Zxct1032, Zxct1032 timing in over-current condition, Zxct1032 normal operation – Diodes ZXCT1032 User Manual
Page 7
ZXCT1032
© Zetex Semiconductors plc 2007
2 The output voltage also increases due to the load current powering up the load and charging
any capacitance. After the initial soft start (load current stabilizing) the timing capacitor
charges up to 4V and the device enters its normal mode of operation. The external MOSFET
will be now fully enhanced minimizing any serial voltage drop.
The ZXCT1032 has now entered its over-current detector mode; it is effectively “transparent”
to the load until the current monitor output exceeds the trip point.
3 Fuse operation is provided by the trip comparator whose threshold voltage is set by V
ISET
(internally nominally 2.1V, although this threshold can easily be overdriven). As the load
current increases, so does the monitor voltage. When the current monitor output voltage
exceeds V
ISET
, the trip comparator output goes high and sets the latch with the following
results:
a The output drive is disabled.
b The open collector Flag output goes low to indicate a fault condition.
c
The 200
A current source is turned off and C
T
starts to discharge slowly via a 3.3
A current
source.
ZXCT1032 Normal Operation
0
2
4
6
8
10
12
14
16
18
20
0
5
10
15
20
Time ms
T
iming capacitor voltage - V
0
0.2
0.4
0.6
0.8
1
Load Current - A
V
CT
I
LOAD
V
IN+
= 18V
R
SENSE
= 0.2
Ω
C
T
= 220nF
V
ISET
= 2.1V
Trip current = 1A
10*V
SENSE
V
ISET
V
LOAD
ZXCT1032 Timing in over-current condition
0
0.5
1
1.5
2
2.5
0
5
1
0
0
1
0
5
0
Time (ms)
V
o
lt
ag
es
-
V
0
0.5
1
1.5
2
2.5
Lo
a
d
C
u
rre
nt
-
A
V
IN+
= 18 V
R
SENSE
= 0.2
⍀
I
LOAD
> 1 A
C
T
= 220 nF
V
ISET
= 2.1 V
Trip current = 1 A
V
ISET
V
CT
I
LOAD