ADS-325A Datel, Inc., ADS-325A Datasheet - Page 5

• Manufacturer Part Number: ADS-325A
• Description: 10-Bit,20MHz, Sampling A/D Converter
• Manufacturer: Datel, Inc.

Re-initiating the Start-up Calibration
The start-up calibration function can be re-initiated at any time
desired after the power and the references are supplied. Apply
a positive pulse to CE pin (pin 24) or a negative pulse to
RESET pin (pin 15). The pulse width of these pulses must be
equal to or wider than one A/D clock cycle. Also due to this
feature, you can make sure of a proper start-up calibration at
power-up by making a C-R delay connection with the RESET
pin as shown in Figure 4c.
Using Start-up Calibration Function Only
Internal and external calibration functions need not be
employed after start-up calibration. To use only the start-up
calibration function, connect the SEL pin (pin 17) to AGND and
the CAL pin (pin 14) to +AV
®
ANALOG
OUTPUT
CLOCK
Figure 4b. Conditions for Start-Up Calibration
INPUT
DATA
SENSE AMP #1
SENSE AMP #2
Tsd
T
+1.65V
DL
T
N
PW1
CLR
+1.65V (+DV = +3.3V)
+2.5V (+DV = +5.0V)
A/D CLOCK
T
+2.5
N–3
PW0
RESET
+5
AGND
0
RESET = HIGH, CE = LOW
+AV
S
V
V
S
CE
RB
RT
S
N+1
S
®
1V
or AGND.
AMP #1
AMP #2
SENSE
SENSE
N–2
N+2
1/16
Figure 4a Internal Calibration Pulse Generation Circuit
N–1
+AV
V
V
RB
= SAMPLING POINT
RT
Figure 5. ADS-325A Timing Diagrams
S
N+3
TIME
N
14-BIT COUNTER
24-BIT COUNTER
N+4
CLR
CLR
ENABLE (OE)
5
OUTPUT
OUTPUT
Auto Calibration Function
After the start up calibration is completed, the internal
calibration function can periodically and automatically generate
calibration pulses when the auto calibration mode is enabled.
To enable this function connect the SEL pin (pin 17) and the
CAL pin (pin 41) to +AV
counted with every 16 A/D clock cycles and the carry-out is
used as the calibration pulse. The period of the calibration
pulse generated is as follows:
For the case when the A/D clock frequency is 14.3MHz, the
calibration pulse generation cycle is 18.8 seconds. Since a
single calibration process is performed once every seven
pulses, the total calibration cycle is approximately
132 seconds.
DATA
Period of Auto-calibration pulse = 1/f
+2.5V (+DV = +5.0V)
+1.65V (+DV = +3.3V)
CO
CO
+AV
SEL
CAL
S
S
ACTIVE
S
15
Figure 4c. Start-up Calibration using RESET
D
CLR
+AV
Q
T
S
PEZ
5V
S
HIGH IMPEDENCE
. In this mode a 24-bit counter is
V
+AV
V
T
RT
RB
PZE
RESET
S
CLK
OUT
CE = "L"
x 16 x 16,777,216
+2.5V (+DV = +5.0V)
+1.65V (+DV = +3.3V)
ACTIVE
ADS-325A
S
S