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 MOTOR DRIVER L9997 FOR DOOR CONTROL SYSTEMS Years ago, a car door was considered as a "chip free" area, but today a whole series of electronic functions activate the car door: lock control, mirror and window winders. Small DC motors activated by buttons on a joy-stick, now control the outside mirrors giving the driver an optimal view. ST's economic smart power circuit, the L9997ND is an optimum solution for these tasks. The device includes two DMOS half bridges with an on resistance of 800m½ per transistor - either one motor in a bridge configuration or two motors with the support of another external half bridge.  For maximum flexibility, each half bridge has a separate control input and a common enabling pin provides maximum flexibility by activating both half bridges. In low status the end stages are in tristate mode so the IC is in standby mode and consumes very little quiescent current. Operation over pin 30 is thus possible. Shorts to Vbatt, ground or over the load are no problem, since a current limiter as well as overtemperature protection ensure safe operation even under these circumstances. Should an overload occur, activating the overtemperature protection, this is communicated via an open drain diagnostic output to the microcontroller. The bridge stage is dimensioned so that simultaneous operation of both mirror motors uses minimum power consumption -- significantly below 1W. A circuit board cooling over the 8 middle connections of the SO20 package is hence sufficient.  |
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