DEMO MANUAL DC1741A
LTC4370
Two-Supply Diode-OR
Current Balancing Controller
DESCRIPTION
Demonstration circuit DC1741A features the LTC4370, a
two supply diode-OR current sharing controller in a typical
2.9V to 18V, 16A sharing application.
The maximum MOSFET voltage drop V
FR
= V
IN
– OUT is
set with an external resistor, up to 600mV. A fast gate
turn-on reduces the load voltage droop during supply
switchover. If the input supply fails or is shorted, a fast
turn-off minimizes the transient reverse current.
Disabling the load sharing function turns the LTC4370
into a dual ideal diode controller.
Two enable input pins,
EN1
and
EN2,
allow enabling and
disabling each rail’s MOSFET individually while the MOS-
FETs’ inherent diodes create diode-OR connection when
the MOSFETs are disabled. The LTC4370 provides a rich
set of features to support shared current diode-ORed ap-
plications including:
• Load Sharing Between Two Supplies
• Elimination of the Need for Active Control of Input
Supplies
• Elimination of "Share Bus”
• Reverse Current Blocking
• Elimination of Shoot-Through Current During Start-Up
or Faults
Design files for this circuit board are available at
http://www.linear.com/demo
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
PERFORMANCE SUMMARY
SYMBOL
V
IN
V
CC(EXT)
V
CC(REG)
V
EA(OS)
g
m(EA)
V
FR
ΔV
GATE
I
GATE
PARAMETER
V
IN1
and V
IN2
Input Voltage Operating Range
Specifications are at T
A
= 25°C
MIN
2.9
0
2.9
4.5
5
0
150
TYP
MAX
18
V
CC
6.0
5.5
±2
25
50
14
9
–1.9
1.9
160
620
1.1
16.6
UNITS
V
V
V
mV
μS
mV
mV
V
V
A
A
μA
mV
V
A
CONDITIONS
With External V
CC
Supply
V
CC
External Supply Operating Range
V
CC
Regulated Voltage
Error Amplifier Input Offset
Error Amplifier Gain
Forward Regulation Voltage (V
IN
– V
OUT
)
MOSFET Gate Drive (GATE-V
IN
)
GATE1, GATE2 Fast Pull-Up Current
GATE1, GATE2 Fast Down-Up Current
GATE1, GATE2 Off Pull-Down Current
EN1, EN2
Threshold Voltage
Maximum Continuous Load Current
V
IN1
, V
IN2
≤ V
CC
V
IN
=1.2V, V
CC
= 5V
V
IN
=12V
V
FWD
= 0.2V; I = 0, –1μA; Highest V
IN
= 12V
V
FWD
= 0.2V; I = 0, –1μA; Highest V
IN
= 2.9V
V
FWD
= 0.4V, ΔV
GATE
= 0V, CPO = 17V
V
FWD
= –2V, ΔV
GATE
= 5V,
Corresponding
EN
=1V, ΔV
GATE
= 2.5V
EN
Falling
FETON Transitions High
Sharing active, limited by SUM85N03 FET Dissipation
2
2
10
4.5
–0.9
0.9
65
580
0.28
12
25
12
7
–1.4
1.4
110
600
0.7
V
EN(TH)
I
OUT
ΔV
GATE(ON)
MOSFET On-Detect Threshold (GATE-V
IN
)
dc1741af
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DEMO MANUAL DC1741A
OPERATING PRINCIPLES
The LTC4370 controls N-channel MOSFETs, M1 and
M2, to share the load between two input rails.The error
amplifier compares OUT1 and OUT2, and controls servo
amplifiers which regulate MOSFET forward voltage drop
to V
FR
. Combined action of the error amplifier and servo
amplifiers forces OUT1 and OUT2 to be equal and as a
result the rail currents are equal. The board RANGE resistor
R3 = 30.1k defines maximum regulation voltage range as
265mV to 375mV.
The board is assembled with SUM85N03-06P N-channel
MOSFETs, which in a single channel application has
current capability up to 20A. In the load share mode the
installed components guarantee continuous proper load
sharing up to 16.6A total load. For a short test time of 3
to 5 seconds it is possible to double this load.
Two LEDs, OFF1 and OFF2, indicate the MOSFETs’ status.
Each LED lights up, when the gate voltage is less than
0.7V above V
IN
.
Pay special attention to the power supply features used
with the LTC4370.
This controller may not work properly with supplies utilizing
synchronized rectification in the output stage unless the
internal circuit of the supply has the ability to limit negative
current or to block it completely. Exercise caution when
using the controller with this type of supply unless it is
determined that it contains the required circuitry.
dc1741af
2
DEMO MANUAL DC1741A
QUICK START PROCEDURE
Demonstration circuit DC1741A is easy to set up to evalu-
ate the performance of the LTC4370. Refer to Figure 1
for proper measurement equipment setup for load share
observation.
1. Turn both supplies on. Adjust two 5V supplies’ outputs
to a 215mV difference, which equals the minimum
ΔV
IN(MIN)
load share breakpoint (265mV–50mV).
Load the LTC4370 output with minimal current so that
both supplies contribute current to the common load.
Increase load up to 35A and observe the LTC4370 op-
eration mode with accurate load sharing. It is easy to
estimate load share accuracy by measuring a voltage
between two sense resistors. Since the MOSFETs will
be dissipating excessive power, limit this measurement
to 3 to 5 seconds when at the 35A level.
2. Reduce the load current to a total of 7.5A. Adjust the
two 5V supplies’ outputs to a voltage difference of 373
mV which equals the maximum ΔV
IN(MAX)
load share
breakpoint (375mV–2mV). As the difference between
power supplies output is greater than the maximum
voltage regulation, the LTC4370 channel with the higher
voltage will provide most of the current. Increase the
voltage until all of the current is provided by the higher
voltage supply. This is the point at which the MOSFET
of the higher voltage channel MOSFET is fully enhanced
while the MOSFET of the lower channel voltage is
completely cut off. Observe that the LED of the lower
supply is illuminated.
VARIABLE
LOAD
+
POWER
SUPPLY 1
–
mV
+
POWER
SUPPLY 2
–
DC1741A F01
Figure 1. Load Share Performance Measurement
dc1741af
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DEMO MANUAL DC1741A
PARTS LIST
ITEM
1
2
3
4
5
6
7
8
9
10
11
12
13
QTY
1
1
2
2
2
7
4
2
2
1
2
0
1
REFERENCE
CC
CV
CC
C1, C2
D1, D2
D3, D4
E1, E2, E3, E4, E5, E7, E8
J1, J2, J4, J5
M1, M2
R1, R2
R3
R4, R6
R5, R7
U1
PART DESCRIPTION
Cap., X7R, 0.18μF, 25V, 10%, 0805
Cap., X7R, 0.1μF, 50V, 10%, 0805
Cap., X7R, 0.039μF, 50V, 10%, 0805
LED, RED
Current Limiting Diode, 3.2V, SOD-80
Turret, Testpoint 0.063"
Connector, Banana Jack
MOSFET N-Channel, 30V, D2PAK
Res., WSL 0.002 1W, 1%, 2512
Res., Chip 30.1k, 0.1W 1%, 0805
Res., Chip 10k, 0.1W, 5%, 0805
Res., 0805
I.C., Diode-OR Load Share Cont., DFN16DE-4
×
3
MANUFACTURER/PART NUMBER
AVX, 08053C184KAT2A
AVX, 08055C104KAT2A
AVX, 08055C393KAT2A
Panasonic, LN1251C-TR
Central Semi. Corp. CCLM3500
Mill-Max, 2308-2-00-80-00-00-07-0
Keystone, 575-4
Vishay, SUM85N03-06P-E3
Vishay, WSL25122L000FEA
Vishay, CRCW080530K1FKEA
Vishay, CRCW080510K0JNEA
OPT
Linear Technology Corp., LTC4370CDE
Required Circuit Components
dc1741af
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1
2
3
4
5
REVISION HISTORY
ECO
M1
SUM85N03-06P
REV
2
2ND PROTOTYPE
VLADIMIR O. 01-17-12
DESCRIPTION
APPROVED
DATE
_
J1
A
VINA
18V MAX
C1
0.039uF
50V
11
CPO1
16
EN1
VCC
FETON1
8
7
3
CC
0.18uF
R2
0.002
1W 1%
2512
FETON2
FETON1
9
R1
0.002
1W 1%
2512
14
CVCC
0.1uF
15
17
R3 30.1k
2
RANGE
EN2
CPO2
6
C2
0.039uF
50V
4
5
VIN2
GATE2
COMP
OUT2
RANGE
1
EP
GND
FETON2
VIN1
10
GATE1
OFF1
13
12
D1 RED
D3
LN1251C-TR
CCLM3500
1
2 2
1
E1
A
VCC
E3
SCHEMATIC DIAGRAM
EN1
E2
R4
10K
U1
OUT1
LTC4370CDE
J2
OUTPUT
E4
B
B
R5
OPT
R7
OPT
EN2
E5
R6
10K
D2 RED
D4
LN1251C-TR
CCLM3500
1
2 2
1
OFF2
C
VINB
18V MAX
M2
SUM85N03-06P
J4
C
E7
NOTES: UNLESS OTHERWISE SPECIFIED
1. ALL RES ARE IN OHMS, 0805.
2. ALL CAP ARE IN MICROFARAD, 0805.
J5
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
GND
E8
CUSTOMER NOTICE
APPROVALS
TECHNOLOGY
TITLE: SCHEMATIC
1630 McCarthy Blvd.
Milpitas, CA 95035
Phone: (408)432-1900
www.linear.com
Fax: (408)434-0507
LTC Confidential-For Customer Use Only
D
D
LINEAR TECHNOLOGY HAS MADE A BEST EFFORT TO DESIGN A
CIRCUIT THAT MEETS CUSTOMER-SUPPLIED SPECIFICATIONS;
HOWEVER, IT REMAINS THE CUSTOMER'S RESPONSIBILITY TO PCB DES.
KIM T.
VERIFY PROPER AND RELIABLE OPERATION IN THE ACTUAL
APP ENG. VLADIMIR O.
APPLICATION. COMPONENT SUBSTITUTION AND PRINTED
CIRCUIT BOARD LAYOUT MAY SIGNIFICANTLY AFFECT CIRCUIT
PERFORMANCE OR RELIABILITY. CONTACT LINEAR
TECHNOLOGY APPLICATIONS ENGINEERING FOR ASSISTANCE.
TWO-SUPPLY DIODE-OR CURRENT SHARING CONTROLLER
SIZE
IC NO.
N/A
SCALE = NONE
3
THIS CIRCUIT IS PROPRIETARY TO LINEAR TECHNOLOGY AND
SUPPLIED FOR USE WITH LINEAR TECHNOLOGY PARTS.
2
DEMO CIRCUIT 1741A
DATE:
LTC4370CDE
4
REV.
2
01/17/2012, 11:31 AM
SHEET
5
1
OF
1
1
DEMO MANUAL DC1741A
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