Datasheet

TMC262 / TMC262C DATASHEET (Rev. 2.22 / 2019-FEB-22) 43
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11 Diagnostics and Protection
11.1 Short Protection
The TMC262 protects the MOSFET power stages against a short circuit or overload condition by
monitoring the voltage drop in the high-side MOSFETs (Figure 11.1). The TMC262C also allows
monitoring the voltage drop in sense resistor and low-side MOSFETs. A programmable short detection
delay (shortdelay) allows adjusting the detector to work with different power stages and load
conditions. Additionally, the short detection is protected against single events, e.g. caused by ESD
discharges, by retrying three times before switching off the motor continuously. The low side short
detector provides a good overcurrent detection. It needs to be explicitly enabled by programming.
The short detection status is indicated by two bits:
Status
Description
Range
Comment
S2GA
These bits identify a short to GND condition on
coil A and coil B persisting for multiple chopper
cycles. The bits are cleared when the MOSFETs
are disabled. For TMC262C, a short detected on
the low-side also is signaled by these bits.
0 / 1
0: No short detected.
1: Short condition
detected.
S2GB
An overload condition on the high-side MOSFET (“short to GND”) is detected by monitoring the coil
voltage during the high-side on phase. Under normal conditions, the high-side power MOSFET reaches
the bridge supply voltage minus a small voltage drop during the on-phase. If the bridge is
overloaded, the voltage cannot rise to the detection level within the time defined by the internal
detection delay setting. When an overload is detected, the bridge is switched off. The short to GND
detection delay needs to be adjusted for the slope time, because it must be longer than slope, but
should not be unnecessarily long.
Short
detection
Valid area
BMxy
Hxy
V
VS
-
V
BMS2G
0V
0V
V
VS
t
S2G
BM voltage
monitored
Short to GND
monitor phase
Driver
enabled
0V
t
S2G
Short detecteddelaydelay inactiveinactive
Short to GND
detected
Driver off
Figure 11.1 Short to GND detection timing
TMC262C allows short to supply detection in the same way, by measuring voltage drop across sense
resistors plus low-side MOSFETs during the conduction phase. As the low-side short detection includes
the sense resistor, it is sensitive to the actual sense resistor and provides a good precision of
overcurrent detection. This way, it will safely cover most overcurrent conditions. For compatibility,
short to VS protection is disabled by default.