
General Description
The RT9248A is a cost-effective multi-phase buck DC/DC
controller integrated with all control functions for GHz CPU
VRM. The RT9248A controls 2 or 3 buck switching stages
operating in interleaved phase set automatically. The multi-
phase architecture provides high output current while
maintaining low power dissipation on power devices and
low stress on input and output capacitors. The high
equivalent operating frequency also reduces the component
dimension and the output voltage ripple in load transient.
RT9248A controls both voltage and current loops to achieve
good regulation, response & power stage thermal balance.
Precise current loop using RDS(ON) as sense component
builds precise load line for strict VRM DC & transient
specification and also ensures thermal balance of different
power stages. The settings of current sense, droop tuning,
VCORE initial offset and over current protection are
independent to compensation circuit of voltage loop. The
feature greatly facilitates the flexibility of CPU power supply
design and tuning.
The DAC output of RT9248A supports VRM9 & VRD10 by
VID125 multi-level input, precise initial value & smooth
VCORE transient at VID jump. The IC monitors the VCORE
voltage for PGOOD and over-voltage protection. Soft-start,
over-current protection and programmable under-voltage
lockout are also provided to assure the safety of micro-
processor and power system.
Ordering Information
RT9248A
Package Type
C : TSSOP-28
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.
DS9248A-06 March 2006
Features
z Multi-Phase Power Conversion with Automatic
Phase Selection
z VRM9 & VRD10 DAC Output with Active Droop
Compensation for Fast Load Transient
z Smooth VCORE Transition at VID Jump
z Multi-Level VID125 Input for VRM9 & VRD10
Selection
z Power Stage Thermal Balance by RDS(ON) Current
Sense
z Hiccup Mode Over-Current Protection
z Programmable Switching Frequency (50kHz to
400kHz per Phase), Under-Voltage Lockout and
Soft-Start
z High Ripple Frequency Times Channel Number
z RoHS Compliant and 100% Lead (Pb)-Free
Applications
z Intel® Processors Voltage Regulator: VRM9 and VRD10
z Low Output Voltage, High Current DC-DC Converters
z Voltage Regulator Modules
Pin Configurations
VID4
VID3
VID2
VID1
VID0
VID125
SGND
FB
COMP
PGOOD
DVD
SS
RT
VOSS
(TOP VIEW)
28
2 27
3 26
4 25
5 24
6 23
7 22
8 21
9 20
10 19
11 18
12 17
13 16
14 15
TSSOP-28
VCC
PWM1
PWM2
PWM3
NC
ISP1
ISP2
ISP3
ISN
GND
ADJ
VDIF
VSEN
IMAX
www.richtek.com
1
1 page  
Preliminary
RT9248A
Table 1. Output Voltage Program
Pin Name
Nominal Output Voltage DACOUT
VID4
1
VID3
1
VID2
1
VID1
1
VID0
1
VID125 = H
No CPU
VID125 = L
No CPU
01001
0.850V
1.625V
01000
0.875V
1.650V
00111
0.900V
1.675V
00110
0.925V
1.700V
00101
0.950V
1.725V
00100
0.975V
1.750V
00011
1.000V
1.775V
00010
1.025V
1.800V
00001
1.050V
1.825V
00000
1.075V
1.850V
11110
1.100V
1.100V
11101
1.125V
1.125V
11100
1.150V
1.150V
11011
1.175V
1.175V
11010
1.200V
1.200V
11001
1.225V
1.225V
11000
1.250V
1.250V
10111
1.275V
1.275V
10110
1.300V
1.300V
10101
1.325V
1.325V
10100
1.350V
1.350V
10011
1.375V
1.375V
10010
1.400V
1.400V
10001
1.425V
1.425V
10000
1.450V
1.450V
01111
1.475V
1.475V
01110
1.500V
1.500V
01101
1.525V
1.525V
01100
1.550V
1.550V
01011
1.575V
1.575V
01010
1.600V
1.600V
Note: (1) 0: Connected to GND
(2) 1: Open
(3) For VID125, H: VCC, L: GND
DS9248A-06 March 2006
www.richtek.com
5
5 Page 
Preliminary
RT9248A
Design Example
Given:
Apply for three phase converter
VIN = 12V
VCORE = 1.5V
ILOAD (max) = 60A
VDROOP = 120mV at full load
OCP trip point set at 30A for each channel (S/H)
RDS(ON) = 6mΩ of low side MOSFET at 27°C
L = 2μH
COUT = 9,000μF with 2mΩ ESR.
1. Compensation Setting
a. Modulator Gain, Pole and Zero:
From the following formula:
V IN 12V
Modulator Gain = VRAMP
=
1.9V
×
3
=
4.2
(12.46dB)
2
where VRAMP : ramp amplitude of sawtooth wave
1
LC Filter Pole = 2π x LC = 1.2kHz and
1
ESR Zero = 2π x ESR x COUT = 8.8kHz
b. EA Compensation Network:
Select R1 = 2.4kΩ, R2 = 24kΩ, C1 = 6.6nF,
C2 = 33pF and use the type 2 compensation
scheme shown in Figure 5.
R2 C1
R3 C3
COMP
C2 R1
> VDIF
-
+
DACOUT
FB
R3,C3 are used in type
3 compensation scheme
(left NC in type 2)
Figure 5.
From the following formulas:
FZ
=
2π
x
1
R
2
x
C1
,
FP
Middle Band Gain = R 2
=
1
2π
x R2 x
⎜⎛
⎝
C1
C1
×
+
C2
C2
⎟⎞
⎠
R1
By calculation, the FZ = 1kHz, FP = 200kHz and
Middle Band Gain is 10 (i.e 20dB).
The asymptotic bode plot of EA compensation and
PWM loop gain is shown as Figure 6.
DS9248A-06 March 2006
Asymptotic Bode Plot of PWM Loop Gain
100
80
60
Uncompensated EA Gain
40
20
0
Compensated EA Gain
-20 PWM Loop Gain
-40 Modulator Gain
-60
1100
110000 110K00 11000K00 10100000K0 1010M0000 1010000M000
Frequency (Hz)
Figure 6.
2. Droop & DAC Offset Setting
For each channel the load current is 60A / 3 = 20A
and the ripple current, ΔIL, is given as:
5us x 1.5V x ⎜⎛1− 1.5V ⎟⎞ = 3.28A
2uH ⎝ 12V ⎠
The
load
current,
IL,
at
S/H
is 20A
−
ΔIL
2
= 18.36A
.
Using the following formula to select the appropriate
IX (MAX) for the S/H of GM amplifier:
IX (MAX) = R DS(ON) × 18.36A
R SP
The suggested IX is in the order of 40 to 50μA, select
RSP = 2.4kΩ then IX (MAX) will be 45.9μA.
VDROOP = 120mV = 45.9μA × 2 × 3 (phase no.) ×
RADJ, therefore RADJ will be 435Ω.
The RDS(ON) of MOSFET varies with temperature
rise. When the low side MOSFET working at 70°C
and 5000ppm/°C temperature coefficient of RDS(ON),
the RDS(ON) at 70°C is given as:
6mΩ × {1+ (70°C − 27°C) × 5000ppm/°C} = 7.3mΩ.
RADJ at 70°C is given as:
RADJ_27°C × (RDS(ON)_27°C / RDS(ON)_70°C) = 358Ω
3. Over-Current Protection Setting
OCP trip point set at 30A for each channel,
IX
=
RDS(ON) × 30A
RSP
= 1.4 × 0.6V ,
RIMAX
RIMAX =
11.2kΩ
Take the temperature rise into account, the RIMAX at
70°C will be:
RIMAX_27°C × (RDS(ON)_27°C / RDS(ON)_70°C) = 9.2kΩ
4. Soft-Start Capacitor Selection
CSS = 0.1μF is the suitable value for most application.
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11
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| PDF Descargar | [ Datasheet RT9248A.PDF ] | |
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