FUNCTIONAL DESCRIPTION
The device has a diagnostic output which
indicates open load in on-state, open load in
off-state, over temperature conditions and
stuck-on to V
CC
.
From the falling edge of the input signal, the
status output, initially low to signal a fault
condition (overtemperature or open load
on-state), will go back to a high state with a
different delay in case of overtemperature (tpovl)
and in case of open open load (tpol) respectively.
This feature allows to discriminate the nature of
the detected fault. To protect the device against
short circuit and over current condition, the
thermal protection turns the integrated Power
MOS off at a minimum junction temperature of
140
o
C. When this temperature returns to 125
o
C
the switch is automatically turned on again. In
short circuit the protection reacts with virtually no
delay, the sensor being located inside the Power
MOS area. An internal function of the devices
ensures the fast demagnetization of inductive
loads with a typical voltage (V
demag
) of -18V. This
function allows to greatly reduces the power
dissipation according to the formula:
P
dem
= 0.5
•
L
load
•(Ι
load
)
2
•
[(V
CC
+V
demag
)/V
demag
]
•
f
where f = switching frequency and
V
demag
= demagnetization voltage.
The maximum inductance which causes the chip
temperature to reach the shut-down temperature
in a specified thermal environment is a function of
the load current for a fixed V
CC
, V
demag
and f
according to the above formula. In this device if
the GND pin is disconnected, with V
CC
not
exceeding 16V, it will switch off.
PROTECTING THE DEVICE AGAINST
REVERSE BATTERY
The simplest way to protect the device against a
continuous reverse battery voltage (-26V) is to
insert a Schottky diode between pin 1 (GND) and
ground, as shown in the typical application circuit
(fig.3).
The consequences of the voltage drop across this
diode are as follows:
If the input is pulled to power GND, a negative
voltage of -V
f
is seen by the device. (Vil, Vih
thresholds and Vstat are increased by Vf with
respect to power GND).
The undervoltage shutdown level is increa- sed
by Vf.
If there is no need for the control unit to handle
external analog signals referred to the power
GND, the best approach is to connect the
reference potential of the control unit to node [1]
(see application circuit in fig. 3), which becomes
the common signal GND for the whole control
board avoiding shift of V
ih
, V
il
and V
stat
. This
solution allows the use of a standard diode.
Switching Time Waveforms
VND05BSP
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