LTC4225CGN-1#TRPBF Linear Technology, LTC4225CGN-1#TRPBF Datasheet - Page 18

• Manufacturer Part Number: LTC4225CGN-1#TRPBF
• Manufacturer: Linear Technology

Specifications of LTC4225CGN-1#TRPBF

• Lead Free Status / RoHS Status: Compliant

LTC4225-1/LTC4225-2
applicaTions inForMaTion
Power Prioritizer
Figure 8 shows an application where either of two supplies
is passed to the output on the basis of priority, rather than
simply allowing the highest voltage to prevail. The 5V pri-
mary supply (INPUT 1) is passed to the output whenever
it is available; power is drawn from the 12V backup supply
(INPUT 2) only when the primary supply is unavailable. As
long as INPUT 1 is above the 4.3V UV threshold set by the
R1-R2 divider at the ON1 pin, M
INPUT 1 to the output. When M
low, which in turn pulls ON2 low and disables the IN2
path by turning M
INPUT 1 drops below 4.3V, ON1 turns off M
goes high, allowing ON2 to turn on M
INPUT 2 to the output. Diode D1 ensures that ON2 remains
above 0.6V while in the off state so that when ON2 goes
high, M
100ms turn-on delay. When INPUT 1 returns to a viable
voltage, M
MOSFETs M
to the other under any condition.
18
H2
PRIMARY
SUPPLY
BACKUP
SUPPLY
is turned on immediately without invoking the
H1
D1
5V
49.9k
12V
turns on and M
20k
R2
R1
and M
+
H2
INPUT 1
INPUT 2
D2
off. If the primary supply fails and
C
0.1µF
F1
prevent backfeeding of one input
R4
41.2k
H2
H1
turns off. The ideal diode
0.1µF
H1
is turned on connecting
C1
is on, PWRGD1 goes
Z1
SMAJ13A
Z2
SMAJ13A
H2
and connect the
H1
EN1
ON1
INTV
GND
ON2
EN2
CPO1
CPO2
3.92k
Figure 8. 2-Channel Power Prioritizer
R3
and PWRGD1
CC
C
0.1µF
C
0.1µF
CP1
CP2
LS4148
IN1
IN2
D1
0.006
0.006
R
R
S1
S2
SENSE1 DGATE1
SENSE2 DGATE2
LTC4225
SiR466DP
SiR466DP
Additional Applications
In most applications, the back-to-back MOSFETs are con-
figured with the MOSFET on the supply side as the ideal
diode and the MOSFET on the load side as the Hot Swap
control. But for some applications, the arrangement of the
MOSFETs for the ideal diode and the Hot Swap control may
reversed as shown in Figure 9. The Hot Swap MOSFET is
placed on the supply side and the ideal diode MOSFET on
the load side with the source terminals connected together.
If this configuration is operated with 12V supplies, the
gate-to-source breakdown voltage of the MOSFETs can
be exceeded when the input or output is connected to
ground as the LTC4225’s internal 12V clamps only limit
the DGATE-to-IN and HGATE-to-OUT pin voltages. Choose
a MOSFET whose gate-to-source breakdown voltage is
rated for 25V or more as 24V voltage can appear across
the GATE and SOURCE pins of the MOSFET during an
input or output short. As shown in Figure 9, if a MOSFET
with a lower rated gate-to-source breakdown voltage is
chosen, an external Zener diode clamp is required between
the GATE and SOURCE pins of the MOSFET to prevent it
from breaking down.
M
M
D1
D2
10
R
SiR466DP
SiR466DP
HGATE1
HGATE2
H1
M
M
H1
H2
R
47
HG1
C
33nF
PWRGD2
PWRGD1
HG1
FAULT2
FAULT1
OUT1
OUT2
TMR1
TMR2
C
47nF
T2
+
422512 F08
C
47nF
C
470µF
T1
L
V
5A
OUT
422512f