R/C
tW
tB
BUSY
tDBC
tAP
tDBE
tAP
Convert
Converter
Mode
Acquire
Convert
tC
Acquire
tA
tDD
Hi-Z State
tHDR and tHL
Data
BUS
Data
Valid
Data
Valid
Hi-Z State
Hi-Z State
FIGURE 7. Read Mode: R/C Pulse HIGH— Outputs Enabled Only When R/C is High.
SYMBOL
PARAMETER
MIN
TYP
MAX
UNITS
tW
R/C Pulse Width
BUSY delay from R/C
40
10
80
ns
ns
tDBC
tB
150
2.7
BUSY LOW
2.5
13
µs
tAP
∆tAP
tC
Aperture Delay
ns
Aperture Jitter
150
2.47
100
75
ps, rms
µs
Conversion Time
2.70
tDBE
tDB
tA
BUSY from End of Conversion
BUSY Delay after Data Valid
Acquisition Time
ns
25
200
300
3.0
ns
130
2.6
50
ns
tA+tC
tHDR
tS
Throughput Time
µs
Valid Data Held After R/C LOW
CS or HBE LOW before R/C Falls
CS or HBE LOW after R/C Falls
Data Valid from CS LOW, R/C HIGH, and HBE in Desired State (Load = 100pF)
Valid Data Held After R/C Low
Delay to Hi-Z State after R/C Falls or CS Rises (3kΩ Pullup or Pulldown)
20
25
25
ns
5
ns
tH
0
ns
tDD
tHDR
tHL
65
150
150
ns
20
50
ns
50
ns
TABLE III. Timing Specifications (TMIN to TMAX).
Pin 24 may be slightly more sensitive than pin 23 to supply
variations, but to maintain maximum system accuracy, both
should be well isolated from digital supplies with wide load
variations.
tS
tH
CS or
HBE
To limit the effects of digital switching elsewhere in a
system on the analog performance of the system, it often
makes sense to run a separate +5V supply conductor from
the supply regulator to any analog components requiring
+5V, including the ADS7800.
tW
R/C
tDBC
BUSY
The VS pins (23 and 24) should be connected together and
bypassed with a parallel combination of a 6.8µF tantalum
capacitor and a 0.1µF ceramic capacitor located close to the
converter to obtain noise-free operation. (See Figure 2.) The
–VS pin 22 should be bypassed with a 1µF tantalum
capacitor, again as close as possible to the ADS7800.
Data
Bus
Data Valid
Hi-Z State
tHDR and tHL
FIGURE 8. Conversion Start Timing.
Noise on the power supply lines can degrade converter
performance, especially noise and spikes from a switching
power supply. Appropriate supplies or filters must be used.
The GND pins (4 and 13) are also separated internally, and
should be directly connected to a ground plane under the
®
10
ADS7800
BB [ BURR-BROWN CORPORATION ]
