LTC4224-2 Linear Technology, LTC4224-2 Datasheet - Page 6

• Manufacturer Part Number: LTC4224-2
• Description: Compact Dual Low Voltage Hot Swap Controller
• Manufacturer: Linear Technology

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OPERATION
LTC4224-1/LTC4224-2
The LTC4224 is designed to control power on a live back-
plane, allowing boards to be safely inserted and removed. It
controls two supplies (V
between 1V and 6V via two external N-channel MOSFETs.
For applications where the total load current is 5A or less,
dual MOSFETs such as the FDS6911 can be used to save
board area. The two supplies can be turned on and off
independently using the active low ON1 and ON2 pins.
Internal 10μA current sources pull these pins to V
Pulling the ON pin low turns on a charge pump which
sources 10μA at the GATE pin thereby ramping up the gate
of the external MOSFET. When the MOSFET turns on, the
inrush current is limited at a level set by an external sense
resistor. Inrush current can be further reduced, if desired,
by adding a capacitor from GATE to GND. To protect the
external MOSFET, the GATE pins are clamped to about
5.5V above the higher of the two supplies.
APPLICATIONS INFORMATION
The typical LTC4224 application is in a high availability
system where two positive supply voltages are distributed
to power individual cards. The LTC4224 detects board
presence during insertion and removal, allowing power
to be delivered in a controlled manner without damaging
the connector. It reports overcurrent faults to the system
controller through its FAULT pin, which can light an LED
or can be monitored by a system controller.
6
BYPASS CAPACITOR
BYPASS CAPACITOR
BULK SUPPLY
BULK SUPPLY
3.3V
CC1
5V
, V
CC2
) with operating voltages
R3
390
D1
FAULT
V
CC1
0.015Ω
R1
Figure 1. Typical Application
SENSE1
CC
.
V
CC2
LTC4224
0.010Ω
R2
SENSE2 GATE1 GATE2
Each supply is continuously monitored for undervoltage
and overcurrent conditions. The undervoltage monitor
shuts off the external MOSFET when the corresponding
supply is too low.
Current is monitored by an active current limit amplifi er
(ACL) and a timed electronic circuit breaker (ECB). Like
all timing delays in the LTC4224, the ECB delay of 5ms is
generated internally without requiring any external timing
capacitors. The ECB threshold is slightly below the ACL
threshold and shuts off the external MOSFET after 5ms.
FAULT is latched low to indicate an overcurrent fault.
The LTC4224-1 remains latched off until reset by either
turning off and then on the affected supply or its ON pin.
The LTC4224-2 automatically restarts after four seconds
to allow time for the MOSFET to cool down.
The basic LTC4224 application circuit is shown in Figure 1.
The following sections cover V
turn-on and turn-off sequence, various fault conditions
and recovery from fault situations. External component
selection is discussed in detail in the Design Example
section.
FDS6911
Q1
GND
ON1
ON2
Q2
CONNECTOR
PLUG-IN CARD
CC
MOD DETECT
selection, the normal
5V
1A
3.3V
2A
R
1k
MOD_DET
GND
422412fa