LTC4225-2_15 Datasheet, PDF (18/24 Pages) Linear Technology – Dual Ideal Diode and Hot Swap Controller

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_H1 is turned on connecting
INPUT 1 to the output. When M_H1 is on, PWRGD1 goes
low, which in turn pulls ON2 low and disables the IN2
path by turning M_H2 off. If the primary supply fails and
INPUT 1 drops below 4.3V, ON1 turns off M_H1 and PWRGD1
goes high, allowing ON2 to turn on M_H2 and connect the
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_H2 is turned on immediately without invoking the
100ms turn-on delay. When INPUT 1 returns to a viable
voltage, M_H1 turns on and M_H2 turns off. The ideal diode
MOSFETs M_D1 and M_D2 prevent backfeeding of one input
to the other under any condition.
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.
5V
PRIMARY
SUPPLY
INPUT 1
R_S1
0.006Ω
Z1
SMAJ13A
C_CP1
0.1µF
M_D1
M_H1
SiR466DP SiR466DP
R_H1
R_HG1
10Ω
47Ω
C_HG1
33nF
R2
49.9k
R1
20k
C_F1
0.1µF
C1
R4 0.1µF
41.2k
CPO1
EN1
IN1 SENSE1 DGATE1 HGATE1
ON1
INTV_CC
GND
LTC4225
ON2
12V ₊
BACKUP
SUPPLY
INPUT 2
EN2
CPO2 IN2
C_CP2
0.1µF
SENSE2 DGATE2
HGATE2
Z2
SMAJ13A
R3
3.92k
R_S2
0.006Ω
D1
LS4148
M_D2
M_H2
SiR466DP SiR466DP
OUT1
FAULT1
PWRGD1
TMR1
TMR2
PWRGD2
FAULT2
OUT2
Figure 8. 2-Channel Power Prioritizer
18
+ _CL
470µF
V_OUT
5A
C_T2
47nF
C_T1
47nF
422512 F08
422512f