3.2
Operations
3.2.1
Power-on and testing environment
Connect a 50 V power supply to CN3, the load on CN4. The telecommand section is not activated in this
evaluation board. The analog and digital telemetries are accessible on the R
TM
and R
STS
resistors respectively.
Figure 6.
Testing environment
3.2.2
Trip-on and trip-off time programming
In re-triggerable mode, if the duration of the overcurrent is greater than the trip-off time T
ON
, the external
MOSFET is switched OFF after the T
ON
time has elapsed and stays OFF for the recovery time T
OFF
. When the
T
OFF
time elapses, the device restarts autonomously to its normal condition, turning on again the MOSFET, if the
current limitation cause is removed. Otherwise it switches cyclically on and off again while the overload persists
(hic-up mode).
The trip-off time T
ON
is set by the C
ON
capacitor connected between the pins T
ON
and GND, and it is calculated
by the following equation:
TON = RIR*CON
(7)
In the same way, the recovery time T
OFF
is set through the external capacitor C
OFF
connected between the pins
T
OFF
and GND. The C
OFF
capacitor is charged with a constant current whose value is a fraction (typ. 1/20) of I
REF
current (externally set by the resistor R
IR
connected between the I_REF pin and GND). The charging phase of
C
OFF
capacitor starts as soon as the T
ON
time has elapsed, therefore the T
OFF
time is equal to the C
OFF
charging
time defined by:
TOFF = 20*RIR*COFF
(8)
In the equations above, unit for T
ON
and T
OFF
are in seconds, for resistance in Ω and for capacitance in Farads.
The typical behavior of the device configured in re-triggerable mode is depicted below (timing is not in scale).
UM2605
Operations
UM2605
-
Rev 1
page 7/27