ST2202A
15.2.2 Two-Pin Two Ended Mode (8-bit Accuracy)
TwoꢁPinꢀTwoꢁEndedꢀmodeꢀisꢀdesignedꢀforꢀuseꢀwithꢀaꢀsingleꢀ
transistorꢀamplifier.ꢀItꢀrequiresꢀtwoꢀpinꢀthatꢀPSG0ꢀandꢀPSG1.ꢀ
WhenꢀtheꢀDACꢀvalueꢀisꢀpositive,ꢀPSG1ꢀgoesꢀhighꢀwithꢀaꢀ
Figureꢀ13ꢁ5ꢀshowsꢀexamplesꢀofꢀDACꢀoutputꢀwaveformsꢀwithꢀ
differentꢀoutputꢀvalues.ꢀEachꢀpulseꢀofꢀtheꢀDACꢀisꢀdividedꢀ
intoꢀ128ꢀsegmentsꢀperꢀsampleꢀperiod.ꢀForꢀaꢀpositiveꢀoutputꢀ
valueꢀx=0ꢀtoꢀ127,ꢀPSG1ꢀgoesꢀhighꢀforꢀXꢀsegmentsꢀwhileꢀ
PSG0ꢀstaysꢀhigh.ꢀForꢀaꢀnegativeꢀoutputꢀvalueꢀx=0ꢀtoꢀꢁ127,ꢀ
PSG0ꢀgoesꢀlowꢀforꢀ|X|ꢀsegmentsꢀwhile PSG1ꢀstaysꢀlow.ꢀ
ꢀ
dutyꢀcycleꢀproportionalꢀtoꢀtheꢀoutputꢀvalue,ꢀwhileꢀPSG0
ꢀ
staysꢀhigh.ꢀWhenꢀtheꢀDACꢀvalueꢀisꢀnegative,ꢀPSG0ꢀgoesꢀ
lowꢀwithꢀaꢀdutyꢀcycleꢀproportionalꢀtoꢀtheꢀoutputꢀvalue,ꢀwhileꢀ
PSG1ꢀstaysꢀlow.ꢀThisꢀmodeꢀoffersꢀaꢀresolutionꢀofꢀ8ꢀbits.ꢀ
ꢀ
High
PSG0
Low
X
32
96
127
High
PSG1
128-X
96
32
DAC = 96
1
Low
DAC = X
Where X=0 to 127
DAC = 32
80
DAC = 127
128+X
High
PSG0
|X|
48
Low
High
PSG1
Low
DAC = X
Where X=0 to -128
DAC = -48
DAC = 0
DAC = -128
ꢀ
FIGURE 15-4 Two-Pin Two Ended Mode Wave-Form
ꢀ
ꢀ
ꢀ
Verꢀ2.5ꢀ
39
/75
ꢀ
9/16/2008ꢀ
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