Datasheet
LTC4226
20
4226f
applicaTions inForMaTion
At the occurrence of severe load transient, the GATE1
voltage undershoots the voltage needed for current limit
regulation. The R
G1
and C
CG1
network between GATE1 and
OUT1 help restore GATE1 voltage quickly to the voltage
needed for current limit regulation. When a heatsink is a
used and gate interconnect has significant capacitance and
inductance, optional resistors R1 and R2 can be inserted
close to the MOSFET’s gate to prevent parasitic oscillation.
The product of R1 and MOSFET C
ISS
add delay to the cur-
rent limit response. For short PCB gate interconnection,
these optional resistors are not needed.
Tw o Hot Swap channels with identical sense resistors
and MOSFETs can have their outputs connected together
to almost double the current output capability without
significant improvement in MOSFET’s SOA. OUTPUT1 in
Figure 14 can be connected to OUTPUT2 to give 178A.
FTMR1 and FTMR2 should be kept separate as capaci-
tors C
T1
and C
T2
individually monitor the sense voltages
across R
S1
and R
S2
respectively. In the event of a current
fault, one channel may time out earlier than the adjacent
channel due to mismatch. If FAULT1 and FAULT2 are kept
separate, the
current in the channel of the first fault is
diverted to the adjacent channel with a second fault time
out occurring later.
Now consider the case where FAULT1 and FAULT2 are tied
together during a current fault. First fault channel FAULT1
pulls low and this causes an input low at FAULT2 with
GATE2 pulling low immediately. FTMR2 does not time out
due to the common FAULT connection with GATE2 disabled
earlier than the case of separate FAULT connection. The
MOSFET Q1 where the first occurrence of current fault
occurs would not be stressed as much as Q2 since the
fully enhanced Q2 determines the parallel channels V
CC
and OUT voltage drop. Common ON pin connections are
preferred for parallel channel applications.
Figure 13. Dual Continuous 44A Typical Output
Z1
SM6S15AHE3/2D
FTMR1
GND
C
T1
10nF
12V
R
S1
1mΩ
Q1
IRF2804S-7PPBF
R
S2
1mΩ
Q2
IRF2804S-7PPBF
C
T2
10nF
FTMR2
ON1
V
CC1
SENSE1 GATE1
LTC4226-2
OUT1
V
CC2
SENSE2 GATE2 OUT2
FAULT1
CLS
FAULT2
ON2
ON1
FAULT1
FAULT2
ON2
OUTPUT1
12V, 44A
OUTPUT2
12V, 44A
4226 F13
R2
10k
R1
10k
C1
1000µF
25V
+
R
G1
10Ω
C2
22µF
×10
25V
X5R
C3
1000µF
25V
+
C4
22µF
×10
25V
X5R
C
G1
10nF
R
G2
10Ω
C
G2
10nF