Input either to switch internal/external mode or to measure the voltage drop on an external
shunt resistor to detect over-current
Output
Not connected. Connect these pins to GND.
PIN Connections QFN16-VEED-
1VN4
File:
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03.08.2010
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confidential and protected by law and international trades. It must not be shown to any third party nor be copied in any form without our written permission
.
5
V
DD
7
13
14
15
16
GND
IN
STATUS
He
epc701/epc703
Functional Description
Normal Operation
During typical operation the OUT follows the IN as shown in Figure 1. In the the other state (when IN is set to high level), the internal switch is
closed pulling the OUT pin to V
DD
. As long as the output current does not exceed the current threshold, OUT is stable ON and STATUS is
stable HIGH-Z. The delay from IN to OUT is defined as t
ON
and t
OFF
for the rising and the falling edge respectively.
IN
OUT (without
external Transistor
OUT (with
external Transistor
SHORT
SENS
STATUS
epc700
STATUS
epc702
0
VDD-⎮V
Sat
⎮
HIGH-Z
VDD
t
on
0
VDD
V
th sens
0
t
off
HIGH-Z
HIGH-Z
Figure 1: Normal operation
Please note that the status of the pin OUT is dependent whether the chip is operated with or without external driver transistor. In the
subsequent diagrams, the version without external driver transistor is shown only.
IN
0
OUT
0
0
V
DD
SHORT
SENS
V
th sens
t
ext
t
del
STATUS
epc701
HIGH-Z
STATUS
HIGH-Z
epc703
t
LED
Figure 2: Short circuit detection
t
Note: The parameter t
ext
used in this paper is described in Figure 7.
LED
t
LED
Over-current Sequence
A short on the load side will lead to an over-current through OUT. If an over-current stays longer than the time t
del
and t
ext
, OUT is turned off as
shown in the figure below. At the same time STATUS changes its state to indicate an over-current situation to an external controller. STATUS
can also be used to drive directly an indicator LED due to its 10mA driving capability. epc701 delivers a constant on-signal, whereas epc703
has a flashing output.
Timing diagram operation mode
epc700
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05.01.2011
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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
DD
SENS
V
th 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 at least 1,000 times longer than the time t
del
.
IN
OUT
0
0
SHORT
SENS
0
V
th sens
t
ext
t
del
t
minOFF
V
DD
STATUS
HIGH-Z
epc701
STATUS
HIGH-Z
epc703
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
SENS
V
DD
V
th sens
t
ext
t
del
<t
minOFF
File:
...
STATUS
HIGH-Z
LST
Timing diagram not enough
overcurrent epc700
Figure 5: Over-current status reset
05.01.2011
Page 1
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