WM5615
Detailed Description (Continued)
SK
SCLK
SCK
SCLK
DIN
SO
DIN
MOSI
I/O
Microwire
Port
WM5615
WM5615
SPI
I/O
SI
Port
CS
CS
DOUT
MISO
DOUT
Figure 2 - Microwire Connection
Figure 3 - SPI/QSPI Connection
Note: The DOUT-MISI connection is not required for writing to the WM5615, but may be used for verifying data transfer.
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,
Output
Voltage
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.
DAC Code
Negative
Offset
Linearity, Offset and Gain Error using Single End
Supplies
Figure 4 - Effect of Negative Offset (Single Supply)
When an amplifier is operated from a single supply, the
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.
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.
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.
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.
Wolfson Microelectronics
9
WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
