Integration Manual

TOBY-L2 and MPCI-L2 series - System Integration Manual
UBX-13004618 - R26 Design-in
Page 112 of 162
2.6.3 DDC (I
2
C) interface
The I
2
C bus compatible Display Data Channel interface is not available on MPCI-L2 series modules.
2.6.3.1 Guidelines for DDC (I
2
C) circuit design
I
2
C bus function is not supported by TOBY-L2 series modules “00”, “01”, “60” and TOBY-L201-02S
product versions: the pins should not be driven by any external device.
The DDC I
2
C-bus master interface can be used to communicate with external I
2
C-bus slaves as an audio codec.
Beside the general considerations reported below, see the section 2.7.1 for an application circuit example with an
external audio codec I
2
C-bus slave.
To be compliant with the I
2
C bus specifications, the module bus interface pads are open drain output and pull up
resistors must be mounted externally. Resistor values must conform to I
2
C bus specifications [13]: for example, 4.7
k resistors can be commonly used. Pull-ups must be connected to a supply voltage of 1.8 V (typical), since this is
the voltage domain of the DDC pins which are not tolerant to higher voltage values (e.g. 3.0 V).
Connect the DDC (I
2
C) pull-ups to the V_INT 1.8 V supply source, or another 1.8 V supply source enabled
after V_INT, as any external signal connected to the DDC (I
2
C) interface must not be set high before the
switch-on of the V_INT supply of DDC (I
2
C) pins, to avoid latch-up of circuits and let a proper boot of the
module.
The signal shape is defined by the values of the pull-up resistors and the bus capacitance. Long wires on the bus
will increase the capacitance. If the bus capacitance is increased, use pull-up resistors with nominal resistance value
lower than 4.7 k, to match the I
2
C bus specifications [13] regarding rise and fall times of the signals.
Capacitance and series resistance must be limited on the bus to match the I
2
C specifications (1.0 µs is the
maximum allowed rise time on the SCL and SDA lines): route connections as short as possible.
If the pins are not used as DDC bus interface, they can be left unconnected.
ESD sensitivity rating of the DDC (I
2
C) pins is 1 kV (Human Body Model according to JESD22-A114). Higher
protection level could be required if the lines are externally accessible and it can be achieved by mounting
an ESD protection (e.g. EPCOS CA05P4S14THSG varistor array) close to accessible points.
2.6.3.2 Guidelines for DDC (I
2
C) layout design
The DDC (I
2
C) serial interface requires the same consideration regarding electro-magnetic interference as any other
digital interface. Keep the traces short and avoid coupling with RF line or sensitive analog inputs, since the signals
can cause the radiation of some harmonics of the digital data frequency.