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ADS-953ME

18-Bit, 1MHz, Low-Distortion Sampling A/D Converters

Murata Power Solutions 

ADS-953

®

®

THERMAL REQUIREMENTS

All DATEL sampling A/D converters are fully characterized and

specified over operating temperature (case) ranges of 0 to

+70°C and –40 to +110°C. All room-temperature (TA = +25°C)

production testing is performed without the use of heat sinks or

forced-air cooling. Thermal impedance figures for each device

are listed in their respective specification tables.

These devices do not normally require heat sinks, however,

standard precautionary design and layout procedures should

be used to ensure devices do not overheat. The ground and

power planes beneath the package, as well as all pcb signal

runs to and from the device, should be as heavy as possible

to help conduct heat away from the package. Electrically-

insulating, thermally-conductive "pads" may be installed under-

neath the package. Devices should be soldered to boards

rather than "socketed", and of course, minimal air flow over the

surface can greatly help reduce the package temperature.

CALIBRATION PROCEDURE

Connect the converter per Table 1 for the appropriate input volt-

age range. Any offset/gain calibration procedures should not

be implemented until the device is fully warmed up. To avoid

interaction, adjust offset before gain. The ranges of adjustment

for the circuits in Figure 2 are guaranteed to compensate for

the ADS-953's initial accuracy errors and may not be able to

compensate for additional system errors.

A/D converters are calibrated by positioning their digital outputs

exactly on the transition point between two adjacent digital

output codes. This is accomplished by connecting LED's to

the digital outputs and performing adjustments until certain

LED's "flicker" equally between on and off. Other approaches

employ digital comparators or microcontrollers to detect when

the outputs change from one code to the next.

For the ADS-953, offset adjusting is normally accomplished

when the analog input is 0 minus ½LSB (–19µV). See Table 2

for the proper bipolar output coding.

Gain adjusting is accomplished when the analog input is at

nominal full scale minus 1½LSB's (–4.999943V).

Zero/Offset Adjust Procedure

1. Apply a train of pulses to the START CONVERT input

(pin 16) so that the converter is continuously converting.

2. For bipolar zero/offset adjust, apply –19µV to the ANALOG

INPUT (pin 4).

3. Adjust the offset potentiometer until the output code flickers

equally between 01 1111 1111 1111 1111 and 10 0000

0000 0000 0000.

Gain Adjust Procedure

1. Apply –4.999943V to the ANALOG INPUT (pin 4).

2. Adjust the gain potentiometer until all output bits are 1's

and the LSB flickers between 1 and 0.

3. To confirm proper operation of the device, vary the applied

input voltage to obtain the output coding listed in Table 2.

Table 1. Input Connections

INPUT VOLTAGE

RANGE

±5V

ZERO ADJUST

(–½ LSB)

–19µV

GAIN ADJUST

(–FS +1½ LSB)

–4.999943

BIPLOAR

SCALE

+FS –1 LSB

+3/4 FS

+1/2 FS

0

–1/2 FS

–3/4 FS

–FS +1 LSB

–FS

Table 2. Output Coding

COMPLEMENTARY

OFFSET BINARY

INPUT

OUTPUT CODING

VOLTAGE ±5V MSB

LSB

+4.999962

+3.750000

+2.500000

+0.000000

–2.500000

–3.750000

–4.999962

–5.000000

00 0000 0000 0000 0000

00 0111 1111 1111 1111

00 1111 1111 1111 1111

01 1111 1111 1111 1111

10 1111 1111 1111 1111

11 0111 1111 1111 1111

11 1111 1111 1111 1110

11 1111 1111 1111 1111

4

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