Z89135 Datasheet, PDF (8/66 Pages) Zilog, Inc. – Low-Cost DTAD Controller

Z89135/136 (ROMless)
Low-Cost DTAD Controller
A/D CONVERTER (ADC)
Figure 4 shows the input circuit of the ADC. When conver-
sion starts, the analog input voltage from the input is con-
nected to the MSB and LSB flash converter inputs as
shown in the Input Impedance CKT diagram. Shunting 31
parallel internal resistances of the analog switches and si-
multaneously charging 31 parallel 1 pF capacitors is equiv-
alent to a 400 Ohms input impedance in parallel with a 31
pF capacitor. Other input stray capacitance adds about 10
Zilog
pF to the input load. Input source resistances up to 2 Ko-
hms can be used under normal operating conditions with-
out any degradation of the input settling time. For larger in-
put source resistance, longer conversion cycle times may
be required to compensate the input settling time problem.
V_REF is set using the V_REF + pin.
CMOS Switch
on Resistance
2-5k Ω
R Source
C Parasitic
V Ref
V Ref
C .5 pF
C .5 pF
V Ref
C .5 pF
Figure 4. Input Impedance of ADC
31 CMOS Digital
Comparators
ABSOLUTE MAXIMUM RATINGS
Symbol
Description
Min
V_CC
T_STG
T_A
Supply Voltage (*)
Storage Temp
Oper Ambient Temp
–0.3
–65°
Notes:
Voltage on all pins with respect to GND.
† See Ordering Information.
Max Units
+7.0 V
+150° C
†
C
Stresses greater than those listed under Absolute Maxi-
mum Ratings may cause permanent damage to the de-
vice. This is a stress rating only; operation of the device at
any condition above those indicated in the operational sec-
tions of these specifications is not implied. Exposure to ab-
solute maximum rating conditions for an extended period
may affect device reliability.
1-8
PRELIMINARY
DS97TAD0300