DN397 - AdvancedTCA Hot Swap Controller Monitors Power Distribution

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 office telecom environments.
PICMG® 3.0 defines, 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 preserve 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 the current is possible via
the I2C port, with 10-bit resolution and 8A full scale.
Cutting Diode Dissipation
ATCA’s redundant –48V power feeds are combined
on-card with ORing diodes. At 5A current consumption
09/06/397
even Schottky rectifiers 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 rectifiers 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 telecom equipment standards stipulating 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 reservoir capacitor which is charged
through resistors. This technique dictates the use of bulky
high voltage storage capacitors, such as 100V (or rare 80V)
rated units which can handle the maximum 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 configuration 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 flows 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.
Data Sheet Download
www.linear.com
(408) 432-1900
1630 McCarthy Blvd., Milpitas, CA 95035-7417
Linear Technology Corporation
dn3mlf LT/TP 0906 305K • PRINTED IN THE USA
FAX: (408) 434-0507 ● www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2006
●
For applications help,
call (408) 432-1900, Ext. 2452
–48V_B
–48V_A
ENABLE_A
ENABLE_B
VRTN_B
VRTN_A
7A
7A
MEDIUM LONG
MEDIUM SHORT
1M
100k
SHORT
1M
100k
VDB–
1μF
VDB+
SHORT
LONG 10A
LONG 10A VDA–
1μF
VDA+
FDS3672
GB VSS VSS
FDS3672
FDS3672
DB GA
2k
2k
10k
SMBT70A
1μF
D: 1N4148WS
HZS5C1
1μF
NC
22nF
100V
91Ω
100nF
SENSE
GND
100k
100nF
VFB
VCC
ITH/RUN NGATE
LTC3803ES6
22k
10.2k
100nF
137k
D
33Ω
•
2.49k
330nF
VIN
1.1k
1.1k
1.1k
1.1k
8mΩ
47nF
1μF
IRF1310NS
1M
1k
+
2.4k
×7
33nF
10nF
100V
PG
SCL
SDAI
SDAO
ALERT
PGIO
PGI
ADIN
FMMT591
PDS5100H
GATE DRAIN RAMP
10k
10Ω
SENSE
LTC4261CGN
TMR VEE
VDB–
1μF
VDB+
VDA–
1μF
VDA+
330nF
UVH
UVL
ADIN2
OV
ON
INTVCC
FLTIN
EN
ADR1
ADR0 SS
D
D
100nF
•
•
PULSE
P0926
107k
ZVN3320F
100Ω
100nF
100V
100Ω
Figure 1. AdvancedTCA Hot Swap Controller with I2C Current and Voltage Monitor
DA
2k
LTC4354CS8
FMMT5401
D 100k
VCC
GA DB DA
FMMT5401
D 100k
D
2k
LTC4354CS8
VCC
FDS3672
GA DB DA
VSS VSS
VSS VSS
D
VCC
LTC4354CS8
8.2k
D
1mF
50V
×4
DN397 F01
–48VOUT
BZT52C47
–48VRTN(OUT)
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