RC5058M [FAIRCHILD]
Current-Mode SMPS Controller ; 电流模式开关电源控制器\n
| 型号： | RC5058M |
| 厂家： | 
FAIRCHILD SEMICONDUCTOR |
| 描述： | Current-Mode SMPS Controller
|
| 文件： | 总18页 (文件大小：258K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
www.fairchildsemi.com
RC5058
High Performance Programmable Synchronous
DC-DC Controller for Multi-Voltage Platforms
Features
Applications
• Programmable output for Vcore from 1.3V to 3.5V using
• Power supply for Pentium® III Camino Platform
• Power supply for Pentium III Whitney Platform
• VRM for Pentium III processor
an integrated 5-bit DAC
•
Controls adjustable linears for Vagp (selectable 1.5V/3.3V),
Vclock (2.5V), and Vtt (1.5V) or Vnorthbridge (1.8V)
• Programmable multi-output power supply
• Meets VRM specification with as few as 5 capacitors
• Meets 1.550V +40/-70mV over initial tolerance,
temperature and transients
Description
The RC5058 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 Camino,
and provides a complete solution for the Intel Whitney and other
high-performance processors. The RC5058 features remote
voltage sensing, independently adjustable current limit, and a
proprietary Programmable Active Droop™ for optimal converter
transient response. The RC5058 uses a 5-bit D/A converter
to program the output voltage from 1.3V to 3.5V. The RC5058
uses a high level of integration to deliver load currents in excess
• Remote sense
• Programmable Active Droop™ (Voltage Positioning)
• Drives N-Channel MOSFETs
• Overcurrent protection using MOSFET sensing
• 85% efficiency typical at full load
• Integrated Power Good and Enable/Soft Start functions
• 24 pin SOIC package
Block Diagram
+5V
VCCA 21
+3.3V
19
-
+
9
+
-
REF
RD
PWRGD,
OCL
10
+1.5V
+2.5V
VCCP
OCL
11
12
+
-
REF
+12V
+5V
PWRGD,
OCL
18
20
-
+
RS
OSC
-
+
VCCP
HIDRV
24
1
15
14
13
Digital
2
VCC
Control
-
+
+
-
V
-
23 LODRV
+
PWRGD, OCL
22
3.3/1.5V
GNDP
1.24V
Reference
5-Bit
DAC
17
Power
Good
PWRGD
8 7 6 5 4
3
16
ENABLE/SS
VID4
VID0VID2
GNDA
VID1 VID3
Pentium is a registered trademark of Intel Corporation. Programmable Active Droop is a trademark of Fairchild Semiconductor.
Rev. 1.0.0
RC5058
PRODUCT SPECIFICATION
of 16A from a 5V source with minimal external circuitry.
Synchronous-mode operation offers optimum efficiency over
the entire specified output voltage range. An on-board precision
low TC reference achieves tight tolerance voltage regulation
without expensive external components, while Programmable
Active Droop™ permits exact tailoring of voltage for the most
demanding load transients. The RC5058 includes linear regulator
controllers for Vtt termination (1.5V), Vclock (2.5V), and
Vnorthbridge (1.8V) or Vagp (selectable 1.5V/3.3V), each adjust-
able with an external divider. The RC5058 also offers integrated
functions including Power Good, Output Enable/Soft Start and
current limiting, and is available in a 24 pin SOIC package.
Pin Assignments
24
23
22
21
20
19
18
17
16
15
14
13
VCCP
LODRV
GNDP
VCCA
VFB
HIDRV
SW
1
2
GNDA
3
VID4
4
VID3
VID2
VID1
VID0
5
6
7
8
DROOP
ILIM
RC5058
PWRGD
SS/ENABLE
TYPEDET
VAGPGATE
VAGPFB
VTTGATE
VTTFB
VCKGATE
VCKFB
9
10
11
12
Pin Definitions
Pin
Number Pin Name
Pin Function Description
1
HIDRV
High Side FET Driver. Connect this pin through a resistor to the gate of an N-channel
MOSFET. The trace from this pin to the MOSFET gate should be <0.5".
2
SW
High side Driver Source and Low side Driver Drain Switching Node. Together with
DROOP and ILIM pins allows FET sensing for Vcc current.
3
GNDA
VID0-4
Analog Ground. Return path for low power analog circuitry. This pin should be
connected to a low impedance system ground plane to minimize ground loops.
4-8
Voltage Identification Code Inputs. These open collector/TTL compatible inputs will
program the output voltage over the ranges specified in Table 2. Pull-up resistors are
internal to the controller.
9
VTTGATE
VTTFB
Gate Driver for VTT Transistor. For 1.5V output.
Voltage Feedback for VTT.
10
11
12
13
14
15
16
VCKGATE
VCKFB
Gate Driver for VCK Transistor. For 2.5V output.
Voltage Feedback for VCK.
VAGPFB
Voltage Feedback for VAGP.
VAGPGATE Gate Driver for VAGP Transistor. For 3.3/1.5V output.
TYPEDET Type Detect. Sets 3.3V or 1.5V for AGP.
ENABLE/SS Output Enable. A logic LOW on this pin will disable all outputs. An internal current source
allows for open collector control. This pin also doubles as soft start for all outputs.
17
18
PWRGD
ILIM
Power Good Flag. An open collector output that will be logic LOW if any output voltage
is more than ±12% outside of the nominal output voltage setpoint.
Vcc Current Feedback. Pin 18 is used in conjunction with pin 2 as the input for the Vcc
current feedback control loop. Layout of these traces is critical to system performance.
See Application Information for details.
19
20
DROOP
VFB
Droop set. Use this pin to set magnitude of active droop.
Vcc Voltage Feedback. Pin 20 is used as the input for the Vcc voltage feedback control
loop. See Application Information for details regarding correct layout.
21
22
23
VCCA
GNDP
LODRV
Analog VCC. Connect to system 5V supply and decouple with a 0.1µF ceramic capacitor.
Power Ground. Return pin for high currents flowing in pin 24 (VCCP).
Vcc Low Side FET Driver. Connect this pin through a resistor to the gate of an N-channel
MOSFET for synchronous operation. The trace from this pin to the MOSFET gate should
be <0.5".
24
VCCP
Power VCC. For all FET drivers. Connect to system 12V supply through a 33Ω, and
decouple with a 1µF ceramic capacitor.
2
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PRODUCT SPECIFICATION
RC5058
Absolute Maximum Ratings
Supply Voltage VCCA to GND
Supply Voltage VCCP to GND
Voltage Identification Code Inputs, VID0-VID4
All Other Pins
13.5V
15V
VCCA
13.5V
Junction Temperature, TJ
150°C
Storage Temperature
-65 to 150°C
300°C
Lead Soldering Temperature, 10 seconds
1
Thermal Resistance Junction-to-ambient, ΘJA
75°C/W
Note:
1. Component mounted on demo board in free air.
Recommended Operating Conditions
Parameter
Conditions
Min.
4.5
Typ.
Max.
Units
V
Supply Voltage VCCA
Input Logic HIGH
5
5.25
2.0
V
Input Logic LOW
0.8
70
V
Ambient Operating Temperature
Output Driver Supply, VCCP
0
°C
V
10.8
12
13.2
Electrical Specifications
(VCCA = 5V, VCCP = 12V, VOUT = 2.0V, and TA = +25°C using circuit in Figure 1 unless otherwise noted.)
The • denotes specifications which apply over the full operating temperature range.
Parameter
Conditions
Min.
Typ.
Max.
Units
VCC Regulator
Output Voltage
Output Current
Initial Voltage Setpoint
See Table 1
•
1.3
3.5
V
A
18
ILOAD = 0.8A,VOUT = 2.400V
2.397 2.424 2.454
2.000 2.020 2.040
1.550 1.565 1.580
V
V
V
V
OUT = 2.000V
VOUT = 1.550V
Output Temperature Drift
TA = 0 to 70°C,VOUT = 2.000V
•
•
+8
+6
mV
mV
V
OUT = 1.550V
Line Regulation
VIN = 4.75V to 5.25V
ILOAD = 0.8A to 12.5A
•
-4
mV/V
KΩ
Internal Droop Impedance
Maximum Droop
Output Ripple
13.0
14.4
60
15.8
mV
20MHz BW, ILOAD = 18A
11
mVpk
V
Total Output Variation,
Steady State1
VOUT = 2.000V
VOUT = 1.550V3
•
•
1.940
1.480
2.070
1.590
Total Output Variation,
Transient2
ILOAD = 0.8A to 18A, VOUT = 2.000V
VOUT = 1.550V3
•
•
1.900
1.480
2.100
1.590
V
Short Circuit Detect Current
Efficiency
•
45
50
85
50
50
60
µA
%
ILOAD = 18A, VOUT = 2.0V
Output Driver Rise & Fall Time See Figure 3
nsec
nsec
Output Driver Deadtime
See Figure 3
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3
RC5058
PRODUCT SPECIFICATION
Electrical Specifications (Continued)
(VCCA = 5V, VCCP = 12V, VOUT = 2.0V, and TA = +25°C using circuit in Figure 1 unless otherwise noted.)
The • denotes specifications which apply over the full operating temperature range.
Parameter
Conditions
Min.
0
Typ.
Max.
100
4.26
9.35
17
Units
%
Duty Cycle
5V UVLO
•
•
•
3.74
7.65
5
4
V
12V UVLO
8.5
10
V
Soft Start Current
VTT Linear Regulator
Output Voltage
µA
ILOAD ≤ 2A
•
•
1.455
2.375
1.5
80
1.545
2.625
V
Under Voltage Trip Level
VCLK Linear Regulator
Output Voltage
Over Current
%VO
ILOAD ≤ 2A
2.5
80
V
Under Voltage Trip Level
VAGP Linear Regulator
Output Voltage
Over Current
%VO
ILOAD ≤ 2A, TYPEDET=0V
•
•
1.425
3.135
1.5
3.3
80
1.575
3.465
V
V
Output Voltage
ILOAD ≤ 2A, TYPEDET=OPEN
Under Voltage Trip Level
Common Functions
Oscillator Frequency
PWRGD Threshold
Over Current
%VO
•
255
310
30
345
kHz
Logic HIGH, All Outputs
Logic LOW, Any Output
•
•
92
88
108
112
%VOUT
Linear Regulator Under Voltage Over Current
Delay Time
µsec
Notes:
1. Steady State Voltage Regulation includes Initial Voltage Setpoint, Droop, Output Ripple and Output Temperature Drift and is
measured at the converter’s VFB sense point.
2. As measured at the converter’s VFB sense point. For motherboard applications, the PCB layout should exhibit no more than
0.5mΩ trace resistance between the converter’s output capacitors and the CPU. Remote sensing should be used for optimal
performance.
3. Using the VFB pin for remote sensing of the converter’s output at the load, the converter will be in compliance with Intel’s VRM 8.4
specification of +50, –80mV. If Intel specifications on maximum plane resistance from the converter’s output capacitors to the CPU
are met, the specification of +40, –70mV at the capacitors will also be met.
4
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PRODUCT SPECIFICATION
RC5058
Table 1. Output Voltage Programming Codes
VID4
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
VID3
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
VID2
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
VID1
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
0
0
VID0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
Nominal VOUT
1.30V
1.35V
1.40V
1.45V
1.50V
1.55V
1.60V
1.65V
1.70V
1.75V
1.80V
1.85V
1.90V
1.95V
2.00V
2.05V
2.0V
2.1V
2.2V
2.3V
2.4V
2.5V
2.6V
2.7V
2.8V
2.9V
3.0V
3.1V
3.2V
3.3V
3.4V
3.5V
Note:
1. 0 = processor pin is tied to GND.
1 = processor pin is open.
REV. 1.0.0 6/30/00
5
RC5058
PRODUCT SPECIFICATION
Typical Operating Characteristics
(VCCA = 5V, VCCP = 12V, and TA = +25°C using circuits in Figure 1, unless otherwise noted.)
Droop, VCPU = 2.0V, RD = 8K Ω
VCPU Efficiency vs. Output Current
2.04
2.03
2.02
2.01
2.00
1.99
1.98
1.97
1.96
1.95
1.94
88
86
84
82
80
78
76
74
72
70
68
66
64
VOUT = 2.000V
VOUT = 1.550V
0
3
6
9
12
15
18
Output Current (A)
0
3
6
9
12
15
18
Output Current (A)
CPU Output Voltage vs. Output Current
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
0
5
10
15
20
25
Output Current (A)
Output Programming, VID4 = 1
Output Programming, VID4 = 0
2.1
3.5
3.0
2.5
2.0
1.5
1.0
1.9
1.7
1.5
1.3
1.1
1.30 1.40 1.50 1.60 1.70 1.80 1.90 2.00
2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3.0 3.1 3.2. 3.3 3.4 3.5
DAC Setpoint
DAC Setpoint
6
REV. 1.0.0 6/30/00
PRODUCT SPECIFICATION
RC5058
Typical Operating Characteristics (continued)
Transient Response, 12.5A to 0.5A
Output Ripple, 2.0V @ 18A
1.590V
1.550V
1.480V
Time (100µs/div)
Time (1µs/div)
Switching Waveforms, 18A Load
Transient Response, 0.5A to 12.5A
HIDRV
pin
1.590V
1.550V
LODRV
pin
1.480V
Time (1µs/div)
Time (100µs/div)
Output Startup from Enable
Output Startup, System Power-up
Time (10ms/div)
Time (10ms/div)
REV. 1.0.0 6/30/00
7
RC5058
PRODUCT SPECIFICATION
Typical Operating Characteristics (continued)
Linear Regulator Noise
2.042
2.040
2.038
2.036
2.034
2.030
2.028
2.026
0
25
70
100
Time (100µs/div)
Temperature (°C)
Application Circuit
L1
(Optional)
+5V
CIN*
C1
R6
R7
R5
C2
R2
R1
1
Q1
Q2
24
+12V
L2
2
3
23
22
C5
VO
4
21
20
19
COUT
*
VID4
U1
RC5058
R3
5
6
7
8
9
D1
VID3
VID2
VID1
C3
Q5
VCC
R4
18
17
3.3V IN
Q3
VID0
PWRGD
C6
16
15
14
ENABLE/SS
10
11
C10
C11
TYPEDET
C4
3.3/1.5V
(AGP)†
12
13
Q4
1.5V†
C8
C7
2.5V†
C12
C9
* Refer to Appendix for values of CIN, COUT
R5 and R7.
,
† Adjustable with an external divider.
Figure 1. Typical Application Circuit
(Worst Case Analyzed! See Appendix for Details)
8
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PRODUCT SPECIFICATION
RC5058
Table 2. RC5058 Application Bill of Materials
(Components based on Worst Case Analysis—See Appendix for Details)
Reference Manufacturer Part #
Quantity
Description
Requirements/Comments
C1
AVX
1
4.7µF, 10V Capacitor
TAJB475M010R5
C2, C5
C3-4,C6
C7-9
Panasonic
ECU-V1C105ZFX
2
3
3
1µF, 16V Capacitor
Panasonic
ECU-V1H104ZFX
100nF, 50V Capacitor
1000µF, 6.3V Electrolytic
Sanyo
6MV1000FA
C10-12
CIN
Any
3
*
22µF, 6.3V Capacitor
Low ESR
IRMS = 2A
Sanyo
10MV1200GX
1200µF, 10V Electrolytic
COUT
D1
Sanyo
6MV1500GX
*
1
1500µF, 6.3V Electrolytic
8A Schottky Diode
ESR ≤ 44mΩ
Motorola
MBRD835L
L1
Any
Any
Optional
2.5µH, 8A Inductor
DCR ~ 10mΩ
See Note 1.
L2
1
1
1.3µH, 20A Inductor
N-Channel MOSFET
DCR ~ 2mΩ
Q1
Fairchild
RDS(ON) = 20mΩ @
FDB6030L
VGS = 4.5V See Note 2.
Q2
Fairchild
FDB7030BL
1
3
N-Channel MOSFET
N-Channel MOSFET
RDS(ON) = 10mΩ @
VGS = 4.5V See Note 2.
Q3-5
Fairchild
FDB4030L
R1
R2-3
R4
R5
R6
R7
U1
Any
Any
Any
Any
Any
Any
1
2
1
1
1
1
1
33Ω
4.7Ω
10KΩ
*
10Ω
*
Fairchild
DC/DC Controller
RC5058M
Notes:
1. Inductor L1 is recommended to isolate the 5V input supply from noise generated by the MOSFET switching, and to comply
with Intel dI/dt requirements. L1 may be omitted if desired.
2. For 17.4A designs using the TO-220 MOSFETs, heatsinks with thermal resistance Θ < 20°C/W should be used. For designs
SA
using the TO-263 MOSFETs, adequate copper area should be used. For details and a spreadsheet on MOSFET selections,
refer to Applications Bulletins AB-8 and AB-15.
*Refer to Appendix for values.
REV. 1.0.0 6/30/00
9
RC5058
PRODUCT SPECIFICATION
L1
(Optional)
+5V
CIN*
C1
R6
R7
R5
C2
R2
R1
1
Q1
Q2
24
+12V
C5
L2
2
3
23
22
R8
VO
COUT
4
21
20
19
*
VID4
U1
RC5058
R3
5
6
7
8
9
D1
VID3
VID2
VID1
C3
Q5
VCC
R4
18
17
3.3V IN
Q3
VID0
PWRGD
16
15
14
ENABLE/SS
C6
10
11
C10
C11
TYPEDET
C4
3.3/1.5V
(AGP)†
12
13
Q4
1.5V†
C8
C7
2.5V†
C12
C9
*Refer to Table 4 for values of COUT and CIN
.
† Adjustable with an external divider.
Figure 2. Application Circuit for Coppermine/Camino Motherboards
(Typical Design)
10
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PRODUCT SPECIFICATION
RC5058
Table 3. RC5058 Application Bill of Materials for Intel Coppermine/Camino Motherboards
(Typical Design)
Reference Manufacturer Part #
Quantity
Description
Requirements/Comments
C1
AVX
1
4.7µF, 10V Capacitor
TAJB475M010R5
C2, C5
C3-4,C6
C7-9
Panasonic
ECU-V1C105ZFX
2
3
3
1µF, 16V Capacitor
Panasonic
ECU-V1H104ZFX
100nF, 50V Capacitor
1000µF, 6.3V Electrolytic
Sanyo
6MV1000FA
C10-12
CIN
Any
3
3
22µF, 6.3V Capacitor
Low ESR
IRMS = 2A
Sanyo
10MV1200GX
1200µF, 10V Electrolytic
COUT
D1
Sanyo
6MV1500GX
12
1
1500µF, 6.3V Electrolytic
8A Schottky Diode
ESR ≤ 44mΩ
Motorola
MBRD835L
L1
Any
Any
Optional
2.5µH, 5A Inductor
DCR ~ 10mΩ
See Note 1.
L2
1
1
1.3µH, 15A Inductor
N-Channel MOSFET
DCR ~ 3mΩ
Q1
Fairchild
RDS(ON) = 20mΩ @
FDB6030L
VGS = 4.5V See Note 2.
Q2
Fairchild
FDB7030BL
1
3
N-Channel MOSFET
N-Channel MOSFET
RDS(ON) = 10mΩ @
VGS = 4.5V See Note 2.
Q3-5
Fairchild
FDB4030L
R1
Any
Any
Any
Any
Any
N/A
1
2
1
2
1
1
1
33Ω
R2-3
R4
4.7Ω
10KΩ
R5, R7
R6
6.24KΩ
10Ω
R8
3.0mΩ
DC/DC Controller
PCB Trace Resistor
U1
Fairchild
RC5058M
Notes:
1. Inductor L1 is recommended to isolate the 5V input supply from noise generated by the MOSFET switching, and to comply
with Intel dI/dt requirements. L1 may be omitted if desired.
2. For 12.5A designs using the TO-220 MOSFETs, heatsinks with thermal resistance Θ < 20°C/W should be used. For
SA
designs using the TO-263 MOSFETs, adequate copper area should be used. For details and a spreadsheet on MOSFET
selections, refer to Applications Bulletins AB-8 and AB-15.
REV. 1.0.0 6/30/00
11
RC5058
PRODUCT SPECIFICATION
High Current Output Drivers
Test Parameters
The RC5058 contains two identical high current output drivers
that utilize high speed bipolar transistors in a push-pull config-
uration. The drivers’ power and ground are separated from
the chip’s power and ground for switching noise immunity.
The power supply pin, VCCP, is supplied from an external
12V source through a series 33Ω resistor. The resulting volt-
age is sufficient to provide the gate to source drive to the
tR
tF
5V
2V
HIDRV
to SW
5V
2V
tDT
tDT
external MOSFETs required in order to achieve a low RDS,ON
.
LODRV
2V
2V
Internal Voltage Reference
Figure 3. Ouput Drive Timing Diagram
The reference included in the RC5058 is a precision band-gap
voltage reference. Its internal resistors are precisely trimmed
to provide a near zero temperature coefficient (TC). Based on
the reference is the output from an integrated 5-bit DAC. The
DAC monitors the 5 voltage identification pins, VID0-4. When
the VID4 pin is at logic HIGH, the DAC scales the reference
voltage from 2.0V to 3.5V in 100mV increments. When VID4
is pulled LOW, the DAC scales the reference from 1.30V to
2.05V in 50mV increments. All VID codes are available, includ-
ing those below 1.80V.
Application Information
The RC5058 Controller
The RC5058 is a programmable synchronous DC-DC con-
troller IC. When designed around the appropriate external
components, the RC5058 can be configured to deliver more
than 16A of output current, as appropriate for the Katmai and
Coppermine and other processors. The RC5058 functions as
a fixed frequency PWM step down regulator.
Power Good (PWRGD)
Main Control Loop
The RC5058 Power Good function is designed in accordance
with the Pentium II and III DC-DC converter specifications
and provides a continuous voltage monitor on the VFB pin.
The circuit compares the VFB signal to the VREF voltage
and outputs an active-low interrupt signal to the CPU should
the power supply voltage deviate more than ±12% of its
nominal setpoint. Power Good outputs an open collector
high when the output voltage is within ±8% of its nominal
setpoint. The Power Good flag provides no other control
function to the RC5058.
Refer to the RC5058 Block Diagram on page 1. The RC5058
implements “summing mode control”, which is different from
both classical voltage-mode and current-mode control. It
provides superior performance to either by allowing a large
converter bandwidth over a wide range of output loads.
The control loop of the regulator contains two main sections:
the analog control block and the digital control block. The
analog section consists of signal conditioning amplifiers feeding
into a comparator which provides the input to the digital control
block. The signal conditioning section accepts input from the
DROOP (current feedback) and VFB (voltage feedback) pins
and sets up two controlling signal paths. The first, the voltage
control path, amplifies the difference between the VFB signal
and the reference voltage from the DAC and presents the
output to one of the summing amplifier inputs. The second,
current control path, takes the difference between the DROOP
and SW pins when the high-side MOSFET is on, reproducing
the voltage across the MOSFET and thus the input current; it
presents the resulting signal to another input of the summing
amplifier. These two signals are then summed together. This
output is then presented to a comparator looking at the oscillator
ramp, which provides the main PWM control signal to the
digital control block.
Output Enable/Soft Start (ENABLE/SS)
The RC5058 will accept an open collector/TTL signal for
controlling the output voltage. The low state disables the output
voltage. When disabled, the PWRGD output is in the low state.
Even if an enable is not required in the circuit, this pin should
have attached a capacitor (typically 100nF) to softstart the
switching. A larger value may occasionally be required if the
converter has a very large capacitor at its output.
Over-Voltage Protection
The RC5058 constantly monitors the output voltage for protec-
tion against over-voltage conditions. If the voltage at the VFB
pin exceeds the selected program voltage, an over-voltage
condition is assumed and the RC5058 disables the output
drive signal to the external high-side MOSFET. The DC-DC
converter returns to normal operation after the output voltage
returns to normal levels.
The digital control block takes the analog comparator input
and the main clock signal from the oscillator to provide the
appropriate pulses to the HIDRV and LODRV output pins.
These two outputs control the external power MOSFETs.
There is an additional comparator in the analog control section
whose function is to set the point at which the RC5058 current
limit comparator disables the output drive signals to the
external power MOSFETs.
Oscillator
The RC5058 oscillator section uses a fixed frequency of
operation of 300KHz.
12
REV. 1.0.0 6/30/00
PRODUCT SPECIFICATION
RC5058
95%).
Some margin should be maintained away from both Lmin and
Lmax. Adding margin by increasing L almost always adds
expense since all the variables are predetermined by system
performance except for CO, which must be increased to
increase L. Adding margin by decreasing L can be done by
purchasing capacitors with lower ESR. The RC5058 pro-
vides significant cost savings for the newer CPU systems
that typically run at high supply current.
Design Considerations and Component
Selection
Additional information on design and component selection
may be found in Fairchild’s Application Note 57.
MOSFET Selection
This application requires N-channel Logic Level Enhancement
Mode Field Effect Transistors. Desired characteristics are as
follows:
RC5058 Short Circuit Current Characteristics
The RC5058 protects against output short circuit on the core
supply by turning off both the high-side and low-side
MOSFETs and resetting softstart. The short circuit limit is
set with the RS resistor, as given by the formula
• Low Static Drain-Source On-Resistance, RDS,ON < 20mΩ
(lower is better)
• Low gate drive voltage, VGS = 4.5V rated
• Power package with low Thermal Resistance
• Drain-Source voltage rating > 15V.
ISC *RDS, on
RS
=
IDetect
The on-resistance (RDS,ON) is the primary parameter for
MOSFET selection. The on-resistance determines the power
dissipation within the MOSFET and therefore significantly
affects the efficiency of the DC-DC Converter. For details
and a spreadsheet on MOSFET selection, refer to Applica-
tions Bulletin AB-8.
with IDetect ≈ 50µA, ISC is the desired current limit, and
RDS,on the high-side MOSFET’s on resistance. Remember to
make the RS large enough to include the effects of initial tol-
erance and temperature variation on the MOSFET’s RDS,on
Alternately, use of a sense resistor in series with the source
of the MOSFET eliminates this source of inaccuracy in the
current limit. The value of RS should be less than 8.3KΩ. If a
greater value is necessary, a lower RDS,on MOSFET should
be used instead.
.
Inductor Selection
Choosing the value of the inductor is a tradeoff between
allowable ripple voltage and required transient response. The
system designer can choose any value within the allowed
minimum to maximum range in order to either minimize ripple
or maximize transient performance. The first order equation
(close approximation) for minimum inductance is:
As an example, Figure 4 shows the typical characteristic of
the DC-DC converter circuit with an FDB6030L high-side
MOSFET (RDS = 20mΩ maximum at 25°C * 1.25 at 75°C =
25mΩ) and a 8.2KΩ RS.
(V – Vout
in
)
Vout
Vin
ESR
Lmin
=
x
x
Vripple
f
CPU Output Voltage vs. Output Current
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
where:
Vin = Input Power Supply
Vout = Output Voltage
f = DC/DC converter switching frequency
ESR = Equivalent series resistance of all output capacitors in
parallel
Vripple = Maximum peak to peak output ripple voltage budget.
The first order equation for maximum allowed inductance is:
0
5
10
15
20
25
(V – Vout) Dm Vtb
in
2CO
=
Lmax
Figure 4. RC5058 Short Circuit Characteristic
2
Ipp
The converter exhibits a normal load regulation characteristic
until the voltage across the MOSFET exceeds the internal
short circuit threshold of 50µA * 8.2KΩ = 410mV, which
occurs at 410mV/25mΩ = 16.4A. (Note that this current limit
level can be as high as 410mV/15mΩ = 27A, if the MOSFET
has typical RDS,on rather than maximum, and is at 25°C).
where:
Co = The total output capacitance
Ipp = Maximum to minimum load transient current
Vtb = The output voltage tolerance budget allocated to load
transient
Dm = Maximum duty cycle for the DC/DC converter (usually
REV. 1.0.0 6/30/00
13
RC5058
PRODUCT SPECIFICATION
converter, and to limit the inrush current into the input capac-
itors during power up. A value of 2.5µH is recommended.
At this point, the internal comparator trips and signals the con-
troller to discharge the softstart capacitor. This causes a drastic
reduction in the output voltage as the load regulation collapses
into the short circuit control mode. With a 40mΩ output short,
the voltage is reduced to 16.4A * 40mΩ = 650mV. The output
voltage does not return to its nominal value until the output
current is reduced to a value within the safe operating ranges
for the DC-DC converter.
It is necessary to have some low ESR aluminum electrolytic
capacitors at the input to the converter. These capacitors
deliver current when the high side MOSFET switches on.
Figure 5 shows 3 x 1000µF, but the exact number required
will vary with the speed and type of the processor. For the
top speed Katmai and Coppermine, the capacitors should be
rated to take 9A and 6A of ripple current respectively.
Capacitor ripple current rating is a function of temperature,
and so the manufacturer should be contacted to find out the
ripple current rating at the expected operational temperature.
For details on the design of an input filter, refer to Applica-
tions Bulletin AB-15.
If any of the linear regulator outputs are loaded heavily
enough that their output voltage drops below 80% of nominal
for >30µsec, all RC5058 outputs, including the switcher, are
shut off and remain off until power is recycled.
Schottky Diode Selection
2.5µH
Vin
The application circuit 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 MOSFET
is turning off and the lower MOSFET is turning on. It is
undesirable for this diode to conduct because its high forward
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 forward voltage of
the MOSFET’s body diode.
5V
1000µF, 10V
0.1µF
Electrolytic
Figure 5. Input Filter
™
Programmable Active Droop
The RC5058 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 Figure 1.
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 capacitance 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.
To program the amount of droop, use the formula
14.4KΩ *Imax *Rsense
RD
VDroop *18
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 example, to
get 30mV of droop with a maximum output current of 12.5A
and a 10mΩ sense resistor, use RD = 14.4KΩ * 12.5A * 10mΩ/
(30mV * 18) = 3.33KΩ. Further details on use of the
Programmable Active Droop™ may be found in Applications
Bulletin AB-24.
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.
Remote Sense
The RC5058 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 RC5058 may
be found in Applications Bulletin AB-24.
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
14
REV. 1.0.0 6/30/00
PRODUCT SPECIFICATION
RC5058
traces that connect to pins 3, 20 and 21.
• Place the 0.1µF decoupling capacitors as close to the
RC5058 pins as possible. Extra lead length on these
reduces their ability to suppress noise.
Adjusting the Linear Regulators’Output Voltages
Any or all of the linear regulators’ outputs may be adjusted
high to compensate for voltage drop along traces, as shown
in Figure 6.
• Each VCC and GND pin should have its own via to the
appropriate plane. This helps provide isolation between pins.
• Place the MOSFETs, inductor, and Schottky as close
together as possible for the same reasons as in the first
bullet above. Place the input bulk capacitors as close to
the drains of the high side MOSFETs as possible. In
addition, placement of a 0.1µF decoupling cap right on
the drain of each high side MOSFET helps to suppress
some of the high frequency switching noise on the input
of the DC-DC converter.
VGATE
VOUT
R
VFB
10KΩ
• Place the output bulk capacitors as close to the CPU as
possible to optimize their ability to supply instantaneous
current to the load in the event of a current transient.
Additional space between the output capacitors and the
CPU will allow the parasitic resistance of the board traces
to degrade the DC-DC converter’s performance under
severe load transient conditions, causing higher voltage
deviation. For more detailed information regarding
capacitor placement, refer to Application Bulletin AB-5.
Figure 6. Adjusting the Output Voltage of the Linear
Regulator
The resistor value should be chosen as
Vout
R = 10KΩ*
–1
Vnom
• A PC Board Layout Checklist is available from Fairchild
Applications. Ask for Application Bulletin AB-11.
For example, to get the VTT voltage to be 1.55V instead of
1.50V, use R = 10KΩ * [(1.55/1.50) – 1] = 333Ω.
Additional Information
For additional information contact Fairchild Semiconductor at
http://www.fairchildsemi.com/cf/tsg.htm or contact an autho-
rized representative in your area.
Using the RC5058 for Vnorthbridge = 1.8V
In some motherboards, Intel requires that the AGP power can not
be greater than 2.2V while the chipset voltage (Vnorthbridge =
1.8V) is less than 1.0V. The RC5058 can accomplish this by
using the VTT regulator to generate Vnorthbridge. Use the circuit
in Figure 6 with R = 2KΩ. Since the linear regulators on the
RC5058 all rise proportionally to one another, when Vnorth-
bridge = 1.0V, Vagp = 1.8V, meeting the Intel requirement.
PCB Layout Guidelines
• Placement of the MOSFETs relative to the RC5058 is
critical. Place the MOSFETs such that the trace length of
the HIDRV and LODRV pins of the RC5058 to the FET
gates is minimized. A long lead length on these pins will
cause high amounts of ringing due to the inductance of the
trace and the gate capacitance of the FET. This noise radiates
throughout the board, and, because it is switching at such
a high voltage and frequency, it is very difficult to suppress.
• In general, all of the noisy switching lines should be kept
away from the quiet analog section of the RC5058. That
is, traces that connect to pins 1, 2, 23, and 24 (HIDRV, SW,
LODRV and VCCP) should be kept far away from the
REV. 1.0.0 6/30/00
15
RC5058
PRODUCT SPECIFICATION
The value of R7 must be ≤ 8.3KΩ. If a greater value is calcu-
lated, RD must be reduced.
Appendix
Worst-Case Formulae for the Calculation of
Cin, Cout , R5, R7 and Roffset (Circuits similar to
Figure 1 only)
Number of capacitors needed for Cout = the greater of:
ESR * IO
The following formulae design the RC5058 for worst-case
operation, including initial tolerance and temperature dependence
of all of the IC parameters (initial setpoint, reference tolerance
and tempco, internal droop impedance, current sensor gain),
the initial tolerance and temperature dependence of the MOSFET,
and the ESR of the capacitors. The following information
must be provided:
X =
VT-
+ VS+ – .024 * Vnom
or
ESR * IO
V
S+, the value of the positive static voltage limit;
|VS-|, the absolute value of the negative static voltage limit;
T+, the value of the positive transient voltage limit;
Y =
14400 * IO * RD
18 * R5 * 1.1
VT+ – VS+
+
V
|VT-|, the absolute value of the negative transient voltage limit;
IO, the maximum output current;
Example: Suppose that the static limits are +89mV/-79mV,
transient limits are ±134mV, current I is 14.2A, and the
nominal voltage is 2.000V, using MOSFET current sensing.
We have VS+ = 0.089, |VS-| = 0.079, VT+ = |VT-| = 0.134, IO
= 14.2, Vnom = 2.000, and ∆RD = 1.67. We calculate:
Vnom, the nominal output voltage;
Vin, the input voltage (typically 5V);
Irms, the ripple current rating of the input capacitors, per cap
(2A for the Sanyo parts shown in this datasheet);
Since Y > X, we choose Y, and round up to find we need 7
capacitors for COUT
.
RD, the resistance of the current sensor (usually the MOSFET);
∆RD, the tolerance of the current sensor (usually about 67%
for MOSFET sensing, including temperature); and
A detailed explanation of this calculation may be found in
Applications Bulletin AB-24.
ESR, the ESR of the output capacitors, per cap (44mΩ for
the Sanyo parts shown in this datasheet).
2
2.000
5
2.000
5
–
14.2 *
2
=
3.47
4 caps
Cin
=
Vnom
Vin
Vnom
Vin
2
IO*
–
Cin
=
0.089 – .024 * 2.000
*1000 20.3Ω
=
Roffset
=
Irms
1.01 * 2.000
14.2 * 0.010 * (1 + 0.67)
45 * 10-6
5.25KΩ
VS+ – .024 * Vnom
=
R7 =
* 1KΩ
Roffset
=
1.01 * Vnom
14400 * 14.2 * 0.020 * (1 + 0.67) * 1.1
3.48KΩ
=
R5 =
IO* RD * (1 + ∆RD)
18 * (0.089 + 0.079 – .024 * 2.000)
R7 =
45 * 10-6
0.044 * 14.2
= 3.57
X =
0.134 + 0.089 – .024 * 2.00
14400 * IO* RD * (1 + ∆RD) *1.1
R5 =
0.044 * 14.2
= 6.14
Y =
18 * (VS+ + VS- – .024 * Vnom
)
14400 * 14.2 * 0.020
0.134 – 0.089 +
18 * 3640 * 1.1
16
REV. 1.0.0 6/30/00
PRODUCT SPECIFICATION
RC5058
Mechanical Dimensions
24 Lead SOIC
Notes:
Inches
Millimeters
Symbol
Notes
1. Dimensioning and tolerancing per ANSI Y14.5M-1982.
Min.
Max.
Min.
Max.
2. "D" and "E" do not include mold flash. Mold flash or
protrusions shall not exceed .010 inch (0.25mm).
A
.093
.004
.013
.009
.599
.290
.104
.012
.020
.013
.614
.299
2.35
0.10
0.33
0.23
15.20
7.36
2.65
0.30
0.51
0.32
15.60
7.60
A1
B
3. "L" is the length of terminal for soldering to a substrate.
4. Terminal numbers are shown for reference only.
5. "C" dimension does not include solder finish thickness.
6. Symbol "N" is the maximum number of terminals.
C
D
E
5
2
2
e
.050 BSC
1.27 BSC
.394
.010
.016
.419
.020
.050
10.00
0.25
0.40
10.65
0.51
1.27
H
h
L
3
6
N
α
24
24
0°
8°
0°
8°
ccc
—
.004
—
0.10
24
13
E
H
1
12
h x 45°
D
C
A1
A
α
SEATING
PLANE
– C –
L
B
e
LEAD COPLANARITY
ccc C
REV. 1.0.0 6/30/00
17
RC5058
PRODUCT SPECIFICATION
Ordering Information
Product Number
Package
RC5058M
24 pin SOIC
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FAIRCHILD SEMICONDUCTOR RESERVES THE RIGHT TO MAKE CHANGES WITHOUT FURTHER NOTICE TO ANY
PRODUCTS HEREIN TO IMPROVE RELIABILITY, FUNCTION OR DESIGN. FAIRCHILD DOES NOT ASSUME ANY
LIABILITY ARISING OUT OF THE APPLICATION OR USE OF ANY PRODUCT OR CIRCUIT DESCRIBED HEREIN; NEITHER
DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS.
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FAIRCHILD’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES
OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR
CORPORATION. As used herein:
1. Life support devices or systems are devices or systems
which, (a) are intended for surgical implant into the body,
or (b) support or sustain life, or (c) whose failure to perform
when properly used in accordance with instructions for use
provided in the labeling, can be reasonably expected to
result in significant injury to the user.
2. A critical component is any component of a life support
device or system whose failure to perform can be
reasonably expected to cause the failure of the life support
device or system, or to affect its safety or effectiveness.
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