LTC4370IDE-TRPBF View Datasheet(PDF) - Linear Technology
Part Name
Description
Manufacturer
LTC4370IDE-TRPBF Datasheet PDF : 20 Pages
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LTC4370
Applications Information
High availability systems often employ parallel-connected
power supplies or battery feeds to achieve redundancy
and enhance system reliability. ORing diodes have been
a popular means of connecting these supplies at the point
of load. System uptime improves further if these paralleled
supplies also share the load current.
VINA
5V
C1
39nF
M1
SUM85N03-06P
EN1 CPO1 VIN1 GATE1
OUT1
CVCC VCC
0.1µF GND
LTC4370
FETON1
R3
30.1k
RANGE
EN2 CPO2
FETON2
OUT2
VIN2 GATE2 COMP
C2
VINB 39nF
5V
M2
SUM85N03-06P
D1 R4
820Ω
SHARE
OFF
R1
2.5mΩ OUT
R2
10A
2.5mΩ
CC
0.18µF
D1: RED LED
LN1251C
4370 F01
Figure 1. 5V Diode-OR Load Share with Status Light
Current Sharing Characteristic
The LTC4370 load shares the two supplies by dropping
their voltage difference across the MOSFETs in series
with them (see Figure 1). The MOSFET on the lower sup-
ply drops the minimum servo voltage VFR(MIN) (12mV
or 25mV depending on supply voltage levels), while the
other MOSFET drops VFR(MIN) plus the supply voltage
difference. This equalizes both the OUT pin voltages, and
by Ohm’s law the current that flows through the sense
resistors. Figure 2a illustrates this. It shows the higher
supply’s MOSFET forward voltage drop, VFWD, increasing
to compensate the supply difference up to ±500mV.
The upper limit of the servo command adjustment is the
minimum servo plus the RANGE pin voltage (500mV in
Figure 2). Hence, when the two supplies differ by a volt-
age equal to VRANGE, the higher supply’s VFWD is pinned
at the maximum servo voltage VFR(MAX). If the supplies
diverge by more than VRANGE, the OUT pin voltages start
I2
NORMALIZED
VRANGE = 500mV
CURRENT
1
I1
1
SLOPE
=
2RS
0.5
I1
I2
0
–500mV
0
500mV
SHARING CAPTURE RANGE ±∆VIN(SH)
VIN1 – VIN2
IL • RS
MAXIMUM M2
MOSFET POWER
DISSIPATION
VFWD2
MOSFET
FORWARD
DROP
VFR(MAX)
525mV
MAXIMUM M1
MOSFET POWER
DISSIPATION
VFWD1
I2
I1
VFWD2
NORMALIZED VRANGE = 500mV
CURRENT
1
I1
1
SLOPE
=
2RS
2RS + RDS(ON)
0.5
VFR(MIN)
IL • RDS(ON)
I2
0
–400mV
0
400mV
SHARING CAPTURE RANGE
±∆VIN(SH)
MOSFET
FORWARD
DROP
525mV
VIN1 – VIN2
100mV + IL • RS
VFWD1
VFR(MIN) 25mV
0.5IL • RDS(ON) 125mV
25mV
–500mV
0
500mV
VIN1 – VIN2
–400mV
0
400mV
(2a) Low RDS(ON): Can Servo 25mV Minimum
Forward Regulation Voltage at Half Load
DRAWING IS NOT TO SCALE!
(2b) High RDS(ON): Fully-On MOSFET
Drops 125mV at Half Load
Figure 2. Load Sharing Characteristics
VIN1 – VIN2
4370 F02
4370f
9
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