4.6 Over Temperature Protection

L7250 has a temperature protection circuit consisting of a temperature sense circuit and two comparators. The temperature sense circuit generates a voltage proportional to the absolute die temperature. One comparator trips when the die temperature exceeds 140 deg C, asserting the temperature warning signal in the status register (ThWarn in the Reg 00H -> b3). The thermal warning comparator has nominally 20 deg C hysteresis.

The thermal Shutdown comparator trips when the die temperature exceeds 160 deg C, indicates an over temperature condition in the status register (ThShutdown in the Reg00H -> b4). The status register is transparent to the thermal shutdown information.

If the ThShutdown bit is equal to zero only the flag on the status register is activated, else the L7250 is driven into thermal shutdown mode, which initiates Unload of the Voice Coil Motor (no actions on the Spindle motor has been taken). Hysteresis of 25 deg C on this comparator allows the die temperature to stabilize before it is re-enabled.

If the ThShutdown bit is set to 1, the thermal Shutdown condition is latched, then to re-enable the function a reset cycle is needed (ThShutdown bit must be programmed to 0, then set again to 1).