DEMO MANUAL DC684A
LT4256-3
48V Hot Swap Controller
Description
Demonstration circuit 684A is a 48V Hot Swap™ controller
featuring the
LT4256-3
in a 2A application. The LT4256-3
is ideally suited for demanding power distribution control
in 12V, 24V and 48V applications for hot board insertion
protection, high side power switching, and electronic
circuit breaker functions. The LT4256-3 provides a rich
set of features to support Hot Swap applications including:
• Overvoltage Shutdown
• Undervoltage Lockout
• Foldback Inrush Current Limiting
• Overcurrent Circuit Breaker with Programmable
Cutout Time
• Programmable Output Voltage Ramp Rate
• Selectable Auto Retry or Latchoff on Overcurrent Faults
• Power Good Monitor
• Open MOSFET Detection
Available in a 16-lead SSOP package, the LT4256-3 is
showcased on demonstration circuit 684A configured for
a 48V, 2A application. By changing a few passive compo-
nents, 12V and 24V applications can easily be evaluated
at up to 10A provided the thermal considerations of pass
FET Q1 are taken into account.
Design files for this circuit board are available at
http://www.linear.com/demo/DC684A
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
Hot Swap is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
performance summary
PARAMETER
Minimum Input Voltage
Maximum Input Voltage
Undervoltage L to H Threshold
Overvoltage L to H Threshold
Power Good L to H Threshold
Power Good H to L Threshold
Current Breaker Trip Point
Open Circuit Detection Threshold
Specifications are at T
A
= 25°C
VALUE
37V
76V
36.3V ±1.5%
72.5V ±1.5%
44.9V ±1.5%
40.2V ±1.5%
2.75A ±20%
<150mA
CONDITION
Determined by UVLO
Determined by TVS D2 Breakdown Voltage
UVLO Pin Threshold 4V ±1%
OVLO Pin Threshold 4V ±1%
FB L to H Threshold 4.45V ±1%
FB H to L Threshold 3.99V ±1%
(V
CC
– V
SENSE
) = 55mV ±20%
(V
CC
– V
SENSE
) < 3mV
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DEMO MANUAL DC684A
Quick start proceDure
Demonstration circuit 684A is easy to set up to evaluate
the performance of the LT4256-3. Refer to Figure 1 for
proper measurement equipment setup and follow the
procedure below:
Demonstration circuit 684A has two user configurable
jumper options:
•
J1 Retry:
Set to ON for auto retry or OFF for latchoff
on overcurrent faults.
•
J2 LED Function:
Select PWRGD or VOUT PRESENT.
In the former position, LED D6 will only illuminate
when the output voltage crosses the 44.9V threshold.
In the latter position, D6 will illuminate whenever Q1
is enhanced.
With power off, connect a nominal 48V power supply
capable of supplying 3A to the VIN and GND turrets.
Connect a logic level supply to the turrets labeled VLOGIC
and GND to monitor the PWRGD state on the turret la-
beled PWRGD. This same supply can also be connected
to the turret Vmicro to monitor the OPEN pin on the turret
labeled OPEN
NOTE: The OPEN and PWRGD pins are provided with
separate supplies to facilitate connection of the PWRGD
to a DC/DC power converter which may require a different
voltage than the system processor which would monitor
the OPEN state.
Connect a suitable load to the VOUT and GND turrets. This
load can be an electronic load or power resistors (24W at
100W for 2A at 48V) can be used.
NOTE: Because the LT4256 incorporates foldback current
limiting, the nominal startup current supplied to the load
is 700mA and can be as low as 500mA. This current limit
increases linearly until the FB pin exceeds 2V (VOUT >
20V). An electronic constant current load set to 2A will
not permit the circuit to turn on unless it is gated on by
the PWRGD signal (as would be the case with a DC/DC
converter controlled by the PWRGD signal). Resistive
loading will not have this problem.
+
+
V
IN
–
+
–
+
+
–
–
–
LOAD
+
+
V
OPEN
+
–
–
V
PWRGD
VOUT OR SYSTEM
PWRGD SUPPLY
–
V
MICRO
Figure 1. Proper Measurement Equipment Setup
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DEMO MANUAL DC684A
Quick start proceDure
Turn on the power supplies, verify the input voltage is 48V.
Verify the output voltage and the load current, the OPEN
turret should present a logic LOW if the load current is
>150mA and the PWRGD turret should present a logic
HIGH. LED D5 and D6 should be illuminated.
With the circuit functioning, additional evaluations can now
be performed. Test the undervoltage lockout and PWRGD
functionality by reducing the input voltage below 35V.
Observe the trip points of the PWRGD and undervoltage
lockout. Increase the input voltage back to 48V and again
observe the trip point of the PWRGD.
The overvoltage function can also be tested, but be aware
that if resistive loads are used, the value must be increased
to 36Ω to prevent an overcurrent fault. This test can also
be performed without a load.
Overcurrent faults can be evaluated by increasing the out-
put load current and observing the overcurrent trip point.
Circuit Testing Notes: As in all high current testing, it is
a good idea to use twisted pair power leads to minimize
circuit inductance. Under step loads, significant voltage
spikes can occur as a result of this inductance causing
false overvoltage or undervoltage trips. If there is sig-
nificant lead length between the power supply and the
DC684A, add additional bulk capacitance across the VIN
and GND turrets. This capacitance may also be needed if
stepping the load results in significant voltage steps on
the input, particularly if performing tests of the circuit
breaker function.
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DEMO MANUAL DC684A
parts List
ITEM
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
QTY
1
1
1
1
1
1
1
1
1
2
2
2
4
1
1
3
2
1
1
1
1
2
9
1
0
REFERENCE
CL
C1
C2
C3
C4
D1
D2
D3
D4
D5, D6
JP2, JP1
JP2, JP1
J1, J3, J4, J5
Q1
R1
R2, R3, R9
R11, R4
R5
R6
R7
R8
R10, R12
TP2, TP6, TP7-TP13
U1
U1 - ALTERNATE
PART DESCRIPTION
CAP, ELECTROLYTIC 10µF 100V 20%
CAP, X7R 0.01µF 100V 10% 1206
CAP, X7R 0.033µF 50V 5% 0805
CAP, X7R 0.1µF 50V 10% 0603
CAP, X5R 1µF 25V 20% 1206
DIODE, DUAL, ZENER 300mW
DIODE, TRANSIENT VOLTAGE SUPPRESSOR
DIODE, 1N4148W SOD123
DIODE, S1G 1A SMA
LED, GREEN
HEADER, 3PIN, 2mm
SHUNT
JACK, BANANA
XSTR, HEXFET POWER MOSFET
RES, 64.9k 1% 1/4W 1206
RES, 4.02k 1% 1/10W 0603
RES, 10k 5% 1/2W 2010
RES, 0.02Ω 5% 1W 2512
RES, 10Ω 1% 1/10W 0603
RES, 100Ω 5% 1/10W 0603
RES, 36.5k 1% 1/4W 1206
RES, 10k 5% 1/10W 0603
TURRET
IC, LT4256-3CGN HOT SWAP CONTROLLER
IC, LT4254CGN HOT SWAP CONTROLLER
MANUFACTURER/PART NUMBER
SANYO 100CV10FS
AVX 12061C103KATMA
AVX 08055C333JAT
TDK C1608X7R1H104K
TAIYO YUDEN TMK316BJ105ML
DIODES INC. AZ23C11
DIODES INC. SMAT70A
DIODES INC. 1N4148W
DIODES INC. S1G
PANASONIC LN1351C-(TR)
COMM CON 2802S-03G2
COMM CON CCIJ2MM-138G
KEYSTONE 575-4
INT. RECT. IRF540NS
AAC CRL18-6492FM
AAC CR16-4021FM
AAC CR12-103JM
IRC LRF2512-01-R020-J
AAC CR16-10R0FM
AAC CR16-101JM
AAC CRL18-3652FM
AAC CR16-103JM
MILL-MAX 2501-2
LINEAR TECH. LT4256-3CGN
LINEAR TECH. LT4254CGN
Required Circuit Components
dc684af
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5
4
3
2
1
LTC CONFIDENTIAL - For Customer Use Only
ECO
2
2.1
CHANGED, C-GRADE PART NUMBER
TP7
01/03/14
PROTO
06/10/04
REV
DESCRIPTION
DATE
APPROVED
REVISION HISTORY
TP8
VIN
Q1
IRF540NS
R5
2
VOUT
3
J4
VOUT
D
D
J1
VIN
1
0.02
1
D1
AZ23C11
+
D4
2
S1G
2
J3
2
1
3
R4
10K
CL
10uF
VIN
VOUT
48V@2A
48V
[1]
1
R1
64.9K
D2
SMAT70A
R11
10K
[1]
LED
FUNCTION
JP2
1
2
PWRGD
J5
2
16
15
schematic Diagram
GND
C3
Vcc
2
UV
GATE
D3
10nF
VOUT
1N4148W
R9
FB
4.02K
10
2
OV
U1
4.02K
12
13
SENSE
1
R7 100
0.1uF
C1
R8
36.5K
3
VOUT
PRESENT
[1]
R6
10
[1]
[1]
GND
TP13
D5
D6
TP12
GND
[1]
[1]
1
2
1
R2
4.02K
1
VIN
PRESENT
LED
GND
GRN
GRN
PWRGD
LED
C
TP11
C
TP10
R3
Vmicro
LT4256-3CGN
[1]
4
OPEN
PWRGD
5
VLOGIC
R12
10K
TP6
R10
10K
OPEN
RETRY
9
TIMER
GND
2
PWRGD
TP2
C4
1uF
RETRY
JP1
7
ON 1
3 OFF
C2
8
0.033uF
TP9
B
B
GND
[1]
IC
LT4254CGN/LT4256-3CGN (24V app)
10nF 50V
C1
CL
10uF 50V
D1
DZ23C12
Q1
IRFZ34VS
R1
32.4K
R4
20K
R8
14K
VERSION
VIN
VOUT
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.
CONTRACT NO.
APPROVALS
DRAWN
CHECKED
APPROVED
ENGINEER
DESIGNER
MEI
24V
24V
24V@2A
DATE
05/15/03
TECHNOLOGY
TITLE
1630 McCarthy Blvd.
Milpitas, CA 95035
Phone: (408)432-1900
Fax: (408)434-0507
A
SCH, LT4256-3CGN 48V 2A, HOT SWAP CONTROLLER
SIZE CAGE CODE
DWG NO
REV
A
This circuit is proprietary to Linear Technology and supplied
for use with Linear Technology parts.
Customer Notice:Linear
Technology has made a best effort to
design a circuit that meets customer-supplied specifications;
however, it remains the customers responsibility to verify proper
and reliable operation in the actual application, Component
substitution and printed circuit board layout may significantly
affect circuit performance or reliability. Contact Linear
Applications Engineering for assistance.
4
DC684A
01/06/14 05:39:59
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2.1
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FILENAME:
684A-2.1.DSN
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DEMO MANUAL DC684A
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