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WM8978GEFL/V Datasheet(PDF) 22 Page - Wolfson Microelectronics plc |
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WM8978GEFL/V Datasheet(HTML) 22 Page - Wolfson Microelectronics plc |
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22 / 119 page  WM8978 Pre-Production w PP Rev 3.0 May 2006 22 Notes: 1. This step enables the internal device bias buffer and the VMID buffer for unassigned inputs/outputs. This will provide a startup reference voltage for all inputs and outputs. This will cause the inputs and outputs to ramp towards VMID (NOT using output 1.5x boost) or 1.5 x (AVDD/2) (using output 1.5x boost) in a way that is controlled and predictable (see note 2). 2. Choose the value of the VMIDSEL bits based on the startup time (VMIDSEL=10 for slowest startup, VMIDSEL=11 for fastest startup). Startup time is defined by the value of the VMIDSEL bits (the reference impedance) and the external decoupling capacitor on VMID. 3. Setting DACEN to off while operating in x1.5 boost mode will cause the VMID voltage to drop to AVDD/2 midrail level and cause an output pop. In addition to the power on sequence, it is recommended that the zero cross functions are used when changing the volume in the PGAs to avoid any audible pops or clicks. V pora DGND Internal POR active Device Ready No Power V por_off Power Supply POR I2S Clocks ADC Internal State t midrail_on Analogue Inputs ADCDAT pin GD ADCEN bit Power down Init Normal Operation Normal Operation Init PD Power down ADC enabled ADC enabled ADC off t adcint DNC INPPGAEN bit t adcint INPPGA enabled DNC GD GD GD POR POR Undefined VMID enabled VMIDSEL/ BIASEN bits AVDD/2 t midrail_off (Note 1) (Note 2) (Note 3) (Note 4) V por_on Figure 9 ADC Power Up and Down Sequence (not to scale) SYMBOL MIN TYPICAL MAX UNIT tmidrail_on 500 ms tmidrail_off >10 s tadcint 2/fs n/fs ADC Group Delay 29/fs n/fs Table 4 Typical POR Operation (typical simulated values) |
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