AMIS−30532
www.onsemi.com
18
PWMsh
Icoil=0
SLAT
SLA−pin
SLAT=0 => SLA−pin is not ”transparent” during
V
BEMF
sampling @ Coil Current Zero Crossing.
SLA−pin is updated when leaving current−less state.
SLAT=1 => SLA−pin is ”transparent” during
V
BEMF
sampling @ Coil Current Zero
Crossing. SLA−pin is updated ”real−time”.
last sample
is retained
retain last sample
previous output is kept at SLA pin
buf
Ssh Sh
Ch
Csh
SLAT
NOT(Icoil=0)
Icoil=0
PWMsh
SLA−pin
V
COIL
div2
div4
V
BEMF
t
t
V
COIL
Figure 15. Timing Diagram of SLA−pin
Warning, Error Detection and Diagnostics
Feedback
Thermal Warning and Shutdown
When junction temperature rises above T
TW
, the thermal
warning bit <TW> is set (Table 16 SPI Status registers
Address SR0). If junction temperature increases above
thermal shutdown level, then the circuit goes in “Thermal
Shutdown” mode (<TSD>) and all driver transistors are
disabled (high impedance) (see Table 16 SPI Status registers
Address SR2). The conditions to reset flag <TSD> is to be
at a temperature lower than T
TW
and to clear the <TSD> flag
by reading it using any SPI read command.
Overcurrent Detection
The overcurrent detection circuit monitors the load
current in each activated output stage. If the load current
exceeds the overcurrent detection threshold, then the
over−current flag is set and the drivers are switched off to
reduce the power dissipation and to protect the integrated
circuit. Each driver transistor has an individual detection bit
in (see Table 16 SPI Status registers Address SR1 and SR2:
<OVCXij> and <OVCYij>). Error condition is latched and
the microcontroller needs to clean the status bits to reactivate
the drivers.
Note: Successive reading the SPI StatusRegisters 1 and 2 in
case of a short circuit condition, may lead to damage to the
drivers.
Open Coil/Current Not Reached Detection
Open coil detection is based on the observation of 100%
duty cycle of the PWM regulator. If in a coil 100% duty cycle
is detected for longer than 200 ms then the related driver
transistors are disabled (high−impedance) and an
appropriate bit in the SPI status register is set (<OPENX> or
<OPENY>). (Table 16)
When the resistance of a motor coil is very large and the
supply voltage is low, it can happen that the motor driver is
not able to deliver the requested current to the motor. Under
these conditions the PWM controller duty cycle will be
100% and after 200 ms the error pin and <OPENX>,
<OPENY> will flag this situation (motor current is kept
alive). This feature can be used to test if the operating
conditions (supply voltage, motor coil resistance) still allow
reaching the requested coil−current or else the coil current
should be reduced.
Charge Pump Failure
The charge pump is an important circuit that guarantees
low R
DS(on)
for all drivers, especially for low supply
