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PDF FAN5056MV85 Data sheet ( Hoja de datos )

Número de pieza FAN5056MV85
Descripción High Performance Programmable Synchronous DC-DC Controller for Multi-Voltage Platforms
Fabricantes Fairchild Semiconductor 
Logotipo Fairchild Semiconductor Logotipo



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FAN5056MV85
High Performance Programmable Synchronous
DC-DC Controller for Multi-Voltage Platforms
Features
• Output programmable in 25mV steps from 1.05V to
1.825V using a dynamically programmable integrated
5-bit DAC
• Controls adjustable linears for Vclock (2.5V),
Vnorthbridge (1.8V) or Vagp (selectable 1.5V/3.3V), and
Vadj (1.2V nominal)
• Remote sense
• Programmable Active Droopup to 200mV
• Drives N-Channel MOSFETs
• Overcurrent protection using MOSFET sensing
• Overvoltage protection including startup
• 85% efficiency typical at full load
• Integrated Power Good and Enable/Soft Start functions
• Meets Intel VRM8.5 specifications using minimum
number of external components
• 24 pin SOIC package
Applications
• Power supply for Pentium® III Platforms
• VRM for Pentium III processor
• Programmable multi-output power supply
Block Diagram
Description
The FAN5056 is a synchronous mode DC-DC controller IC
which provides a highly accurate, programmable set of output
voltages for multi-voltage platforms such as the Intel Pentium III,
and provides a complete solution for all Intel VRM8.5 CPU
applications, and for other high-performance processors. The
FAN5056 features remote voltage sensing, independently
adjustable current limit, and a proprietary wide-range Pro-
grammable Active Droopfor optimal converter transient
response and VRM8.5 compliance. The FAN5056 uses a 5-bit
D/A converter to dynamically program the output voltage dur-
ing operation from 1.05V to 1.825V in 25mV steps. The
FAN5056 uses a high level of integration to deliver load cur-
rents in excess of 28A from a 5V source with minimal exter-
nal circuitry. Synchronous-mode operation offers optimum
efficiency over the entire specified output voltage range. An
on-board precision low TC reference achieves 0.8% voltage
regulation without expensive external components. The
FAN5056 includes linear regulator controllers for Vclock
(2.5V),Vnorthbridge (1.8V) or Vagp (selectable 1.5V/3.3V),
and Vadjustable (1.2V nominal) each adjustable with an
external divider. The FAN5056 also offers integrated functions
+3.3V
+1.2V/Adj
9+
-
10
VCCP
11 +
-
12
+2.5V
OSC
REF
PWRGD,
OCL
REF
PWRGD,
OCL
+5V
VCCA 21
-
+
OCL
-
+
-
+
19
RD
+12V
18
RS
20
24 VCCP
1 HIDRV
+5V
15
14
13
3.3/1.5V
V
PWRGD, OCL
-
+
5-Bit
DAC
1.24V
Reference
-
+
Digital
Control
Power
Good
2
23 LODRV
22
GNDP
17
PWRGD
VCC
8 765 4
VID0VID2 VID4
VID1 VID3
3
GNDA
16
ENABLE/SS
Pentium is a registered trademark of Intel Corporation. Programmable Active Droop is a trademark of Fairchild Semiconductor.
REV. 1.0.6 6/26/01

1 page




FAN5056MV85 pdf
FAN5056MV85
Table 1. Output Voltage Programming Codes for FAN5056MV85
VID25mV
VID3
VID2
VID1
0010
1010
0001
1001
0001
1001
0000
1000
0000
1000
0111
1111
0111
1111
0110
1110
0110
1110
0101
1101
0101
1101
0100
1100
0100
1100
0011
1011
0011
1011
0010
1010
Note:
1. 0 = processor pin is tied to GND.
1 = processor pin is open
PRODUCT SPECIFICATION
VID0
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
Nominal VOUT
1.050V
1.075V
1.100V
1.125V
1.150V
1.175V
1.200V
1.225V
1.250V
1.275V
1.300V
1.325V
1.350V
1.375V
1.400V
1.425V
1.450V
1.475V
1.500V
1.525V
1.550V
1.575V
1.600V
1.625V
1.650V
1.675V
1.700V
1.725V
1.750V
1.775V
1.800V
1.825V
5 REV. 1.0.6 6/26/01

5 Page





FAN5056MV85 arduino
PRODUCT SPECIFICATION
FAN5056MV85
controller to reduce the converter’s duty cycle to approxi-
mately 20%. This causes a drastic reduction in the output
voltage as the load regulation collapses into the short circuit
control mode. With a 4moutput short, the voltage is
reduced to 29A * 4m= 116mV. The output voltage does
not return to its nominal value until the output current is
reduced to a value within the safe operating range for the
DC-DC converter.
deliver current when the high side MOSFET switches on.
Figure 4 shows 3 x 1000µF, but the exact number required
will vary with the speed and type of the processor. Capacitor
ripple current rating is a function of temperature, and so the
manufacturer should be contacted to find out the ripple cur-
rent rating at the expected operational temperature. For
details on the design of an input filter, refer to Applications
Bulletin AB-15.
Schottky Diode Selection
The application circuits of Figure 1 shows a Schottky diode,
D1, which is used as a free-wheeling diode to assure that the
body-diode in Q2 does not conduct when the upper MOS-
FET is turning off and the lower MOSFET is turning on. It is
undesirable for this diode to conduct because its high for-
ward voltage drop and long reverse recovery time degrades
efficiency, and so the Schottky provides a shunt path for the
current. Since this time duration is very short, the selection
criterion for the diode is that the forward voltage of the
Schottky at the output current should be less than the for-
ward voltage of the MOSFET’s body diode.
Output Filter Capacitors
The output bulk capacitors of a converter help determine its
output ripple voltage and its transient response. It has
already been seen in the section on selecting an inductor that
the ESR helps set the minimum inductance, and the capaci-
tance value helps set the maximum inductance. For most
converters, however, the number of capacitors required is
determined by the transient response and the output ripple
voltage, and these are determined by the ESR and not the
capacitance value. That is, in order to achieve the necessary
ESR to meet the transient and ripple requirements, the
capacitance value required is already very large.
The most commonly used choice for output bulk capacitors
is aluminum electrolytics, because of their low cost and low
ESR. The only type of aluminum capacitor used should be
those that have an ESR rated at 100kHz. Consult Application
Bulletin AB-14 for detailed information on output capacitor
selection.
The output capacitance should also include a number of
small value ceramic capacitors placed as close as possible to
the processor; 0.1µF and 0.01µF are recommended values.
Input Filter
The DC-DC converter design may include an input inductor
between the system +5V supply and the converter input as
shown in Figure 5. This inductor serves to isolate the +5V
supply from the noise in the switching portion of the DC-DC
converter, and to limit the inrush current into the input capac-
itors during power up. A value of 2.5µH is recommended.
5V
0.1µF
2.5µH
Vin
1000µF, 10V
Electrolytic
Figure 4. Input Filter
Programmable Active Droop
The FAN5056 includes Programmable Active Droop: as
the output current increases, the output voltage drops, and
the amount of this drop is user adjustable. This is done in
order to allow maximum headroom for transient response of
the converter. The current is typically sensed by measuring
the voltage across the RDS,on of the high-side MOSFET
during its on time, as shown in Figures 1 and 2.
To program the amount of droop, use the formula
14.4K*Imax *Rsense
RD
VDroop *3
where Imax is the current at which the droop occurs, and
Rsense is the resistance of the current sensor, either the source
resistor or the high-side MOSFET’s on-resistance. For exam-
ple, to get 120mV of droop with a maximum output current
of 30A and a 10msense resistor, use RD = 14.4K* 30A *
10m/(120mV *3) = 12K. The value of the product
Imax*Rsense must be < 600mV for proper functioning of
the droop circuit. If this product is exceeded, a lower resis-
tance MOSFET must be used. Further details on use of the
Programmable Active Droopmay be found in Applications
Bulletin AB-24.
Remote Sense
The FAN5056 offers remote sense of the output voltage to
minimize the output capacitor requirements of the converter.
It is highly recommended that the remote sense pin, Pin 20,
be tied directly to the processor power pins, so that the
effects of power plane impedance are eliminated. Further
details on use of the remote sense feature of the FAN5056
may be found in Applications Bulletin AB-24.
It is necessary to have some low ESR aluminum electrolytic
capacitors at the input to the converter. These capacitors
REV. 1.0.6 6/26/01
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