AMIS-30421 Datasheet, PDF (23/41 Pages) ON Semiconductor – Micro-Stepping Stepper Motor Bridge Controller

AMIS−30421
WARNING, ERROR DETECTION AND DIAGNOSTICS FEEDBACK
Thermal Warning and Shutdown
AMIS−30421 has 4 thermal ranges which can be read out
through SPI bits <TR[1:0]> and <TSD>. Thermal Range 1
goes from −40°C up to T₁. Thermal Range 2 goes from T₁
to T₂ and Thermal Range 3 goes from T₂ up to T₃ (T₁, T₂ and
T₃ can be found in Table 4). Once above T₃ the 4^th thermal
level is reached which is the thermal warning range.
When junction temperature rises above T_TW (= T₃), the
ERRb−pin will be activated. If junction temperature
increases above thermal shutdown level (T_TSD), then the
circuit goes in Thermal Shutdown Mode and all driver
transistors are disabled (high impedance). The condition to
get out of the Thermal Shutdown Mode is to be at a
temperature lower than T_TW and by clearing the <TSD> SPI
bit.
T_TSD
ÏÂÏÂ _{T3= TTW}
ÈÈÏÂÈÈÏÂ _T2
ÇÇÈÇÇÈ _T1
ÀÀÀÇÀÀÀÇ _{−40°C}
Thermal Range 4 = Thermal Warning (ERRb−pin active)
Thermal Range 3
Thermal Range 2
Thermal Range 1
Figure 22. Thermal Ranges
Over−Current Detection
The over−current detection circuit monitors the load
current in each activated output stage. If the load current
exceeds the over−current detection threshold, the ERRb−pin
will be activated and the drivers are switched off (motor
driver disabled) to reduce the power dissipation and to
protect the H−bridge. Each driver has an individual
detection bit (see Status Register 1 and 2). The error
condition is latched and the microcontroller needs to read
out the error to reset the error and to be able to re−enable the
motor driver again.
Note: Successive resetting the motor driver in case of a short
circuit condition may damage 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 a certain time, an open coil will be latched (see
Status Register 1 and 2) and the ERRb−pin will be activated
(drivers are disabled). The time this 100% duty cycle needs
to be present is adjustable with SPI bits
<OPEN_COIL[1:0]>. A short time will result in fast
detection of an open−coil but could also trigger unwanted
open−coil errors. Increase the timing if this is the case.
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 the ERRb−pin will flag this situation. 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.
Note: A short circuit could trigger an open coil.
Charge Pump Failure
The charge pump is an important circuit that guarantees
low R_DS(on) for all external MOSFET’s, especially for low
supply voltages. If supply voltage is too low or external
components are not properly connected to guarantee a low
R_DS(on) of the drivers, a charge pump failure is latched
(<CPFAIL>), the ERRb−pin is activated and the driver is
disabled (<MOTEN> = ‘0’). One needs to read Status
Register 1 to clear the charge pump failure.
After power on reset (POR) the charge pump voltage will
need some time to exceed the required threshold. During that
time the ERRb−pin will be active but not latched for 250us.
If the slope of the power supply V_BB is slow during power
up (charge pump not started after 250 ms), a charge pump
failure will be latched and the ERRb−pin is activated (see
also Figure 23).
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