ML2264 datasheet(11/17 Pages) MICRO-LINEAR

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ML2264

1.4 REFERENCE

The +VREF and –VREF inputs are the reference voltages that

determine the full scale and zero input voltages,

respectively, for the A/D converter. Thus, +VREF defines

the analog input which produces a full scale output and

–VREF defines the analog input which produces an output

code of all zeroes. The transfer function for the A/D

converter is shown in Figure 10.

+VREF and –VREF can be set to any voltage between GND

and VCC. This means that the reference voltages can be

offset from GND and the difference between +VREF+ and

–VREF– can be made small to increase the resolution of the

conversion. Note that the total unadjusted error increases

when [+VREF – (–VREF)] decreases.

1.5 POWER SUPPLY AND REFERENCE DECOUPLING

A 0.1µF ceramic disc capacitor is recommended to bypass

VCC to GND, using as short a lead length as possible.

If REF+ and REF– inputs are driven by long lines, they

should be bypassed by 0.1µF ceramic disc capacitors at

the reference input pins.

Figure 9. Operating Sequence (WR-RD Mode)

ACQUISITION

OR SAMPLING

PERIOD. ALL

COMPARATORS

AUTOZEROED.

MSB

COMPARATORS

DECIDING.

LSB

COMPARATORS

DECIDING.

CONVERSION

STARTS.

VIN SAMPLING

ENDS. HOLD

TIME STARTS.

MSB

COMPARATOR

RESULTS ARE

LATCHED.

RD BROUGHT LOW

LATCHES LSB

COMPARATOR

RESULTS AND

BRINGS INT LOW.

(a) T/H Mode

(a) S/H Mode

ALL

COMPARATORS

AUTOZEROED.

ACQUISITION

PERIOD. MSB

COMPARATORS

ARE TRACKING

VIN. LSB

COMPARATORS

ARE SAMPLING

VIN.

LSB

COMPARATORS

DECIDING.

CONVERSION

STARTS.

VIN SAMPLING

ENDS. MSB

COMPARATOR

RESULTS ARE

LATCHED.

RD BROUGHT LOW

LATCHES LSB

COMPARATOR

RESULTS AND

BRINGS INT LOW.

Figure 10. A/D Transfer Characteristic

FULL SCALE

TRANSITION

OUTPUT

CODE

11111111

11111110

11111101

00000011

00000010

00000001

00000000

FS – 1LSB

AIN, INPUT VOLTAGE (IN TERMS OF LSB’S)

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