
W561XXX DESIGN GUIDE
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/RESET
Active low reset input with an internal pull-high resistance of 500 K
. The falling edge of the
/RESET pin will reset the W56XXX totally, just like the POR condition. Right at the rising
edge of the /RESET input, the W56XXX starts to awake and proceeds to undergo the POI
process.
Originally, the /RESET pin is used to function as a last resort to rescue the POR failure issue,
which is encountered in some occasions where the internal POR circuit of the W56XXX can't
operate properly. If customers failed to discharge the VDD to ground level and re-power up
the W56XXX, it may function abnormally, causing unpredictable operations. Users may then
reset the W56XXX by sending a pulse through the /RESET pin to re-start the operation from
the very beginning: POI. Maybe, this is the safest way to get around all the annoying POR
issues.
DAC1, DAC2
The DAC1 ( DAC2 ) pin is a current-type voice output, which is connected to the output of the
internal D/A converter. The full scale output of the 8-bit D/A converter is 5 mA, which is able
to drive the external 8-W speaker through the amplification of a low-power NPN transistor
with a
β
of around 120 - 160. ( Usually, the selection of an 8050D transistor is appropriate. )
DAC1/2
R
C
8050D NPN transistor
Figure 0-3. DAC Current-type Voice Output
The shunt resistor R in Figure 0-3 is used to reduce the current that enters into the base of
the NPN transistor for driving the external speaker without distortions, which may occur in the
above simple scheme.
Distortions result from two facts: one is the saturation phenomenon of the transistor due to
large I
B
, the other is the introduction of R that cuts small signals too much out of the original
waveform. A typical value of the shunt resistor is around 470Ohm - 1KOhm . The smaller the
resistance, the smaller the current enters the transistor and vice versa. Users have to trade
off what value of R could be added without causing these two kind of distortions.
The capacitor C is used for low-pass filtering the unwanted high-frequency noises that are
generated from D/A converters during sample transitions. Users may adjust the capacitance
to reach a better perceptual hearing. It could be simply omitted without affecting the voice
quality too much.
For W562xx there is no DAC2.