L9780 datasheet(22/56 Pages) STMICROELECTRONICS

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Main functionalities

L9780

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DocID026356 Rev 3

4.12

Timing state machine

The internal temporization of A/D conversion and of the impedance test are defined by an

internal state machine that acts as shown in Figure 8.

Figure 8. State machine diagram

The A/D conversion results give an indication about the

 parameter of the sensor (that is in

relation with INRC pin voltage), about the VCCS output current (from FV voltage evaluation)

and about the sensor temperature (from the double conversion of the output of RCT2

amplifier the external μP is able to evaluate the impedance of the reference cell and

consequently the temperature).

All times are defined in Table 16; some of them (the state machine clock period (Tsmc), the

duration of RCT1 switch and band-gap switch pulses (tR and tB) and the second portion of

INRC switch pulse (tINRC)) can be defined by SPI (using bits MCP[1..0], ITPT[6..0],

CBT[6..0], ISPT[2..0]), while the first portion of INRC switch pulse is determined by the

summation of different events. The SPI selectable variables can not change during the

measurement; if any change occurs while a measurement is on going, the new values will

be applied in the next measurement cycle.

In SO output frame, 3 bits are dedicated to the measurement cycle counter (COUNT[2..0]);

the value measured by the counter is cleared after every power on reset, is automatically

incremented by one at every falling edge of measurement clock and latched in SO output

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