DEMO MANUAL DC2027A
LTC4364HDE-1, 2
12V Surge Stopper
with Ideal Diode
Description
Demonstration circuit 2027A showcases the
LTC
®
4364
surge stopper with ideal diode in a 12V, 1A application.
DC inputs of up to 80V and transients to 250V are limited
to just 28.7V at the output. Sagging and reverse-polarity
inputs of up to –24V are isolated from the output by a
reverse-blocking MOSFET configured as an ideal diode.
Further, the output is protected against backfeeding. The
output may be driven –20V to +30V without circuit damage
or backfeeding into the input.
A 4.7μF timer capacitor and robust forward MOSFET
permit the load to operate through ISO-7637-2 load dump
waveform 5A. Sustained overvoltage or overcurrent condi-
tions cause the LTC4364 to turn off after a timer delay.
The LTC4364-1 (DC2027A-A) latches off and is reset
by pulling
SHDN
low for at least 100μs. The LTC4364-2
(DC2027A-B) automatically retries after a three minute
cool down delay. Start-up and retry are inhibited in the
presence of an input overvoltage.
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
PARAMETER
Input Voltage Limits
Specifications are at T
A
= 25°C
MIN
6.6
–24
27.2
–20
2.125
TYP
12
MAX
27
80
250
30.3
30
1
2.875
UNITS
V
V
V
V
V
A
A
CONDITIONS
Operating
DC Survival
1ms Transient
Regulation Voltage
DC Backfeed Protection
Operating
Current Limit
Output Voltage Limits
Output Current Capability
28.7
2.5
Quick start proceDure
DANGER! HIGH VOLTAGE TESTING SHOULD BE
PERFORMED BY QUALIFIED PERSONNEL ONLY.
As a safety precaution at least two people
should be present during high voltage testing.
Board Layout
DC2027A is a 2-layer board. There are planes for input,
output and ground; these are replicated on each layer. The
93mil input and output connection turrets are not swaged
and may be removed for attachment of up to 12 AWG wire.
Banana jacks facilitate bench testing. 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 nonconductive
and clear of any wire, solder and other conductive debris.
The input plane is designed to have at least 78mil (2mm)
clearance to adjacent conductors. This is adequate for
100V
DC
standoff and transients to 250V. Spikes and surges
are withstood by RLED1, QLED1, ROV1, RUV1, R4, Q1 (if
present), D3, M1, RSNUB and CSNUB. These components
are chosen for wide pad spacing, pulse power capability
and voltage stand off, but ultimately limit the maximum
transient input voltage to ≈250V. The time spent above
80V is limited by the pulse power capability of R4.
dc2027af
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DEMO MANUAL DC2027A
Quick start proceDure
OPERATION
DC2027A has been designed for 12V operation with a load
of up to 1A. M1 limits surges, spikes and transients, such
as are commonly encountered in automotive applications.
For positive-going events, the output is regulated at 28.7V.
Spikes of up to 250V are permissible for 1ms, limited by
the pulse capability of R4. The load may continue operating
during positive transients, including load dump, without
interruption.
Reverse inputs of up to –24V
DC
are blocked from reaching
the load by M2. Beyond –24V, a 400W transient voltage
suppressor, D4, clamps the input. Consult the SMAJ24A
data sheet for specific information about peak current and
time duration for spikes exceeding –24V.
DC2027A-A is fitted with the LTC4364-1. This device
latches off after a sustained overcurrent or overvoltage
fault. Operation is resumed after cycling the supply, or
after pulsing
SHDN
low for at least 100μs.
DC2027A-B is fitted with the LTC4364-2, which also shuts
off the output in the presence of a sustained fault condi-
tion, but automatically retries after a cool-down delay of
180 seconds. The cool-down delay may be prematurely
interrupted by pulsing
SHDN
low for at least 100μs.
In both cases, retry is inhibited by the OV pin if the input
is higher than 16.8V, as is start-up.
INPUT
R4
270k
1206
D4
SMAJ24A
D3
ES1G
Q1
PZTA42
While a maximum load current of 1A is permitted during
start-up and overvoltage conditions, current limit is set
to 2.5A. This higher current level is permissible during
normal (12V) operation. In short-circuit conditions where
V
OUT
= 0V, current limit folds back to 1.25A.
The output is protected against backfeeding over a range
of –20V to 30V. If the output is connected to a low imped-
ance source of less voltage than the input, M1 will likely
go into current limit and fault off. If the output is higher
than the input, M2 will block backfeeding. In the case that
the output is higher than the 28.7V regulation voltage, the
timer will run and M1 will fault off.
Optional Components
The pulse power limitations of R4 may be avoided by
adding Q1. Pads are located on the bottom of the board.
Remove RVCC (a 0Ω jumper) and increase R4 to 270k
(see Figure 1). Remember that the board spacing is only
78mils, and that this is inadequate for creepage and clear-
ance at 250V
DC
.
Pads are included on the bottom of the board for optional
output capacitors COUT3 and COUT4, in the event additional
bypassing is desired.
Through-hole pads are included for adapting DC2027A to
an off-board power stage, as shown in Figure 2.
RVCC
REMOVED
C1
100nF
100V
D1
CMZ5945B
68V
LTC4364
V
CC
dc2027a F01
Figure 1. Remove RVCC and Add Q1 to Withstand Prolonged Inputs of Up to 250V. R4 Is Increased to 270k
dc2027af
2
DEMO MANUAL DC2027A
Quick start proceDure
Small Turrets
No connection to any of the small turrets is necessary
to make the board operate—the LTC4364 defaults to the
ON state.
SHDN
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 LTC4364.
FLT
is an open-drain output which pulls low after a TMR
interval if there is a sustained input overvoltage, and does
so 94ms before the output shuts down. In overcurrent
there is a brief early warning delay, the exact time of which
depends on the severity of the overload. There is no pull-up
resistor for
FLT;
it must be pulled up to an external logic
supply or to the output with an external resistor.
FLT
can
sink up to 2mA.
ENOUT
is an open-drain output which goes high when
the output rises to within 700mV of the VCC pin. ENOUT
is latched and does not pull low again until the LTC4364
output drops below 2.2V. There is no pull-up resistor for
ENOUT; it must be pulled up to an external logic supply
or to the output with an external resistor. ENOUT can sink
up to 2mA.
TMR
is made available so that its operation may be ex-
amined easily with an oscilloscope, by way of a 10MΩ
probe. Do not load or short this turret to ground as the
timer function will be defeated and an overload may de-
stroy M1. TMR normally sits at ground, and charges to
1.35V in a fault condition. This turret also finds use for
connecting different values of CTMR: simply remove the
existing CTMR and solder substitutes between the TMR
and GND turrets.
CSNUB
RSNUB 10nF
100
HIGH CURRENT
12V INPUT
M1
R5
10
M2
RSNS
RESR
C
OUT
HIGH CURRENT
OUTPUT
dc2027a F02
Figure 2. Connections to an Off-Board Power Stage. Remove M1, M2, RSNS, RSNUB
and RESR from Board. Keep Wires Short to Avoid Parasitic Oscillations in M1
dc2027af
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DEMO MANUAL DC2027A
Quick start proceDure
HOW TO OPERATE DC2027A
DANGER! HIGH VOLTAGE TESTING SHOULD BE
PERFORMED BY QUALIFIED PERSONNEL ONLY.
As a safety precaution at least two people
should be present during high voltage testing.
To operate DC2027A, connect a 12V supply to the in-
put and a 1A load to the output, as shown in Figure 3.
The circuit will turn on automatically when power is
applied. Up to –24V
DC
may be applied to the input with-
out damage to DC2027A or the load. The output may be
backfed with –20V to 30V, without damage to DC2027A
or backfeeding of the input.
The preferred method of coupling a transient to the input
without backfeeding the 12V supply is to simply isolate
the sources with blocking diodes, as shown in Figure 4.
12V
SUPPLY
1A LOAD
(12 )
dc2027a F03
Figure 3. Basic Test Setup
dc2027af
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DEMO MANUAL DC2027A
Quick start proceDure
INPUT FROM
SURGE GENERATOR
MUR460
MUR460
12V
SUPPLY
1A LOAD
(12 )
dc2027a F04
Figure 4. Simple Means of Coupling Surges, Transients and Spikes
dc2027af
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