RC5057资料

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RC5057High Performance Programmable Synchronous DC-DC Controller for Low Voltage MicroprocessorsFeatures•Programmable output from 1.3V to 3.5V using an integrated 5-bit DAC•Remote sense•Active Droop•85% efficiency typical at full load•Integrated Power Good and Enable/Soft Start functions•Drives N-channel MOSFETs•Overcurrent protection using MOSFET sensing•16 pin SOIC package•Meets Intel Pentium II & III specifications using minimum number of external componentsDescriptionThe RC5057 is a synchronous mode DC-DC controller IC which provides a highly accurate, programmable output voltage for all Pentium II & III CPU applications and other high-perfor-mance processors. The RC5057 features remote voltage sensing, adjustable current limit, and active droop for optimal converter transient response. The RC5057 uses a 5-bit D/A converter to program the output voltage from 1.3V to 3.5V. The RC5057 uses a high level of integration to deliver load cur-rents in excess of 16A 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 tight tolerance voltage regulation without expensive external components, while active droop permits exact tailoring of voltage for the most demanding load transients. The RC5057 also offers integrated functions including Power Good, Output Enable/Soft Start and current limiting, and is available in a 16 pin SOIC package.Applications•••••Power supply for Pentium® II & IIIVRM for Pentium II & III processorTelecom line cardsRouters, switches & hubsProgrammable step-down power supplyBlock Diagram+5VVCCA5-+-+3RS1048VCCP9HIDRV+12V+5VOSC-+ -+DigitalControl76LODRVGNDPPowerGood111ENABLE/SS2PWRGDVO5-BitDAC16151413121.24VReferenceVID0VID2VID4VID1VID3GNDAPentium is a registered trademark of Intel CorporationRev. 1.2.0

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RC5057PRODUCT SPECIFICATION

Pin Assignments

ENABLE/SSPWRGDIFBVFBVCCAGNDPLODRVVCCP12345678RC5057161514131211109VID0VID1VID2VID3VID4GNDASWHIDRVPin Definitions

Pin Number

1

Pin NameENABLE/SS

Pin Function Description

Output Enable/Softstart. A logic LOW on this pin will disable the output. An internal current source allows for open collector control. This pin also doubles as soft start.

Power Good Flag. An open collector output that will be logic LOW if the output voltage is not within ±12% of the nominal output voltage setpoint.

Current Feedback. Pin 3 is used in conjunction with pin 10, as the input for the current feedback control loop. Layout of these traces is critical to system performance. See Application Information for details.

Voltage Feedback. Pin 4 is used as the input for the 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 8 (VCCP). Connect to a low impedance ground.

Low Side FET Driver. Connect this pin 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 both high side and low side FET drivers. Connect to system 12V supply, and decouple with a 4.7µF tantalum and a 0.1µF ceramic capacitor. High Side FET Driver. Connect this pin 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 IFB pin allows FET sensing for 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.

23

PWRGDIFB

4567

VFBVCCAGNDPLODRV

101112–16

VCCPHIDRVSWGNDAVID0-4

2REV. 1.2.0 2/10/00

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PRODUCT SPECIFICATIONRC5057

Absolute Maximum Ratings

Supply Voltage VCCA to GNDSupply Voltage VCCP to GND

Voltage Identification Code Inputs, VID0-VID4Junction Temperature, TJStorage Temperature

Lead Soldering Temperature, 10 secondsPower Dissipation, PD

Thermal Resistance Junction-to-case, ΘJC

13.5V15VVCCA150°C-65 to 150°C300°C750mW105°C/W

Recommended Operating Conditions

Parameter

Supply Voltage VCCAInput Logic HIGHInput Logic LOW

Ambient Operating TemperatureOutput Driver Supply, VCCP

011.4

12

Conditions

Min.4.52.0

0.87013.2

Typ.5

Max.5.25

UnitsVVV°CV

REV. 1.2.0 2/10/003

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RC5057

PRODUCT SPECIFICATION

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

Output VoltageOutput CurrentInitial Voltage Setpoint

ILOAD = 0.8A, VOUT = 2.400V VOUT = 2.000V VOUT = 1.550VTA = 0 to 70°C, VOUT = 2.000V VOUT = 1.550VVCCA = 4.75V to 5.25V, VOUT = 2.000VVOUT at ILOAD = 0.8A to Imax20MHz BW, ILOAD = ImaxVOUT = 2.000VVOUT = 1.550V3

ILOAD = 0.8A to Imax,VOUT = 2.000V VOUT = 1.550V3ILOAD = Imax, VOUT = 2.0VSee Figure 4 for tR and tFSee Figure 7 for tDT

•

Logic HIGHLogic LOW

••••

255093883.747.65

48.51940

•

5

10

17

•••••

1.9401.4801.9001.48045

855050300

3451001071124.269.35

•••

-442.3942.0001.550

See Table 1

Conditions

•

Min.1.3

182.4242.0201.565+8+6±2-4011

2.0701.5902.1001.59060-362.4542.0401.580

Typ.

Max.3.5

UnitsVAVVVmVmVmVmVmVpkVVµA%nsecnseckHz%%VoutVVmAmAµA

Output Temperature DriftLine RegulationInternal Droop3Output RippleTotal Output Variation, Steady State1Total Output Variation, Transient2

Short Circuit Detect CurrentEfficiency

Output Driver Rise & Fall TimeOutput Driver DeadtimeOscillator FrequencyDuty CyclePWRGD ThresholdVCCA UVLOVCCP UVLOVCCA Supply CurrentVCCP Supply Current4Soft Start Current

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 capac-itors to the CPU are met, the specification of +40, -70mV at the capacitors will also be met.4.Includes gate current.

4REV. 1.2.0 2/10/00

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PRODUCT SPECIFICATION

RC5057

Table 1. Output Voltage Programming Codes

VID400000000000000001111111111111111

VID311111111000000001111111100000000

VID211110000111100001111000011110000

VID111001100110011001100110011001100

VID010101010101010101010101010101010

Nominal VOUT

1.30V1.35V1.40V1.45V1.50V1.55V1.60V1.65V1.70V1.75V1.80V1.85V1.90V1.95V2.00V2.05V2.0V2.1V2.2V2.3V2.4V2.5V2.6V2.7V2.8V2.9V3.0V3.1V3.2V3.3V3.4V3.5V

Note:

1.0 = processor pin is tied to GND.

1 = processor pin is open.

REV. 1.2.0 2/10/005

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RC5057

PRODUCT SPECIFICATION

Typical Operating Characteristics (VCCA = 5V, VCCP = 12V, and TA = +25°C using circuit in Figure

1, unless otherwise noted.)

Efficiency vs. Output Current8886Efficiency (%)84828078767472706866VOUT = 1.550V2.04VOUT = 2.000V2.032.022.01VOUT (V)2.001.991.981.971.961.951.940 3 6 9 12 15 18Output Current (A)0 3 6 9 12 15 18 Output Current (A)Droop, VOUT = 2.0VOutput Voltage vs. Output Current3.53.02.5VOUT (V)2.01.51.00.500 5 10 15 20 25 Output Current (A)Output Programming, VID4 = 02.11.9VOUT (V)VOUT (V)1.71.51.31.11.30 1.40 1.50 1.60 1.70 1.80 1.90 2.00 DAC Setpoint3.53.02.52.01.51.0Output Programming, VID4 = 12.1 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 3.5DAC Setpoint6REV. 1.2.0 2/10/00

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PRODUCT SPECIFICATION

RC5057

Typical Operating Characteristics (continued)Output Ripple, 2.0V @ 18ATransient Response, 12.5A to 0.5AVOUT(20mV/div)VCPU (50mV/div)1.590V1.550V1.480VTime (1µs/division)Time (100µs/div)Transient Response, 0.5A to 12.5AVCPU (50mV/div)1.590V1.550V1.480VTime (100µs/div)Switching Waveforms, 18A LoadOutput Startup, System Power-up5V/div 5V/divHIDRVpinLODRVpinTime (1µs/division)VO UT (1V/div)VIN (2V/div)Time (10ms/division)REV. 1.2.0 2/10/007

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RC5057

PRODUCT SPECIFICATION

Typical Operating Characteristics (continued)Output Startup from Enable2.042 VOUT(1V/div) ENABLE (2V/div)2.0402.038VOUT (V)2.0362.0342.0302.0282.0260 25 70 100 Time (10ms/division)Temperature (°C)VOUT Temperature VariationApplication Circuit+12VL1 (Optional)2.5µH+5VCIN*R133ΩC51µFC21µFR24.7ΩL21.3µHVOQ2D1MBRD835LCOUT*R610ΩC14.7µF91011121314151687654321Q1R34.7ΩVID4VID3VID2VID1VID0U1RC5057C30.1µFR5*ENABLE/SSC40.1µFVCCR410KΩPWRGDC60.1µF*Refer to Appendix for valuesof COUT, R5, and CIN.Figure 1. Typical Application Circuit(Worst Case Analyzed! See Appendix for Details)8REV. 1.2.0 2/10/00

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PRODUCT SPECIFICATION

RC5057

Table 2. RC5057 Application Bill of Materials

(Components based on Worst Case Analysis—See Appendix for Details)ReferenceC1C2, C5C3-4,6CINCOUTD1L1L2Q1

Manufacturer Part #AVX

TAJB475M010R5Panasonic

ECU-V1C105ZFXPanasonic

ECU-V1H104ZFXSanyo

10MV1200GXSanyo

6MV1500GXMotorolaMBRD835LAnyAny

Fairchild

FDP6030L or FDB6030LFairchild

FDP7030BL or FDB7030BLAnyAnyAnyAnyAnyFairchild RC5057M

Quantity

123**1Optional

11

Description4.7µF, 10V Capacitor1µF, 16V Capacitor100nF, 50V Capacitor1200µF, 10V Electrolytic1500µF, 6.3V Electrolytic8A Schottky Diode2.5µH, 10A Inductor1.3µH, 20A InductorN-Channel MOSFET(TO-220 or TO-263)N-Channel MOSFET(TO-220 or TO-263)33Ω4.7Ω10KΩ*10Ω

DC/DC Controller

DCR ~ 6mΩSee Note 1.DCR ~ 2mΩ

RDS(ON) = 20mΩ @ VGS = 4.5V See Note 2.

RDS(ON) = 10mΩ @ VGS = 4.5V See Note 2.IRMS = 2AESR ≤44mΩ

Requirements/Comments

Q21

R1R2-3R4R5R6U1

*See Appendix.

121111

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 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 Bulletin AB-8.

REV. 1.2.0 2/10/009

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RC5057

PRODUCT SPECIFICATION

+12VL1 (Optional)2.5µH+5VCIN*C51µFD21N4148R24.7ΩR133ΩR610ΩC14.7µFC21µFQ1L2R101.3µH10mΩR72.2mΩVOQ2D1MBRD835LCOUT*R34.7Ω91011121314151687654321VID4VID3VID2VID1VID0U1RC5057C30.1µFR52.80KΩR82.1ΩR91KΩVCCENABLE/SSC40.1µFR410KΩPWRGDC60.1µF*Refer to Table 4 for valuesof COUT, and CIN.Figure 2. Application Circuit for Coppermine/Camino Processors(Worst Case Analyzed! See Appendix for Details)10REV. 1.2.0 2/10/00

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PRODUCT SPECIFICATION

RC5057

Table 3. RC5057 Application Bill of Materials for Coppermine/Camino Processors

(Components based on Worst Case Analysis—See Appendix for Details)ReferenceC1C2, C5C3-4,6CINCOUTD1D2L1L2Q1Q2

Manufacturer Part #AVX

TAJB475M010R5Panasonic

ECU-V1C105ZFXPanasonic

ECU-V1H104ZFXSanyo

10MV1200GXSanyo

6MV1500GXMotorolaMBRD835LFairchild1N4148AnyAny

Fairchild

FDP6030L or FDB6030LFairchild

FDP7030BL or FDB7030BLAnyAnyAnyAnyAnyN/AAnyAny

Dale

WSL-2512-.01ΩFairchild RC5057M

Quantity

12331011Optional

111

Description4.7µF, 10V Capacitor1µF, 16V Capacitor100nF, 50V Capacitor1200µF, 10V Electrolytic1500µF, 6.3V Electrolytic8A Schottky DiodeSignal Diode2.5µH, 10A Inductor1.3µH, 20A InductorN-Channel MOSFET (TO-220 or TO-263)N-Channel MOSFET (TO-220 or TO-263)33Ω4.7Ω10KΩ2.80KΩ10Ω1.8mΩ2.1Ω1KΩ

10mΩ, 1W ResistorDC/DC Controller

PCB Trace ResistorDCR ~ 6mΩ See Note 1.DCR ~ 2mΩ

RDS(ON) = 20mΩ @ VGS = 4.5V See Note 2.

RDS(ON) = 10mΩ @ VGS = 4.5V See Note 2.IRMS = 2AESR ≤ 44mΩ

Requirements/Comments

R1R2-3R4R5R6R7R8R9R10U1

1211111111

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 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 Bulletin AB-8.

REV. 1.2.0 2/10/0011

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RC5057

PRODUCT SPECIFICATION

+12VL1 (Optional)2.5µH+5VCIN*C51µFC21µFR24.7ΩL21.3µHD1MBRD835LR73mΩVOQ2COUT*R133ΩR610ΩC14.7µF91011121314151687654321Q1R34.7ΩVID4VID3VID2VID1VID0U1RC5057C30.1µFR56.24KΩENABLE/SSC40.1µFVCCR410KΩPWRGDC60.1µF*Refer to Table 4 for valuesof COUT, and CIN.Figure 3. Application Circuit for Coppermine/Camino Processors

(Typical Design)

12REV. 1.2.0 2/10/00

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PRODUCT SPECIFICATION

RC5057

Table 4. RC5057 Application Bill of Materials for Coppermine/Camino Processors(Typical Design)ReferenceC1C2, C5C3-4,6CINCOUTD1L1L2Q1-2Manufacturer Part #AVX TAJB475M010R5Panasonic ECU-V1C105ZFXPanasonic ECU-V1H104ZFXSanyo 10MV1200GXSanyo 6MV1500GXMotorola MBRD835LAnyAnyFairchild FDP6030L or FDB6030LAnyAnyAnyAnyAnyN/AFairchild RC5057MQuantity123381Optional12Description4.7µF, 10V Capacitor1µF, 16V Capacitor100nF, 50V Capacitor1200µF, 10V ElectrolyticIRMS = 2A1500µF, 6.3V Electrolytic3A Schottky Diode2.5µH, 10A Inductor1.3µH, 20A InductorN-Channel MOSFET (TO-220 or TO-263)33Ω4.7Ω10KΩ6.24KΩ10Ω3.0mΩDC/DC ControllerPCB Trace ResistorDCR ~ 6mΩ See Note 1.DCR ~ 2mΩRDS(ON) = 20mΩ @ VGS = 4.5V See Note 2.ESR ≤ 44mΩRequirements/CommentsR1R2-3R4R5R6R7U11211111Notes: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 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 Bulletin AB-8.Test ParameterstR90%10%tDT2V2V90%2VtDT2VLODRV10%tFHIDRVFigure 4. Output Drive Timing DiagramREV. 1.2.0 2/10/0013

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RC5057

PRODUCT SPECIFICATION

Application Information

The RC5057 Controller

The RC5057 is a programmable synchronous DC-DC con-troller IC. When designed around the appropriate external components, the RC5057 can be configured to deliver more than 16A of output current, as appropriate for the Katmai and Coppermine and other processors. The RC5057 func-tions as a fixed frequency PWM step down regulator.

Internal Voltage Reference

The reference included in the RC5057 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.

Main Control Loop

Refer to the RC5057 Block Diagram on page 1. The RC5057 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 IFB (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 IFB 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 look-ing 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. There is an additional comparator in the analog control section whose function is to set the point at which the RC5057 current limit comparator disables the output drive signals to the external power MOSFETs.

Power Good (PWRGD)

The RC5057 Power Good function is designed in accordance with the Pentium II & 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. The output is guaranteed open-collector high when the power supply voltage is within ±7% of its nomi-nal setpoint. The Power Good flag provides no other control function to the RC5057.

Output Enable/Soft Start (ENABLE/SS)

The RC5057 will accept an open collector/TTL signal for con-trolling 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 RC5057 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 RC5057 disables the output drive signal to the external high-side MOSFET. The DC-DC converter returns to normal operation after the fault has been removed. If it is desired to have an active over-voltage pro-tection circuit, the RC5052, which includes all the features of the RC5057, may be chosen instead of the RC5057.

High Current Output Drivers

The RC5057 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 resistor. The resulting voltage is sufficient to provide the gate to source drive to the external MOSFETs required in order to achieve a low RDS,ON.

Oscillator

The RC5057 oscillator section uses a fixed frequency of operation of 300KHz. If it is desired to adjust this frequency for reasons of efficiency or component size, the RC5052, which includes all of the features of the RC5057, may be chosen instead of the RC5057.

Design Considerations and Component Selection

Additional information on design and component selection may be found in Fairchild’s Application Note 57.

REV. 1.2.0 2/10/00

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PRODUCT SPECIFICATION

RC5057

MOSFET SelectionThis application requires N-channel Logic Level Enhance-ment Mode Field Effect Transistors. Desired characteristics are as follows:•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.Dm = Maximum duty cycle for the DC/DC converter (usually 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 RC5057 pro-vides significant cost savings for the newer CPU systems that typically run at high supply current.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.RC5057 Short Circuit Current CharacteristicsThe RC5057 protects against output short circuit by turning off both the high-side and low-side MOSFETs and resetting softstart. The short circuit limit is set with the R5 resistor, as given by the formulaR5=ISC x RDS, onIDetectInductor SelectionChoosing 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 rip-ple or maximize transient performance. The first order equa-tion (close approximation) for minimum inductance is:Lmin=(Vin – Vout)fxVoutVinxESRVripplewhere:Vin = Input Power SupplyVout = Output Voltagef = DC/DC converter switching frequencyESR = Equivalent series resistance of all output capacitors in parallelwith IDetect ≈ 50µA, ISC the desired current limit, and RDS,on the high-side MOSFET’s on resistance. Remember to make R5 large enough to include the effects of initial tolerance and temperature variation on the MOSFET’s RDS,on. However, the value of R5 should be less than 8.3KΩ. If a greater value is necessary, a lower RDS,on MOSFET should be used instead. Alternately, use of a sense resistor in series with the source of the MOSFET, as shown in Figure 6, eliminates this source of inaccuracy in the current limit. Note the addition of the diode, which is necessary for proper operation of this cir-cuit.As an example, Figure 5 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 R5. 3.53.02.5VOUT (V)Vripple = Maximum peak to peak output ripple voltage budget.The first order equation for maximum allowed inductance is:Lmax=2C0(Vin – Vout) Dm VtbIpp22.01.51.00.500 5 10 15 20 25 Output Current (A)where:Co = The total output capacitanceIpp = Maximum to minimum load transient currentVtb = The output voltage tolerance budget allocated to load transientFigure 5. RC5057 Short Circuit CharacteristicThe 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 REV. 1.2.0 2/10/0015

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RC5057

PRODUCT SPECIFICATION

has typical RDS,on rather than maximum, and is at 25°C. This is the reason for using the external sense resistor.) At this point, the internal comparator trips and signals the controller to discharge the softstart capacitor. This causes a drastic reduc-tion 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 range for the DC-DC converter.1N4148The 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 7. 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.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 7 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 RMS 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-15.2.5µH5V0.1µFVin1000µF, 10VElectrolyticR5IFBRSENSESWVOUTFigure 6. Precision Current SensingSchottky Diode SelectionThe 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 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.Figure 7. Input FilterActive DroopThe RC5057 includes active droop: as the output current increases, the output voltage drops. This is done in order to allow maximum headroom for transient response of the con-verter. The current is sensed by measuring the voltage across the high-side MOSFET during its on time. Note that this makes the droop dependent on the temperature of the MOSFET. However, when the formula given for selecting RS (current limit) is used, there is a maximum droop possible (-40mV), and when this value is reached, additional drop across the MOSFET will not cause any increase in droop—until current limit is reached.Additional droop can be added to the active droop using a discrete resistor (typically a PCB trace) outside the control loop, as shown in Figure 2. This is typically only required for the most demanding applications, such as for the next gener-ation Intel processor (tolerance = +40/-70mV), as shown in Figure 2.Output Filter CapacitorsThe 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.16

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PRODUCT SPECIFICATION

RC5057

PCB Layout Guidelines•Placement of the MOSFETs relative to the RC5057 is critical. Place the MOSFETs such that the trace length of the HIDRV and LODRV pins of the RC5057 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 RC5057. That is, traces that connect to pins 7, 9, 10, and 8 (LODRV, HIDRV, SW and VCCP) should be kept far away from the traces that connect to pins 3 through 5, and pin 11.•Place the 0.1µF decoupling capacitors as close to the RC5057 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.AppendixWorst-Case Formulae for the Calculation of Cout, R5, and Cin (Circuit of Figure 1 Only)The following formulae design the RC5057 for worst-case operation, including initial tolerance and temperature depen-dence of all of the IC parameters (initial setpoint, reference tolerance and tempco, active droop tolerance, current sensor gain), the initial tolerance and temperature dependence of the MOSFET, and the ESR of the capacitors. The following information must be provided:VT+, the value of the positive transient voltage limit;|VT-|, the absolute value of the negative transient voltage limit;IO, the maximum output current;Vnom, the nominal output voltage;Vin, the input voltage (typically 5V);ESR, the ESR of the output caps, per cap (44mΩ for the Sanyo parts shown in this datasheet);RD, the on-resistance of the MOSFET (10mΩ for the FDB7030);∆RD, the tolerance of the current sensor (usually about 67% for MOSFET sensing, including temperature).Irms, the rms current rating of the input caps (2A for the Sanyo parts shown in this datasheet).2IO*Cin=VnomVinIrms–VnomVinAdditional InformationFor additional information contact Fairchild Semiconductor at http://www.fairchildsemi.com/cf/tsg.htm or contact an autho-rized representative in your area.R5=IO* RD * (1 + ∆RD) * 1.1050 * 10-6The value of R5 must be ≤ 8.3KΩ. If a greater values is calculated, RD must be reduced.Number of capacitors needed for Cout = the greater of:X=ESR * IOVT-orESR * IO VT+ –0.004 * Vnom +14400 * IO * RD18 * R5 * 1.1Y=REV. 1.2.0 2/10/0017

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RC5057

PRODUCT SPECIFICATION

Example: Suppose that the transient limits are ±134mV, current I is 14.2A, and the nominal voltage is 2.000V, using MOSFET current sensing and the usual caps. We have VT+ = |VT-| = 0.134, IO = 14.2, Vnom = 2.000, and ∆RD = 0.67. We calculate:2Y== 3.47 ⇒ 4 capsR5=14.2 * 0.010 * (1 + 0.67) * 1.10 50 * 10-6=5.2KΩX=0.044 * 14.20.134=4.6614.2*Cin=2.00052–2.00050.044 * 14.20.134 – 0.004 * 2.000+14400 * 14.2 * 0.02018 * 10400 * 1.1=4.28Since X > Y, we choose X, and round up to find we need 5 capacitors for COUT.18REV. 1.2.0 2/10/00

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PRODUCT SPECIFICATION

RC5057

Mechanical Dimensions16 Lead SOICInchesMin.Max..053.069.004.010.013.020.008.010.386.394.150.158.050 BSC.228.010.016160°—8°.0040°—.244.020.050MillimetersMin.Max.1.351.750.100.250.330.510.190.259.8010.003.814.001.27 BSC5.800.250.40168°0.106.200.501.27Notes:Notes1.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.5225.\"C\" dimension does not include solder finish thickness.6.Symbol \"N\" is the maximum number of terminals.SymbolAA1BCDEeHhLNαccc36169EH18DA1AeBSEATINGPLANE– C –LEAD COPLANARITYcccCαh x 45°CLREV. 1.2.0 2/10/0019

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RC5057

PRODUCT SPECIFICATION

Ordering InformationProduct NumberRC5057MPackage16 pin SOICDISCLAIMER 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.LIFE SUPPORT POLICY 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.www.fairchildsemi.com

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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.