Datasheet
LTC4226
10
4226f
applicaTions inForMaTion
The typical LTC4226 application is in high availability
systems that distribute positive voltage supplies between
4.5V to 44V to hot-swappable ports or cards. It can also
be used in daisy chain port applications like FireWire to
provide instant current limit.
The basic two channel applications are shown in Figure 1
and Figure 2. Figure 1 shows the LTC4226 in a card resident
application with an upstream connector. Figure 2 shows the
LTC4226 on a backplane or motherboard with a downstream
connector. Each Hot Swap channel has a power path con-
trolled by an external MOSFET switch and a sense resistor
for monitoring current.
Turn-On Sequence
During turn-on, a 9µA current charges the gate of the
MOSFET switch: Q1 for channel 1. The current limit am-
plifier monitors the current in the channel 1 power path
by sensing the voltage across the resistor, R
S1
.
At start-up, the switch current is typically dominated by
the current charging the load capacitor, C
L1
. If the sense
voltage reaches V
LIMIT
, the current limit amplifier controls
the gate of the MOSFET in a closed loop. This keeps the
start-up inrush current at the current limit.
Several conditions must be present before
the external
MOSFET can be turned on. The fault timer FTMR is reset
by either UVLO or ON low status. The external supply V
CC
must exceed its undervoltage lockout level V
CC(UVL)
for
more than 50ms. The ON pin must be high for more than
10ms and the FAULT pin must be high before the external
MOSFET turns on with no additional delay.
If the channel is not in UVLO, the ON pin low to high asser-
tion delay is 10ms. The FAULT pin must be high before the
external switch turns on. When the channel is not in UVLO
and the ON pin is high, there is no delay from the FAULT
low to high transition to turn on of the external switch.
Figure 1. 2-Channel Card Resident Controller with Upstream Connector
5V
Z2
SMCJ7V0A
R
S2
10mΩ
Q2
FDMS86500DC
OR Si7164DP
FTMR1
GND
C
T1
33nF
C
L1
100µF
R1
720k
Z1
SMCJ15A
R
S1
5mΩ
Q1
FDMS86500DC
OR Si7164DP
C
T2
33nF
FTMR2
ON1
V
CC1
SENSE1 GATE1
LTC4226-1
OUT1
V
CC2
SENSE2 GATE2 OUT2
FAULT1
CLS
FAULT2
ON2
ON1
12V
FAULT2
ON2
12V
8.9A
OUT
4226 F01
CONNECTOR
1
CONNECTOR
2
BACKPLANE PLUG-IN
CARD
GND
FAULT1
CLS
+
C
L2
220µF
5V
4.45A
OUT
+
R2
100k
C1
470pF
R3
240k
R7
1k
R6
1k
R4
100k
C2
470pF
C3
22nF
R5
10k