L9780 datasheet(13/56 Pages) STMICROELECTRONICS

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L9780

Main functionalities

4.4

Power on reset

A power on reset (POR) circuit is present into the device; this circuit monitors VCCA,

VCCCP, VCCD, GNDA, GNDCP, GNDD voltage levels. If one of the supplies falls below (or

one of the grounds exceeds) the defined POR threshold (defined in Table 10) all the outputs

are driven in inactive state, all the registers are set at their default state and the time state

machine and all the timers are fixed in the reset state. All these actions are applied after a

typical filter time of 15 μs (possible range is defined in Table 15). When the supply that has

caused POR condition reaches POR value plus hysteresis (or the ground decreases under

POR threshold) all the outputs are re-enabled.

During reset condition an internal switch connects the charge pump output voltage (CP pin)

to GNDA.

4.5

Pin INRC functionalities: INRC amplifier, clean currents, pull-

down current

Pin INRC in the application is connected to the sensor reference cell; the voltage generated

by this cell and applied on L9780 INRC pin is a function of the

parameter of the sensor and

gives information about how much the λ parameter is far from the target value. The final

purpose is to obtain λ =1, that in terms of electrical parameters means to have 450 mV as

output of the reference cell (and applied on INRC pin). In the device this pin is the input of

an amplifier (INRC amplifier) with gain selectable via SPI (using bit INRCGAIN). The output

of this amplifier is one of the multiplexed inputs of the A/D converter (in order to give the μP

the estimation of the λ parameter of the sensor via SPI) and is also internally connected by

a switch (INRC switch) to C1A or C1B pin and the external compensation network. The

selection of channel A or B is possible using bit COMPSEL. Electrical parameters of INRC

amplifier and INRC switches are specified in Table 10.

On INRC pin is present a diagnostic circuitry able to detect short to battery/ground

conditions and communicate it via SPI (bits STBS2 and STGRC of SPI output register);

short to battery detection is always enabled, while the short to ground detection is disabled

by default; it can be enabled using bit STGINRC. INRC short to battery/ground thresholds

typical values are 3.2 V and 200 mV (possible ranges are defined in Table 13). The

consequences of the detection of each one of these faults are described in Section 5.1 and

5.2.

The INRC pin is connected to the clean current generator: it is a pull-up current source used

to clean the air reference of the sensor; the generated current value is selectable via SPI

(using bits CCS[3..0]). Possible clean current values are specified in Table 10.

On the same pin a 500 μA pull-down current source is also available, used in order to

prevent the presence of false short to battery detection due to capacitive commutations. The

activation of this current is selectable via SPI (bit INRCPD); pull-down current range is

specified in Table 10.

A detailed bit description is present in Section 6.3 and 6.4.

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