TC35679FSG-002

2018-01-17

24

4.5.3.

Selection of External Pull-up Resistor Value

An external pull-up resistor value needs to be selected by the following equations in case of I2C bus interface. Its maximum value is

defined by equation (1), in which tr is rise time of serial clock and data and Cb is I

2C bus capacity. Its minimum value is defined by

equation (2), in which VDDIO is a supply voltage for TC35679, Vol_max is the maximum value of low level output voltage, and Iol is

the low level output current. Please set the pull-up resistor value between these lower and upper limits.

b

r

C

t

×

=

8473

.

0

Rext_max

(1)

ol

ol

I

V

VDDIO

max

_

ext_min

R

−

=

(2)

TC35679 supports I2C bus standard mode (Max 100 kHz) and I2C bus fast mode (Min 100 kHz to Max 400 kHz). The rise time tr is

1000 ns for the standard mode and it is 300 ns for the fast mode. Cb can vary depending on the IC board and how it is

implemented. Table 4-3 and Table 4-4 show examples when I2C bus capacity is 20 pF.

Table 4-3 External pull-up resistor value for I

2

C standard mode (Cb = 20 pF)

I

2Cbus frequency

Max 100 kHz

tr [ns]

1000

Cb [pF]

20

VDDIO [V]

1.8

3.0

3.6

Vol_max [V]

0.3

0.4

0.4

Iol [mA]

1

2

4

1

2

4

1

2

4

Rext_min [kΩ]

1.50 0.75 0.38 2.60 1.30 0.65 3.20 1.60 0.80

Rext_max [kΩ]

59.01

Table 4-4 External pull-up resistor value for I

2

C fast mode (Cb = 20 pF)

I

2Cbus frequency

Min 100 to Max 400 kHz

tr [ns]

300

Cb [pF]

20

VDDIO [V]

1.8

3.0

3.6

Vol_max [V]

0.3

0.4

0.4

Iol [mA]

1

2

4

1

2

4

1

2

4

Rext_min [kΩ]

1.50 0.75 0.38 2.60 1.30 0.65 3.20 1.60 0.80

Rext_max [kΩ]

17.70