Inverse Operation Behavior
of the BTS6143 and its family members
Inverse operation behavior
Figure 3
shows a typical scope screen shot of this situation.
forward mode
inverse mode
forward mode
voltage across
sense resistor
Current through
DMOS stage
V
IS
I
L
(5A/div)
Varying output
voltage
Varying battery
voltage
V
OUT
V
BB
InverseShort.emf
Figure 3
transient inverse current condition for very short duration
Observation: It can be seen, that due to a variation in the supply voltage, an inverse current condition occurred for
a certain duration (see CH3, 2nd and 3rd division). The duration was short enough to not cause the device to
internally switch OFF. Therefore the output voltage follows the battery voltage before, during and after inverse
operation. The sense reports during inverse operation no current and provides during normal forward load current
condition a defined ratio of the load current.
3.2.1.2
Transient inverse currents
As soon as the inverse current condition lasts for a duration, where the internal switch OFF is reached, the
resulting DMOS power stage voltage will increase from initially -V
DS(inv)
=R
DS(ON)
*(-I
L(inv)
) to finally
V
DS(inv)
=V
BodyDiode
.
The inverse current flow which flowed initially through the activated DMOS power stage (R
DS(ON)
) will finally flow
through the body diode of the DMOS power stage (-V
DS(inv)
=f(-I
L(inv)
)). Such inverse current flow -I
L
through the
body diode of the DMOS power stage will cause a voltage drop -V
DS
(also named -V
ON
,
V
inv
, -V
ON(inv)
) which
depends on the inverse current
I
L(inv)
and the junction temperature
T
j
. The respective values are outlined in the data
sheet. As soon as the inverse current flows across the body diode of the DMOS a parasitic effect in the DMOS
power stage causes a signalling of an “virtual” over temperature event towards the control logic. This “virtual” over-
temperature signal causes the power stage to remain switched OFF until the “virtual” over-temperature signal is
removed. During such inverse operation condition no current will be provided at the diagnosis pin IS except a small
leakage current (see data sheet parameter
I
IS(LH)
). It is important to state, that the “virtual” over-temperature event
can remain for a certain duration even after the transition from inverse load current back to normal forward mode
(see data sheet parameter
t
d(inv)
). Only once the “virtual” over-temperature event is cleared, the power stage will
switch ON.
The pin IS will provide during inverse current condition minimum a leakage current (see data sheet parameter
I
IS(LH)
). Whenever the voltage condition changes from inverse to normal forward mode, the pin IS will report the
“virtual” over-temperature event until the “virtual” over-temperature event signal is cleared. Once the signal is
cleared the power stage will switch ON and the pin IS will provide a defined sense current
I
IS
=+I
L
/K
ILIS
considering
the current sense settling time.
Application Note
5
V1.1, 2008-03-31