ZSSC3122 Datasheet

© 2018 Integrated Device Technology, Inc.

21

June 8, 2018

10.1 Power-On Sequence

Figure 10.2 shows the power-on sequence of the ZSSC3122. On system power-on reset (POR), the ZSSC3122 wakes as an I2C device

regardless of the output protocol programmed in EEPROM. After power-on reset, the ZSSC3122 enters the command window. It then waits for

a Start_CM command for 3ms if the Fast_Startup EEPROM bit is set or 10ms otherwise (see Table 12.5). If the ZSSC3122 receives the

Start_CM command during the command window, it enters and remains in Command Mode. Command Mode is primarily used in the calibration

environment. See section 11 for details on Command Mode.

If during the power-on sequence, the command window expires without receiving a Start_CM or if the part receives a Start_NOM command in

Command Mode, the device will immediately assume its programmed output mode and will perform one complete measurement cycle. Timing

for the initial measurement is described in section 10.2. At the end of the capacitance DSP calculation, the first data is written to the output

register. Beyond this point, conversions are performed according to the programmed measurement mode settings (see section 10.3).

Figure 10.2

Power-On Sequence with Fast Startup Bit Set in EEPROM

Note: See section 10.2 for timing of the measurement cycle. Timing values shown are typical; for the worst case values, multiply by 1.1

(nominal frequency ±10%).

10.2 Measurement Cycle

Figure 10.3 shows a typical measurement cycle. At the start of a measurement, there is a small wakeup period and then an internal temperature

conversion/temperature DSP calculation is performed followed by a capacitance conversion/capacitance DSP calculation. The length of these

conversions depends on the setting of the Resolution bits (see Table 10.1). The resolution can be found in EEPROM words C_Config and

T_Config (see Table 12.3 and Table 12.4 for bit numbers). Each conversion cycle is followed by a DSP calculation, which uses the programmed

calibration coefficients to calculate corrected temperature and capacitance measurements. In Update Mode, a temperature conversion is not

performed every measurement cycle because it is considered a slower moving quantity. In this case, the measurement cycle timing is the same

as Figure 10.3 without the temperature conversion/ temperature DSP calculation (see section 10.3.1 for more information).

Measurement Cycle

Power applied to device.

Command window starts after

a short power-on-reset window.

1st corrected signal measurement written

to output register (I2C, SPI, PDMs,

Alarms)

Command

Window

Capacitance

Conversion

(Cap Conv)

3ms

When the Fast Startup bit is not set in EEPROM, the

command window is 10ms.

Temperature

Conversion

(Temp Conv)

Temp DSP

Calculation

(Temp Calc)

Cap DSP

Calculation

(Cap Calc)