Datasheet

LTC4228-1/LTC4228-2
10
422812f
applicaTions inForMaTion
High availability systems often employ parallel-connected
power supplies or battery feeds to achieve redundancy
and enhance system reliability. Power ORing diodes are
commonly used to connect these supplies at the point of
load, but at the expense of power loss due to significant
diode forward voltage drop. The LTC4228 minimizes this
power loss by using external N-channel MOSFETs for the
pass elements, allowing for a low voltage drop from the
supply to the load when the MOSFETs are turned on. When
an input source voltage drops below the output common
supply voltage, the appropriate MOSFET is turned off,
thereby matching the function and performance of an ideal
diode. By adding a current sense resistor in between the
two external MOSFETs that are separately controlled, the
LTC4228 enhances the ideal diode performance with inrush
current limiting and overcurrent protection (see Figure 1).
This allows the boards to be safely inserted and removed
from a live backplane without damaging the connector.
Internal V
CC
Supply
The LTC4228 can operate with input supplies from 2.9V
to 18V at the IN pins. The power supply to the device is
internally regulated at 5V by a low dropout regulator (LDO)
with an output at the INTV
CC
pin. An internal diode-OR
circuit selects the highest of the supplies at the IN and OUT
pins to power the device through the LDO. The diode-OR
scheme permits the device’s power to be temporarily kept
alive by the OUT load capacitance when the IN supplies
have collapsed or shut off.
An undervoltage lockout circuit prevents all of the MOSFETs
from turning on until the INTV
CC
voltage exceeds 2.2V. A
0.1µF capacitor is recommended between the INTV
CC
and
GND pins, close to the device for bypassing. No external
supply should be connected at the INTV
CC
pin so as not
to affect the LDO’s operation.
A small external load of less
than 500µA can be connected at the INTV
CC
pin.
Turn-On Sequence
The board power supply at the OUT pin is controlled with
two external N-channel MOSFETs (M
D
, M
H
). The MOSFET
M
D
on the supply side functions as an ideal diode, while
M
H
on the load side acts as a Hot Swap controlling the
power supplied to the output load. The sense resistor, R
S
,
Figure 1. µTCA Application Supplying 12V Power to Two µTCA Slots
CPO1
ON1
R2
137k
R4
137k
V
IN2
12V
V
IN1
12V
ON2
INTV
CC
GND
C1
0.1µF
C
F1
10nF
C
F2
10nF
C
CP1
0.1µF
C
CP2
0.1µF
C
T2
47nF
C
HG1
15nF
BULK
SUPPLY
BYPASS
CAPACITOR
BULK
SUPPLY
BYPASS
CAPACITOR
C
T1
47nF
12V
7.6A
PLUG-IN
CARD 1
PLUG-IN
CARD 2
BACKPLANE
422812 F01
IN1 SENSE1
–
SENSE1
+
DGATE1
M
D1
Si7336ADP
M
H1
Si7336ADP
LTC4228
R
S1
0.004Ω
M
D2
Si7336ADP
M
H2
Si7336ADP
R
S2
0.004Ω
HGATE1 OUT1
CPO2 IN2 SENSE2
–
SENSE2
+
DGATE2 HGATE2 OUT2
STATUS1
FAULT1
PWRGD1
EN1
EN2
PWRGD2
FAULT2
STATUS2
R
H1
10Ω
R
HG1
47Ω
C
HG2
15nF
R
H2
10Ω
R
HG2
47Ω
R5
100k
R6
100k
V
SENSE1
+
R7
100k
R8
100k
R9
100k
V
SENSE2
+
R10
100k
R1
20k
R3
20k
12V
7.6A
C
L1
1600µF
+
C
L2
1600µF
+
TMR1
TMR2