Datasheet RC5058 Datasheet (Fairchild Semiconductor)

www.fairchildsemi.com

RC5058

High Performance Programmable Synchronous
DC-DC Controller for Multi-Voltage Platforms

Features

•P rogrammable output for Vcore from 1.3V to 3.5V using

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)

• Meets VRM specification with as few as 5 capacitors

• Meets 1.550V +40/-70mV over initial tolerance,
temperature and transients

• 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

+3.3V

+1.5V

+2.5V

9

+

10

VCCP

11

+

12

OSC

REF

­PWRGD,

OCL

REF

-

PWRGD,
OCL

OCL

VCCA

-

+

Applications

• Power supply for Pentium

• Power supply for Pentium III Whitney Platform

• VRM for Pentium III processor

• Programmable multi-output power supply

®

III Camino Platform

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
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

+5V

21

-

+

-

+

19

18

20
24

1

R

R

S

VCCP
HIDRV

D

+12V

™

for optimal converter

+5V

15

14

+

V

-

5-Bit

DAC

VID2

PWRGD, OCL

VID4

VID3

3.3/1.5V

Pentium is a registered trademark of Intel Corporation. Programmable Active Droop is a trademark of Fairchild Semiconductor.

13

87654

VID0

VID1

-

+

1.24V

Reference

-

+

3

GNDA

Digital

Control

16

ENABLE/SS

Power

Good

2

23

22

17

LODRV

GNDP

PWRGD

VCC

Rev. 1.0.0

2

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 adjust­able 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 Definitions

Pin

Number Pin Name Pin Function Description

1 HIDRV

2SW

3 GNDA

4-8 VID0-4

9 VTTGATE Gate Driver for VTT Transistor. For 1.5V output.
10 VTTFB
11 VCKGATE Gate Driver for VCK Transistor. For 2.5V output.
12 VCKFB
13 VAGPFB
14 VAGPGATE Gate Driver for VAGP Transistor. For 3.3/1.5V output.
15 TYPEDET Type Detect. Sets 3.3V or 1.5V for AGP.
16 ENABLE/SS Output Enable. A logic LOW on this pin will disable all outputs. An internal current source

17 PWRGD

18 ILIM

19 DROOP
20 VFB

21 VCCA
22 GNDP
23 LODRV

24 VCCP

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".

High side Driver Source and Low side Driver Drain Switching Node. Together with

DROOP and ILIM pins allows FET sensing for Vcc current.

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.

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.

Voltage Feedback for VTT.

Voltage Feedback for VCK.
Voltage Feedback for VAGP.

allows for open collector control. This pin also doubles as soft start for all outputs.

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.

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.

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".

Power VCC. For all FET drivers. Connect to system 12V supply through a 33 Ω , and

decouple with a 1µF ceramic capacitor.

Pin Assignments

HIDRV

SW

GNDA

VID4
VID3
VID2

VID1

VID0

VTTGATE

VTTFB

VCKGATE

VCKFB

1
2
3
4
5
6
7
8
9
10
11
12

RC5058

24
23
22
21
20
19
18
17
16
15
14
13

VCCP
LODRV
GNDP
VCCA
VFB
DROOP
ILIM
PWRGD
SS/ENABLE
TYPEDET
VAGPGATE
VAGPFB

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PRODUCT SPECIFICATION RC5058

Absolute Maximum Ratings

Supply Voltage VCCA to GND 13.5V
Supply Voltage VCCP to GND 15V
Voltage Identification Code Inputs, VID0-VID4 VCCA
All Other Pins 13.5V
Junction Temperature, T

J

150°C
Storage Temperature -65 to 150°C
Lead Soldering Temperature, 10 seconds 300°C
Thermal Resistance Junction-to-ambient, Θ

Note:

1. Component mounted on demo board in free air.

JA

1

75°C/W

Recommended Operating Conditions

Parameter Conditions Min. Typ. Max. Units

Supply Voltage VCCA 4.5 5 5.25 V
Input Logic HIGH 2.0 V
Input Logic LOW 0.8 V
Ambient Operating Temperature 0 70 °C
Output Driver Supply, VCCP 10.8 12 13.2 V

Electrical Specifications

(V

= 5V, V

CCA

The • denotes specifications which apply over the full operating temperature range.

Parameter Conditions Min. Typ. Max. Units
VCC Regulator

Output Voltage See Table 1 • 1.3 3.5 V
Output Current 18 A
Initial Voltage Setpoint I

Output Temperature Drift T

Line Regulation V
Internal Droop Impedance I
Maximum Droop 60 mV
Output Ripple 20MHz BW, I
Total Output Variation,

Steady State

Total Output Variation,

Transient
Short Circuit Detect Current • 45 50 60 µA
Efficiency I
Output Driver Rise & Fall Time See Figure 3 50 nsec
Output Driver Deadtime See Figure 3 50 nsec

CCP

2

= 12V, V

1

= 2.0V, and T

OUT

= +25°C using circuit in Figure 1 unless otherwise noted.)

A

= 0.8A,V

LOAD

= 0 to 70°C,V

A

= 4.75V to 5.25V • -4 mV/V

IN

= 0.8A to 12.5A 13.0 14.4 15.8 K Ω

LOAD

V

= 2.000V

OUT

V

= 1.550V

OUT

I

= 0.8A to 18A, V

LOAD

= 18A, V

LOAD

= 2.400V

OUT

V

= 2.000V

OUT

V

= 1.550V

OUT

= 2.000V

OUT

V

= 1.550V

OUT

= 18A 11 mVpk

LOAD

3

= 2.000V

OUT

V

= 1.550V

OUT

= 2.0V 85 %

OUT

3

2.397

2.000

1.550

•

•

••1.940

1.480

••1.900

1.480

2.424

2.020

1.565
+8

+6

2.454

2.040

1.580

2.070

1.590

2.100

1.590

V
V
V

mV
mV

V

V

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3

4

≤

≤

≤

≤

RC5058 PRODUCT SPECIFICATION

Electrical Specifications

(V

CCA

= 5V, V

CCP

= 12V, V

OUT

(Continued)

= 2.0V, and T

= +25°C using circuit in Figure 1 unless otherwise noted.)

A

The • denotes specifications which apply over the full operating temperature range.

Parameter Conditions Min. Typ. Max. Units

Duty Cycle 0 100 %
5V UVLO • 3.74 4 4.26 V
12V UVLO • 7.65 8.5 9.35 V
Soft Start Current • 5 10 17 µA

VTT Linear Regulator

Output Voltage I

2A • 1.455 1.5 1.545 V

LOAD

Under Voltage Trip Level Over Current 80 %V

VCLK Linear Regulator

Output Voltage I

2A • 2.375 2.5 2.625 V

LOAD

Under Voltage Trip Level Over Current 80 %V

VAGP Linear Regulator

Output Voltage I
Output Voltage I

2A, TYPEDET=0V • 1.425 1.5 1.575 V

LOAD

2A, TYPEDET=OPEN • 3.135 3.3 3.465 V

LOAD

Under Voltage Trip Level Over Current 80 %V

Common Functions

Oscillator Frequency • 255 310 345 kHz
PWRGD Threshold Logic HIGH, All Outputs

Linear Regulator Under Voltage

Logic LOW, Any Output
Over Current 30 µsec

•

92

•

88

108
112

Delay Time

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

0.5m Ω 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.

%V

O

O

O

OUT

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PRODUCT SPECIFICATION RC5058

Table 1. Output Voltage Programming Codes

VID4 VID3 VID2 VID1 VID0 Nominal V

01111 1.30V
01110 1.35V
01101 1.40V
01100 1.45V
01011 1.50V
01010 1.55V
01001 1.60V
01000 1.65V
00111 1.70V
00110 1.75V
00101 1.80V
00100 1.85V
00011 1.90V
00010 1.95V
00001 2.00V
00000 2.05V
11111 2.0V
11110 2.1V
11101 2.2V
11100 2.3V
11011 2.4V
11010 2.5V
11001 2.6V
11000 2.7V
10111 2.8V
10110 2.9V
10101 3.0V
10100 3.1V
10011 3.2V
10010 3.3V
10001 3.4V
10000 3.5V

OUT

Note:

1. 0 = processor pin is tied to GND.
1 = processor pin is open.

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5

RC5058 PRODUCT SPECIFICATION

V

Typical Operating Characteristics

(V

= 5V, V

CCA

88
86
84
82
80
78
76

Efficiency (%)

74
72
70
68
66
64

0 3 6 9 12 15 18

= 12V, and T

CCP

V

Efficiency vs. Output Current

CPU

V

= 1.550V

OUT

Output Current (A)

= +25°C using circuits in Figure 1, unless otherwise noted.)

A

Droop, V

2.04

V

= 2.000

OUT

2.03

2.02

2.01

2.00

1.99

(V)

1.98

OUT

V

1.97

1.96

1.95

1.94
0 3 6 9 12 15 18

= 2.0V, RD = 8K Ω

CPU

Output Current (A)

6

CPU Output Voltage vs. Output Current

3.5

3.0

2.5

2.0

(V)

OUT

1.5

Output Programming, VID4 = 0

2.1

1.9

1.7

(V)

1.5

CPU

V

1.3

V

1.0

0.5
0

0 5 10 15 20 25

Output Current (A)

3.5

3.0

2.5

(V)

2.0

CPU

V

1.5

Output Programming, VID4 = 1

1.1

1.30 1.40 1.50 1.60 1.70 1.80 1.90 2.00

DAC Setpoint

1.0

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

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PRODUCT SPECIFICATION RC5058

Typical Operating Characteristics

Output Ripple, 2.0V @ 18A

(20mV/div)

CPU

V

Time (1µs/div)

Transient Response, 0.5A to 12.5A

1.590V

(50mV/div)

CPU

V

1.550V

1.480V

(continued)

Transient Response, 12.5A to 0.5A

(50mV/div)

CPU

V

Switching Waveforms, 18A Load

5V/div 5V/div

1.590V

1.550V

1.480V

Time (100µs/div)

HIDRV
pin

LODRV
pin

(2V/div)

IN

(1V/div) V

CPU

V

Time (100µs/div)

Output Startup, System Power-up

Time (10ms/div)

Time (1µs/div)

Output Startup from Enable

(1V/div) ENABLE (2V/div)

CPU

V

Time (10ms/div)

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7

RC5058 PRODUCT SPECIFICATION

Typical Operating Characteristics (continued)

Linear Regulator Noise

2.042

2.040

2.038

(10mV/div)

OUT

(V)

CPU

V

2.036

2.034

2.030

2.028

2.026
0 25 70 100

Application Circuit

L1

+5V

(Optional)

VO

C

OUT

C10 C11

*

L2

3.3V IN

1.5V†

C8

Temperature (°C)

CIN*

C2

Q1

Q2

D1

Q3

2.5V†

AC COUPLED V

Time (100µs/div)

R7

R5

R2

R3

Q4

C9

R6

VID4

VID3
VID2

VID1

VID0

C1

C4

R1

+12V

C5

ENABLE/SS

VCC

R4

PWRGD

C6

, C

IN

OUT

,

1
2

3
4

U1

5

RC5058

6
7
8
9

10
11

12

24
23

22
21

20
19
18
17
16
15

14
13

TYPEDET

C12

C3

Q5

3.3/1.5V
(AGP)†

C7

* Refer to Appendix for values of C

R5 and R7.

† Adjustable with an external divider.

Figure 1. Typical Application Circuit

(Worst Case Analyzed! See Appendix for Details)

8 REV. 1.0.0 6/30/00

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

TAJB475M010R5

C2, C5 Panasonic

ECU-V1C105ZFX

C3-4,C6 Panasonic

ECU-V1H104ZFX

C7-9 Sanyo

6MV1000FA
C10-12 Any 3 22µF, 6.3V Capacitor Low ESR
C

IN

Sanyo

10MV1200GX
C

OUT

Sanyo

6MV1500GX
D1 Motorola

MBRD835L
L1 Any Optional 2.5µH, 8A Inductor DCR ~ 10mΩ

L2 Any 1 1.3µH, 20A Inductor DCR ~ 2mΩ
Q1 Fairchild

FDB6030L
Q2 Fairchild

FDB7030BL
Q3-5 Fairchild

FDB4030L
R1 Any 1 33Ω
R2-3 Any 2 4.7Ω
R4 Any 1 10KΩ
R5 Any 1 *
R6 Any 1 10Ω
R7 Any 1 *
U1 Fairchild

RC5058M

1 4.7µF, 10V Capacitor

2 1µF, 16V Capacitor

3 100nF, 50V Capacitor

3 1000µF, 6.3V Electrolytic

* 1200µF, 10V Electrolytic I

RMS

= 2A

* 1500µF, 6.3V Electrolytic ESR ≤ 44mΩ

1 8A Schottky Diode

See Note 1.

1 N-Channel MOSFET R

DS(ON)

= 20mΩ @

VGS = 4.5V See Note 2.

1 N-Channel MOSFET R

V

= 10mΩ @

DS(ON)

= 4.5V See Note 2.

GS

3 N-Channel MOSFET

1 DC/DC Controller

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 ΘSA < 20°C/W should be used. For 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.

*Refer to Appendix for values.

REV. 1.0.0 6/30/00 9

RC5058 PRODUCT SPECIFICATION

L1

+5V

(Optional)

CIN*

VO

C

*

OUT

C10 C11

R7

R5

C2

Q1

L2

R8

Q2

D1

3.3V IN

Q3

1.5V†

C8

2.5V†

R2

R3

Q4

C9

R6

VID4
VID3
VID2

VID1
VID0

C1

C4

R1

+12V

C5

ENABLE/SS

VCC

OUT

R4

PWRGD

C6

and CIN.

1
2

3
4

U1

5

RC5058

6
7
8
9

10
11

12

24
23

22
21

20
19
18
17
16
15

14
13

TYPEDET

C12

C3

Q5

3.3/1.5V
(AGP)†

C7

*Refer to Table 4 for values of C

† Adjustable with an external divider.

Figure 2. Application Circuit for Coppermine/Camino Motherboards

(Typical Design)

10 REV. 1.0.0 6/30/00

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

TAJB475M010R5

C2, C5 Panasonic

ECU-V1C105ZFX

C3-4,C6 Panasonic

ECU-V1H104ZFX

C7-9 Sanyo

6MV1000FA
C10-12 Any 3 22µF, 6.3V Capacitor Low ESR
C

IN

Sanyo

10MV1200GX
C

OUT

Sanyo

6MV1500GX
D1 Motorola

MBRD835L
L1 Any Optional 2.5µH, 5A Inductor DCR ~ 10mΩ

L2 Any 1 1.3µH, 15A Inductor DCR ~ 3mΩ
Q1 Fairchild

FDB6030L
Q2 Fairchild

FDB7030BL
Q3-5 Fairchild

FDB4030L
R1 Any 1 33Ω
R2-3 Any 2 4.7Ω
R4 Any 1 10KΩ
R5, R7 Any 2 6.24KΩ
R6 Any 1 10Ω
R8 N/A 1 3.0mΩ PCB Trace Resistor
U1 Fairchild

RC5058M

1 4.7µF, 10V Capacitor

2 1µF, 16V Capacitor

3 100nF, 50V Capacitor

3 1000µF, 6.3V Electrolytic

3 1200µF, 10V Electrolytic I

RMS

= 2A

12 1500µF, 6.3V Electrolytic ESR ≤ 44mΩ

1 8A Schottky Diode

See Note 1.

1 N-Channel MOSFET R

V

1 N-Channel MOSFET R

V

= 20mΩ @

DS(ON)

= 4.5V See Note 2.

GS

= 10mΩ @

DS(ON)

= 4.5V See Note 2.

GS

3 N-Channel MOSFET

1 DC/DC Controller

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
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

< 20°C/W should be used. For

SA

RC5058 PRODUCT SPECIFICATION

Test Parameters

t

R

5V

2V

t

DT

2V

Figure 3. Ouput Drive Timing Diagram

5V

2V

t

F

HIDRV
to SW

t

DT

2V

LODRV

Application Information

The RC5058 Controller

The RC5058 is a programmable synchronous DC-DC con­troller 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.

Main Control Loop

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.

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.

High Current Output Drivers

The RC5058 contains two identical high current output drivers
that utilize high speed bipolar transistors in a push-pull config­uration. 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 volt­age is sufficient to provide the gate to source drive to the
external MOSFETs required in order to achieve a low R

DS,ON

Internal Voltage Reference

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, includ­ing those below 1.80V.

Power Good (PWRGD)

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.

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 protec­tion 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.

.

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.

12 REV. 1.0.0 6/30/00

Oscillator

The RC5058 oscillator section uses a fixed frequency of
operation of 300KHz.

PRODUCT SPECIFICATION RC5058

95%).

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:

• Low Static Drain-Source On-Resistance, R

DS,ON

< 20mΩ

(lower is better)

• Low gate drive voltage, VGS = 4.5V rated

• Power package with low Thermal Resistance

• Drain-Source voltage rating > 15V.

The on-resistance (R

is the primary parameter for

DS,ON)

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 Applica­tions Bulletin AB-8.

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:

(V

– V

)

in

L

=

min

out

f

V

out

x

V

where:
Vin = Input Power Supply

= Output Voltage

V

out

f = DC/DC converter switching frequency
ESR = Equivalent series resistance of all output capacitors in
parallel
V

= Maximum peak to peak output ripple voltage budget.

ripple

The first order equation for maximum allowed inductance is:

(V

– V

in

L

max

2C

=

O

out

2

I

pp

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

x

in

) Dm V

ESR

V

ripple

tb

Some margin should be maintained away from both L
L

. Adding margin by increasing L almost always adds

max

min

and

expense since all the variables are predetermined by system
performance except for C

, which must be increased to

O

increase L. Adding margin by decreasing L can be done by
purchasing capacitors with lower ESR. The RC5058 pro­vides significant cost savings for the newer CPU systems
that typically run at high supply current.

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

I

*R

SC

R

=

S

with I
R

DS,on

≈ 50µA, I

Detect

the high-side MOSFET’s on resistance. Remember to

is the desired current limit, and

SC

make the RS large enough to include the effects of initial tol­erance and temperature variation on the MOSFET’s R
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 R
be used instead.

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.

CPU Output Voltage vs. Output Current

3.5

3.0

2.5

2.0

(V)

OUT

1.5

V

1.0

0.5
0

0 5 10 15 20 25

Figure 4. RC5058 Short Circuit Characteristic

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 R

rather than maximum, and is at 25°C).

DS,on

I

Detect

DS, on

MOSFET should

DS,on

DS,on

.

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 con­troller 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,
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.

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.

Schottky Diode Selection

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.

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.

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.

2.5µH

™

Vin

1000µF, 10V
Electrolytic

5V

0.1µF

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 R

of the high-side MOSFET during

DS,on

its on time, as shown in Figure 1.

To program the amount of droop, use the formula

where I

14.4KΩ *I

R

D

is the current at which the droop occurs, and R

max

V

max

Droop

*R

*18

sense

sense

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 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

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.
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.

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.

VGATE

VOUT

R

VFB

10KΩ

Figure 6. Adjusting the Output Voltage of the Linear

Regulator

The resistor value should be chosen as

V

R 10KΩ* –1

=

out

V

nom

For example, to get the VTT voltage to be 1.55V instead of

1.50V, use R = 10KΩ * [(1.55/1.50) – 1] = 333Ω.

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 Vnorth­bridge = 1.0V, Vagp = 1.8V, meeting the Intel requirement.

• 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.

• 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.

• 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.

• A PC Board Layout Checklist is available from Fairchild
Applications. Ask for Application Bulletin AB-11.

Additional Information

For additional information contact Fairchild Semiconductor at
http://www.fairchildsemi.com/cf/tsg.htm or contact an autho­rized representative in your area.

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

Appendix

Worst-Case Formulae for the Calculation of
Cin, Cout , R5, R7 and Roffset

Figure 1 only)

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:

V

, the value of the positive static voltage limit;

S+

|, the absolute value of the negative static voltage limit;

|V

S-

V

, the value of the positive transient voltage limit;

T+

|VT-|, the absolute value of the negative transient voltage limit;

IO, the maximum output current;

V

, the nominal output voltage;

nom

Vin, the input voltage (typically 5V);

I

, the ripple current rating of the input capacitors, per cap

rms

(2A for the Sanyo parts shown in this datasheet);

RD, the resistance of the current sensor (usually the MOSFET);

(Circuits similar to

The value of R7 must be ≤ 8.3KΩ. If a greater value is calcu­lated, R

Number of capacitors needed for C

must be reduced.

D

X=

= the greater of:

out

ESR * I

O

V

+ V

T-

– .024 * V

S+

nom

or

Y

=

VT+ – V

S+

ESR * I

+

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, V

= 2.000, and ∆RD = 1.67. We calculate:

nom

Since Y > X, we choose Y, and round up to find we need 7
capacitors for C

OUT

.

O

14400 * I

O

18 * R5 * 1.1

* R

D

∆RD, the tolerance of the current sensor (usually about 67%
for MOSFET sensing, including temperature); and

ESR, the ESR of the output capacitors, per cap (44mΩ for
the Sanyo parts shown in this datasheet).

2

–

nom

-

V

nom

V

in

* 1KΩ

6

C

R

in

offset

V

nom

*IO

V

in

=

I

rms

V

– .024 * V

S+

=

1.01 * V

IO* RD * (1 + ∆RD)

R7

=

nom

45 * 10

14400 * IO* RD * (1 + ∆RD) *1.1

R5 =

18 * (V

S+

+ V

– .024 * V

S-

nom

)

A detailed explanation of this calculation may be found in
Applications Bulletin AB-24.

2.000

*14.2

=

C

in

R

offset

R7

14400 * 14.2 * 0.020 * (1 + 0.67) * 1.1

=

R5

Y

18 * (0.089 + 0.079 – .024 * 2.000)

X==

=

0.134 – 0.089

5

0.089 – .024 * 2.000

=

1.01 * 2.000

14.2 * 0.010 * (1 + 0.67)

=

0.134 + 0.089 – .024 * 2.00

0.044 * 14.2

2.000

–

2

45 * 10

0.044 * 14.2

14400 * 14.2 * 0.020

+

18 * 3640 * 1.1

2

5

-6

=

3.47 ⇒ 4 caps

20.3Ω*1000

=

5.25KΩ

=

3.48KΩ

=

3.57

6.14

=

16 REV. 1.0.0 6/30/00

PRODUCT SPECIFICATION RC5058

Mechanical Dimensions

24 Lead SOIC

Symbol

A .093 .104 2.35 2.65
A1 .004 .012 0.10 0.30
B .013 0.33
C .009 .013 0.23 0.32
D .599 .614 15.20 15.60
E .290 .299 7.36 7.60
e
H
h
L .016 .050 0.40 1.27
N24 24

α

ccc .004 0.10——

24 13

Inches

Min. Max. Min. Max.

.020 0.51

.050 BSC 1.27 BSC

.394 .419 10.00 10.65
.010 .020 0.25 0.51

0° 8° 0° 8°

Millimeters

Notes

5
2
2

3
6

H

E

Notes:

1.

Dimensioning and tolerancing per ANSI Y14.5M-1982.

2.

"D" and "E" do not include mold flash. Mold flash or
protrusions shall not exceed .010 inch (0.25mm).

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.

112

D

A

e

B

A1

SEATING
PLANE

– C –

LEAD COPLANARITY

ccc C

h x 45°

C

α

L

REV. 1.0.0 6/30/00 17

RC5058 PRODUCT SPECIFICATION

Ordering Information

Product Number Package

RC5058M 24 pin SOIC

DISCLAIMER

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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