Datasheet
LTC4228-1/LTC4228-2
17
422812f
µTCA Application
In the µTCA application shown in Figure 1, the output
load capacitor is required to hold up the supply to the
downstream load for a short duration when all of the in-
put supplies are not available. This happens when the IN
supply collapses to ground momentarily while the other
redundant supply to the diode-ORed output is not turned
on. As soon as the reverse voltage between IN and OUT
pins is detected, DGATE is pulled down quickly to turn off
the ideal diode MOSFET. By placing the sense resistor in
between the ideal diode and Hot Swap MOSFET, it allows
the SENSE
+
pin voltage to be held up by the output load
capacitance temporarily when the input supply collapses.
This prevents the SENSE
+
voltage from entering into un-
dervoltage lockout and turning off the Hot Swap MOSFET.
As the IN supply recovers, it charges up the depleted load
capacitance and provides power to the downstream load
instantly if the Hot Swap MOSFET is not turned off.
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
INPUT1 drops below 4.3V, ON1 turns off M
H1
and PWRGD1
Figure 7. Recommended PCB Layout for Power MOSFETs and Sense Resistors
applicaTions inForMaTion
28 27 26 25 24 23
9
1
2
3
4
5
6
7
8
22
21
20
19
18
17
16
15
10 11 12 13 14
LTC4228UFD
C1
R
H1
C
CP1
R
H2
Z1
Z2
VIAS TO GND PLANE
R
S1
IN1
OUT1
OUT2
422812 F07
CURRENT FLOW
TO LOAD
•
•
••
•
••
M
D1
PowerPAK SO-8
M
H1
PowerPAK SO-8
S
D
S D
S D
G D
M
D2
PowerPAK SO-8
M
H2
PowerPAK SO-8
S
D
S D
S D
G D
D G
D S
D S
D S
D G
D S
D S
D S
•
•
•• •
•• •
R
S2
CURRENT FLOW
TO LOAD
CURRENT FLOW
TO LOAD
CURRENT FLOW
TO LOAD
TRACK WIDTH W:
0.03" PER AMPERE
ON 1oz Cu FOIL
W
IN2
W W
W
C
CP2