Wolfson Microelectronics

9

WM5615

DIN

SCLK

CS

DOUT

SCK

MOSI

I/O

MISO

WM5615

SPI

Port

Figure 2 - Microwire Connection

Figure 3 - SPI/QSPI Connection

Daisy-Chaining Devices

The serial output, DOUT, allows cascading of two or

more DACs. The data at DIN appears at DOUT, delayed

by 16 clock cycles plus one clock width. For low power,

DOUT does not require an external pull-up resistor. DOUT

does not go into a high-impedance state when CS is

high. DOUT changes on SCLK's falling edge when CS is

low. When CS is high, DOUT remains in the state of the

last data bit.

Any number of DACs can be daisy-chained by connect-

ing the DOUT of one device to the DIN of the next device

in the chain.

Linearity, Offset and Gain Error using Single End

Supplies

When an amplifier is operated from a single supply, the

voltage offset can still be either positive or negative. With

a positive offset, the output voltage changes on the first

code change. With a negative offset, the output voltage

may not change with the first code depending on the

magnitude of the offset voltage.

The output amplifier, with a negative voltage offset,

attempts to drive the output to a negative voltage.

However, because the most negative supply rail is

ground, the output cannot drive to a negative voltage. So

when the output offset voltage is negative, the output

voltage remains at zero volts until the input code value

produces a sufficient output voltage to overcome the

inherent negative offset voltage, resulting in the transfer

function shown in figure 4.

Figure 4 - Effect of Negative Offset (Single Supply)

Note: The DOUT-MISI connection is not required for writing to the WM5615, but may be used for verifying data transfer.

DAC Code

Negative

Offset

Output

Voltage

This negative offset, not the linearity error, produces this

breakpoint. The transfer function would have followed

the dotted line if the output buffer could drive to a

negative voltage.

For a DAC, linearity is measured between zero input

code (all inputs 0) after offset and full-scale are adjusted

out or accounted for in some way. However, single

supply operation does not allow for adjustment when

the output is negative due to the breakpoint in the

transfer function. So the linearity is measured between

the full-scale and the lowest code which produces a

positive output voltage. For the WM5615, the zero scale

(offset) is plus or minus 3LSB maximum. The code is

calculated from the maximum specification for the

negative offset.

DIN

CS

DOUT

WM5615

SCLK

SK

SO

I/O

SI

Microwire

Port