SPT574

The gain adjustment should be done at positive full scale. The

ideal input corresponding to the last code change is applied.

This is 1 and 1/2 LSB below the nominal full scale which is

+9.9963 V for the 10 V range and +19.9927 V for the 20 V

range. Adjust the gain potentiometer R2 for flicker between

codes 1111 1111 1110 and 1111 1111 1111. If calibration is

not necessary for the intended application, replace R2 with a

50

Ω, 1% metal film resistor and remove the network from the

BIP OFF pin. Connect the BIP OFF pin to AGND. Connect the

analog input to the 10 V IN pin for the 0 to 10 V range or to the

20 V IN pin for the 0 to 20 V range.

BIPOLAR

The gain and offset errors listed in the specification may be

adjusted to zero using the potentiometers R1 and R2. (See

figure 6.) If adjustment is not needed, either or both pots may

be replaced by a 50

Ω, 1% metal film resistor.

To calibrate, connect the analog input signal to the 10 V IN pin

for a

±5 V range or to the 20 V IN pin for a ±10 V range. First

apply a DC input voltage 1/2 LSB above negative full scale

which is -4.9988 V for the

±5 V range or -9.9976 V for the ±10

V range. Adjust the offset potentiometer R1 for flicker be-

tween output codes 0000 0000 0000 and 0000 0000 0001.

Next, apply a DC input voltage 1 and 1/2 LSB below positive

full scale which is +4.9963 V for the

±5 V range or +9.9927 V

for the

±10 V range. Adjust the gain potentiometer R2 for

flicker between codes 1111 1111 1110 and 1111 1111 1111.

The analog and digital common pins should be tied together

as close to the package as possible to guarantee best

performance. The code dependent currents flow through the

pins.

RANGE CONSIDERATIONS

The SPT574 may be operated by a microprocessor or in the

stand-alone mode. The part has four standard input ranges:

0 V to +10 V, 0 V to +20 V,

±5 V and ±10 V. The maximum

errors that are listed in the specifications for gain and offset

may be adjusted externally to zero as explained in the next

two sections.

CALIBRATION & CONNECTION PROCEDURES

UNIPOLAR

The calibration procedure consists of adjusting the

converter’s most negative output to its ideal value for offset

adjustment and then adjusting the most positive output to its

ideal value for gain adjustment.

Starting with offset adjustment and referring to figure 5, the

midpoint of the first LSB increment should be positioned at

the origin to get an output code of all 0s. To do this, an input

of +1/2 LSB or +1.22 mV for the 10 V range and +2.44 mV for

the 20 V range should be applied to the SPT574. Adjust the

offset potentiometer R1 for code transition flickers between

0000 0000 0000 and 0000 0000 0001.

Figure 5 - Unipolar Input Connections

VRef In

Control

Logic

Nibble A

Nibble B

Nibble C

Three-State Buffers And Control

Oscillator

12-Bit SAR

12-Bits

12-Bits

Ref

Offset/Gain

Trim Network

Ref

Amp

Sample/Hold

Output Bits

VRef Out

BIP Off

20 V In

10 V In

STS

VDD

DGND

MSB

LSB

Strobe

Analog

Inputs

(Calibration)

.1 µF

+5 V

R2

100

Ω

0 to 10 V

0 to 20 V

Ao

CE

CS

R/C

12/8

100 k

Ω

100 k

Ω

-15 V

+15 V

R1

100

Ω

CDAC

Comp

VEE

Control

Logic

Nibble A

Nibble B

Nibble C

Three-State Buffers And Control

Oscillator

12-Bit SAR

12-Bits

12-Bits

Ref

Offset/Gain

Trim Network

Ref

Amp

Sample/Hold

Output Bits

VRef Out

BIP Off

20 V In

10 V In

STS

VDD

DGND

MSB

LSB

Strobe

VRef In

Analog

Inputs

.1 µF

+5 V

±5 V

±10 V

Ao

CE

CS

R/C

12/8

CDAC

Comp

100

Ω

R1

100

Ω

R1

VEE

Figure 6 - Bipolar Input Connections

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