LINEAR TECHNOLOGY LTC4261 Technical data

AdvancedTCA Hot Swap Controller Monitors Power Distribution

Design Note 397

Mitchell Lee

Introduction

AdvancedTCA® is a modular computing architecture
developed by the PCI Industrial Computer Manufacturers
Group for use in central offi ce telecom environments.

®

PICMG

3.0 defi nes, among other things, the electrical
and mechanical attributes of the backplane, connectors
and removable cards in these –48V systems.

Each removable card, or front board, is designed for live
insertion into a working system. A power draw of up to
200W per front board is allowed, placing the maximum
load current in the 4A to 5A range.

Card-centric inrush limiting and quantitative current
and voltage monitoring are highly desirable to sanitize
the incoming battery feeds, minimize power plane
disturbances, allow for budgeting power consumption
and permit failure prediction in an otherwise functional

®

system. The LTC

4261 Hot Swap™ controller provides
these features. Also included is a digital interface for
controlling the functions of the LTC4261, and for reading
the current and voltage measurement registers.

Circuit Solutions

Figure 1 shows a complete circuit designed to handle up
to the maximum available power. The LTC4261’s accu­rate current limit is set to provide at least 5.5A under all
conditions, a comfortable margin for 200W, yet trips off
just under 7A to pr eserve fuse integrity in the presence
of nuisance overloads. At insertion the LTC4261 allows
contact bounce to settle, then soft starts the load using
a ramped current. Inrush current is increased gradually
to a few hundred milliamperes and held there until the
MOSFET is fully on.

Current is monitored by the SENSE pin and an 8mΩ shunt
resistor. Direct measurement of t he curren t is possible via

2

C port, with 10-bit resolution and 8A full scale.

the I

Cutting Diode Dissipation

ATCA’s redundant –48V power feeds are combined
on-card with ORing diodes. At 5A current consumption

even Schottky rectifi ers present a serious problem in
terms of both voltage drop and power dissipation: a
conducting pair drop more than 1V and dissipate 6W.
Following the diode manufacturer’s recommendations,
8 square inches of board area are needed to satisfy the
heat sinking requirements.

Diode dissipation, voltage loss and board area is reduced
in Figure 1 by using MOSFETs as active rectifi ers with
the LTC4354 diode OR driver. Total dissipation is cut to
less than 1W for two conducting “diodes” at maximum
load.

Zero Volt Transient

The so-called Zero Volt Transient requirement is a legacy
of earlier tele com equipment standards st ipulating uninter­rupted system operation during the course of a 5ms input
voltage dropout. An energy of 1J is needed to sustain a
200W load during this interval.

The accepted method of energy storage to satisfy the 1J
requirement is a bulk reser voir capacitor which is charge d
through resistor s. This technique dictates the us e of bulky
high voltage stor age capacitors, such as 100V (or rare 80V )
rated unit s which can handle the ma ximum input voltage of
75V. Since the zero volt transient test commences at 44V,
nothing is gained by storing a higher voltage. Compact
50V capacitors are used instead, by limiting the charging
voltage with a simple zener-transistor circuit.

The ATCA connector pin confi guration presents a special
design challenge. Here extraction is inferred from the dif­ference between each ENABLE and its associated VRTN,
thereby ignoring input dropouts. A PNP transistor pulls
up on EN in the event of an ENABLE disconnect, shutting
down the LTC4261 and permitting safe extraction with
no connector damage. During a zero volt transient, no
signal reaches the EN pin; power fl ows uninterrupted to
the load when the input voltage recovers.

, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
Hot Swap is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.

09/06/397

–48VRTN(OUT)

PULSE

–

•••

P0926

100Ω

100nF

1mF

+

DB

V

100V

50V

1μF

D

×4

+

DB

V

BZT52C47

D

–

DA

V

1μF

D

ZVN3320F

FMMT591

+

DA

V

100Ω

8.2k

2.4k

×7

PDS5100H

10k

33Ω

D

1.1k

1.1k

1.1k

1.1k

–48VOUT

DN397 F01

33nF

10nF

330nF

2.49k

10.2k

47nF

10Ω

100V

1k

1M

IRF1310NS

8mΩ

C Current and Voltage Monitor

2

PG

SCL

1μF

IN

V

UVH

UVL

137k 107k

SDAI

SDAO

ADIN2OVON

PGI

PGIO

ALERT

LTC4261CGN

CC

FLTINENADR1

INTV

100nF

ADIN

RAMP

SENSE

EE

V

TMR GATE DRAIN

SS

ADR0

330nF

100nF

CC

V

/RUN NGATE

TH

I

NC

DADB

GA

LTC4354CS8

SS

V

SS

V

1μF

SENSE

LTC3803ES6

1μF

2k

FB

V

–

V

10A

LONG

DB

GND

FDS3672

DD

FMMT5401

100k

SHORT

100k

D

FMMT5401

100k

SHORT

D

100k

10k

100nF

100k

HZS5C1

CC

V

1μF

SS

V

SS

V

GB

GA

LTC4354CS8

DBDA

D: 1N4148WS

2k

2k

7A

MEDIUM LONG

FDS3672

FDS3672

Figure 1. AdvancedTCA Hot Swap Controller with I

7A

MEDIUM SHORT

100nF

1M1M

22k

22nF

100V

91Ω

SMBT70A

2k

DADB

GA

CC

V

LTC4354CS8

SS

V

SS

V

+

1μF

DA

V

–

DA

V

10A

LONG

FDS3672

CC

V

+

DB

V

VRTN_A

Data Sheet Download

www.linear.com

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

[phone]

●

FAX: [phone] ● www.linear.com

ENABLE_B

VRTN_B

ENABLE_A

–48V_A

–48V_B

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call [phone], Ext. 2452

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© LINEAR TECHNOLOGY CORPORATION 2006