ADS-118MM-C Murata, ADS-118MM-C Datasheet - Page 4

• Manufacturer Part Number: ADS-118MM-C
• Description: buffers. 1v input range, no pipeline delay, -55 c to +125 c temperature range, rohs compliant....
• Manufacturer: Murata

DATEL
CALIBRATION PROCEDURE
OFFSET
ADJUST
Any offset and/or gain calibration procedures should not be implemented
A/D converters are calibrated by positioning their digital outputs exactly on
LED’s to the digital outputs and adjusting until certain LED's "fl icker"
For the ADS-118, offset adjusting is normally accomplished at the point
Gain adjusting is accomplished when all bits are 1’s and the LSB just
ZERO/
until devices are fully warmed up. To avoid interaction, offset must be ad-
justed before gain. The ranges of adjustment for the circuits in Figures 2a
and 2b are guaranteed to compensate for the ADS-118's initial accuracy
errors and may not be able to compensate for additional system errors.
the transition point between two adjacent digital output codes. This can be
accomplished by connecting
equally between on and off. Other approaches employ digital comparators
or microcontrollers to detect when the outputs change from one code to
the next.
where the MSB is a 1 and all other output bits are 0’s and the LSB just
changes from a 0 to a 1. This digital output transition ideally occurs when
the applied analog input is
+½LSB (+244μV for ADS-118; +305μV for ADS-118A).
changes from a 1 to a 0. This transition ideally occurs when the ana-
log input is at +full scale minus 1½ LSB's (+0.99927V for ADS-118;
+1.249085V for ADS-118A).
SIGNAL
®
INPUT
–15V
+15V
20kΩ
ADJUST
GAIN
Figure 2a. Optional ADS-118 External
Gain and Offset Adjust Circuits
50Ω
1.98kΩ
1.2MΩ
BIPOLAR SCALE
+FS –1 LSB
–FS +1 LSB
®
+3/4 FS
+1/2 FS
–1/2 FS
–3/4 FS
–FS
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0
+15V
–15V
2kΩ
Table 1. Output Coding for Bipolar Operation
To Pin19
of ADS-118
ADS-118 INPUT
RANGE (±1V)
+0.99951V
+0.75000V
+0.50000V
–0.50000V
–0.75000V
–0.99951V
–1.00000V
0.00000V
OFFSET
OUTPUT CODING
1111 1111 1111
1110 0000 0000
1100 0000 0000
1000 0000 0000
0100 0000 0000
0010 0000 0000
0000 0000 0001
0000 0000 0000
MSB
Zero/Offset Adjust Procedure
1. Apply a train of pulses to the START CONVERT input (pin 16) so the con-
2. Apply +244μV (ADS-118) or +305μV (ADS-118A) to the ANALOG INPUT
3. Adjust the offset potentiometer until the output bits are 1000 0000 00000
Gain Adjust Procedure
1. Apply +0.99927V (ADS-118) or +1.249085V (ADS-118A) to the ANALOG
2. Adjust the gain potentiometer until all output bits are 1's and the LSB
3. To confi rm proper operation of the device, vary the input signal to obtain
12-Bit, 5MHz, Low-Power Sampling A/D Converters
verter is continuously converting.
(pin 19).
and the LSB fl ickers between 0 and 1.
INPUT (pin 19).
fl ickers between 1 and 0.
the output coding listed in Table 1.
Potentiometer is at 25Ω during the device's factory trim procedure.
BINARY
LSB
SIGNAL
INPUT
RANGE (±1.25V)
OFFSET
ADJUST
ADS-118 INPUT
ZERO/
Gain and Offset Adjust Circuits
Figure 2b. Optional ADS-118A
+1.2494V
+0.9375V
+0.6250V
–0.6250V
–0.9375V
–1.2494V
–1.2500V
–15V (or –5V)
+15V (or +5V)
0.0000V
ADJUST
ADS-118, ADS-118A
GAIN
50Ω
20kΩ
To Pin17
of ADS-118A
31 Mar 2011 ADS-118.B03 Page 4 of 8
To Pin19
of ADS-118A