PIC17C7XX_13 Datasheet, PDF (175/306 Pages) Microchip Technology – High-Performance 8-bit CMOS EPROM Microcontrollers with 10-bit A/D

PIC17C7XX
15.3 Connection Considerations for
I²C Bus
For standard mode I²C bus devices, the values of
resistors R_p R_s in Figure 15-42 depends on the follow-
ing parameters:
• Supply voltage
• Bus capacitance
• Number of connected devices (input current +
leakage current)
The supply voltage limits the minimum value of resistor
R_p due to the specified minimum sink current of 3 mA
at VOL max = 0.4V for the specified output stages. For
example, with a supply voltage of VDD = 5V +10% and
VOL max = 0.4V at 3 mA, R_p min = (5.5-0.4)/0.003 =
1.7 k VDD as a function of R_p is shown in Figure 15-
42. The desired noise margin of 0.1 VDD for the low
level, limits the maximum value of R_s. Series resistors
are optional and used to improve ESD susceptibility.
The bus capacitance is the total capacitance of wire,
connections and pins. This capacitance limits the max-
imum value of R_p due to the specified rise time
(Figure 15-42).
The SMP bit is the slew rate control enabled bit. This bit
is in the SSPSTAT register and controls the slew rate of
the I/O pins when in I²C mode (master or slave).
FIGURE 15-42:
SAMPLE DEVICE CONFIGURATION FOR I²C BUS
VDD + 10%
R_p
R_p
DEVICE
R_s
R_s
SDA
SCL
C_b = 10 - 400 pF
Note: I²C devices with input levels related to VDD must have one common supply line to which the pull-up resistor is
also connected.
 1998-2013 Microchip Technology Inc.
DS30289C-page 175