WM8718

Production Data

w

PD Rev 4.3 November 2006

13

Figure 6 Typical Power Up Sequence Where AVDD is Powered Before DVDD

Typical POR Operation (typical values, not tested)

SYMBOL

MIN

TYP

MAX

UNIT

0.5

0.7

1.0

V

0.5

0.7

1.1

V

1.0

1.4

2.0

V

0.6

0.8

1.0

V

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 VMID 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 VMID must have reached the threshold Vporr before the device is ready

and can 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 VMID.

A 10uF cap is recommended for decoupling on VMID. The charge time for VMID will dominate the

time required for the device to become ready after power is applied. The time required for VMID

to reach the threshold is a function of the VMID resistor string and the decoupling capacitor. The

Resistor string has a typical equivalent resistance of 33kohm (+/-20%). Assuming a 10uF

capacitor, the time required for VMID to reach threshold of 1V is approx 74ms.