LTM9004
23
9004fa
For more information
www.linear.com/LTM9004
Supply Sequencing
The V
CC
pins provide the supply to the mixer and all am-
plifiers and the V
DD
pins provide the supply to the ADC.
The mixer, amplifiers and ADC are separate integrated
circuits within the LTM9004; however, there are no sup-
ply sequencing considerations beyond standard practice.
Grounding and Bypassing
The LTM9004 requires a printed circuit board with a
clean unbroken ground plane; a multilayer board with an
internal ground plane is recommended. The pinout of the
LTM9004 has been optimized for a flowthrough layout so
that the interaction between inputs and digital outputs is
minimized. A continuous row of ground pads facilitates
a layout that ensures that digital and analog signal lines
are separated as much as possible.
The LTM9004 is internally bypassed with the ADC (V
DD
),
mixer and amplifier (V
CC
) supplies returning to a common
ground (GND). The digital output supply (OV
DD
) is returned
to OGND. A 0.1µF bypass capacitor should be placed at
each of the two OV
DD
pins. Additional bypass capacitance
is optional and may be required if power supply noise is
significant.
Heat Transfer
Most of the heat generated by the LTM9004 is transferred
through the bottom-side ground pads. For good electrical
and thermal performance, it is critical that all ground pins
are connected to a ground plane of sufficient area with as
many vias as possible.
Recommended Layout
The high integration of the LTM9004 makes the PCB
board layout simple. However, to optimize its electrical
and thermal performance, some layout considerations
are still necessary.
•
Use large PCB copper areas for ground. This helps to
dissipate heat in the package through the board and
also helps to shield sensitive on-board analog signals.
Common ground (GND) and output ground (OGND)
are electrically isolated on the LTM9004, but can be
connected on the PCB underneath the part to provide
a common return path.
•
Use multiple ground vias. Using as many vias as pos-
sible helps to improve the thermal performance of the
board and creates necessary barriers separating analog
and digital traces on the board at high frequencies.
•
Separate analog and digital traces as much as possible,
using vias to create high frequency barriers. This will
reduce digital feedback that can reduce the signal-to-
noise ratio (SNR) and dynamic range of the LTM9004.
Figures 11 through 14 give a good example of the recom-
mended layout.
The quality of the paste print is an important factor in
producing high yield assemblies. It is recommended to
use a type 3 or 4 printing no-clean solder paste. The sol-
der stencil design should follow the guidelines outlined
in Application Note 100.
The LTM9004 employs gold-finished pads for use with
Pb-based or tin-based solder paste. It is inherently Pb-free
and complies with the JEDEC (e4) standard. The materials
declaration is available online at http://www.linear.com/
leadfree/mat_dec.jsp.
applicaTions inForMaTion
