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dc2442af
DEMO MANUAL DC2442A
Operating Principles
The LTC4282 is a low voltage, high current Hot Swap
controller that has a 2.9V to 33V operating range and
a 45V absolute maximum operating voltage for the V
DD
pin. The DC2442A is populated for +12V operation and is
configured for a “Low Stress Staged Start” configuration.
For details on this configuration refer to the “Low Stress
Staged Start Configuration” section.
The DC2442A is populated with a total of eight 0.9mΩ
MOSFETs and one 11mΩ MOSFET in a LFPAK package.
A total of sixteen 1mΩ sense resistors are used, provid-
ing typically 207A of load current. The current limit and
circuit breaker thresholds can be adjusted by changing
the sense resistors R25, R30, R35, R41, R47, R53, R58,
R63, R80, R85, R90, R95, R100, R105, R110 and R115
and/or the value of ∆V
SENSE
via registers in the LTC4282.
On the DC2442A, the LTC4282 is preprogrammed for a
∆V
SENSE
of 12.5mV to reduce power dissipation in the
sense resistors at such high currents; it has not been
tested for ∆V
SENSE
greater than 12.5mV. It is strongly
advised not to adjust this threshold on the DC2442A
without careful consideration of the power dissipation in
the sense resistors.
Low Stress Staged Start Configuration
In the Low Stress Staged Start configuration, the dual
gates are taken advantage of where one channel works as
a trickle charging channel, responsible for trickle charg-
ing the output during turn on and the other channel is the
bypass channel which turns on only when the power to
the output is good (within 0.7V of the input). The power
good signal is used to hold the bypass channel gate off, by
keeping it in artificial current limit, until the trickle channel
has powered up the load. The start-up trickle MOSFET Q1
is a compact, inexpensive device with small SOA and is
configured for a low current limit with a GATE capacitor
to limit inrush current. When the load is fully charged and
the start-up MOSFET is fully enhanced, the power good
signal is asserted, releasing the bypass channel’s sense
pin and enabling it. The bypass side has a high current
limit to deliver the full load current, and uses low R
DS(ON)
,
low SOA switching regulator class MOSFETs. The TIMER
capacitor is selected for a short time within the SOA of
the bypass MOSFETs.
This architecture minimizes the cost of MOSFETs to achieve
a given load current and R
DS(ON)
. However, with the short
current limit time, it has limited ability to ride through a
load surge in current limit or input voltage steps, and due
to the low start-up current cannot start up a resistive load
such as a heating element or incandescent lamp.
QUICK START PROCEDURE
