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epc701/epc703
Application Information
epc701 and epc703 have two modes of operation, where the SENS pin is used to define the mode. When SENS is tied to GND, the chip ope-
rates as a source driver capable to drive max. 50mA at 30VDC (refer to Figure 6). The load is connected directly between the OUT pin and
ground GND. If the current through the internal switch exceeds 50mA, the switch is turned off.
If the SENS pin is connected to a shunt resistor RS as shown in Figure 7, the OUT pin is driven by a sink driver also capable to drive 50mA to
control an external power transistor. This mode is used if the required output current has to be higher than 50mA, e.g. 1A and/or the output
voltage exceeds 30VDC.
The load current is measured by monitoring the voltage drop over a resistor. If the internal switch is used, also the current measurement
resistor is located internally (Figure 6). In the case of using an external power transistor as shown in Figure 7, the current measurement
resistor RS has to be placed externally. If the voltage drop at RS exceeds the threshold of -200 mV referenced to VDD, the output stage is deac-
tivated. The timing diagrams of the signals can be found in section “Functional Description”.
The IN signal must be low during power-up (tSTARTUP) for proper function of the chip. The epc70x has a built in pull down resistor, so not
external active driving is needed during startup.
epc701 or epc703 Using the Internal Switch
VDD
Figure 6 shows the epc701/703 in the mode using the internal switch. To enable this
mode, the SENS pin has to be connected to GND. Note that the GND of the chip and
VDD
the GND at the load must be connected together. The factor frt between minimum off-
time and delay-time must be maintained in order not to damage the chip due to over-
STATUS
IN
SENSE
OUT
heating. This factor has to be higher than 1,000. In the worst case scenario a peak
current of approx. 0.6A is flowing from the load at 30V into the chip with a tDel set at
50μs if a short-circuit occurs. If the recovery time tminoff in this case is smaller then
50ms, the average power dissipation exceeds the safe operation condition and the
device will get damaged.
R1≥50Ω
epc701
epc703
Diode D1 is to protect the internal switch against voltage surges when inductive loads
are turned off.
D
R
L
L
GND
D1
R1 is to protect the internal switch in case of a short circuit on the load when a very
low impedance power supply is used.
GND ≥GND
GND
L
Please note that is this configuration, the GND voltage of the load must not be below
the GND of the chip. Otherwise, a parasitic diode between GND and OUT turns on
and can be damaged. Thus, always connect the GND of the load directly with the
GND of the chip.
Figure 6: epc701 or epc703 using internal switch
to drive a load of up to 50mA /30VDC
epc701 or epc703 Using an External Switching Transistor
Figure 7 shows the operation mode using an external switch T1 in order to extend the
output current/voltage drive capability. In this example, a bipolar transistor is used,
whereas the base current is limited by the resistor RB. The maximum base current is
50mA. In order not to damage the chip, the user has to select the resistor R B such that
chip does not need to drive more than 50mA. Other possible switches are a NPN BJT
or an n-channel MOSFET.
VDD
C
RSENSE
VDD
T
R
T
STATUS
IN
SENSE
OUT
The load is turned on and off by setting the pin IN to high respectively to low level.
When the load is turned on, the load current flows from VDD through the resistor RS
and through transistor T1 to GNDExt. This current creates a voltage drop over RS. The
resulting voltage is applied to pin SENS, which measures the voltage drop. If it
exceeds the threshold of an internal comparator, set to -200mV referenced to VDD, the
output is turned off after the given delay time tdel. If the delay time should be extended
to a value above the possible settings of tdel (refer to Table 3), an RC network can
added, designated as RT and CT in Figure 7. The additional time delay can be calcu-
lated approx. as RT x CT. However, the time varies according to the current through
RS. This design concept is especially useful, when a large capacitor in the load path
needs to be charged. The additional delay in the over-current detection helps in such
a situation.
R1
T1
epc701
epc703
D
R
L
GND
L
GND
GND
L
Note that GND of the chip and GNDExt on the load are different in most of the applica-
tions. The value of VDD to the chip GND must be between 9.6 and 30V. GNDExt of the
load instead, can be on a level which is appropriate to the external switching tran-
sistor.
Figure 7: epc701 or epc703 using
an external switching transistor.
In case of a short-circuit in the load the turn-off delay
can be extended by an external RC network.
This network adds text to the internal delay tdel.
The diode D1 is to protect the transistor T1 against voltage surges when inductive
loads are turned off.
© 2011 ESPROS Photonics Corporation
Characteristics subject to change without notice
6
Datasheet epc701_703 - V2.2
www.espros.ch
EPC [ ESPROS PHOTONICS CORP ]
