epc700/epc702
Current Peak at OUT
A short current peak when OUT is turned on, typically generated by a capacitive load, could trigger the short-circuit protection logic. However,
if the current peak is shorter than t
ext
plus t
del
, the over-current peak will be ignored.
Make sure that the energy drawn by such a current peak does not destroy the internal/external output transistor.
IN
OUT
HIGH-Z
STATUS
V
th sens
SENS
t
ext
<t
del
Figure 3: Short over-current pulse, i.e., by switching a capacitive load
Over-current Reset Sequence
If there is a permanent short circuit at OUT, such short circuit will be detected and OUT is turned off. After a waiting time t
minOFF
, the device tries
to turn on OUT again. If the short circuit is still present, OUT is immediately turned off again. This sequence continues until the short circuit is
removed or IN goes to LOW or power is turned off. This mode is called self-healing since the device tries to self-heal the short circuit end to
switch back into normal operation.
As a consequence in the case of a permanent over-current , short current peaks are issued into the load, respectively short.
The time t
minOFF
has to be set to a value that the internal/external switch cannot be damaged by a too high power dissipation. Without an exter -
nal switch, the time t
minOFF
has to be 1,000 times longer than the time t
del
.
IN
OUT
0
0
SHORT
SENS
0
V
th sens
0
t
ext
t
del
t
minOFF
STATUS
HIGH-Z
epc700
STATUS
HIGH-Z
epc702
t
LED
Figure 4: Over-current reset sequence
If one wants to reduce the waiting time in case of a short circuit situation, it can be done by simply taking IN to a low state and then to high
again. Please refer to the timing diagram in Figure 5. However, make sure that the maximum power dissipation of the chip or the external
switching transistor will never be exceeded above the allowed maximum.
IN
OUT
SHORT
V
th sens
SENS
t
ext
t
del
Timing diagram not enough
HIGH-Z
overcurrent epc700
File:
STATUS
LST
<t
minOFF
01.08.2010
Page 1
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.
Figure 5: Over-current status reset
© 2011 ESPROS Photonics Corporation
Characteristics subject to change without notice
5
Datasheet epc700_702 - V2.2
www.espros.ch
EPC [ ESPROS PHOTONICS CORP ]
