Datasheet

MAX5851
Dual, 8-Bit, 80Msps, Current-Output DAC
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DA0–DA7
8
MAX5851
1/2
50Ω
100Ω
50Ω
OUTPA
OUTNA
V
OUTA
,
SINGLE ENDED
DB0–DB7
8
MAX5851
1/2
50Ω
100Ω
50Ω
OUTPB
OUTNB
V
OUTB
,
SINGLE ENDED
CV
DD
DV
DD
AV
DD
CGNDDGNDAGND
Figure 7. Application with Output Transformer (Coilcraft
TTWB3010-1) Performing Differential-to-Single-Ended Conversion
DA0–DA7
8
MAX5851
1/2
1/2
50Ω
50Ω
CV
DD
DV
DD
AV
DD
CGNDDGNDAGND
OUTPA
OUTNA
DB0–DB7
8
MAX5851
50Ω
50Ω
OUTPB
OUTNB
Figure 8. Application with DC-Coupled Differential Outputs
Applications Information
Differential-to-Single-Ended Conversion
The MAX5851 exhibits excellent dynamic performance
to synthesize a wide variety of modulation schemes,
including high-order QAM modulation with OFDM.
Figure 7 shows a typical application circuit with output
transformers performing the required differential-to-
single-ended signal conversion. In this configuration,
the MAX5851 operates in differential mode, which
reduces even-order harmonics, and increases the
available output power.
Differential DC-Coupled Configuration
Figure 8 shows the MAX5851 output operating in differ-
ential, DC-coupled mode. This configuration can be
used in communication systems employing analog
quadrature upconverters and requiring a baseband
sampling, dual-channel, high-speed DAC for I/Q syn-
thesis. In these applications, information bandwidth can
extend from 10MHz down to several hundred kilohertz.
DC-coupling is desirable to eliminate long discharge
time constants that are problematic with large, expen-
sive coupling capacitors. Analog quadrature upcon-
verters have a DC common-mode input requirement of
typically 0.7V to 1.0V. The MAX5851 differential I/Q out-
puts can maintain the desired full-scale level at the
required 0.7V to 1.0V DC common-mode level when
powered from a single 2.85V (±5%) supply. The
MAX5851 meets this low-power requirement with mini-
mal reduction in dynamic range while eliminating the
need for level-shifting resistor networks.
Power Supplies, Bypassing,
Decoupling, and Layout
Grounding and power-supply decoupling strongly influ-
ence the MAX5851 performance. Unwanted digital
crosstalk can couple through the input, reference,