LTM9001-AX_15 Datasheet, PDF (26/30 Pages) Linear Technology – 16-Bit IF/Baseband Receiver Subsystem

LTM9001-Ax/LTM9001-Bx
APPLICATIONS INFORMATION
Grounding and Bypassing
The LTM9001 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
LTM9001 has been optimized for a flow-through layout
so that the interaction between inputs and digital outputs
is minimized. A continuous row of ground pads facilitate
a layout that ensures that digital and analog signal lines
are separated as much as possible.
The LTM9001 is internally bypassed with the amplifier (V_CC)
and ADC (V_DD) supplies returning to a common ground
(GND). The digital output supply (0V_DD) is returned to
OGND. Additional bypass capacitance is optional and may
be required if power supply noise is significant.
The differential inputs should run parallel and close to each
other. The input traces should be as short as possible to
minimize capacitance and to minimize noise pickup.
Heat Transfer
Most of the heat generated by the LTM9001 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 LTM9001 makes the PC board
layout very simple and easy. However, to optimize its electri-
cal and thermal performance, some layout considerations
are still necessary, see Figures 15-18.
• 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 LTM9001, 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 pos-
sible, 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
LTM9001.
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 solder
stencil design should follow the guidelines outlined in
Application Note 100.
The LTM9001 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 materi-
als declaration is available online at http://www.linear.
com/designtools/leadfree/mat_dec.jsp.
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