Rainbow Electronics MAX5139 - Manual (Page 14)

MAX5138/MAX5139
Applications Information
Power-On Reset (POR)
On power-up, the input register is set to zero, and the
DAC output powers up to zero or midscale, depending
on the configuration of M/Z. Connect M/Z to AGND to
power the output to AGND. Connect M/Z to AVDD to
power the output to midscale.
To guarantee DAC linearity, wait until the supplies have
settled. Set the LIN bit in the DAC linearity register; wait
10ms, and clear the LIN bit.
Unipolar Output
The MAX5138/MAX5139 unipolar output voltage range is
0 to V
REFI . The output buffer drives a 2kΩ load in parallel
with 200pF.
Bipolar Output
Use the MAX5138/MAX5139 in bipolar applications with
additional external components (see the
Typical
Operating Circuit ).
Power Supplies and
Bypassing Considerations
For best performance, use a separate supply for the
MAX5138/MAX5139. Bypass both DVDD and AVDD
with high-quality ceramic capacitors to a low-imped-
ance ground as close as possible to the device.
Minimize lead lengths to reduce lead inductance.
Connect both MAX5138/MAX5139 AGND inputs to the
analog ground plane.
Layout Considerations
Digital and AC transient signals on AGND inputs can
create noise at the outputs. Connect both AGND inputs
to form the star ground for the DAC system. Refer
remote DAC loads to this system ground for the best
possible performance. Use proper grounding tech-
niques, such as a multilayer board with a low-induc-
tance ground plane, or star connect all ground return
paths back to the MAX5138/MAX5139 AGND. Do not
use wire-wrapped boards and sockets. Use shielding
to improve noise immunity. Do not run analog and digi-
tal signals parallel to one another (especially clock sig-
nals) and avoid routing digital lines underneath the
MAX5138/MAX5139 package.
Definitions
Integral Nonlinearity (INL)
INL is the deviation of the measured transfer function
from a best fit straight line drawn between two codes.
This best fit line for the MAX5138 is a line drawn
between codes 3072 and 64,512 of the transfer func-
tion and the best fit line for the MAX5139 is a line drawn
between codes 192 and 4032 of the transfer function,
once offset and gain errors have been nullified.
Differential Nonlinearity (DNL)
DNL is the difference between an actual step height
and the ideal value of 1 LSB. If the magnitude of the
DNL is greater than -1 LSB, the DAC guarantees no
missing codes and is monotonic.
Low-Power, Single, 16-/12-Bit,
Buffered Voltage-Output DACs
14 ______________________________________________________________________________________
DAC LATCH CONTENTS
MSB LSB
ANALOG OUTPUT, V OUT
1111 1111 1111 1111 V REF x (65,535/65,536)
1000 0000 0000 0000 V REF x (32,768/65,536) = 1/2 V REF
0000 0000 0000 0001 V REF x (1/65,536)
0000 0000 0000 0000 0
Table 2. MAX5138 Input Code vs. Output
Voltage
DAC LATCH CONTENTS
MSB LSB
ANALOG OUTPUT, V OUT
1111 1111 1111 XXX V REF x (4095/4096)
1000 0000 0000 XXX V REF x (2048/4096)
0000 0000 0001 XXX V REF x (1/4096)
0000 0000 0000 XXX 0
Table 3. MAX5139 Input Code vs. Output
Voltage