LINEAR TECHNOLOGY LTC4223 Technical data
Hot Swap Solution Meets AMC and MicroTCA Standards
Design Note 437
Vladimir Ostrerov
Introduction
The LTC®4223 is a dual Hot Swap™ controller that meets
the power requirements of the Micro Telecommunication
Computing Architecture (MicroTCA) specifi cation recently
ratifi ed by the PCI Industrial Computer Manufacturers
Group (PICMG).
The LTC4223 includes an internal pass FET for the 3.3V
auxiliary supply and a driver for an external N-channel
pass FET for the 12V payload supply. Inrush current for
both supplies is controlled: the auxiliary supply has a
fi xed 240mA active current limit and the 12V ramp rate
is controlled by an external capacitor. A timed circuit
breaker and fa st current limit protect bo th supplies against
severe overcurrent faults. It also features an adjustable
analog current limit with a circuit breaker timeout for
the 12V supply.
12V
6mΩ Si7336ADP
10Ω
The LTC4223 monitors 12V load current by sensing
voltage across an external resistor and outputs a groundreferenced voltage (at the 12IMON pin) proportional to
the load current. It also provides separate power-good
outputs for the two supplies and a single, common fault
output. Additional features include card detection and
independent control of the two supplies. The LTC42231 latches off after a circuit breaker fault timeout expires
while the LTC4223-2 provides automatic retry after a
fault. A fault on the 12V supply shuts down only the 12V
path, leaving t he 3.3V auxiliary power available for system
management functions. A fault on the 3.3V AUX supply
shuts down both supplies.
Advanced Mezzanine Card Application
Figure 1 shows a typical MicroTCA application. The current limit on the 12V rail is 7.6A, determined by the 6mΩ
L, 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.
12V
7.4A
15nF
47Ω
03/08/437
IPMC
12V
12V
SENSE
LTC4223-1/LTC4223-2
TIMER
GND
GATE
0.1μF
3.3V
ADC
51Ω
330nF
12V
IN
AUXIN
V
CC
AUXON
12ON
AUXPGOOD
12PGOOD
FAULT
12IMON
Figure 1. Advanced Mezzanine Card Application
12V
OUT
AUXOUT
DN437 F01
EN
CARRIER
CONNECTOR
3.3V
150mA
MODULE
CONNECTOR
sense resistor. Auxiliary rail current limit is internally set
A
to 240mA. (Section 4.2.1 of the MicroTCA specifi cation
details th e requirements for payload and aux iliary voltage,
current, and protection.) Figure 2 shows the power-up
transients when a card is inserted. Figures 3 and 4 show
EN
5V/DIV
AUXOUT
5V/DIV
12V
OUT
5V/DIV
UXPGOOD
5V/DIV
12PGOOD
5V/DIV
20ms/DIV
Figure 2. Normal Power-Up Waveform
FAULT
5V/DIV
I
LOAD
5A/DIV
12V
OUT
5V/DIV
DN437 F02
the two modes of overcurrent protection on the 12V
supply. In Figure 3, the load current is increased above
the analog current limit (ACL) threshold. The LTC4223
responds by reducing the current to the ACL threshold,
allowing the card to ride out short overcurrent faults. If
the fault persists, the timer expires and power is turned
off. In the event of a severe overcurrent fault, load current
is reduced to the ACL limit in 8μs as shown in Figure 4.
Once again, if the fault persists and the timer expires,
power is turned off entirely.
Conclusion
The LTC4223 aims to simplify Hot Swap control for Advanced Mez zanine Cards in ATCA and MicroTCA systems.
It succeeds by meeting all MicroTCA requirements for
controlling both payload and auxiliary power with only
a 5mm × 4mm DFN package and a few minimal external
components. Individual card monitoring and control
functions are further simplifi ed by LTC4223’s status and
control lines.
ΔV
SENSE
200mV/DIV
12V
OUT
5V/DIV
12V
GATE
5V/DIV
Figure 3. Overcurrent Fault on 12V Output
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100μs/DIV
DN437 F03
12V
GATE
5V/DIV
5μs/DIV
DN437 F04
Figure 4. Short-Circuit Fault on 12V Output
For applications help,
call (408) 432-1900, Ext. 3899
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507 ● www.linear.com
dn437 LT/TP 0308 387K • PRINTED IN THE USA
© LINEAR TECHNOLOGY CORPORATION 2008
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