Issue 4 - June 2007
1
www.zetex.com
?Zetex Semiconductors plc 2007
ZXCT1032
High-side inrush controller and electronic fuse
Description
Ordering information
The ZXCT1032 is a high-side current monitor
that  drives  a  PMOS  or  PNP  transistor  to
provide in-rush current limit and over-current
protection.  The  ZXCT1032  includes  a  high
accuracy high-side current monitor, a start-up
timer and a re-try inhibit timer.
The ZXCT1032 takes the voltage developed
across a current shunt resistor and compares
this with an externally set trip point. It works
in three modes:
"   Linear soft-start
"   Over-current detector
"   Over-current disconnect/fuse
Linear soft-start
Upon power up the ZXCT1032 enters a linear
soft-start  mode.  During  which  the  output
current ramps up from zero to a maximum
user defined trip point. The trip point is set by
the voltage on I
SET
 pin and R
SENSE
.
The ramp rate is determined by capacitor C
T
.
The soft start ensures that capacitive loads are
smoothly  charged  without  causing  excessive
power supply startup transients.
Over-current detectior
When  external  capacitor  CT  has  charged  up
above the V
ISET
 the ZXCT1032 switches from its
soft-start  mode  to  its  over-current  detection
mode. During this mode the external MOSFET
will be fully enhanced reducing the its voltage
drop and power dissipation. 
While in this mode the internal current monitor
continually  checks  the  output  current  and
compares it to the trip-current level determined
by V
ISET
.
Over-current disconnect/fuse
If the trip current limit is exceeded at any time the
ZXCT1032   enters   its   Over-current   disconnect
mode. The drive pin is driven high, turning the
pass  MOSFET  off;  the  flag  output  goes  low
indicating a fault. 
The  drive  and flag outputs  are  latched  in  these
states for a period determined by C
T
, V
ISET
 and the
internally set discharge current (3礎(chǔ) typical). After
C
T
  has  discharged  to  80mV  the  ZXCT1032  will
restart into its linear soft-start mode.
The C
T
 charge and discharge times have been
ratioed to so that the power dissipation in the
pass MOSFET should allow indefinite operation
in the event of a continuous load failure.
Pin 3 description:
Determines  the  load  current  trip  level  or
constant  current  level.  ISET  can  be  left  open
circuit (internal 2.1V reference) or driven via a
DC  voltage  or  礐  PWM  output.  Its  source
impedance is 50k.
Features
"   Accurate high-side current sensing
"   User defined and dynamically adjustable
trip current
"   Load switch control
"   Fault flag logic output
"   User defined ramp and inhibit timers
"   SO8 package
"   Temperature range -40 to 85癈
Applications
"   Electronic fuse
"   Short circuit protected supply feed
"   Hot swap
"   Power over twisted pair
Order code
Pack
Part mark
Reel size
Tape width
Quantity per reel
ZXCT1032N8TA
SO8
1032
7
12mm
500