DC1018B-C Datasheet DC1018B-C | P1-P3

LT4356

FEATURES

Stuffed for Automotive Applications up to 3A

Triple Layout for D-Pak, D2-Pak or S-8 M OSFETs

0.093-inch Turret Holes Accommodate 12 AW G W ire

LEDs Show Input, Outputs, Fault and Enable

Latches Off after Faults

Easily M odified for up to 20A

AP P L IC ATIO N S

Servers, Routers, Switches

M ass Storage

Fan Trays

Automotive M odules

D ESC RIP TIO N

Demonstration Circuit DC-1018B-C showcases the

LT4356-3 Surge Stopper in a 12V, 3A application. Input

transients of up to 60V are limited to 16V at the output;

sustained overvoltage conditions cause the limiter to trip

off and retry after the overvoltage is removed.

LEDs indicate the presence of +12V input and output, as

well as state of the fault output, FLT# and enable output,

EN.

, LTC, LTM , LT, Burst M ode, OPTI-LOOP, Over-The-Top and PolyPhase are registered

trademarks of Linear Technology Corporation. Adaptive Power, C-Load, DirectSense, Easy

Drive, FilterCAD, H ot Swap, LinearView, µM odule, M icropower SwitcherCAD, M ultimode

Dimming, No Latency , No Latency Delta-Sigma, No R

SENSE

, O perational Filter, PanelProtect,

PowerPath, PowerSOT, SmartStart, SoftSpan, Stage Shedding, SwitcherCAD, ThinSOT,

UltraFast and VLDO are trademarks of Linear Technology Corporation. Other product names

may be trademarks of the companies that manufacture the products.

P ERFO RM AN C E SUM M ARY

Specifications are at TA = 25°C

SYM BOL PARAM ETER CONDITIONS M IN TYP M AX UNITS

Input Operating Range

4 12 60 V

Peak Input Voltage Clipped by Transient Voltage Suppressor 100 V

LIM IT

Output Limiting Voltage 15.3 16 16.7 V

OUT

M aximum Load Current

3.5

Board Layout

DEMO

CIR CU IT

1 0 1 8

Q U ICK S TA R T G U IDE

L T 4 35 6

Ov e rv o lta g e P ro te c tio n

R e g u la to r

LT4356

DC1018B-C is a 4-layer board. There are planes for

input, output, drain and ground; these are replicated on

each layer.

DC1018B-C is stuffed with the LT4356CDE-3 which

has a 7µA typical shutdown current. The LT4356CDE-

3 latches off after faults, so the OVLO components are

not stuffed. R 8 is included to provide a modest but

predictable rise time on the SHDN # pin and ensure

proper reset of the internal fault latch.

The 93 mil input and output connection turrets are not

swaged and may be removed for attachment of up to

12 gauge wire. Banana jacks facilitate bench testing.

Sufficient copper is available to support applications of

at least 20A.

LEDs are included as quick debug indicators. These

LEDs show:

LED1 12V input Green

LED3 12V output Green

LED4 FLT# Red

LED5 EN Green

The enable and fault LEDs are both powered in such a

way that the signals present on their associated turrets

are limited in voltage (see schematic). To this end a

simple series regulator (Q 2 and D6) has been included

on the demo board for powering the FLT# output; the

FLT# pin itself is rated to 80V.

M odifying Current Lim it

DC1018B-C is designed for 3.5A maximum load cur-

rent and may be modified for higher or lower current

levels. Sense resistor RSNS1-3 pads are designed for

1206 or 2010 sense resistors. The LT4356-3 current

sense voltage is 50mV, with limiting occurring at

50mV/RSNS. Optional footprints for D2-pak or S-8

M OSFETs allow for much higher or lower current lev-

els. Sufficient copper is present to handle in excess of

20A. If the S-8 footprint is used, move R 3 (10 ohms)

to the bottom of the board, R3B. This is the gate resis-

tor for the S-8 M OSFET.

At higher currents the clamp DCL must be proportion-

ately increased. This catches the locally generated

spike at the M OSFET drain when the output goes into

regulation. The energy content of this spike is a direct

function of input slew rate and output load capacitance.

Changing Output Regulation Level

The output limiting or regulation voltage is easily modi-

fied by simply changing R1 and R2 to values appropri-

ate for the application. The FB pin servo voltage is

1.25V. See the data sheet for a full description of this

pin and equations. As built, the demo board clamps at

16V.

The actual operating voltage is independent of the

clamping voltage, and may be anything from the mini-

mum operating voltage of 4V up to the clamping volt-

age. Thus while the demo board is labeled "12V", it can

operate with any other sub-16V input such as a 5V

regulated supply, a 6V gelcell, or a stack of 8 NiM H

cells, or a 9V impedance limited wall cube, to name but

a few possible inputs.

Supply Current

The low shutdown current of the LT4356-3 is impossi-

ble to measure on the demo board because of the

presence of the input LED, LED1, and the LED Supply.

Remove R10 and R17 to eliminate these paths.

Note that above 16V, D 4 will draw current. Below 16V

leakage in D4, Q2's collector-base junction in series

with D6 and Q1 will add to the LT4356-3's supply cur-

rent. These effects are insignificant at room tempera-

ture.

Sm all Turrets

No connection to any of the small turrets is necessary

to make the board operate--the LT4356-3 defaults to

LT4356

the O N state.

SHD N# 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 LT4356-3.

FLT# pulls low after a TM R interval if there is a sus-

tained input overvoltage, and does so 2ms before the

output shuts down. Otherwise FLT# is high, pulled up

by LED4 and the 5V LED Supply.

EN is an output. It goes high when the 12V output rises

to within 700mV of the input. EN is latched and does

not pull low again until the LT4356-3 trips off from a

sustained overvoltage or is shut down. EN is pulled up

to the output through a 3.9 kilo-ohm resistor, and is

shunted by LED5. Use EN to enable downstream cir-

cuitry.

Input Overvoltage Behavior

The LT4356-3 is designed to block transient voltages

and surges from reaching load circuitry of limited volt-

age capability. This has a profound impact on the volt-

age rating of downstream components as well as to-

pology where dc-to-dc converters are concerned, not

to mention elimination of bulky input filter inductors

and capacitors.

To this end, Q1 is selected for a 3A application where

the surges and transients are consistent with an auto-

motive environment.

DC1018B-C is designed to ride through input tran-

sients of 1 or 2ms duration, but will shut down during

load dump. Q1 must dissipate significant energy to

support a 3A load during load dump, so a larger

M OSFET is necessary if Q 1 is to survive. CTM R must

be increased to accommodate the proposed time inter-

val if this modification is contemplated.

Locally Generated Drain Spikes

W hen an input transient waveform is applied to an op-

erating LT4356-3, the M OSFET is fully on and a large

magnitude displacement current flows into the load

capacitors, CL1 and CL2 (collectively, CL) and any

other off-board load capacitors. The LT4356-3 has a

relatively soft current limit amplifier to prevent detec-

tion of current pulses generated by noise spikes. This

soft response prevents the LT4356-3 from responding

to the initial current surge in CL.

The current surge is limited only by the feedpoint im-

pedance of the supply, the transient rising slew rate

and the capacitance and ESR of CL. The current surge

is commutated by the M OSFET once CL charges to

Vgate-Vthreshold, and results in a wide-bandwidth

voltage spike at the input, limited only by the break-

down of input clamp D CL. W ithout DCL the input volt-

age could easily exceed 100V and destroy the LT4356-

Under normal conditions (typical automotive transients

and surges) the input rise time is 10µs or more, and

the CL displacement current is moderate. Drain spikes

are thereby limited in amplitude.

W hen bench testing, input rise times may easily reach

100ns creating an environment for destructive drain

spikes, generated by the M OSFET itself.

To protect the LT4356-3 from damage during bench

testing with fast-rising input edges, an SM AJ58A Tran-

sZorb has been chosen for diode clamp DCL. This

component clamps the drain spike to less than 100V.

The knee is around 64V. If a dc voltage higher than

60V is connected to DC1018B-C, DCL will be de-

stroyed. Transients to 80V are permissible as the cur-

rent in DCL will be limited by wiring inductance. Fur-

ther, the energy is limited because the time spent in

conduction by DCL is short.

Basic Operation

Connect a 12V supply to input, and the load to output.

The circuit will turn on automatically when power is

P1-P3 P4-P5

DC1018B-C

Mfr. #:

Buy DC1018B-C

Manufacturer:

Analog Devices Inc.

Description:

Power Management IC Development Tools LT4356CDE-3 Demo - Overvoltage Protectio

Lifecycle:

New from this manufacturer.

Delivery:

DHL FedEx Ups TNT EMS

Payment:

T/T Paypal Visa MoneyGram Western Union

Products related to this Datasheet

DC1018B-C