ZHCSHY2 March 2018 TLV320ADC3100
PRODUCTION DATA.
The TLV320ADC3100 includes several programmable settings to control the analog input pins, particularly when the pins are not selected for connection to an ADC PGA. The default option allows unselected inputs to be put into a high-impedance state. However, the pins on the device do include protection diode circuits connected to AVDD and AVSS. Thus, if any voltage is driven onto a pin approximately one diode drop (~0.6 V) above AVDD or one diode drop below AVSS, these protection diodes begin conducting current, resulting in an effective impedance that no longer appears as a high-impedance state.
Another programmable option for unselected analog inputs is to weakly hold those inputs at the common-mode input voltage of the ADC PGA (determined by an internal band-gap voltage reference). This feature is useful to keep the AC-coupling capacitors connected to the analog inputs biased up at a normal DC level, thus avoiding the need for them to charge up suddenly when the input is changed from being unselected to selected for connection to an ADC PGA. This option is controlled in page 1, register 52 through page 1, register 57. This option must be disabled when an input is selected for connection to an ADC PGA or selected for the analog input bypass path, because the input can corrupt the recorded input signal if left operational when an input is selected.
In most cases, the analog input pins on the TLV320ADC3100 must be AC-coupled to analog input sources, the only exception generally being if an ADC is used for DC voltage measurement. The AC-coupling capacitor causes a high-pass filter pole to be inserted into the analog signal path, so the size of the capacitor must be chosen to move that filter pole sufficiently low in frequency to cause minimal effect on the processed analog signal. The input impedance of the analog inputs, when selected for connection to an ADC PGA, varies with the setting of the input-level control, starting at approximately 35 kΩ with an input-level control setting of 0 dB, and 62.5-kΩ when the input-level control is set at –6 dB. For example, using a 0.1-µF, AC-coupling capacitor at an analog input results in a high-pass filter pole of 45.5 Hz when the 0-dB, input-level control setting is selected. Table 5 lists various mixer gains and microphone PGA ranges to set a high-pass corner for the application.
| MIXER GAIN (dB) | MICROPHONE PGA RANGE (dB) | INPUT IMPEDANCE (Ω) |
|---|---|---|
| 0 | 0–5.5 | 35,000 |
| 0 | 6–11.5 | 38,889 |
| 0 | 12–17.5 | 42,000 |
| 0 | 18–23.5 | 44,074 |
| 0 | 24–29.5 | 45,294 |
| 0 | 30–35.5 | 45,960 |
| 0 | 36–40 | 46,308 |
| –6 | 0–5.5 | 62,222 |
| –6 | 6–11.5 | 70,000 |
| –6 | 12–17.5 | 77,778 |
| –6 | 18–23.5 | 84,000 |
| –6 | 24–29.5 | 88,148 |
| –6 | 30–35.5 | 90,588 |
| –6 | 36–40 | 91,919 |