TLE7185-1E Datasheet, PDF (14/23 Pages) Infineon Technologies AG – 3-Phase Bridge Driver IC

TLE7185-1E
5.2
Protection and Diagnostic Functions
5.2.1 Short Circuit Protection
The TLE7185-1E provides a short circuit protection for the external MOSFETs. It is a monitoring of the drain-
source voltage of the external MOSFETs. As soon as this voltage is higher than the short circuit detection level, a
timer will start to run.
The short circuit detection level is programmable from outside by applying a voltage divider at the SCDL pin. The
applied voltage at this pin will be used as short circuit detection level up to the specified maximum level. Above
this level the short circuit detection is deactivated.
After a delay t_SCP all external MOSFETs will be switched off until the driver is reset by the ENA pin. The error flag
is set.
The drain-source voltage monitoring of the short circuit detection for a certain external MOSFET is active as soon
as the corresponding input is set to "on" and the dead time is expired.
For safety reasons a pull up resistor at the SCDL pin assures that in case of an open pin the SCDL voltage is pulled
to high levels. In this case, the SCD is deactivated an error signal is set. This function is self clearing when the
voltage at SCDL returns to the specified level.
The short circuit detection filter is realized with a capacitor, which is discharged with a current source with X µA.
In case the output stage is switched on and the VDS of the MOSFET is still above SCDL, the capacitor is charged
with a current source with Y µA. If this capacitor is charged to a specific voltage level, the short circuit is detected,
the ERR signals are set and the MOSFETs switched off. The SCD charge and discharge ratio is defined as
(Y-X)/X.
This ratio defines down to which duty cycle the short circuit can be detected.
It has to be considered that the high side and the low side output of one phase are working with the same capacitor,
defining the maximum switching time, which is allowed without short circuit detection. This maximum allowed
switching time in normal operation is defined by d_noSCD/2*f_PWM.
This behavior is specified as “maximum duty cycle for no short circuit detection” and “minimum duty cycle for
periodic short circuit detection”
5.2.2 Dead Time and Shoot Through Protection
In bridge applications it has to be assured that the external high side and low side MOSFETs are not "on" at the
same time, connecting directly the battery voltage to GND. The dead time generated in the TLE7185-1E is fixed
to a minimum value if the DT pin is connected to GND. This function assures a minimum dead time if the input
signals coming from the µC are faulty.
The dead time can be increased beyond the internal fixed dead time by connecting the DT pin via a dead time
resistor R_DT to GND - the larger the dead time resistor the larger the dead time (for details pls. see the “Dynamic
Characteristic” table in the MOSFET driver section).
The exact dead time of the bridge is usually controlled by the PWM generation unit of the µC.
In addition to this dead time, the TLE7185-1E provides a locking mechanism, avoiding that both external
MOSFETs of one half bridge can be switched on at the same time. This functionality is called shoot through
protection.
If the command to switch on both high and low side switches in the same half bridge is given at the input pins, the
command will be ignored.
Data Sheet
14
Rev. 2.4, 2010-07-16