TLE7188F Datasheet, PDF (16/28 Pages) Infineon Technologies AG – 3-Phase Bridge Driver IC

TLE7188F
Protection and Diagnostic Functions
5.2
Protection and Diagnostic Functions
5.2.1 Short Circuit Protection
The TLE7188F 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 limit, a capacitor
will be charged. The high side and the low side output stage of the same half bridge use the same capacitor (see
Figure 3 ). This capacitor is discharged permanently with a current which is smaller than the charging current. This
charge and discharge ratio is specified by means of duty cycles at which a short circuit is detected or not detected.
After a delay of about 12 µs 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.
The short circuit detection level is adjustable in an analogue manner by the voltage setting at the SCDL pin. There
is a 1:1 translation between the voltage applied to the SCDL pin and the drain-source voltage limit. For instance
to trigger the SCD circuit at 1 V drain-source voltage, the SCDL pin must be set to 1 V as well. The drain-source
voltage limit can be chosen between 0.5 ... 2.5 V.
A setting of 5 V at the SCDL pin will disable the short circuit protection function. Disabling the short circuit
protection function has no impact on the overcurrent warning (see next chapter).
5.2.2 Over current Warning
The TLE7188F offers the possibility to shut down the output stages if a current threshold is reached (see Figure 4 ).
The output of the current sense OpAmp is connected to an integrated comparator, comparing the amplified current
sense signal with an external adjustable threshold value. After the comparator a blanking time (1.5 µs typ.) is
implemented to avoid false triggering caused by overswing of the current sense signal.
If the overcurrent situation is detected, only an error signal is given. During overcurrent the driver IC works
normally. The error signal disappears as soon as the current decreases below the overcurrent limit set on the
VTHOC pin. The error signal disappears as well when the current commutates from the low side MOSFET to the
associated high side MOSFET (no current through the shunt resistor).
It is the decision of the user to react on the over current signal by modifying the Ixx patterns to lower the current.
The overcurrent warning can be disabled by connecting the overcurrent threshold pin to GND (V_THOC = 0 V).
5.2.3 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 TLE7188F is fixed to
a minimum value. This function assures a minimum dead time if the input signals coming from the µC are faulty.
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 TLE7188F 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.
5.2.4 Under voltage Shut Down
The TLE7188F has an integrated under voltage shut down, to assure that the behavior of the device is predictable
in all voltage ranges.
Data Sheet
16
V2.1, 2007-06-20