TOBY-L4 series - System Integration Manual
UBX-16024839 - R04
Design-in
Page 94 of 143
2.6.4
DDC (I
2
C) interfaces
DDC (I
2
C) interfaces are not supported by the "50" product version.
2.6.4.1
General guidelines for DDC (I
2
C) circuit design
The DDC I
2
C-bus pins of the module are open drain outputs conforming to the
I
2
C bus specifications
[6]. External
pull-up resistors to a suitable 1.8 V supply (e.g.
V_INT
) are required for operations: for example, 4.7 k
resistors
can be commonly used.
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
(e.g., as the GNSS 1.8 V supply present in Figure 54 application circuit), 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 allow a clean 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 a nominal resistance
value lower than 4.7 k
, to match the
I
2
C bus specifications
[6] regarding the rise and fall times of the signals.
Figure 53 and Table 38 describe typical application circuits for connecting TOBY-L4 series modules to 1.8 V I2C
devices (see Figure 53 top side) or 3 V I2C devices (see Figure 53 bottom side).
1.8V I2C Device
SDA
SCL
1V8
5
V_INT
R1
R2
1V8
1V8
SDAx
SCLx
TOBY-L4 series
R1
R2
3V0
SDAx
SCLx
R3
R4
1V8
SDA_A
SDA_B
GND
U1
SCL_A
SCL_B
VCCA
VCCB
I2C-bus Bidirectional
Voltage Translator
5
V_INT
C1
C2
SDA
SCL
OE
GND
GND
3V I2C Device
TOBY-L4 series
GND
GND
Figure 53: Application circuit for connecting TOBY-L4 series modules to 1.8 V or 3 V I2C devices
Reference
Description
Part Number - Manufacturer
R1, R2, R3, R4
4.7 k
Resistor 0402 5% 0.1 W
RC0402JR-074K7L - Yageo Phycomp
C1, C2
100 nF Capacitor Ceramic X7R 0402 10% 16 V
GRM155R71C104KA01 - Murata
U1
I2C-bus Bidirectional Voltage Translator
TCA9406DCUR
19
- Texas Instruments
Table 38: Components for connecting TOBY-L4 series modules to 1.8 V or 3 V I2C devices
The ESD sensitivity rating of the DDC (I
2
C) pins is 1 kV (Human Body Model according to JESD22-A114).
A 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 the accessible points.
If the pins are not used as DDC bus interface, they can be left unconnected.
19
Voltage translator providing partial power down feature so that the external 3 V supply can be also ramped up before
V_INT
1.8 V supply
