CS53L30 datasheet(43/67 Pages) CIRRUS

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DS992F2

CS53L30

5.4 Capture-Path Inputs

Figure 5-2. Differential Analog Input Signal to IN±, with Protection Diodes Shown

Figure 5-3. Differential Analog Input Signal to IN±, Voltage-Level Details Shown

As shown in Fig. 5-2, it is worth noting that a differential analog signal of 4•Vx VPP actually delivers a 2•Vx VPP signal

centered around VA/2 at each of the analog pin pairs. Thus, the signal peak (at the pin) of Vx + VA/2 should not exceed

VA + 0.3 V; the signal trough of –Vx + VA/2 (at the pin) should not be lower than GNDA – 0.3 V.

Although it is safe to use an input signal with resulting peak up to VA + 0.3 V and trough of GNDA – 0.3 V at the pin, signal

distortion at these maximum levels may be significant. This is caused by the onset of conduction of the protection diodes.

It is recommended that capture-path pin voltages stay between GNDA and VA to avoid signal distortion and clipping from

the slightly conductive state of protection diodes in the VA to VA + 0.3-V region and GNDA – 0.3-V to GNDA region.

5.4.1.2 ADC Fullscale Input Level

If the signal peaks are kept below the protection diode turn-on region per instructions in Section 5.4.1.1, the maximum

capture-path signal level becomes solely a function of the applied analog gain, with the ADC fullscale input level being

constant, hard limit for the path. Fig. 4-4 shows all analog gain blocks in the analog signal path in relation to the input pin

and ADC. All signals levels mentioned refer to differential signals in VPP.

For any given input pin pairs (INx±), the product of the signal level at those input pins and the total analog gain must be

less than the ADC fullscale input level, i.e.,

By rearranging terms, substituting register bit names for the analog gain stages, the following inequality is obtained:

The ADC fullscale input level is specified in Table 3-5. PREAMPx and PGAxVOL refer to the dB values set by the

respective register bits.

IN+

IN–

4Vx Vpp Differential signal

GNDA

+Vx

–Vx

GNDA

+Vx

–Vx

GNDA

+Vx

–Vx

VA/2

Vx + VA/2

–Vx + VA/2

GNDA

+Vx

–Vx

VA/2

Vx + VA/2

–Vx + VA/2

To IN+

To IN–

VA + 0.3

GNDA – 0.3

VA + 0.3

GNDA – 0.3

4Vx Vpp Differential signal

Input Signal Level

Preamp and PGA gain





ADC Fullscale Input Level



Input Signal Level 10

PREAMPx PGAxVOL

--------------------------------------------------------------------





–

0.82

 VA





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