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L9821 Datasheet(PDF) 4 Page - STMicroelectronics |
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L9821 Datasheet(HTML) 4 Page - STMicroelectronics |
4 / 7 page FUNCTIONAL DESCRIPTION The L9821is a high sidedrive monolithic switch, dri- ven by TTL, CMOS input logic, able to supply resi- stive or inductive loads up to 6A DC allowing a current peak of 25A with a RDS(ON) = 0.1. The elec- tronicswitch, in additionto its main function,protects itself, the power network and the load against load dump (up to 60V) and overload and it detects short circuit, open load and overtemperature conditions. All these functions (logic control and power actua- tion) are possible on a singlechip thanks to the new mixed ST MultipowerBCD technologythat allows to integrate isolated DMOS power transistors in com- binationwith Bipolarand CMOS signal structureson the same chip. The high side drive connection (series switch bet- ween the load and the positive power source)is par- ticularlysuited in automotiveenvironmentwherethe electrochemical corrosion withstandinghas primary importance. For this connection the best solution is a Power MOS N-channel which requires for driving only a capacitive charge pump completely integra- ted on the switch chip. The L9821 is based on a power DMOS series ele- ment, a driving circuit with a charge pump, an input logic interface and on some protection and fault de- tection circuits. The power DMOS transistor has a RDS(ON) = 0.1 Ω (typ. value @ TJ =25 °C, VGS = 10V). The low value of RDS(ON) is important both to increase the power transferred to the load and to minimize the power dissipated in the device. The charge pump is a capacitivevoltage tripler star- ting from power supply (car battery), driven by a 500kHz oscillator. The input interface is based on a circuitry solution able to guarantee the stability over temperature of the TTL logic levels and very low quiescent current in OFF condition. When the supply reaches the maximum operating voltage (32V) the device is turned OFF, protecting itself and the load ; moreoverlocal zener clamps are provided in some critical points to avoid that VGS of any MOS transistor could reach dangerous values even during 60V load dump transient. The inrush current limiting is a significant feature of the L9821. This functionallows to protect the power supply network and may extend the life of the loads. For example, in the case of the lamps, the tungsten wire resistance value in cold condition is about one tenth of the nominal steadystate and then the inrush current during the turn on is statistically one of the main causes of lamps failures. If the high current condition persists (e.g. load short circuit) and the junctiontemperaturerises above150 °C,the thermal protection circuit turns off the device preventingany damage. The current limiting and the thermal shut- down are sufficient to protectthe device againstany overload becausethe power DMOS has not the se- cond breakdown. When the L9821 is driven and one of the protec- tions (overtemperature, overvoltage, overload) is present, a fault detection open drain output turns on. This output is active also when Iload is lower than 0.6A detecting the open load (disconnected or burned out). The diagnostic output detects fault conditions with 25ms delay in order to avoid spu- rious diagnosys (i.e. : turn on overcurrent, overvol- tage spikes etc.). In OFF conditions the fault detection circuits are not active to allow a minimum quiescent current. The device can drive unipolar DC motors and sole- noids as well becauseit can recirculate an inductive current when the output voltage goes lower than Vclamp value (typically - 6.5V in respect to ground). The possibility to have a start up current is useful also for DC motors allowing the maximum starting torque. TYPICAL APPLICATION OF THE L9821 The L9821 integrated high side driver can be used to replace an electromechanical relay. Inductiveload (i.e. solenoids,motors) can be driven by the L9821. No externalcomponents are required for the coil current recirculation, because the device provides this function internally. L9821 4/7 |
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