WM0832IP datasheet(11/14 Pages) WOLFSON

11 / 14 page

Wolfson Microelectronics

WM0831, WM0832

Initiating Conversion and the Digital Interface

WM0831 and WM0832 are controlled from a processor

via a Chip Select (CS) input and a serial interface

comprising Data Out (DO) and additionally for WM0832 a

Data In (DI) input.

For WM0831 conversion is initiated by pulling chip select

low and inputting a clock signal. On the clock's first falling

edge after CS is brought low, DO output comes out of

high impedance mode. On the second and subsequent

clock falling edges, to a total of nine, the conversion

result is output on DO in MSB to LSB order. WM0831 only

provides output data in MSB first order.

For WM0832 conversion is also initiated by pulling the chip

select (CS) line low and inputting a clock signal but MUX

addressing information has also to be input on DI. The

start bit and the MUX assignment bits on DI are clocked

in on the first three rising edges of the clock input which

may be generated by the processor or run continuously.

WM0832 uses two MUX assignment bits.

When the logic “1” start bit is clocked into the start

conversion location of the multiplexer input register the

analogue MUX inputs are selected. After 1/2 a clock

period delay to allow for the selected MUX output to settle

the conversion commences using the successive

approximation technique.

When conversion begins the A/D conversion result from

the output of the SARS comparator appears at the DO

output on each falling edge of the clock (see Functional

Timing Diagrams).

With the successive approximation A/D conversion

routine the analogue input is compared with the output of

a digital to analogue converter (DAC) for each bit by the

SARS comparator and a decision made on whether the

analogue input is higher or lower than the DAC output.

Successive bits, MSB to LSB, are input to the DAC and

remain in its input if the analogue comparison decides

the analogue input is higher than the DAC output, if not

the bit is removed from the DAC input. There is no sample

and hold. The input needs to be stable during Tconv period

(see Functional Timing Diagrams).

The output from the SARS comparator forms the

resulting input to the DAC and the A/D conversion output

on DO, and is read by the processor as conversion takes

place in MSB to LSB order. After 8 clock periods the

conversion is complete.

Functional Description (continued)

For WM0832 the 8 bits of the conversion are stored in an

output shift register, after a conversion has completed and

MSB first data has been output WM0832 automatically

shifts out LSB first data on the DO output.

CS must be held low through an entire conversion, all

internal registers are cleared when CS is high. To initiate

another conversion CS must make a high to low transition

and for WM0832 MUX address assignments input to DI.

For WM0832 the DI input and DO output can be tied

together and controlled via a bidirectional processor I/O

bit line.

Reference Input

The analogue input voltage range, Vmax to Vmin for

differential inputs is defined by the voltage applied to the

reference input with respect to GND. WM0832 is fixed in a

ratiometric mode with VREF internally tied to Vcc, WM0832

has a separate VREF pin and can be used in either

ratiometric applications or those requiring absolute

accuracy.

A ratiometric reference input, typically the Vcc, is the same

supply used to power analogue input circuitry and

sensors. In such systems under a given input condition

the same code will be output with variations in supply

voltage because the same ratio change occurs in both the

analogue and reference input to the A/D. When used in

applications requiring absolute accuracy a suitable time

and temperature stable voltage reference source should

be used.

The voltage source used to drive the reference input should

be capable of driving the 2.4 k

Ω typical of the SAR

resistor ladder. The maximum input voltage to the

reference input is the Vcc supply voltage. The minimum

for WM0832 can be at least as low as 1 V to allow for

direct conversion of sensor outputs with output voltage

ranges less than 5 V.

WM0832IP Datasheet(PDF) 11 Page - Wolfson Microelectronics plc

WM0832IP Datasheet(HTML) 11 Page - Wolfson Microelectronics plc

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Datasheet Download

Link URL