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# VCA821: Differential input voltage level

Part Number: VCA821

Hello team,

The D/S Table 2 specifies that RG = 18Ohm when G=40 (use case is AVMAX=32dB).

Figure 1 specifies that differential input voltage level should be close to 0.1Vpp when RG=18Ohm.

Is the input voltage level limited to 0.1Vpp even when gain control voltage (VG) is changed to smaller value?

How can I check the acceptable input voltage in different VG?

In my use case, VS=+/-5V and RL=100Ohm.

Regards,

Itoh

• Hello Itoh,

From Section 9.3 in the datasheet, it states that the maximum gain for this device is set by Rg and Rf. But with the gain adjust pin or VG, the gain decreases linearly by dB as the voltage on the pin decreases from 2 to 0V (Figure 65 with RG of 18 Ohms). From Figure 1, there is an equation listed: Vin_Max (Vpp) = 2* RG * IRG_Max; this will not include VG and will not be affected at different VGs. The 2 comes from the factor of two before reaching the multiplier from section 10.2.1.2.

Thank you,

Sima