DC2178A - Demo Manual

DEMO MANUAL DC2178A
LTC4380
Low Quiescent Current
Surge Stopper
Description
Demonstration circuit 2178A showcases the LTC®4380 low
quiescent current surge stopper in an application which
can be configured for 12V, 1A or 24V/28V, 0.5A operation.
The output voltage is clamped by the LTC4380, permitting
the load to operate uninterrupted during transients of up to
250V and load dump surges such as ISO-16750-2 Test A.
The output current is limited to 1.25A. In the presence of
a sustained input overvoltage or output overcurrent fault
the LTC4380 shuts off to prevent damage to the N-channel
MOSFET pass element.
The output clamp voltage is selected by jumper JP1 to a
value of either 27V or 45V, to suit 12V or 24V/28V systems. DC2178A-A features the LTC4380-1 which latches
off after a fault, and DC2178A-B features the LTC4380-2
which automatically retries after a cool down delay.
Design files for this circuit board are available at
http://www.linear.com/demo/DC2178A
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.
Operating Characteristics
System Voltage
12V
24V/28V
Clamp Select
27V
45V
9V to 20V
9V to 37.5V
DC Operating (Full Load)*
DC Survival
Surge Ride-Through**
80V
80V
ISO-16750-2 Test A
ISO-16750-2 Test A
1ms Transient
250V
250V
Onset of Current Limit
1.25A
1.25A
Short Circuit Current
1.55A
1.55A
1A
0.5A
Maximum Load (VIN > 9V)
* Initial production boards are marked with more conservative limits of 19V and 35V. Functionality extends to 4.2V at 25°C. All boards are tested to the
limits shown in the table above.
** Formerly ISO-7637-2 Test Pulse 5A
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1
DEMO MANUAL DC2178A
Operating Characteristics
DANGER! High voltage testing shall be performed by
qualified personnel only. As a safety precaution at least
two people shall be present during high voltage testing.
Board Layout
DC2178A is a 2 layer board. There are planes for input,
output and ground; these are replicated on both layers.
There are exposed conductors on the bottom of the board,
and any banana plugs present will protrude through the
bottom of the board. The underlying surface should be
non-conductive and clear of any wire, solder and other
conductive debris.
The input plane is designed to have at least 79 mil (2mm)
clearance to adjacent conductors, to support 80VDC
standoff and transients to 250V. Spikes and surges are
withstood by R1, RDRN, CSNUB and Q1. These components
are chosen for wide pad spacing, pulse power capability
and voltage standoff, but ultimately limit the maximum
transient input voltage to approximately 250V. The time
spent above 80V is limited by the pulse power capability
of Q1 and R1.
Operation
DC2178A is designed for 12V operation with a load of up
to 1A, and 24V or 28V operation with a load of up to 0.5A.
JP1 selects an output clamping voltage of either 27V or
45V. For 24V and 28V supplies use a clamping voltage
of 45V; 12V supplies may use either 27V or 45V. If the
load tolerates the higher voltage, 45V clamping is better
than 27V in 12V applications because it reduces the drop
across the MOSFET (Q1) and therefore the safe operating
area stress, giving longer ride-through time during an
overvoltage condition.
Q1 is selected to ride through load dump events (such as
ISO 16750-2 Test A) with full load in 12V (1A) and 24V/28V
(0.5A) systems. Ride through is also permissible at 1A
for a 250V input transient of up to 1ms.
Up to 80VDC can be applied to the input. The circuit will trip
off after a delay of approximately 350ms for 1A load and
a 27V clamp, or 800ms for a 0.5A load and a 45V clamp.
The TMR pin charging current is a function of the power
dissipated in Q1 so that the exact delay time is a function
of the input voltage, output voltage and load current.
2
The LTC4380 features current limiting, which is set with
RSNS (40mΩ) to a value of 1.25A. Current limit does not
change with operating voltage or clamping voltage selection. If the output is shorted so that the output voltage falls
to 2V or less, current limit increases to 1.55A. In current
limit, the LTC4380 trips off after a delay that varies as a
function of the dissipation in Q1.
While the LTC4380 is designed to withstand reverse inputs
of up to −60V, DC2178A does not tolerate negative-going
events because Q1’s body diode will pass the negative
voltage straight through to the output and load. Negative inputs are easily blocked by the addition of a series
input diode, or by adding a second MOSFET as shown in
Figures 5 and 7 of the LTC4380 data sheet.
The LTC4380-1/LTC4380-2 VCC pin is rated at 80V maximum. Power is applied from the input to the VCC pin through
a 20kΩ resistor (R1), filtered by a 2.2μF capacitor (C1A),
and clamped by D1 to 68V. This arrangement offers two key
benefits. First, C1 filters the VCC pin to maintain operation
during brief input dropouts and to filter overvoltage spikes.
Second, during load dump in 24V/28V applications VCC is
clamped by D1 to keep the VCC pin safely below 80V. D1
is unnecessary in 12V applications because the filtering
action provided by C1 is sufficient to keep the VCC pin
below 80V, even in load dump.
12V Cold Crank Operation
An FDB33N25 was chosen for MOSFET Q1 to satisfy two
requirements: ability to block load dump (≈200V) in 28V
systems; and wide safe operating area for uninterrupted
operation during load dump events. The penalty for these
features is a high threshold voltage of 5V maximum at
ID = 250μA and 25°C, with no guarantees at temperature
extremes. R1 was chosen to limit the peak current in D1
to a safe level with 250V peak input voltage, but it also
reduces the VCC voltage below the input under normal
conditions. Q1 and R1 impact cold crank operation in
12V systems.
The LTC4380 is designed to deliver 10V of gate drive with
VCC > 8V, and 5V with VCC between 4V and 8V, guaranteed
over temperature. Thus, the FDB33N25 is incompatible
with operation in the 4V to 8V range, although typical
DC2178A assemblies can deliver 500mA load current
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DEMO MANUAL DC2178A
Operating Characteristics
with an input voltage of 4.2V. For full performance in
12V cold crank applications, a logic-level rated MOSFET
is necessary for Q1.
Optional Components
Pads are provided for optional VCC bypassing at C1B (C1A
is stuffed with 2.2μF), and for optional timer capacitance
at CTMR2 (CTMR1 is stuffed with 10μF). C1B and CTMR2
are found on the bottom of the board.
An optional GATE pin clamp (D6) is also located on the
bottom of the board. This clamp is necessary in applications
where a large value gate capacitor (C2 ≥ 100nF) is used.
A 15V Zener is recommended for D6, to safely discharge
C2 during a hard short circuit.
Extra Holes
Five through-hole pads are included for the purpose of
attaching an off-board power stage comprising a MOSFET, gate suppression resistor, sense resistor and output
reservoir capacitor in high current applications, where the
components and current levels are not compatible with
the layout of DC2178A. The pads are labeled on the bottom of the board and noted on the schematic as INPUT,
OUT, GATE, SNS and GND. Remove Q1 and RSNS. Make
short, direct connections between the through-hole pads
and the external components, and use SNS and OUT to
make Kelvin connections to the sense resistor. Depending
on the setup and MOSFET used, a snubber may be needed
between the MOSFET drain and the ground side of the
output reservoir capacitor, or between the MOSFET drain
and source terminals to suppress parasitic oscillations.
Small Turrets
No connection to any of the small turrets is necessary
to make the board operate—the LTC4380 defaults to the
ON state.
ON is pulled high internally. If this turret is left open, the
board will turn on when power is applied. Short this turret
to ground to turn off the LTC4380, or pulse low for at least
100μs to restart the LTC4380-1 (DC2178A-A) after a fault.
FLT pulls low when the LTC4380 faults off from an overcurrent or overvoltage condition. It is reset by pulling the ON
pin low for at least 100μs in the LTC4380-1 (DC2178A-A),
or after a cool down interval in the LTC4380-2 (DC2178A-B).
FLT can sink up to 3mA.
Jumpers
Jumper JP1 sets the state of the SEL pin to select between
a 27V output clamp (SEL grounded) or a 45V output clamp
(SEL connected to OUT). The corresponding clamp voltage at the GATE pin is about 5V higher than these values.
Jumper JP2 disables the output LED (DLED) to facilitate
measurement of the LTC4380’s operating current.
Basic Test Setup
DANGER! High voltage testing shall be performed by
qualified personnel only. As a safety precaution at least
two people shall be present during high voltage testing.
Set the jumper, JP1, for 12V or 24V/48V operation, connect a power supply to the input, and connect a load to
the output as shown in Figure 1. The circuit will turn on
automatically when power is applied, and the presence of
output power is indicated by the output LED.
To perform surge testing, add a diode (such as a 1N4004)
in series with the power supply. Couple the surge generator
through a second diode to the input to test the clamping
action of DC2178A. The diodes protect the power supply
and surge generator against backfeeding.
To measure the operating current, disable the output LED
using JP2, and disconnect the load.
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DEMO MANUAL DC2178A
Operating Characteristics
JP1
INPUT
SUPPLY
OUTPUT
LOAD
Figure 1. Basic Setup. JP1 Is Set to Match Input Supply, 27V Clamp
for 12V Supplies and 45V Clamp for 12V or 24V/28V Supplies
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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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
*
GND
ASSY
A
B
J2
E2
VCC
1
SUFFIX
1
2
D1
CMHZ5266B
68V
U1
LTC4380-1
LTC4380-2
2
J1
INPUT
CTMR1
10uF
10V
1206
CTMR2
OPT
1206
TOP MARK
LGHQ
LGHS
GND
E5
C1A
2.2uF
100V
1210
C1B
OPT
1210
CSNUB
10nF
500V
1206
RSNUB
100
1210
U1
*
RDRN
240k
1206
INPUT
ON
BEHAVIOR
LATCH OFF
AUTO RETRY
TMR
E6
DFN10DD-3X3
TMR
10
INPUT
1
DRN
2
VCC
ON
9
E7
R1
20k
1206
GATE
2
GND
E8
GND
C2
47nF
100V
R2
33
15V
OPT
D6
DDZ9702S
1
2
R3
10
3
Q1
FDB33N25
1
3
GATE
GND
8
4
SNS
FLT
RSNS
0.040
E9
SNS
FLT
7
5
11
OUT
EP
OUT
SEL
6
2
4
45V
27V
ON
OFF
+
1ms TRANSIENT
CURRENT LIMIT
MAXIMUM LOAD
SURGE RIDE-THROUGH
CL
22uF
50V
J4
E4
J3
E3
12V
24 / 28V
27V
45V
4.2V TO 19V
4.2V TO 35V
80V
ISO-7637-2
TEST PULSE 5A
250V
1.25A
1A
0.5A
RLED1
3.6k
1206
RLED2
3.6k
1206
DLED
GREEN
OUTPUT
OPERATING LIMITS
SYSTEM VOLTAGE
CLAMP SELECT
DC OPERATING
DC SURVIVAL
JP1
HD2X2-079
CLAMP
3
4
1
2
JP2
HD2X2-079
1
3
LED
1
2
E1
GND
OUTPUT
DEMO MANUAL DC2178A
Schematic Diagram
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DEMO MANUAL DC2178A
DEMONSTRATION BOARD IMPORTANT NOTICE
Linear Technology Corporation (LTC) provides the enclosed product(s) under the following AS IS conditions:
This demonstration board (DEMO BOARD) kit being sold or provided by Linear Technology is intended for use for ENGINEERING DEVELOPMENT
OR EVALUATION PURPOSES ONLY and is not provided by LTC for commercial use. As such, the DEMO BOARD herein may not be complete
in terms of required design-, marketing-, and/or manufacturing-related protective considerations, including but not limited to product safety
measures typically found in finished commercial goods. As a prototype, this product does not fall within the scope of the European Union
directive on electromagnetic compatibility and therefore may or may not meet the technical requirements of the directive, or other regulations.
If this evaluation kit does not meet the specifications recited in the DEMO BOARD manual the kit may be returned within 30 days from the date
of delivery for a full refund. THE FOREGOING WARRANTY IS THE EXCLUSIVE WARRANTY MADE BY THE SELLER TO BUYER AND IS IN LIEU
OF ALL OTHER WARRANTIES, EXPRESSED, IMPLIED, OR STATUTORY, INCLUDING ANY WARRANTY OF MERCHANTABILITY OR FITNESS
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ANY INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES.
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arising from the handling or use of the goods. Due to the open construction of the product, it is the user’s responsibility to take any and all
appropriate precautions with regard to electrostatic discharge. Also be aware that the products herein may not be regulatory compliant or
agency certified (FCC, UL, CE, etc.).
No License is granted under any patent right or other intellectual property whatsoever. LTC assumes no liability for applications assistance,
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Please read the DEMO BOARD manual prior to handling the product. Persons handling this product must have electronics training and
observe good laboratory practice standards. Common sense is encouraged.
This notice contains important safety information about temperatures and voltages. For further safety concerns, please contact a LTC application
engineer.
Mailing Address:
Linear Technology
1630 McCarthy Blvd.
Milpitas, CA 95035
Copyright © 2004, Linear Technology Corporation
6
dc2178af
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●
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