Vicor Micro Family of DC-DC Converter User Manual

Design Guide & Applications Manual

For Maxi, Mini, Micro Family DC-DC Converter and Accessory Modules

Table of Contents

Maxi, Mini, Micro Family DC-DC Converters Section Pages

High Density DC-DC Converter Technology 1 2 – 4

Control Pin Functions and Applications 2 5 – 11

Design Requirements 3 12 – 17

EMC Considerations 4 18 – 19

Current Sharing in Power Arrays 5 20 – 24

Thermal Performance Information 6 25 – 30

Accessory Modules

Autoranging Rectifier Module (ARM) 7 31 – 35

Filter / Autoranging Rectifier Module (FARM) 8 36 – 40

Modular AC Front-end System (ENMod) 9 41 – 47

High Boost HAM 10 48 – 52

Filter Input Attenuator Module (FIAM) Family 11 53 – 55

Output Ripple Attenuator Module (MicroRAM) 12 56 – 61

Recommended Soldering Methods

Lead Free Pins (RoHS) 13 62 – 66

TIn Lead Pins 14 67 – 71

Mounting Options

Surface Mount Socketing System (SurfMate) 15 72 – 75

Through-hole Socket-mount System (InMate) 16 76 – 79

Glossary of Technical Terms 17 80 – 87

Maxi, Mini, Micro Design Guide Rev 4.9 vicorpower.com

Page 1 of 88

Apps. Eng. 800 927.9474 800 735.6200

1. High Density DC-DC Converter Technology

AC-DC Products

DC-DC Products

Universal 85 – 264 Vac

Autoranging 90 – 132 Vac 180 – 264 Vac

Autoranging 115 – 230 Vac Input

Nominal Input 18 – 425 Vdc

28 Vdc, 48 Vdc, 270 Vdc

24 Vdc, 28 Vdc, 48 Vdc

Harmonic Attenuator Module Unity Power Factor

Up to 675 W per module

Filter / Autoranging Rectifier Module

Up to 1,000 W

Autoranging Rectifier Module

Up to 1,500 W

Front-end System for EN Compliance

Up to 550 W

Transient Protection, Inrush Current Limiting EMI Filter

Up to 25 A

Active EMI Filter Up to 576 W @ 48 V

DC-DC Converter

Up to 600 W per module 1 – 54 Vdc

INIHAM

FARM3

QPI

DC-DC Converter

Up to 300 W per module 1 – 48 Vdc

DC-DC Converter

Up to 150 W per module 1 – 48 Vdc

Single wire paralleling for high power, fault tolerant arrays.

Output Ripple Attenuation Module combines active and passive filtering.

QPO provides active filtering to achieve differential noise attenuation.

QPO

DC-DC Products

High Boost

HAM

or Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies

Design Guide & Applications Manual

The Maxi, Mini, Micro Family of DC-DC converters are an integral part of the company’s overall component power solution strategy, (Figure 1–1), which includes advanced

actory and design automation. The modules are available

f in an unlimited variety of standard versions, to the extent

hat the line between custom and standard DC-DC

t converter bricks becomes almost indistinguishable.

The design of the control, magnetic, switching, and packaging elements of the module resulted in a component with a power density of up to 120 W/in

(7,3 W/cm3) in three package sizes:

Maxi 4.6" x 2.2" x 0.5" (117 x 55,9 x 12,7 mm) Mini 2.28" x 2.2" x 0.5"(57,9 x 55,9 x 12,7 mm) Micro 2.28" x 1.45" x 0.5"(57,9 x 36,8 x 12,7 mm)

The modules have one-third the number of parts of their predecessors.

While the natural by-products of this reduction in parts count has improved reliability and lower cost, the extra space also means that the bulk of the converter can now

be devoted almost exclusively to the power train (i.e., the magnetic and switching elements at the core of the design).

Resistors can be used to trim the output voltage up or down, if necessary. Six pin styles, three baseplate options, and a variety of data collection and reporting options are available. The devices have an operating temperature range of –55°C to 100°C and come in five product grades – E, C, T, H, and M.

Other specifications include a typical no-load to full-load regulation of ±0.5%, a programmable output of 10% to 110%, conversion efficiencies of up to 92% depending on the voltage combination and power level chosen, and an input-to-output isolation test voltage of 3,000 Vrms (4,242 Vdc). All models are parallelable with N+M fault tolerance and current sharing. Paralleling architectures feature DC or AC-coupled interface.

Figure 1–1 — Component power solutions with the Maxi, Mini, Micro Family

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Apps. Eng. 800 927.9474 800 735.6200

Design Guide & Applications Manual

or Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies

1. High Density DC-DC Converter Technology

Key to the design of Maxi, Mini, Micro converters is its high level of component-level integration. (Figure 1–2) With the aid of hybrid technology, the device packs all

ontrol functions and active circuitry into two (primary

c and secondary side) ICs occupying a total volume of less

han 1/10 in

(

1,6 cm

each.

)

With Maxi, Mini, Micro devices, the plated-cavity transformer cores use copper armor, plated onto the ferrite core, to more closely confine the magnetic flux to couple widely separated primary and secondary windings. The wider separation provides greater isolation and therefore lowers input-to-output parasitic capacitance and noise. The plated cavity also serves to conduct heat away from the transformer to the baseplate, thus increasing the power-handling capability of the power train and minimizing temperature rise.

The power-train assembly is contained between the baseplate and a terminal-block assembly, with input and

output pins recessed. This allows the converter body to be mounted into an aperture in the PCB to reduce the height above board. The modules may be wave soldered or

lugged into through-hole or surface-mount sockets.

The Maxi, Mini, Micro devices use a proprietary, low-noise, integrated power device that has an order of magnitude lower parasitic effect.

The advances made in the overall design of the Maxi, Mini, Micro Family DC-DC converters have been complemented by equally significant advances in the technology used to manufacture them. Vicor invested in a custom, fully-automated assembly line specifically designed for the assembly of Maxi, Mini, Micro power components. To further augment its Maxi, Mini, Micro product offering, Vicor has created an online user-interface tool,

PowerBenchTM, that allows customers to specify DC-DC

module requirements anytime, anywhere via the internet.

Bottom View

• Standard MLP power devices

• Efficient pick-and-place assembly

Top View

• Surface mount components for greater manufacturing efficiency

• Standard reflow process

Figure 1–2 — Maxi assembly shows high level of integration.

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Apps. Eng. 800 927.9474 800 735.6200

Baseplate

• Simplified baseplate construction

Serial No. & Date Code

Complete Assembly

• Insert molded terminal block for more accurate pin positioning

• One piece cover with label

• Encapsulated for superior thermal performance

Model Number

1. High Density DC-DC Converter Technology

+ OUT

+ SENSE*

– OUT

– SENSE*

+ IN

– IN

Primary Control IC

Secondary Control IC

or Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies

Design Guide & Applications Manual

The Maxi, Mini, Micro’s ZCS / ZVS power-processing architecture (Figure 1–3) enables efficient, low-noise, high-frequency operation. The main switch is common

rain for improved thermal and noise management,

d the reset switch located within the primary control IC

s common source for ease of control.

The control circuitry is integrated into two (primary and secondary side) ICs. The result is a significant reduction in

parts with the ensuing savings in cost and increase in reliability. This integration also provides extra room for the power train.

Maxi, Mini, Micro transformers place the primary and secondary windings far apart, but contain the magnetic flux using a copper armor plated onto the ferrite core. The armor also conducts excess heat to the baseplate.

Figure 1–3 — Maxi, Mini, Micro: Basic power train and control (*Not included in Micro family)

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Design Guide & Applications Manual

+IN

–IN

4 kΩ

"Module

Enabled"

+IN

–IN

Disable

Disable = PC <2.3 V

+OUT

–S

– O U T

+IN

–IN

Input Undervoltage

2-20 ms typ.

)

Auto

Restart

5.7 Vdc

(0-3 mA)

50 Ω

SW2

SW3

1.23 Vdc

6 K

1 K

SW1

W1, 2, & 3 shown in

"Fault" position

Input Overvoltage (See Note 1) Overtemperature Module Faults

Not applicable for 300 Vdc input family

1 M

Input Undervoltage Input Overvoltage

[a]

Over Temperature Module Faults

2-20 ms typ.

f(VIN)

Auto

Restart

5.7 Vdc

(0-3 mA)

50 Ω

SW2

SW3

1.23 Vdc

6 K

1 K

SW1

SW1, 2, & 3 shown

in "Fault" position

+OUT

–OUT

+IN

–IN

[a]

Not applicable for 300 Vdc Input family

1 M

or Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies

PRIMARY CONTROL (PC PIN)

2. Control Pin Functions and Applications

Module Enable / Disable. The module can be disabled

y pulling the PC below 2.3 V with respect to the –Input.

b This should be done with an open-collector transistor, relay, or optocoupler. Multiple converters may be disabled with a single transistor or relay via “ORing” diodes. When using a mechanical switch or relay to control the PC pin, please ensure that the contacts are properly debounced with a capacitor (10 nF max.) to avoid switch bounce.

: Do not exceed a repetitive on / off rate of

NOTE 1 Hz to the PC pin or input voltage pins.

An optocoupler must be used when converters are located on different PC boards, when a common-mode inductor is used directly at the module input, or when the distance between the converters would cause excessive voltage drops. Under no circumstances should the PC pin be pulled negative more than a diode drop below the module –IN. (Figure 2–1) When the PC pin is pulled low the PC current will pulse similar to the PC voltage shown in Figure 2–4. When the outputs of two or more converters are connected in a parallel array to increase system power the converters should be “group enabled” to ensure that all the converters start at the same time. The PC pins of all converters in the array should be controlled by an external

circuit which will enable the converters once the input

oltage is within the normal operating range.

Primary Auxiliary Supply. At 5.75 V, the PC can source

p to 1.5 mA. In the example shown in Figure 2–3, PC

u powers a LED to indicate the module is enabled. Another example of an isolated on-state indicator is shown in Figure 2–5.

NOTE

: When the module has detected a fault or when the input voltage is above or below the normal operating range the PC voltage will pulse.

Module Alarm. The module contains “watchdog” circuitry that monitors input voltage, operating temperature, and internal operating parameters. (Figures 2–2a and 2–2b) If any of these parameters is outside their allowable operating range, the module will shut down and PC will go low. (Figure 2–4) Then PC will periodically go high and the module will check to see if the fault (as an example, input undervoltage) has cleared. If the fault has not been cleared, PC will go low again and the cycle will restart. The SC pin will go low when a fault occurs and return to its normal state after the fault has been cleared. An example of using a comparator for monitoring on the secondary is shown in Figures 2–6a and 2–6b.

Figure 2–1 — Module Enable / Disable

Figure 2–2b — PC and SC module alarm logic (Micro)

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Page 5 of 88

Figure 2–2a — PC and SC module alarm logic (Maxi / Mini)

Apps. Eng. 800 927.9474 800 735.6200

Figure 2–3 — LED on-state indicator

2. Control Pin Functions and Applications

+IN

–IN

Optocoupler

4 kΩ

Alarm

1.00V

+OUT

–S

–OUT

omparator

Alarm

1.0 0 V

+OUT

–OUT

+IN

–IN

Comparator

2–20 ms typ.

Fault

1.23 V

5.7 V

0 μs typ.

or Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies

Design Guide & Applications Manual

Figure 2–4 — PC / SC module alarm timing Figure 2–5 — Isolated on-state indicator

Figure 2–6a — Secondary side on-state (Maxi / Mini) Figure 2–6b — Secondary side on-state (Micro)

PARALLEL BUS (PR PIN)

A unique feature has been designed into Vicor Maxi, Mini, Micro converter modules that facilitates parallel operation for power expansion or redundancy. The PR pin is a bidirectional port that transmits and receives information between modules. The pulse signal on the parallel (PR) bus serves to synchronize the high-frequency switching of each converter which in turn forces them to load share. These modules possess the ability to arbitrate the leadership role; i.e., a democratic array. The module that assumes command transmits the sync pulse on the parallel bus while all other modules on the bus listen. In the event of a failure of the lead module, the array “elects” a new leader with no interruption of the output power.

Connection methods for the PR bus include:

1. AC-coupled single-wire interface: All PR pins are

connected to a single communication bus through

0.001 µF (500 V) capacitors. This interface supports current sharing and is fault tolerant except for the communication bus. (Figure 2–7) This method may normally be used with a maximum of three converters.

2. Transformer-coupled interface: Modules or arrays of

modules may also be interfaced to share a load while providing galvanic isolation between PR pins via a transformer-coupled interface. For large arrays, buffering may be required. The power source for the buffer circuit may be derived from the PC pins. For arrays of four or more modules, the transformer coupled interface is recommended. (Figure 2–8)

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Apps. Eng. 800 927.9474 800 735.6200

Design Guide & Applications Manual

+IN

–IN

+IN

–IN

Module 2

Module 1

Parallel

Bus

–

0.2 µF

0.001 µF

0.2 µF

0.001 µF

Low inductance ground plane or bus

4.7 nF

Z1*

+IN

–IN

+IN

–IN

Module 2

Module 1

–

0.2 µF

Parallel

Bus

4.7 nF

Z1*

or Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies

PARALLEL OPERATION CONSIDERATIONS

2. Control Pin Functions and Applications

are must be taken to avoid introducing interfering signals

C (noise) onto the parallel bus that may prevent proper load sharing between modules, instability, or module failure. One possible source of interference is input ripple current

onducted via the + and –Input power pins. The PR signal

c and DC power input share a common return, which is the –Input pin. Steps should be taken to decouple AC components of input current from the parallel bus. The input to each converter (designated as + and – pins on the input side of the module) should be bypassed locally with a

0.2 µF ceramic or film capacitor. This provides a shunt path for high frequency input ripple current. A Y-rated 4,700 pF capacitor should be connected between both the + and –Input pins and baseplate of each module, thus creating a shunt path for common-mode components of current. Attention to the PC board artwork should minimize the parasitic impedance between –Input pins of parallel modules to ensure that all PR pins are referenced to the same potential, or use a transformer coupled interface. Modules should be placed physically close to each other and wide copper traces (0.75 in./19 mm, 2 oz. copper) should be used to connect power input pins. A dedicated layer of copper is the ideal solution.

Some applications require physical separation of paralleled modules on different boards, and/or input power from separate sources. For applications using separate sources, please refer to the “Hot-Swap Capability Eliminates Downtime” application note on Vicor’s website. In these cases, transformer coupling of the PR signal, per Figure 2–8, is required to prevent inter-module common-mode noise

rom interfering with the sync pulse transmission. High-

f speed buffering may be required with large arrays or if the distance between modules is greater than a few inches. This is due to the fact that all modules, except the one

hat’s talking, are in the listening mode. Each listener

t presents a load to the master (talker), which is approximately 500 Ω shunted by 30 pF capacitance. Long leads for the interconnection introduce losses and parasitic reactance on the bus, which can attenuate and distort the sync pulse signal. The bandwidth of the bus must be at least 60 MHz and the signal attenuation less than 2 dB. In most cases, transformer coupling without buffering is adequate. Many applications may benefit from the addition of Z1, in series with the PR Pin of each converter. A low Q 33 Ω @ 100 Mhz ferrite bead or a 5 - 15 Ohm resistor may be used to improve the PR signal waveform. Although this is not a requirement, it can be very helpful during the debug stage of large converter arrays to help improve the PR pulse wave shape and reduce reflections. Again, careful attention must be given to layout considerations. When the outputs of two or more converters are connected in a parallel array to increase system power the converters should be “group enabled” to ensure that all the converters start at the same time. The PC pins of all converters in the array should be controlled by an external circuit which will enable the converters once the input voltage is within the normal operating range. Please consult with

Applications Engineering at any Vicor Technical Support Center for additional information.

Figure 2–8 — Transformer-coupled interface

Apps. Eng. 800 927.9474 800 735.6200

Figure 2–7 — AC coupled single-wire interface

Maxi, Mini, Micro Design Guide Rev 4.9 vicorpower.com

Page 7 of 88

2. Control Pin Functions and Applications

Module 2

Module 1

Module N+1

+OUT

–S

–OUT

Load

–

–S

+OUT

–S

–OUT

+OUT

–S

–OUT

+OUT

–S

–OUT

+Sense from

other modules

in the array

+OUT

–OUT

L O A D

Plane

Ground

Plane

Module #1 Designated Master

Module #2 trimmed down 2 %

Module #3 trimmed down 4 %

+OUT

–OUT

+OUT

–OUT

CONTROL FUNCTIONS AND OUTPUT CONSIDERATIONS

or Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies

Design Guide & Applications Manual

arallel Operation (PR Pin). The PR pin supports paral-

leling for increased power with N+1or N+M redundancy. Modules of the same part number will current share if all PR pins are suitably interfaced. Figures 2–9 and 2–10

how connections for the Maxi and Mini modules; Figure

s 2–11 shows connections for Micro array. Applications containing two or more Micro modules must define a designated master (talker) by stagger trimming the output voltage of each subsequent module down by at least 2%, or setting the remaining Micro modules in the system as designated listeners by connecting the SC pin to the negative output pin.

PR Pin Considerations. When paralleling modules, it is important that the PR signal is communicated to all modules within the parallel array. Modules that do not receive a PR pulse in a parallel array will not current share and may be damaged by running in an over-power condition.

The +Out and –Out power buses

• hould be designed to minimize and

s balance parasitic impedance from each module output to the load.

• The +Sense pins should be tied to the same

point on the +Out power bus; (Figure 2-10) the –Sense pins should be tied to the same point on the –Out power bus.

• At the discretion of the power system

designer, a subset of all modules within an array may be configured as slaves by shorting SC to –S.

• ORing diodes may be inserted in series

with the +OUT pins of each module to provide module output fault tolerance.

Figure 2–9 — N+1 module array output connections (Maxi and Mini)

ll modules in an array must be of the same part

A number.Series connection of outputs is accomplished without connecting the PR pins and allowing each module to regulate its own output voltage. Since the same current

asses through the output of each module with the series

p connection, power sharing is inherent. Series connection of inputs requires special precautions, please contact Applications Engineering for assistance.

Array Output Overvoltage Protection (OVP). In order to maintain the highest possible uptime of a parallel array the converters use an output overvoltage protection system (OVP) that is highly resistant to false tripping. For the converter to shut down due to an OVP condition two conditions must be satisfied (logical AND);

1. The voltage at the output terminals must be greater than the OVP set point.

2. The secondary control IC within the converter must be requesting a power conversion cycle from the internal primary control IC.

By using this logic, false tripping of individual converters due to externally induced OVP conditions such as load dumps or, being driven by an external voltage source at the output terminals is minimized.

Modules connected in a parallel array rely on the active master module for OVP of the entire array. Modules acting as boosters (slaves) in the array are receiving external requests for power conversion cycles (PR pulse) and will not shut down from an OVP condition. Therefore it is imperative that the + and -Output pins of modules connected in a parallel array never

be allowed to become open circuited from the output bus. An open circuit at the output terminals will result in terminal voltages far in excess of the normal rating causing permanent damage to the module and possible hazardous conditions.

Figure 2–10 — ORing diodes connections (Maxi and Mini)

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Page 8 of 88

Figure 2–11 — Parallel module array output connections (Micro)

Apps. Eng. 800 927.9474 800 735.6200

• The +Out and –Out power buses should be designed to minimize and balance parasitic impedance from each module output to the load.

• At the discretion of the power system designer, a subset of all modules within an array may be configured as slaves by shorting SC to –Out.

• Do not use output ORing diodes with parallel arrays of the Micro.

Design Guide & Applications Manual

or Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies

CONTROL FUNCTIONS, SECONDARY CONTROL (SC PIN)

utput Voltage Programming. The output voltage of

the converter can be adjusted or programmed via fixed resistors, potentiometers or DACs.

Trim Down. The converter is not

a constant power device; it has a constant current limit. Hence, available output power is reduced by the same percentage that output voltage is trimmed down. Do not exceed maximum rated output current. The trim down resistor must be connected to the –S pin (–Out pin on a Micro). (Figures 2–12a and 2–12b)

Trim Up. The converter is rated for a maximum delivered power. To ensure that maximum rated power is not exceeded, reduce maximum output current requirement in the application by the same percentage increase in output voltage. The trim up resistor must be connected to the +S pin (+OUT pin on a Micro.) Do not trim the converter above maximum trim range (+10%) or the output over voltage protection circuitry may be activated. (Figures 2–13a and 2–13b)

SC Pin and Output Voltage Trimming. If no connection is made to the SC pin, the SC pin voltage will be 1.23 V referenced to –S (-OUT pin on a Micro) and the output of the converter will equal the nominal output voltage. When the SC pin voltage is set by an external source such as a D/A converter, the % change in SC will be equal the % change in the output voltage.

For example, an application requires a +10, 0% (nominal), and a –15% output voltage adjustment for a 48 V output converter. Referring to the table below, the voltage that should be applied to the SC pin would be as follows:

2. Control Pin Functions and Applications

or systems that require an adjustable output voltage, it is

F good practice to limit the adjustment range to a value only slightly greater than that required. This will increase the adjustment resolution while reducing noise pickup.

It is recommended that the maximum rate of change applied to the SC pin be limited to 30 Hz, sinusoidal. Small step-up changes are permissible; however, the resultant change in the output voltage can create significant current demands due to charge requirements of both the internal and external output capacitance. In no case should the converter be driven beyond rated continuous output current. The response to programming a lower output voltage is limited by the energy stored in both the internal and external output capacitance and the load. The converter cannot sink current to lower the output voltage other than a minimal internal preload.

Contact to be dynamically trimmed.

Trimming resistor calculators are available on Vicor’s web site at http://www.vicorpower.com/powerbench. (Figure 2–16)

Resistor values can be calculated for fixed trim up, fixed trim down, and for variable trim up or down. In addition to trimming information, the web also includes design tips, applications circuits, EMC suggestions, thermal design guidelines and PDF data sheets for all Vicor products. Evaluation Boards (Figure 2–15) are available for the Maxi, Mini and Micro DC-DC converters.

Applications Engineering if the module’s output is

Change

VSC VOUT from

nominal

1.046 40.8 –15%

1.230 48.0 0%

1.353 52.8 +10%

Circuits such as op-amps and D/A converters, which directly drive the SC pin, should be designed to limit the applied voltage to the SC pin. It is also important to consider voltage excursions that may occur during initialization of the external circuitry. The external circuit must be referenced to the –S pin (–Out on Micro). See Figure 2–14 for remote sense implementation on Micro.

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Apps. Eng. 800 927.9474 800 735.6200

2. Control Pin Functions and Applications

+OUT

–S

–OUT

Trim Up

Load

Error Amp

1 kΩ

.23 V

0.033 μF

1,000 (Vout –1.2 3) Vnom

1.23 (Vout – Vnom)

RU (ohms) =

– 1,000

Trim Up

Load

rror

1 kΩ

1.2 3 V

.033 µF

OUT

–OUT

–IN

1,000 (Vout –1.23 ) Vnom

1.23 (Vout – Vnom)

RU (ohms) =

– 1,000

––

2.55 k

1.00 k

TLV431

R7 21.0 k

0.22 µF

4.02 k

1.24 k

LM10

–S

+Out

–Out

R Load

PS2701

R11

36.5 k

1.65 k

470 pF

200 mV

Vcc

Gnd

Load

OUT

–S

–OUT

Trim Down

Error Amp

1 kΩ

1.2 3 V

.033 μF

1,000 Vout

Vnom – Vout

(ohms) =

Load

Trim Down

Error Amp

kΩ

1.2 3 V

0.033 μF

+OUT

–OUT

+IN

–IN

1,000 Vout Vnom – Vout

RD (ohms) =

1,000 (Vout –1.23) Vnom

1.23 (Vout – Vnom)

RU (ohms) =

– 1,000

Trim Up

or Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies

Design Guide & Applications Manual

Figure 2–12a — Output voltage trim down circuit (Maxi/Mini)

Figure 2–13a — Output voltage trim up circuit (Maxi/Mini)

Figure 2–12b — Output voltage trim down circuit (Micro)

Figure 2–13b — Output voltage trim up circuit (Micro)

• This module is designed for point of load regulation, where remote sensing is not required. Active voltage drop compensator, as shown here, may be used in applications with significant distribution losses.

Please consult with the for additional information.

Figure 2–14 — Voltage drop compensation (Micro).

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Page 10 of 88

Micro Family Isolated Remote Sense Application Note

Apps. Eng. 800 927.9474 800 735.6200

Figure 2–15 — Evaluation Boards; Available for Maxi, Mini and Micro Family DC-DC converters

Design Guide & Applications Manual

or Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies

2. Control Pin Functions and Applications

EVALUATION BOARDS

• Three styles: Maxi, Mini or Micro

• Short pin and Long pin compatible

• Easy I / O and control connections

• Includes fusing and capacitors

• Can be paralleled for higher power arrays

DESCRIPTION PART NUMBER

Maxi board style 24644R Mini board style 24645R Micro board style 24646R

Figure 2–16 — Online trim calculator

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Apps. Eng. 800 927.9474 800 735.6200

3. Design Requirements

SAFETY CONSIDERATIONS

or Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies

Design Guide & Applications Manual

using. Safety agency conditions of acceptability require

that the module positive (+) Input terminal be fused and the baseplate of the converter be connected to earth ground. The following table lists the acceptable fuse types

nd current rating for the Maxi, Mini, Micro Family of

a DC-DC converters. Safety Certifications on the Vicor web site should always be consulted for the latest fusing requirements.

Acceptable Fuse Types and Current Rating for the Maxi, Mini, Micro Family of Converters

Package Size Input Voltage Output Voltage Output Power Required Fuse

Maxi (A) 375 2 160 Bussmann PC-Tron 5A Maxi (A) 375 3.3 264 / 200 Bussmann PC-Tron 5A Maxi (A) 375 5, 8 400 / 300 Bussmann PC-Tron 5A Maxi (A) 375 12, 15, 24, 28, 32, 36, 48, 54 600 / 400 Bussmann PC-Tron 5A

Mini (B) 375 2 100 Bussmann PC-Tron 5A Mini (B) 375 3.3 150 / 100 Bussmann PC-Tron 5A Mini (B) 375 5, 8 200 / 150 Bussmann PC-Tron 5A Mini (B) 375 12, 15, 24, 28, 36, 48 300 / 200 Bussmann PC-Tron 5A

Micro (C) 375 2 50 Bussmann PC-Tron 3A Micro (C) 375 3.3 75 / 50 Bussmann PC-Tron 3A Micro (C) 375 5, 8 100 / 50 Bussmann PC-Tron 3A Micro (C) 375 12, 15, 24, 28, 36, 48 150 / 75 Bussmann PC-Tron 3A

Maxi (A) 300 2 160 Bussmann PC-Tron 5A Maxi (A) 300 3.3 264 / 200 Bussmann PC-Tron 5A Maxi (A) 300 5, 8 400 / 300 Bussmann PC-Tron 5A Maxi (A) 300 12, 15, 24, 28, 36, 48 500 / 400 Bussmann PC-Tron 5A

Mini (B) 300 2 100 Bussmann PC-Tron 5A Mini (B) 300 3.3 150 / 100 Bussmann PC-Tron 5A Mini (B) 300 5, 8 200 / 150 Bussmann PC-Tron 5A Mini (B) 300 12, 15, 24, 28, 36, 48 250 / 150 Bussmann PC-Tron 5A

Micro (C) 300 2 50 Bussmann PC-Tron 3A Micro (C) 300 3.3 75 / 50 Bussmann PC-Tron 3A Micro (C) 300 5, 8 100 / 50 Bussmann PC-Tron 3A Micro (C) 300 12, 15, 24, 28, 36, 48 150 / 75 Bussmann PC-Tron 3A

Maxi (A) 150 3.3 264 / 200 Bussmann ABC-8 Maxi (A) 150 5, 8 400 / 300 Bussmann ABC-8 Maxi (A) 150 12, 15, 24, 28, 36, 48 500 / 400 Bussmann ABC-8

Mini (B) 150 3.3 150 / 100 Bussmann PC-Tron 5A Mini (B) 150 5, 8 200 / 150 Bussmann PC-Tron 5A Mini (B) 150 12, 15, 24, 28, 36, 48 250 / 150 Bussmann PC-Tron 5A

Micro (C) 150 3.3 75 Bussmann PC-Tron 3A Micro (C) 150 5, 8 100 Bussmann PC-Tron 3A Micro (C) 150 12, 15, 24, 28, 36, 48 150 Bussmann PC-Tron 3A

Maxi (A) 110 3.3 200 / 150 Bussmann ABC-8 Maxi (A) 110 5, 8 300 / 200 Bussmann ABC-8 Maxi (A) 110 12, 15, 24, 28, 36, 48 400 / 300 Bussmann ABC-8

Mini (B) 110 3.3 100 / 75 Bussmann PC-Tron 5A Mini (B) 110 5, 8 150 / 100 Bussmann PC-Tron 5A Mini (B) 110 12, 15, 24, 28, 36, 48 200 / 150 Bussmann PC-Tron 5A

Micro (C) 110 3.3 50 Bussmann PC-Tron 3A Micro (C) 110 5, 8 75 Bussmann PC-Tron 3A Micro (C) 110 12, 15, 24, 28, 36, 48 100 Bussmann PC-Tron 3A

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Design Guide & Applications Manual

or Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies

3. Design Requirements

Acceptable Fuse Types and Current Rating for the Maxi, Mini, Micro Family of Converters

Package Size Input Voltage Output Voltage Output Power Required Fuse

Maxi (A) 72 3.3 264 Bussmann ABC-12 Maxi (A) 72 5, 8 300 Bussmann ABC-12 Maxi (A) 72 12, 15, 24, 28, 36, 48 400 Bussmann ABC-12

Mini (B) 72 3.3 100 Bussmann ABC-8 Mini (B) 72 5, 8 150 Bussmann ABC-8 Mini (B) 72 12, 15, 24, 28, 36, 48 250 Bussmann ABC-8

Micro (C) 72 3.3 75 Bussmann PC-Tron 5A Micro (C) 72 5, 8 100 Bussmann PC-Tron 5A Micro (C) 72 12, 15, 24, 28, 36, 48 150 Bussmann PC-Tron 5A

Maxi (A) 48 3.3 264 Bussmann ABC-10 Maxi (A) 48 5, 8 400 Bussmann ABC-15 Maxi (A) 48 12, 15, 24, 28, 36, 48 500 Bussmann ABC-20

Mini (B) 48 2 100 Bussmann ABC-8 Mini (B) 48 3.3 150 Bussmann ABC-8 Mini (B) 48 5, 8 200 Bussmann ABC-10 Mini (B) 48 12, 15, 24, 28, 36, 48 250 Bussmann ABC-10

Micro (C) 48 2 50 Bussmann PC-Tron 5A Micro (C) 48 3.3 75 / 50 Bussmann PC-Tron 5A Micro (C) 48 5, 8 100 / 75 / 50 Bussmann ABC-8 Micro (C) 48 12, 15, 24, 28, 36, 48 150 / 75 Bussmann ABC-8

Maxi (A) 28 3.3 150 Bussmann ABC-25 Maxi (A) 28 5 175 Bussmann ABC-25 Maxi (A) 28 6.5, 8, 12, 15, 24, 28, 36, 48 200 Bussmann ABC-30

Mini (B) 28 3.3 75 Bussmann ABC-15 Mini (B) 28 5 75 Bussmann ABC-15 Mini (B) 28 12, 15, 24, 28, 36, 48 150 Bussmann ABC-15

Micro (C) 28 3.3 50 Bussmann ABC- 8 Micro (C) 28 5 50 Bussmann ABC-10 Micro (C) 28 12, 15, 24, 28, 36, 48 100 Bussmann ABC-10

Maxi (A) 24 3.3 264 / 200 Bussmann ABC-25 Maxi (A) 24 5, 8, 12, 15, 24, 28, 36, 48 400 / 300 Bussmann ABC-30

Mini (B) 24 3.3 150 / 100 Bussmann ABC-15 Mini (B) 24 5, 8, 12, 15, 24, 28, 36, 48 200 / 150 Bussmann ABC-15

Micro (C) 24 3.3 75 / 50 Bussmann ABC-8 Micro (C) 24 5, 8, 12, 15, 24, 28, 36, 48 100 / 50 Bussmann ABC-10

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3. Design Requirements

or Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies

Design Guide & Applications Manual

The fuse must be in series with the positive (+) Input lead. Fusing the negative (–) Input lead does not provide adequate protection since the PR and PC terminals of the converter

re referenced to the –Input. If a fuse located in the

a –Input lead were to open, the PR and PC terminals could

ise to the potential of the +Input. This may damage any

r converter or circuitry connected to these pins. The fuse should not be located in an area with a high ambient temperature as this will lower the current rating of the fuse.

THERMAL AND VOLTAGE HAZARDS

Vicor component power products are intended to be used within protective enclosures. Vicor DC-DC converters work effectively at baseplate temperatures, which could be harmful if contacted directly. Voltages and high currents (energy hazard) present at the terminals and circuitry connected to them may pose a safety hazard if contacted or if stray current paths develop. Systems with removable circuit cards or covers which may expose the converter(s) or circuitry connected to the converters, should have proper guarding to avoid hazardous conditions.

The module pins are intended for PCB mounting either by wave soldering to a PCB or by insertion into one of the recommended PCB socket solutions. Use of discrete wire soldered directly to the pins may cause intermittent or permanent damage to the module; therefore, it is not recommended as a reliable interconnection scheme for production as a final released product. In addition, modules that have been soldered into printed circuit boards and have subsequently been removed should not be reused.

PC PIN

The PC pin should be used only to; disable the module, provide a bias to input referenced circuitry or communicate status of the module. The PC pin is referenced to the –Input pin. All circuits that connect to the PC pin must use the –Input as the reference. Do not break the connection between the –Input and the circuitry connected to the PC pin or damage to the module will result. Additional requirements include:

HIGH-POWER ARRAYS AND PR PIN

To simplify the implementation of large arrays, a subset of modules within the parallel array should be configured as boosters (listeners) by connecting the SC pin to the –S pin. Modules, which are configured as boosters, cannot assume the role of drivers (talkers) for N+M redundant arrays. Modules configured as boosters may be locally sensed.

Each module within the parallel array must be properly bypassed with capacitors. Film or ceramic types should be used across the input of the module and between each input lead and the baseplate. Modules having input sources, which are not connected to SELV sources, should use X-capacitors across the input and Y-capacitors from each input power pin to the baseplate. When in doubt about capacitor safety approvals, always consult with the governing safety regulatory agency or Vicor Applications Engineering.

A maximum of 12 modules may be directly connected in parallel. Please contact Vicor Applications Engineering for assistance with larger arrays.

The PR pin is referenced to the –In pin; therefore, all modules within the array must have a common lowimpedance connection between each –In pin. Special precautions are necessary if a PCB is not used for interconnection of modules, because the wiring impedance can be significant. Do not allow the connection between the –In pin and the –In bus to become disconnected as damage to the module will result.

Coupling transformers should be used to transmit the PR pulse if long distances between each module are anticipated or if the interconnection impedance of the –In leads is high or questionable. PR coupling transformer(s) should be used if the PR pulse exits the PCB. For example, an array constructed of multiple circuit cards plugged into a backplane with a number of converters on each card should have a PR coupling transformer at the entry point of each card; however, no coupling transformer would be required between each converter on the card of three or less converters on a single PCB. Do not externally drive the PR pin, connection to this pin is limited to Vicor module application only.

• Circuits that derive their power from the PC pin must

not exceed 1.5 mA.

• Do not drive the PC pin with external circuitry.

• Do not attempt to control the output of the converter

by PWM pulsing of the PC pin, or exceed a repetitive on / off rate of 1 Hz.

For applications where the converter will be disabled on a

INPUT SOURCE IMPEDANCE

The impedance of the source feeding the input of the module directly affects both the stability and transient response of the module. In general, the source impedance should be lower than the input impedance of the module by a factor of ten, from DC to 50 kHz.

regular basis or where capacitance is added to this pin, please contact Vicor

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Applications Engineering.

Apps. Eng. 800 927.9474 800 735.6200

Design Guide & Applications Manual

or Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies

3. Design Requirements

To calculate the required source impedance, use the following formula:

Z = 0.1(VLL)2/ Pin

where: Z is required input impedance

s the low line input voltage

VLLi P

in is the input power of the module

Filters, which precede the module, should be well damped to prevent ringing when the input voltage is applied or the load on the output of the module is abruptly changed.

INPUT TRANSIENTS AND SURGES

The voltage applied to the input of the module must not exceed the ratings outlined in the data sheet. Protection devices such as Zener diodes and MOVs should be used to protect the module from short-duration transients. These shunt protection devices are effective only if the source impedance is high relative to the impedance of the protection device when it is conducting. For voltage surges where the abnormal voltage is present for a long period of time, shunt protection devices can easily be damaged by the power dissipated. For this type of condition, a voltage limiter in series with the input of the module may be the best solution. Vicor Applications Engineering can assist in recommending the appropriate type of protection for the module.

NOTE: Do not allow the rate of change of the input voltage to exceed 10 V/µs for any input voltage deviation.

SENSE LEADS (Mini and Maxi only)

The sense leads of the module must always terminate either directly to the output pins (local sense) or at the load (remote sense). When remote sense is used, the output wiring impedance in combination with the load impedance can cause significant loss of phase margin and result in oscillation and possible damage to the module, poor transient response, or activation of the output overvoltage protection. Long sense leads may require a compensation circuit for stability.

Protection circuitry is required if the possibility of reversed sense leads can occur. Please contact Vicor Applications Engineering for specific recommendations.

Do not

exceed 1 V between –S and –Out leads. This is an important consideration if the converter is used in a Hot-Swap application. ORing diodes, if used, should be located in the +Output lead to avoid exceeding this rating.

OUTPUT CONNECTIONS

For systems designed to charge batteries, subject the module output to dynamic loading, or loads that have large reactive components, please contact Vicor Applications Engineering to discuss your application in detail.

Do not externally drive the output of the module 10% above its nominal setpoint voltage.

Modules, that are used to charge batteries should be applied with a diode in series with the output of the module. The charge current must be externally controlled to ensure that the module is not operated in excess of its power or current rating.

Current-carrying conductors should be sized to minimize voltage drops.

Do not

use output ORing diodes with parallel arrays of

the Micro Family converters.

Output Overvoltage Protection (OVP). The OVP detection circuitry within the converter is highly resistant to false tripping. For the converter to shut down due to an OVP condition two conditions must be satisfied (logical AND);

1. The voltage at the output terminals must be greater than the OVP set point.

2. The secondary control IC within the converter must be requesting a power conversion cycle from the internal primary control IC.

By using this logic, false tripping of individual converters due to externally induced OVP conditions such as load dumps or, being driven by external voltage sources at the output terminals is minimized. The user should not test the OVP circuit by back driving the output terminals or by any other means as the OVP circuitry is fully tested as part of the inline manufacturing process.

OVERCURRENT PROTECTION

The Maxi, Mini, Micro converters incorporate a straightline type current limit. (Figure 3–1) As output current is increased beyond Imax, the output voltage remains constant and within its specified limits up to a point, IKNEE, which is typically 5 – 25% greater than rated current, Imax. Beyond IKNEE, the output voltage falls to Ishortcircuit. Typically, modules will automatically recover after the overcurrent condition is removed.

Do not

exceed the rated power of the converter. The total of the power consumed by the load plus the power lost in conductors from the converter to the load must be less than the output power rating of the converter.

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3. Design Requirements

out

NEE

HORT CIRCUIT

out

Figure 3–1 — Typical Maxi, Mini, Micro current limiting

MAXIMUM OUTPUT CAPACITANCE

In general, adding external capacitance to the Maxi, Mini, and Micro’s output is not required. However, it is often common practice with power supply designs to add external capacitance to the converter output for attenuation of output ripple and / or improving dynamic load performance. The Maxi, Mini, Micro converters typically have a faster response to dynamic loads than other power solutions; hence, external capacitors may not be necessary. In addition, the output ripple and noise specification listed on the data sheet may be acceptable for many applications.

A general equation for determining the maximum recommended output capacitance is as follows:

Pout

C(farad) =Vout

(400x10

Vout

)

or Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies

Design Guide & Applications Manual

ABSOLUTE MAXIMUM RATINGS

Please consult the latest module data sheets available on the Vicor website for maximum ratings concerning pin-topin voltages, isolation, temperature, and mechanical ratings.

GROUNDING OF BASEPLATE AND REFERENCING OF INPUT AND OUTPUT TERMINALS

The baseplate of the converter should always be connected to earth ground. If for any reason this is not possible in your application please consult with Vicor Applications Engineering for acceptable alternatives for your application.

The input and output leads of the converter should be referenced to the baseplate at some point to avoid stray voltages. For offline applications the input leads are often referenced to earth ground at the AC source ahead of the bridge rectifier. Either + or –Output terminal may be referenced to earth ground and the baseplate. “Floating” inputs or outputs should at a minimum have a highresistance divider to bleed off stray charges to avoid damage to the insulation system.

HIGH FREQUENCY BYPASSING

All Vicor converters must be bypassed for proper operation. (Figure 3–2) The minimum complement of high-frequency bypass capacitors must consist of the following:

• 0.2 µF ceramic or film type connected between

+In and –In.

• 4.7 nF Y-capacitor between +In and baseplate

and –In and baseplate.

• 10 nF ceramic or film capacitor between +Out and

baseplate and –Out and baseplate.

where: Pout is the output power of the converter

out is the nominal output voltage of the converter

All applications utilizing Maxi, Mini, Micro converters should be properly bypassed, even if no EMC standards need to be met. Bypass Vin and Vout pins to each module baseplate as shown in Figure 3–2. Lead length should

The capacitance value is not the absolute maximum value, but the value for which general application of the converter can be deemed appropriate. Testing will be required to ensure that the module is stable if this value is exceeded. Approximately 10X the value calculated will cause the converter to go into current limit at turn-on.

CAUTION:

If exceeding this value, it is recommended

that Vicor Applications Engineering be consulted.

be as short as possible. Recommended values vary depending on the front end, if any, that is used with the modules, and are indicated on the appropriate data sheet or application note. In most applications, C1 is a 4,700 pF Y-capacitor (Vicor P/N 01000) carrying the appropriate safety agency approval; C2 is a 4,700 pF Y-capacitor (Vicor P/N 01000) or a 0.01 µF ceramic capacitor rated at 500 V. In PC board applications, each of these components is typically small enough to fit under the module baseplate flange. For PCB mounting of the module. Please refer to Figures 3–3 and 3–4.

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Page 16 of 88

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Design Guide & Applications Manual

0. 53

Ch as si s

0. 46

Onboard Mount

Cross-sectional view of pins

and mounting hardware

Inboard Mount

Cross-sectional view of pins

and mounting hardware.

Exploded View Exploded View

P/ N 20 265 Th er mM ate

Ex . V3 00 C1 2M75 BL

(L on g Sol de r Pin ,

Sl ot te d B as ep lat e)

P/ N 18 157 S ta ndo ff K it

PC B th ick nes s is

0. 06 2

" (

1. 5m m)

Tap ped # 4– 40 sc rew h ol e

Pa d a nd pl at ed th ro ughho le c onn ec te d t o ch as si s g roun d p la ne

P/ N 20 265 Th er mM ate

Ex . V3 00 C1 2M75 B

(S ho r t Sol de r Pin,

Sl ot te d B as ep lat e)

P/ N 18 151 S ta ndo ff K it

0. 06 2

" (1.5mm) PCB with

aperture to allow belly

th e mo dul e to re ce ss int o b oa rd

Tap ped # 4– 40 sc rew h ol e

Pa d a nd pl at ed th ro ughho le c onn ec te d t o ch as si s g roun d p la ne

13 ,5m m

11 ,7 mm

’

’’

+OUT

+IN

–IN

–OUT

Maxi, Mini, Micro

C-DC Converter

C1a

C1b

C2a

C2b

Baseplate grounded

Standoffs also provide necessary

mechanical support in order to

prevent mechanical stresses from

damaging the module during shock / vibration.

Standoff sitting on pad / plated through-hole that is connected to the chassis ground plane within the PCB.

Female-female standoffs are s

hown, however standoffs are

also available in male-female versions.

or Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies

3. Design Requirements

Figure 3–2 — Minimum recommended bypassing for Maxi, Mini, and Micro; Keep all leads short.

Figure 3–3 — Recommended mounting method using standoffs

Figure 3–4 — Onboard vs. inboard mounting of (1/4 brick) Micro with slotted baseplate

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Apps. Eng. 800 927.9474 800 735.6200

4. EMC Considerations

FILTERING AND TRANSIENT PROTECTION

or Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies

Design Guide & Applications Manual

ll switching power supplies generate potentially interfer-

A ing signals as a result of high-frequency, high-power switching. The Vicor power converter topology, to a large extent, addresses the problem at the source by the use of a quasi-resonant, zero-current switching (ZCS) and zerovoltage switching (ZVS) topology. The switching current waveform is a half sine wave that generates far less conducted and radiated noise in both frequency spectrum and magnitude. EMI filtering, if properly designed and implemented, reduce the magnitude of conducted noise an additional 40 – 60 dB, and as a result, the noise radiated by the power conductors is reduced proportionally.

BASIC GUIDELINES FOR SUCCESSFUL EMI FILTERING

1. Keep current loops small. The ability of a conductor to

couple energy by induction and radiation is reduced accordingly.

2. For conductor pairs, use wide (low Z) copper traces

aligned above and below each other.

3. Locate filters at the source of interference; i.e., close

to the power converter(s).

4. Filter component values should be chosen with

consideration given to the desired frequency range of attenuation. For example, capacitors are self-resonant at a certain frequency, beyond which they look inductive. Keep bypass capacitor leads as short as possible.

5. Locate components on the PCB with consideration

given to proximity of noise sources to potentially susceptible circuits. For example, the FIAM is an input line filter module that has been optimized for use with Maxi, Mini, and Micro DC-DC converters. When used in conjunction with the recommended external components and layout, it will significantly reduce the differential and common-mode noise returned to the power source. The FIAM meets the requirements of EN55022 “B”, FCC “B”, and Bellcore GR-001089CORE, Issue 2 when used with any combination of Maxi, Mini, and Micro converters up to the FIAM’s maximum rated current.

onducted noise on the input power lines can occur as

C either differential-mode or common-mode noise currents. Differential-mode noise, largely at low frequencies, appears across the input conductors at the fundamental switching frequency and its harmonics. Common-mode noise, which has mostly high-frequency content, is measured between the converter’s input conductors and ground.

The Vicor power converter being an electronic device may be susceptible to high levels of conducted or radiated emissions. It is the responsibility of the user to assess testing protocols in order to determine applicability of the converter in the intended application.

DC-DC converter inputs and outputs must be properly bypassed, to system chassis or earth. Bypass Vin and Vout pins to each DC-DC module baseplate. Capacitor lead length must be as short as possible. (Figure 4–1)

EMI filtering can be application dependent. A packaged filter module may not always be the appropriate solution, and the general practice of bypassing Vin and Vout may not produce optimal results. You may have to adjust the values depending on the severity of common-mode and differential-mode noise. (Figures 4–2 and 4–3)

Input transient suppression should be used in applications where source transients may be induced by load changes, blown fuses, etc. The level of transient suppression required will depend on the expected severity of the transients. A Zener diode, TRANSORB™, or MOV will provide transient suppression, act as a voltage clamp for DC input spikes, and provide reverse input voltage protection. The device voltage rating should be chosen above high-line voltage limits to avoid conducting during normal operation which would result in overheating.

Module shields that provide shielding around the belly (label side) of the Maxi, Mini, Micro are also available for applications that are highly noise sensitive. Module shield information is available on the Vicor website, see links provided, on the following page.

NOTE:

Acoustic Noise. Audible noise may be emitted from the module under no load, light load, or dynamic loading conditions. This is considered normal operation of the module.

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Design Guide & Applications Manual

+IN

–IN

+OUT

–S

–OUT

C3*

4.7nF

.7nF

or C1 – C5, keep leads and connections short.

4.7nF

C4*

4.7nF

F1*

C1*

0.2µF

or Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies

4. EMC Considerations

Figure 4–1 — Recommended bypassing capacitors must be in close proximity, i.e., have short lead length to be effective.

Figure 4–3 — V48B28H250BN with recommended bypass caps (330 µF across input)

Module Shield Information

Module shield for Maxi with threaded or through-hole baseplate P/N 30142

http://asp.vicorpower.com/CADPDF/H7CEX3.PDF

Figure 4–2 — V48B28H250BN without bypass caps (330 µF across input)

Module shield for Maxi with slotted baseplate P/N 30199

http://asp.vicorpower.com/CADPDF/HXE113.PDF

Module shield for Mini with threaded or through-hole baseplate P/N 30180

http://asp.vicorpower.com/CADPDF/UT55TT.PDF

Module shield for Mini with slotted baseplate P/N 30198

http://asp.vicorpower.com/CADPDF/HXE112.PDF

Module shield for Micro with threaded or through-hole baseplate P/N 30143

http://asp.vicorpower.com/CADPDF/9YRD8X.PDF

Module shield for Micro with slotted baseplate P/N 30141

Maxi, Mini, Micro Design Guide Rev 4.9 vicorpower.com

Page 19 of 88

http://asp.vicorpower.com/CADPDF/NG6SIS.PDF

Apps. Eng. 800 927.9474 800 735.6200

5. Current Sharing In Power Arrays

or Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies

Design Guide & Applications Manual

Whenever power supplies or converters are operated in a parallel configuration — whether for higher output power, fault tolerance, or both — current sharing is an

mportant consideration. Most current-sharing schemes

i employed with power converters involve either artificially

ncreasing the output impedance of the converter module

i or actually sensing each output current, forcing all of the currents to be equal by feedback control. In a synchronous current-sharing scheme, however, there is no need for having a current-sensing or current-measuring device on each module, nor is there a need to artificially increase the output impedance, which compromises load regulation.

WHY IS CURRENT SHARING IMPORTANT

Most paralleled power components — transistors, rectifiers, power conversion modules, offline power supplies — will not inherently share the load. In the case of power converters, one or more of the converters will try to assume a disproportionate or excessive fraction of the load unless forced current-share control is designed into the system. One converter — typically the one with the highest output voltage — may deliver current up to its current limit setting, which is beyond its rated maximum. Then the voltage will drop to the point where another converter in the array — the one with the next highest voltage — will begin to deliver current. All of the converters in an array may deliver some current, but the load will be shared unequally. Built-in current limiting may cause all or most converters to deliver current, but the loading will remain unbalanced, and potentially cause damage to the converters.

Consider the situation when one module in a two-module array is providing all of the load. If it fails, the load on the second module must go from no load to full load, during which time the output voltage is likely to droop temporarily. This could result in system problems, including shutdown or reset. If both modules were sharing the load and one failed, however, the surviving module would experience a much less severe transient (one half to full load), and the output voltage would be likely to experience no more than a slight momentary droop. The dynamic response characteristic of all forward converters, resonant or pulsewidth modulated, is degraded when the load is stepped from zero (no load) where the output inductor current is discontinuous.

In the same two-module array example, the module carrying all of the load is also generating all of the heat, resulting in a much lower mean time between failure (MTBF) for that module. An often-quoted rule of thumb says that for each 10°C increase in operating temperature, average component life is cut in half. In a current-sharing system, all of the converters or supplies

run at a lower temperature than some modules would in a system without current sharing. As a result, all of the modules age equally.

Current sharing, then, is important because it improves system performance; it minimizes transient / dynamic response and thermal problems and improves reliability. It is an essential ingredient in most systems that use multiple power supplies or converters for higher output power or for fault tolerance.

CURRENT-SHARING IN POWER EXPANSION ARRAYS

When parallel supplies or converters are used to increase power, current sharing is achieved by a number of approaches. One scheme simply adds resistance in series with the load. A more practical variant of that is the “droop-share” method, which actively causes the output voltage to drop in response to increasing load. The two most commonly used approaches to paralleling converters for power expansion are the driver/booster or master/ slave arrays and analog current-share control. They appear to be similar, but the implementation of each is quite different. Driver/booster arrays usually contain one intelligent module or driver, and one or more power-trainonly modules or boosters. Analog current-share control involves paralleling two or more identical modules, each containing intelligence.

Droop Share. The droop-share method, shown in Figure 5–1, increases the output impedance to force the currents to be equal. It is accomplished by an error signal, which is interjected into the control loop of the converter causing the output voltage to operate as a function of load current. As load current increases, output voltage decreases. All of the modules will have approximately the same amount of current because they are all being summed into one node. If one supply is delivering more current than another supply, its output voltage will be forced down a little so that it will be delivering equal current for an equal voltage out of that summing node. Figure 5–1 illustrates a simple implementation of this scheme where the voltage dropped across the ORing diode, being proportional to current, is used to adjust the output voltage of the associated converter.

Droop share has advantages and disadvantages. One of the advantages is that it can work with any topology. It is also fairly simple and inexpensive to implement. A major drawback, though, is that it requires that the current be sensed. A current-sensing device is needed in each of the converters or power supplies. In addition, a small penalty is paid in load regulation, although in many applications this is not an issue.

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Design Guide & Applications Manual

Return

+OUT

–S

–OUT

–IN

+IN

+OUT

–S

–OUT

–IN

+IN

DC-DC Converter

Maxi or Mini

+IN

– IN

+OUT

DC-DC Converter

Maxi or Mini

or Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies

5. Current Sharing In Power Arrays

In general, it is not recommended to mix and match converters, especially those with incompatible current-sharing schemes. The droop-share method, however, is more

orgiving in this regard than with any of the other

f methods. Current sharing can be achieved using arrays

onstructed from different converter models or even from

c different suppliers with a little external circuitry.

Driver/ Booster Arrays. Most Vicor converters can employ the driver/booster array for increased power. (Figure 5–2) Driver/booster arrays usually contain one intelligent module or driver, and one or more power-trainonly modules or boosters. The driver is used to set and control output voltage, while booster modules are used to increase output power to meet system requirements.

Driver/booster arrays of quasi-resonant converters with identical power trains inherently current share because the per-pulse energy of each converter is the same. If the inputs and outputs are tied together and the units have the same clock frequency, all modules will deliver the same current (within component tolerances). The single intelligent module in the array determines the transient response, which does not change as modules are added. Booster modules require only one connection between units when their outputs are connected; no trimming, adjustments, or external components are required to achieve load sharing. The load sharing is dynamic and usually guaranteed to be within five percent.

It is important to remember that when using boosters, the input voltage, output voltage, and output power of the boosters must be the same as the driver.

The advantages of driver/booster arrays are that they have only a single control loop so there are no loop-withina-loop stability issues, and they have excellent transient response. However, this arrangement is not fault tolerant. If the driver module fails, the array will fail to maintain its output voltage.

Analog Current-Share Control. Analog current-share control, typical of PWM type converters, involves paralleling two or more identical modules, each containing intelligence. The circuit actively adjusts the output voltage of each supply so that the multiple supplies deliver equal currents. This method, however, has a number of disadvantages. Each converter in the array has its own voltage regulation loop, and each requires a current sensing device and current control loop.

Analog current-share control supports a level of redundancy, but it is susceptible to single-point failures within the current-share bus that can, at best, defeat current sharing, and, at worst, destroy every module in the array. The major reason for this is the single-wire galvanic connection between modules.

Figure 5–1 — The droop-share method artificially increases the output impedance to force the currents to be equal.

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5. Current Sharing In Power Arrays

or Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies

Design Guide & Applications Manual

CURRENT SHARING IN FAULT TOLERANT ARRAYS

Current sharing is an essential element in fault-tolerant arrays, and regardless of the approach, there is an inherent additional cost incurred by the addition of at least one redundant converter or supply.

Most applications today that require fault tolerance or redundancy also require Hot-Swap capability to ensure continuous system operation. Hot swappable cards must be designed so that the operator cannot come in contact with dangerous potentials, currents or thermal hazards. It is also essential that when a module fails, the failure is detected and identified by an alarm or notice to provide service. A Hot-Swap system must ensure that during swap out there is minimal disturbance of the power bus. Specifically, the affected voltage bus must not drop enough to cause errors in the system, either on the input bus or the output bus.

N+1 Redundancy. A power supply failure can cripple an entire system, so a redundant converter or supply can be added to ensure that, in the event of a failure, the system will continue to operate. Adding an extra module (N+1) to a group of paralleled modules will significantly increase reliability with only a modest increase in cost.

How redundant converters are implemented is determined in part by the available space and cost requirements. Two 500 W Maxi modules, for example, could be used to provide a 1 kW output with an additional 500 W module for 2+1 redundancy a total of 1.5 kW in a volume of about 16.5 in3 (270 cm3). Four 200 W half-size modules might be used instead with a fifth 200 W module for 4+1 redundancy, a total of 1 kW and 14 in3(229 cm3). Although the second solution uses less space, it increases the accumulated failure rate because it employs more converters, more ORing diodes, more monitoring circuitry, and more assembly.

ORing diodes may be inserted in series with the +Output of each module in a N+1 array to provide output fault tolerance (Figure 5–1). They are important in a redundant power system to maintain fault isolation. Without them, a short-circuit failure in the output of one converter could bring down the entire array. As well, fusing the input of each converter prevents a converter input short from compromising the entire array.

ORing diodes, however, add losses to the power system, reducing overall efficiency (and, potentially, decreasing reliability). To ameliorate this negative effect on efficiency, ORing diodes should run hot, thereby reducing forward voltage drop and improving system efficiency. Reverse leakage current will be an issue only if the output of a converter shorts and the diode is reverse biased. This is an important consideration with regard to operating temperature.

Current sharing, required to ensure system reliability, can be implemented by a multiplicity of methods. Figure 5–1, shown earlier as an example of the droop-share method,

s also an example of N+1 redundancy using ORing diodes.

Synchronous Current Sharing. Synchronous current sharing is available with Maxi, Mini, Micro converters — converters that use the zero-current-switching and zerovoltage-switching topology. Each module has the capability to assume control of the array, that is, they constitute a democratic array. The module that assumes command transmits a pulse on the parallel bus to which all other modules on the bus synchronize.

The converters use this pulse as a current-sharing signal for power expansion and fault-tolerant applications. The pulsed signal on the parallel bus simplifies current-sharing control by synchronizing the high-frequency switching of each converter. The parallel pin is a bi-directional port on each module used to transmit and receive information between modules. If the lead module relinquishes control, another module in the array will transparently take command with little or no perturbation of the output bus. A pulsed signal gives designers the option to use capacitors (Figure 5–2) or transformers between parallel pins, providing DC-blocked coupling. Such coupling prevents certain failure modes internal to a single module from affecting the other modules in the array, thus providing an increased level of fault tolerance.

Use of a current-share bus transformer (Figure 5–3) enables arrays of Maxi, Mini, Micro converters to current share when they are widely separated or operated from independent sources. Since the current-share signal is a pulsed signal, it can be transformer coupled. Transformer coupling this pulsed signal provides a high level of common-mode noise immunity while maintaining SELV isolation from the primary source. This is especially useful when board-to-board load sharing is required in redundant applications.

Synchronous current sharing eliminates the need for current-sensing or current-measuring devices on each module, and load regulation is not compromised. Additional advantages of the synchronous current sharing architecture includes excellent transient response, “no loop within a loop” control problems, and, a high degree of immunity from system noise. The availability of synchronous current sharing in democratically controlled arrays offers power architects new opportunities to achieve simple, non-dissipative current-share control. It provides options that simplify current sharing and eliminates the tradeoffs — such as the need to sense the current from each individual module and adjust each control voltage — as is the case with other current-sharing methods.

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Design Guide & Applications Manual

Ground

Plane

OUT

–

–OUT

–

+IN

OUT

–S

–OUT

–

+IN

Return

DC-DC Converter

Parallel

Bus

-V

or Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies

5. Current Sharing In Power Arrays

The synchronous current-sharing method applies to quasi-resonant, frequency-modulated converters with the necessary intelligence, such as the Vicor Maxi, Mini, Micro

amily of high-density DC-DC converters, where the energy

F per pulse is fixed.

Finally, no matter what method is used, current sharing reduces thermal problems, improves transient response, and helps extend the lifetimes of all modules in an

rray. Nevertheless, all current-sharing schemes require

a careful attention to electrical and mechanical design to

perate effectively.

Figure 5–2 — Synchronous power architecture simplifies current sharing control and enhances fault tolerance.

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5. Current Sharing In Power Arrays

Parallel Bus

-V

+OUT

–S

–OUT

–IN

+OUT

–S

–OUT

–IN

+IN

Return

OUT

-V

DC-DC Converter

or Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies

Design Guide & Applications Manual

Figure 5–3 — Transformer-coupled interface provides load sharing and SELV isolation from the primary source.

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Design Guide & Applications Manual

or Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies

6. Thermal Performance Information

Simplified thermal management is one of the benefits of using Vicor converters. High operating efficiency minimizes heat loss, and the low-profile package features an easily

ccessible, electrically isolated thermal interface surface.

Proper thermal management pays dividends in terms of improved converter and system MTBFs, smaller size, and lower product life-cycle costs. The following pages provide guidelines for achieving effective thermal management of

Consideration should be given to the module baseplate temperature during operation. The maximum baseplate temperature specification for Maxi, Mini, and Micro is

00°C.

Enhanced module cooling can be achieved with free or forced convection by using the appropriate heat sink. The available Vicor heat sinks and thermal interface options are available on the Vicor website.

Vicor converters.

The relevant nomenclature for the tabulated thermal information supplied in this section for the Maxi, Mini, and Micro modules is defined as follows:

Tb = baseplate temperature

Ta = ambient temperature

Pout = module output power

Pin= module input power

η = module efficiency = Pout / Pin

Pdiss = module power dissipation = Pin – Pout = (1/η – 1) • Pout

Supplied thermal resistance values:

θbs = baseplate-to-heatsink thermal resistance

θba = baseplate-to-ambient thermal resistance

Basis of output power versus ambient temperature derating curves:

(Ta)max = (Tb)max – θba • Pdiss = (Tb)max – θba • (1/η – 1) • Pout

Additional Thermal Data

The following pages contain temperature derating curves.

For additional thermal data, see the following link:

http://asp.vicorpower.com/calculators/calculators.asp?calc=5

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6. Thermal Performance Information

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12 - 48V Maxi Thermal Performance Curves - No Heat Sink

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Design Guide & Applications Manual

For Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies

THERMAL PERFORMANCE CURVES (Maxi)

Table Usage: The forced convection thermal impedance data shown in the tables on the next three pages assumes airflow through the heat sink fins. Actual airflow through the fins should be verified. For purposes of heat sink calculation, assume efficiencies listed on Maxi data sheets. Use as a design guide only. Verify final design by actual temperature measurement.

Maxi

bs = 0.07°C/W Baseplate 0.9'' Longitudinal Fins 0.9'' Transverse Fins 0.4'' Longitudinal Fins 0.4'' Transverse Fins

ba (Baseplate-to-Ambient Thermal Resistance Values) vs. Airflow

Free Air 4.98 2.89 2.24 3.72 3.49 200 LFM 3.23 1.30 1.02 2.14 1.53 400 LFM 2.17 0.90 0.72 1.48 1.08 600 LFM 1.73 0.72 0.60 1.10 0.87 800 LFM 1.46 0.59 0.51 0.86 0.70

1,000 LFM 1.27 0.51 0.44 0.71 0.60 1,200 LFM 1.14 0.46 0.41 0.61 0.55

Maxi Output Power vs. Ambient Temperature Derating Curves

Baseplate (No Heat Sink) 0.4'' (10,1 mm) Heat Sink 0.9'' (22,8 mm) Heat Sink

2 V

3.3 V

5 V

12 – 54 V

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