9
ATA5279/ATA5279C [DATASHEET]
9125P–RKE–05/14
3.5 Coil Current Sensing (Zero Cross, Sample and Hold, Integrator)
The coil current flows through an external shunt resistor, causing a current-dependant voltage, which is fed into the IC via
the VSHS pin. By monitoring the zero crossing events of this signal, the phase of the coil current is known and hence the
positive peak value can be sampled. The VSHS voltage is sampled at T/4 after the zero cross event.
The peak coil current is then subtracted from an internal reference voltage that is dependant on the selected coil current,
which results in the regulation difference.
An amplifier stage converts this difference into a current, which is then fed into an externally applied integration capacitor
connected to the CINT pin. The resulting voltage on this capacitor directly influences the amplitude of the sine wave signal. It
also determines the supply voltage generated by the boost converter, if the necessary coil supply voltage exceeds the actual
supply voltage level. Note that during an active transmission, this voltage is internally limited to VCINT,max.
Note that in idle mode, the voltage on the integration capacitor is kept at a value that corresponds to the battery supply
voltage. This ensures that the boost converter, if needed, always performs a soft start from the battery voltage level on.
The desired current can be selected via the SPI. A total of 20 predefined steps are available, divided into the following
sections:
●The lower four steps (50mA to 200mA) are intended for the low-current coils only
●The next ten steps (250mA to 700mA) are intended for both types of coils
●The upper six steps (750mA to 1A) are intended only for the high-current coils
The IC allows the use of a current step not intended for a particular driver group; however, in this case, full functionality,
especially a stabilized coil current, cannot be guaranteed. See also the Control Logic block description for an overview over
the commands.
3.6 Diagnosis
The diagnosis stage monitors both the positive (AxP) and negative (AxN) connection lines of the six coils. If one of these
lines is shorted to battery supply or to ground, the following measures are taken for protection and diagnostic reasons:
●All coil driver stages are shut down, i.e., put into high impedance state
●The shunt resistor is disconnected from the coil return lines
●The reason for the fault shutdown is stored in the fault register
●An interrupt request is triggered (see also control logic block)
In addition to short circuits, a disconnected coil (i.e., open load) or an excessive junction temperature can also lead to such a
fault shutdown.
Note that this type of diagnosis is carried out continuously during normal operation of the IC to protect both the IC and the
peripherals from damage.
It must be avoided to design the system's load profile in such a way that the protection features of the chip are triggered
under normal operating conditions. Consecutive triggering of the overtemperature shutdown may lead to a reduced lifetime.
In the event of such a fault shutdown, the IC can be brought back to operation by resetting its fault register with the
appropriate SPI command (please refer also to the Section 3.9.2 “General Command Description” on page 20 later in this
document). As a result, transmission on non- faulty coils is still possible even if there is a failure of one coil.
Beyond this, the diagnosis of all connected coil lines is a very useful tool for maintenance reasons. The Atmel® ATA5279 has
implemented test structures that can be activated and read out via SPI commands, so that the microcontroller can be
programmed to detect most of the possible faults, for example, shorts between different coil connection lines and multiple
shorts in one pair of lines.