鈥?/div>
8-Pin SOIC
DESCRIPTION
The UCC1913 family of negative voltage circuit breakers provides com-
plete power management, hot swap, and fault handling capability. The IC is
referenced to the negative input voltage and is driven through an external
resistor connected to ground, which is essentially a current drive as op-
posed to the traditional voltage drive. The on-board 10V shunt regulator
protects the IC from excess voltage and serves as a reference for program-
ming the maximum allowable output sourcing current during a fault. All
control and housekeeping functions are integrated, and externally program-
mable. These include the fault current level, maximum output sourcing cur-
rent, maximum fault time, soft start time, and average power limiting. In the
event of a constant fault, the internal timer will limit the on-time from less
than 0.1% to a maximum of 3%. The duty cycle modulates depending on
the current into the PL pin, which is a function of the voltage across the
FET, and will limit average power dissipation in the FET. The fault level is
fixed at 50mV across the current sense amplifier to minimize total dropout.
The fault current level is set with an external current sense resistor. The
maximum allowable sourcing current is programmed with a voltage divider
from VDD to generate a fixed voltage on the IMAX pin. The current level,
when the output appears as a current source, is equal to V
IMAX/
R
SENSE
. If
desired, a controlled current startup can be programmed with a capacitor
on the IMAX pin.
When the output current is below the fault level, the output device is
switched on. When the output current exceeds the fault level, but is less
than the maximum sourcing level programmed by the IMAX pin, the output
remains switched on, and the fault timer starts charging CT. Once CT
charges to 2.5V, the output device is turned off and performs a retry some
time later. When the output current reaches the maximum sourcing current
level, the output appears as a current source, limiting the output current to
the set value defined by IMAX.
Other features of the UCC1913 family include undervoltage lockout, and
8-pin small outline (SOIC) and Dual-In-Line (DIL) packages.
BLOCK DIAGRAM
VDD
3
UVLO
LOGIC
SUPPLY
5.0V
REF
1=
UNDERVOLTAGE
0.2V
+
V
DD
5.0V
7
OVERLOAD COMPARATOR
SD/FLT
1
DISABLE
LINEAR
CURRENT
AMPLIFIER
50鈩?/div>
OUT
V
DD
IMAX
2
8
PL
9.5V SHUNT REGULATOR
V
DD
+
20碌A
SOURCE
ONLY
ON-TIME
CONTROL
OVERCURRENT
COMPARATOR
50mV
6
5
SENSE
VSS
4
CT
UDG-99001
SLUS274 - JANUARY 1999
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