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dc2180af
DEMO MANUAL DC2180A
Quick start proceDure
Overview
DANGER! HIGH VOLTAGE TESTING SHALL BE PER
-
FORMED BY QUALIFIED PERSONNEL ONLY. AS A SAFETY
PRECAUTION AT LEAST TWO PEOPLE SHALL BE PRESENT
DURING HIGH VOLTAGE TESTING.
DC2180A showcases the LTC4371 dual negative voltage
ideal diode-OR controller and monitor in a −48V, 50A
application. 2mΩ maximum, 100V MOSFETs (M1 to M4)
are used (two per channel) to realize a full load drop of
less than 50mV, and a loss of less than 2.5W.
Board Layout
The board comprises four layers, with planes for −48VA,
−48VB, −48VOUT and RTN. These planes are replicated
on each of the four layers to achieve the lowest possible
resistance, minimize conduction loss and convey heat
away from the power MOSFETs.
There are exposed conductors on the bottom of the
board, and the heads of the cap screws protrude through
the bottom of the board. The underlying surface should
be non-conductive and clear of wire, solder and other
conductive debris.
Current and Voltage Limitations
DC2180A is designed to deliver 50A continuous load
current from any combination of current at the −48VA
and −48VB inputs. If the current is concentrated in one
input, the two MOSFETs in that channel will dissipate a
total of slightly less than 2.5W. If the current is shared
equally between both inputs the total dissipation falls to
1.25W, since with all four MOSFETs conducting the total
resistance is effectively halved.
The short term current-carrying capability is limited by
the MOSFET rating of 1200A pulsed at 25°C case tem
-
perature, gradually giving way to dissipation limitations
for longer surges. Up to 100A load current can be easily
handled for one second. See the MOSFET data sheet for
further information.
The input voltage is limited by the BV
DSS
rating of the
MOSFETs to 100V. The MOSFETs can be driven into
breakdown within the limits spelled out in their data sheet.
The LTC4371 V
DD
supply is regulated by an on-chip shunt
regulator at the VZ pin, and biased by 30kΩ series limiting
resistor, R
Z
. Dissipation in R
Z
and R1 (bias resistor for LED
D1) limit the maximum DC operating condition to about
−90V. −85V is suggested as a conservative maximum
DC input voltage, leaving margin for elevated operating
temperatures and brief excursions up to the BV
DSS
rating
of the MOSFETs.
High Current Connections
Panduit S4-14R lugs are provided for connecting 50A
power supplies and a 50A load. The lugs are designed
for crimping to 4 AWG welding cable. A Thomas & Betts
WT115 or equivalent crimper is suggested for the lugs.
Other crimping methods can result in an inferior, high
resistance and short-lived connection whose power dis
-
sipation contributes significantly to board temperature rise.
The importance of properly sized cabling cannot be over
-
stated. 4 AWG welding cable exhibits a resistance of 263μΩ
per foot. The cabling in a typical bench setup can easily
total 10', producing a voltage drop exceeding 100mV and
a power loss of more than 6W in the cable alone. Contrast
this with a voltage drop of 50mV and power dissipation
of 2.5W total in the MOSFETs at 50A.
