DC1018B-B 查看數據表（PDF） - Linear Technology
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DC1018B-B Datasheet PDF : 5 Pages
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LT4356
Board Layout
DC1018B-B is a 4-layer board. There are planes for
input, output, drain and ground;these are replicated on
each layer.
The spare amplifier is kept active during shutdown in
the LT4356CDE-2, resulting in a supply current of
about 50µA.
The 93 milinput 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
LED 4
FLT#
R ed
LED5 EN
G reen
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 (Q2 and D6) has been included
on the demo board for powering the FLT# output; the
FLT# pin itself is rated to 80V.
R8 is an optionalpull-up resistor for the SHDN# pin.
M odifying CurrentLim it
DC1018B-B 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 LT4356-2 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 R3 (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 OutputRegulation 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 fulldescription 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 wallcube, to name but
a few possible inputs.
Supply Current
The low shutdown current of the LT4356-2 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, D4 willdraw current. Below 16V
leakage in D4, Q2's collector-base junction in series
with D6 and Q1 willadd to the LT4356-2's supply cur-
rent. These effects are insignificant at room tempera-
ture.
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