WM8740 Wolfson Microelectronics plc, WM8740 Datasheet - Page 11

• Manufacturer Part Number: WM8740
• Description: 24-bit, High Performance 192khz Stereo Dac
• Manufacturer: Wolfson Microelectronics plc

WM8740
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In a real application the designer is unlikely to have control of the relative power up sequence of
AVDD and DVDD. Using the POR circuit to monitor VMIDLL ensures a reasonable delay between
applying power to the device and Device Ready.
Figure 5 and Figure 6 show typical power up scenarios in a real system. Both AVDD and DVDD must
be established and VMIDL must have reached the threshold V
be written to. Any writes to the device before Device Ready will be ignored.
Figure 5 shows DVDD powering up before AVDD. Figure 6 shows AVDD powering up before DVDD.
In both cases, the time from applying power to Device Ready is dominated by the charge time of
VMIDLL. In the case where AVDD is powered long before DVDD, thus allowing VMIDL to charge
above V
shown in Figure 7.
porr
, the PORB will not release until DVDD passes the V
porr
before the device is ready and can
pord
threshold. This situation is
PD, Rev 4.3, August 2009
Production Data
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