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dc1850aabf

DEMO MANUAL

DC1850A-A/DC1850A-B

overview

The LTC4366 surge stopper operates in a floating topol-

ogy, permitting the design of circuits capable of operating

at virtually unlimited input voltage. DC1850A has been

designed to protect against ±100VDC and 250V for 1ms,

in 28V vehicle applications. The input start-up range is

18V to 41V, while after start-up the input can fall to ap-

proximately 7V while still passing 1.5A load current.

Careful attention has been paid to the layout to provide at

least 87mil (2.2mm) clearance between input and output,

and input and ground. This wide clearance is capable of

withstanding 100VDC and spikes to 250V without arcing.

The operating ranges are shown in silkscreen on the top

of the board. The bottom shows the U1 part number, top

mark and behavior associated with the –A and –B ver-

sions of DC1850A. This same information is shown on

the schematic.

Three ancillary circuits are located on the bottom of the

board.

Shutdown Level Shifter

Since the LTC4366 operates in a floating topology, it is

necessary to level shift ground-referred shutdown signal-

ling. A simple NPN circuit provides level shifting between

the SHUTDOWN turret and the LTC4366’s SD pin.

Wide Voltage Range Constant Current LED Driver

Making an LED operate at constant brightness over a

wide operating range is made possible by a simple, two-

transistor circuit. Input LED (D6) current is held constant

from 18V to 250V, and emits some light as low as 7V.

Output LED (D5) is biased with a 9.1k resistor (R7, on bot-

tom of board). Its brightness will vary with output voltage.

−100V Reverse Voltage Protection Circuit

Reverse polarity inputs of up to −100V are blocked from

reaching the load by M2, whose associated circuitry is

located on the bottom of the board. This circuit blocks

reverse inputs of up to −250VDC, provided the input is

applied from a cold start. If DC1850A is already on and

operating with a positive input voltage, instantaneous

spikes must not exceed −100V.

SHUTDOWN TURRET

If the SHUTDOWN turret is left open, DC1850A defaults

to the ON state and turns on when an input supply is

connected. Pulling SHUTDOWN to 1.8V or higher causes

the LTC4366 to enter its shutdown state. The circuit

board layout limits the maximum SHUTDOWN voltage to

60VDC, while R2 limits the peak applied transient voltage

capability to 100V.

OPTIONAL COMPONENTS

Two optional components, CX and RX are made available

for those who wish to experiment with the frequency

response of the overvoltage regulation loop.

HOW TO OPERATE DC1850A

Operation of DC1850A is straightforward: connect an

input supply of 18V to 41V, and an output load of up to

1.5A. If the SHUTDOWN turret is open circuit the output

will power up. If the input voltage is increased above

≈ 43.1V, the output will limit and shut off after 2.8ms. DC

inputs of up to ±100V may be applied. The basic hookup

is shown in Figure 1.