CS5014 datasheet(11/40 Pages) CIRRUS

11 / 40 page

THEORY OF OPERATION

The CS5012A/14/16 family utilize a successive

approximation conversion technique. The analog

input is successively compared to the output of a

D/A converter controlled by the conversion algo-

rithm. Successive approximation begins by

comparing the analog input to the DAC output

which is set to half-scale (MSB on, all other bits

off). If the input is found to be below half-scale,

the MSB is reset to zero and the input is com-

pared to one-quarter scale (next MSB on, all

others off). If the input were above half-scale, the

MSB would remain high and the next compari-

son would be at three-quarters of full scale. This

procedure continues until all bits have been exer-

cised.

A unique charge redistribution architecture is

used to implement the successive approximation

algorithm. Instead of the traditional resistor net-

work, the DAC is an array of binary-weighted

capacitors. All capacitors in the array share a

common node at the comparator’s input. Their

other terminals are capable of being connected to

AIN, AGND, or VREF (Figure 1). When the de-

vice is not calibrating or converting, all capacitors

are tied to AIN forming Ctot. Switch S1 is closed

and the charge on the array, Qin, tracks the input

signal Vin (Figure 2a).

When the conversion command is issued, switch

S1 opens as shown in Figure 2b. This traps

charge Qin on the comparator side of the capaci-

tor array and creates a floating node at the

comparator’s input. The conversion algorithm op-

erates on this fixed charge, and the signal at the

analog input pin is ignored. In effect, the entire

DAC capacitor array serves as analog memory

AIN

VREF

AGND

C/2

C/4

C/8

MSB

LSB

Bit 11

Bit 10

Bit 9

Bit 8

Bit 0

Dummy

C/X

Bit 13

Bit 15

Bit 12

Bit 14

Bit 11

Bit 13

Bit 10

Bit 12

CS5012A:

CS5014:

CS5016:

C/X

X = 2048

X = 8192

X = 32768

CS5012A

CS5014

CS5016

= C + C/2 + C/4 + ... + C/X

tot

Figure 1. Charge Redistribution DAC

(1-D) C tot

Vfn

To MCU

C tot

D .

VREF

AGND

for

VREF

Vin

= 0V

Figure 2b. Convert Mode

Ctot

Vin

AIN

To MCU

= Vin Ctot

-Q

Figure 2a. Tracking Mode

CS5012A, CS5014, CS5016

DS14F8

2-17

CS5012A CS5014 CS5016

DS14F9

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