L9780 datasheet(17/56 Pages) STMICROELECTRONICS

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L9780

Main functionalities

depend on the VCCS output current multiplied by a resistance value (the resistance of the

pump cell in SNS voltage case and the Rtot resistance in the voltage drop case); from the

same figure it is evident that the maximum SNS voltage dynamic range compatible with

L9780 VCCS architecture is -2 V < SNS < 2.4 V and the maximum drop allowed on Rtot (or

Rout if TG switch is off) is 1.8 V.

Figure 7. VCCS characteristic

At the startup of the device, VCCS structure is disabled by default, that means that all its

pins are in high impedance condition and the “parking functionality” is active; in other words,

the parking amplifier is switched on and a voltage similar to REF2 is present on C3 pin (see

block diagram in Figure 2). Besides, a pull-down resistor is internally connected by default

from OUT1 pin to GNDA; this is done to avoid that a leakage current can increase the

voltage value of VCCS pins until the short to battery condition. When VCCS is enabled or a

sensor short to battery condition is detected, the pull-down resistor is automatically

disconnected from OUT1 pin; when VCCS is disabled and no fault conditions are present,

VCCS pull-down resistor can be re enabled via SPI (using bit VCCSPD).

If no sensor short to battery condition is present, VCCS structure can be enabled and the

output channel selected with an SPI frame (using bits VCCSEN and VCCSOUT); in this

case the “parking functionality” is disabled. When VCCS is enabled, it is also possible to

activate/deactivate clamp functionality via SPI (using bit CLAMPEN), in order to protect the

sensor; when the clamp functionality is activated, a voltage control is enabled on SNS pin

and, if its value is going to exceed the voltage range defined by the user, the clamp circuit

intervenes in order to modify the VCCS output current and make SNS pin reenter the clamp

limits. The clamp limit range can be symmetric or asymmetric; the desired kind of range can

be defined via SPI (bit CLAMPSIM). In case of symmetric range, if VCL is the clamp voltage

defined by the user, the consequent range allowed for SNS voltage is:

-VCL < SNS < +VCL, with 0.75V<VCL<2V

In case of asymmetric range, if VCL is the clamp voltage defined by the user, the

consequent range for SNS voltage is:

-0.8333*VCL < SNS < +VCL, with 0.75 V < VCL < 2.4 V

If the clamp circuit is activated and intervenes while VCCS is working, it is visible also via

SPI because CLAMP bit in SO register is kept = 1 until the clamp circuit is acting during

VCCS activation. The clamp voltage VCL is defined by the user and is equal to the voltage

applied on CL1 or CL2 pin; the input channel chosen to read the clamp voltage can be

selected via SPI (bit CLAMPCL); the non selected pin can be left open.

L9780 Datasheet(PDF) 17 Page - STMicroelectronics