adc12062biv National Semiconductor Corporation, adc12062biv Datasheet - Page 17

• Manufacturer Part Number: adc12062biv
• Description: 12-bit, 1 Mhz, 75 Mw A/d Converter With Input Multiplexer And Sample/hold
• Manufacturer: National Semiconductor Corporation

Applications Information
edge) of an MM74HC4538 one-shot The 1k resistor and 12
pF capacitor set the pulse length to approximately 100 ns
The S H pulse stream for the converter appears on the Q
output of the HC4538 This is the S H clock generator used
on the ADC12062EVAL evaluation board For lower power
a CMOS inverter-based crystal oscillator can be used in
place of the DIP crystal oscillator See Application Note
AN-340 in the National Semiconductor CMOS Logic Data-
book for more information on CMOS crystal oscillators
8 0 COMMON APPLICATION PITFALLS
Driving inputs (analog or digital) outside power supply
rails The Absolute Maximum Ratings state that all inputs
must be between GND
rule is most often broken when the power supply to the
9 0 APPLICATIONS
b
300 mV and V
CC
(Continued)
a
Ping-Ponging between V
300 mV This
2’s Complement Output
17
converter is turned off but other devices connected to it (op
amps microprocessors) still have power Note that if there
is no power to the converter DGND
AV
AGND and DGND
Driving a high capacitance digital data bus The more
capacitance the data bus has to charge for each conver-
sion the more instantaneous digital current required from
DV
back to the analog section decreasing the SNR of the con-
verter While adequate supply bypassing and separate ana-
log and digital ground planes will reduce this problem buff-
ering the digital data outputs (with a pair of MM74HC541s
for example) may be necessary if the converter must drive a
heavily loaded databus
CC
IN1
CC
and V
e
and DGND These large current spikes can couple
0V so all inputs should be within
IN2
TL H 11490 – 24
e
AGND
TL H 11490 – 25
g
e
300 mV of
DV
CC
e