ZSSC3123 datasheet(39/67 Pages) RENESAS

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ZSSC3123 Datasheet

August 16, 2018

An analog output value is created by low-pass filtering the output; a simple first-order RC filter will work in this application. Select the time

constant of the filter based on the requirements for settling time and/or peak-to-peak ripple.

Important: The resistor of the RC filter must be ≥10k

.

The following table shows some filter examples using a 10k

 resistor.

Table 24. Low Pass Filter Example for R = 10k

Filter Capacitance (nF)

PDM_C

Desired Analog

Output Resolution

VPP Ripple (mV/V)

0 to 90% Settling Time (ms)

100

4.3

2.3

400

1.0

9.2

1600

0.3

36.8

6400

0.1

147.2

For a different (higher) resistor, the normalized ripple VPP[mV/V] can be calculated as:





   

VPP mV / V

R k

C nF





4324

()

Equation 14

or the settling time tSETT for a 0% to 90% settling can be calculated as:

 

   

SETT

R k

C nF







0 0023

Equation 15

The ZSSC3123 provides high and low clipping limits for the PDM output. EEPROM words PDM_Clip_High and PDM_Clip_Low (EEPROM

registers 16HEX and 17HEX; see Table 28) are the 14-bit high and low clipping limit registers respectively. The 14-bit values map directly to the

output of the IC and can be calculated as:

* clip _ level _%

PDM _Clip ROUND



()

100

Equation 16

These registers apply to both PDM_C and PDM_T. Since diagnostics are reported via the PDM_C or PDM_T pin (see section 10.4), clipping

limits allow diagnostics to be differentiated from the normal output. For detection of the diagnostic signal, a PDM_Clip_High limit of 97.5%

(3E66HEX) or lower is recommended.

Important: The default values for the high and low clipping limits (00HEX) are not compatible with PDM output, so the clipping limits must be

changed if the PDM output is used. Otherwise, the PDM output will not function as expected. If the PDM output is not used, it is important to

retain the default values of 00HEX for the clipping limits.

10.8 Alarm Output

The alarm output can be used to monitor whether a corrected capacitance reading has exceeded or fallen below pre-programmed values. The

alarm can be used to drive an open-drain load connected to VDD, as demonstrated in section 14.2, or it can function as a full push-pull driver.

If a high voltage application is required, external devices can be controlled with the Alarm pins, as demonstrated in section 14.3.

The two alarm outputs can be used at the same time, and these alarms can be used in combination with any of the other three modes; I2C,

SPI, or PDM.

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