In just a few decades, we’ve come a long way from the days of manually operated car windows, door mirrors and door locks. Now they are all electrically powered without manual binding. Managing and delivering controlled power to the various motors and mechanisms used in the complex door system and its accessories – and it really is a system – is a considerable design challenge.
This is where the STMicroelectronics L99DZ200G the IC door zone system offers a solution. This device allows a single-chip “front-to-rear drives” arrangement to manage a front window, mirror and door light, as well as the rear window regulator. It does this with lower quiescent current, greater reliability, faster assembly, reduced material BOM, and shorter development time than alternative solutions.
A quick history lesson
A historical perspective can be helpful here:1-3 Until about 50 years ago, all car windows were manually operated via a mechanical linkage operated by a simple ‘hand-operated’ rotating crank officially called a ‘window regulator’. Each car occupant had to manage their own window using their arm as a power source (Fig.1)and even the driver of the car could only do the adjacent window rather than all four.
Power windows were first introduced in the 1940s and initially used an electrically operated hydraulic system; small electric motor technology (size, power and control) was not advanced enough to allow the motors to be built into the door. The mechanism that moves the window up and down is called the window regulator. Two basic types of window regulators are used: the cable type and the gear type.
By the 1960s, however, the Cadillac Fleetwood came standard with windows powered only by electric motors, and within a decade or so power windows were a standard feature on most cars – a fairly rapid rate of adoption. in the mass market.
At the turn of the century, the car door was transformed into a complex electromechanical subsystem with all functions electronically activated and electrically implemented. (Fig.2), without a fully mechanical backup system. (There was an intervening period when doors and windows had electrical and mechanical control, to overcome customer hesitation and provide a comfort factor.) Today’s car door subsystems are so advanced that they even have application-specific voltage monitors.4
The Door-Zone integrated circuit
The L99DZ200G incorporates two configurable half-bridges (7.5 A), two further half-bridges (0.5 A), a gate driver for an external MOSFET to control mirror heating, a control block, and a side driver. high for mirror electrochromic dimming, and five high-end LED drivers (Fig.3).
Three of the high-side drivers can operate in constant current mode to power lighting modules that have high input capacity; the other two high-side drivers are suitable for controlling ordinary LEDs. The L99DZ200G also provides power management, with two 5V low-dropout regulators for the host microcontroller and peripherals. Connections for control and communication include a LIN 2.2a transceiver, a high-speed CAN transceiver and an SPI 4.0 interface.
With its two bridge drivers, the L99DZ200G is able to simultaneously control two spindle motors and manage a third so-called “cinch” motor to close a motorized tailgate or trunk. This three-motor control can be used to automatically open and close the car’s electric trunk.
To achieve this, the two spindle motors work in parallel and in the same direction to move the trunk door up and down, while the cinch motor is activated after the trunk movement is complete to lock/unlock the trunk door . Both drivers enable generator-mode operation, which simultaneously activates both low-side MOSFETs to protect the device if an overvoltage is detected in the power rail.
This last point is linked to a subtlety that highlights the reality of the transition from design to a real production line. Automakers have traditionally had to protect their motorized trunk drivers from manual manipulation at the end of the manufacturing process: when machines or workers manually lift the trunk, it automatically spins the motors and turns them into a generator that creates a spike of voltage on the pin of the driver IC, which can then destroy this component.
Protective Features
To solve this problem, designers add appropriate protection components. The L99DZ200G offers a new solution in the form of generator mode, which activates the device’s low-side external MOSFETs when the motors begin to act as a generator. When this happens, the device locks the motors to prevent a voltage spike. Thus, designers no longer need to add external components to deal with this particular situation.
Diagnostic and protection features include temperature monitoring and thermal protection, a dedicated safety block to pull down the gates of high-side external MOSFETs, and open load and overcurrent detection for all outputs. A current monitor output pin is provided for each high side channel. Overcurrent recovery and thermal timeout allow operation to resume automatically after a fault.
There are also reverse battery protection and system safety features, including a configurable window watchdog and a programmable reset generator. The device meets automotive standards as it tolerates 25 kV on its LIN pin and 15 kV on its CAN pin, eliminating the need for external protection components.
Assessment Board
Designers planning to use a highly functional component such as this would greatly benefit from a convenient way to set it up and use it. That’s why ST offers the EVAL-L99DZ200 evaluation committee (Fig.4)with documentation including schematics, board layer drawings and bill of materials.
The system sits on a motherboard (150×120mm) with an SPC582B60 microcontroller, while the L99DZ200G resides on a 36.8×35.6mm daughterboard (Fig.5). The platform includes reverse battery protection and two full bridges made up of four power MOSFETs. The STSW-L99DZ200 Graphical User Interface allows the user to set L99DZ200G control parameters and simultaneously display real-time diagnostic information in the form of current output and battery voltage monitoring.
The AEC-Q100 qualified L99DZ200G is currently in production, packaged as a 10×10mm LQFP64 device. Prices start from $4.20 for orders of 1000 pieces. the Home page L99DZ200G includes links to 198-page data sheet (yes, it’s 198 pages), various application notes including a full 22-page TN1354 technical note”L99DZ200G driving three motors with two H-bridges: configuration and use cases,” and more. There’s also an insightful blog post”L99DZ200G: how a front door driver can also power a rear window, electric trunk, etc..”
The references
1.GoMechanic,”Power windows in cars and the interesting history behind them”
2. Wikipedia, “Electric window”
3. Samarins, “Power window, window motor: problems, testing, replacement”
4. Maxim Integrated/Analog Devices, “MAX16137 – 1% Accuracy Single Window Voltage Monitor with BIST”
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