ADS7800_14 Datasheet, PDF (9/21 Pages) Texas Instruments – 12-Bit 3μs Sampling ANALOG-TO-DIGITAL CONVERTER

R/C
BUSY
Converter
Mode
Data
BUS
t_W
t_B
t_DBC
Acquire
t_DD
Hi-Z State
Data
Valid
t_AP
t_DBE
Convert
t_C
t_HDR and t_HL
Hi-Z State
Acquire
t_A
t_AP
Convert
Data
Valid
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
t_W
t_DBC
t_B
t_AP
∆t_AP
t_C
t_DBE
t_DB
t_A
t_A+t_C
t_HDR
t_S
t_H
t_DD
t_HDR
t_HL
R/C Pulse Width
40
10
ns
BUSY delay from R/C
80
150
ns
BUSY LOW
2.5
2.7
µs
Aperture Delay
13
ns
Aperture Jitter
150
ps, rms
Conversion Time
2.47
2.70
µs
BUSY from End of Conversion
100
ns
BUSY Delay after Data Valid
25
75
200
ns
Acquisition Time
130
300
ns
Throughput Time
2.6
3.0
µs
Valid Data Held After R/C LOW
20
50
ns
CS or HBE LOW before R/C Falls
25
5
ns
CS or HBE LOW after R/C Falls
25
0
ns
Data Valid from CS LOW, R/C HIGH, and HBE in Desired State (Load = 100pF)
65
150
ns
Valid Data Held After R/C Low
20
50
ns
Delay to Hi-Z State after R/C Falls or CS Rises (3kΩ Pullup or Pulldown)
50
150
ns
TABLE III. Timing Specifications (T_MIN to T_MAX).
CS or
HBE
R/C
t_S
t_H
t_W
BUSY
Data _{Data Valid}
Bus
t_DBC
Hi-Z State
t_HDR and t_HL
FIGURE 8. Conversion Start Timing.
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.
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.
The V_S 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
–V_S pin 22 should be bypassed with a 1µF tantalum
capacitor, again as close as possible to the ADS7800.
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
ADS7800
9
SBAS001A
www.ti.com