TMC249 / TMC249A DATA SHEET (V2.09 / 2009-Jul-30)
13
Open load detection
Open load is signaled, whenever there are more than 14 oscillator cycles without PWM switch off. Note
that open load detection is not possible while coil current is set to “0000”, because the chopper is off in
this condition. The open load flag will then always be read as inactive (“0”). During overcurrent and
undervoltage or over temperature conditions, the open load flags also become active!
Due to their principle, the open load flags not only signal an open load condition, but also a torque loss
of the motor, especially at high motor velocities. To detect only an interruption of the connection to the
motor, it is advised to evaluate the flags during stand still or during low velocities only (e.g. for the first
or last steps of a movement).
Standby and shutdown mode
The circuit can be put into a low power standby mode by the user, or, automatically goes to standby on
Vcc undervoltage conditions. Before entering standby mode, the TMC249 switches off all power
transistors, and holds their gates in a disable condition using high ohmic resistors. In standby mode the
oscillator becomes disabled and the oscillator pin is held at a low state. The standby mode is available
via the interface in SPI-mode and via the ENN pin in non-SPI mode.
The shutdown mode even reduces supply current further. It can only be entered in SPI-mode by pulling
the ENN pin high. In shutdown additionally all internal reference voltages become switched off and the
SPI circuit is held in reset.
Power saving
The possibility to control the output current can dramatically save energy, reduce heat generation and
increase precision by reducing thermal stress on the motor and attached mechanical components. Just
reduce motor current during stand still: Even a slight reduction of the coil currents to 70% of the current
of the last step of the movement, halves power consumption! In typical applications a 50% current
reduction during stand still is reasonable.
Copyright © 2005, TRINAMIC Motion Control GmbH & Co KG
TRINAMIC [ TRINAMIC MOTION CONTROL GMBH & CO. KG. ]
