TOBY-L4 series - System Integration Manual
UBX-16024839 - R04
Design-in
Page 101 of 143
2.7
eMMC interface
The eMMC interface is not supported by the "50" product version.
2.7.1.1
Guidelines for eMMC circuit design
TOBY-L4 series modules include a 4-bit embedded Multi-Media Card interface compliant with
JESD84-B451
Embedded Multimedia Card (eMMC) Electrical Standard 4.51
[9], which can be handled by means of the uCPU
API.
The eMMC interface can be connected to an external eMMC / SD memory as defined by the standard.
Pull-up resistors can be added on
MMC_D0
,
MMC_D1
,
MMC_D2
and
MMC_D3
data lines, the
MMC_CLK
clock line and the
MMC_CMD
command line, to increase the rise time on the signals so as to compensate for
any capacitance on the board, even if not strictly required.
The ESD sensitivity rating of eMMC interface pins is 1 kV (HMB according to JESD22-A114). A higher
protection level could be required if the lines are externally accessible and it can be achieved by mounting
a very low capacitance ESD protection (e.g. Tyco Electronics PESD0402-140 ESD) close to the accessible
points.
If the eMMC interface pins are not used, they can be left unconnected on the application board.
2.7.1.2
Guidelines for eMMC layout design
The eMMC interface requires the same considerations regarding electro-magnetic interference as any other high
speed digital interface.
Keep the traces short, avoid stubs and avoid coupling with RF lines / parts or sensitive analog inputs, since the
signals can cause the radiation of some harmonics of the digital data frequency.
Consider the usage of low value series damping resistors to avoid reflections and other losses in signal integrity,
which may create ringing and loss of a square wave shape.
