MC33927 Datasheet, PDF (26/44 Pages) Freescale Semiconductor, Inc – Three-Phase Field Effect Transistor Pre-Driver

FUNCTIONAL INTERNAL BLOCK DESCRIPTION
INTRODUCTION
DRIVER FAULT PROTECTION
The 33927 IC integrates several protection mechanisms
against various faults. The first of them is the Current Sense
Amplifier with the Overcurrent Comparator. These two blocks
are common for all three driver phases.
Current Sense Amplifier
This amplifier is usually connected as a differential
amplifier (see Figure 9). It senses a current flowing through
the external FETs as a voltage across the current sense
resistor R_SENSE. Since the amplifier common mode range
does not extend below ground, it is necessary to use an
external reference to permit measuring both positive and
negative currents.
The amplifier output can be monitored directly (e.g. by the
microcontroller’s ADC) at the AMP_OUT pin, providing the
means for closed loop control with the 33927.
The output voltage is internally compared with the
Overcurrent Comparator threshold voltage (see Figure 17).
Overcurrent Comparator
The amplified voltage across the Rsense is compared with
the pre-set threshold value by the Overcurrent Comparator
input. If the Current Sense Amplifier output voltage exceeds
the threshold of the Overcurrent Comparator it would change
the status of its output (OC_OUT pin) and the fault condition
would be latched (see Figure 15).
The occurrence of this fault would be signalled by the
return value of the Status Register 0. If the proper Interrupt
Mask has been set, this fault condition will generate an
interrupt - the INT pin will be asserted High. The INT will be
held in the High state until the fault is removed, and the
appropriate bit in the Status Register 0 is cleared by the
CLINT0 command. This fault reporting technique is
described in detail in the Logic Commands and Registers
section.
Desaturation Detector
The Desaturation Detector is a comparator integrated into
the output driver of each phase channel. It provides an
additional means to protect against “Short-to-Ground” fault
condition when the output node gets shorted to the supply
voltage (short across the high-side FET).
Figure 13. Short to Ground Detection
When switching from low-side to high-side, the high-side
will be commanded ON after the end of the deadtime. The
deadtime period starts when the low-side is commanded
OFF. If the voltage at P_{X-HS_S} is less than 1.4V below V_BAT
after the blanking time (t_BLANK) a desaturation fault is
initiated. An additional 1ms digital filter is applied from the
initiation of the desaturation fault before it is registered, and
all phase drivers are turned OFF (placed in a high impedance
state). If the desaturation fault condition clears before the
filter time expires, the fault is ignored and the filter timer
resets.
Valid faults are registered in the fault status register, which
can be retrieved by way of the SPI. Additional SPI commands
will mask the INT flag and disable output stage shutdown,
due to desaturation and phase errors. See the Logic
Commands and Registers section for details on masking INT
behavior and disabling the protective function.
33927
26
Analog Integrated Circuit Device Data
Freescale Semiconductor