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| TCA9539_15 Datasheet, PDF (27/42 Pages) Texas Instruments – Low Voltage 16-Bit I2C and SMBus Low-Power I/O Expander | |||
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www.ti.com
TCA9539
SCPS202B â OCTOBER 2009 â REVISED OCTOBER 2015
Typical Application (continued)
9.2.2 Detailed Design Procedure
The pull-up resistors, RP, for the SCL and SDA lines need to be selected appropriately and take into
consideration the total capacitance of all slaves on the I2C bus. The minimum pull-up resistance is a function of
VCC, VOL,(max), and IOL:
Rp(min)
=
VCC
- VOL(max)
IOL
(1)
The maximum pull-up resistance is a function of the maximum rise time, tr (300 ns for fast-mode operation,
fSCL = 400 kHz) and bus capacitance, Cb:
Rp(max)
=
tr
0.8473 ´ Cb
(2)
The maximum bus capacitance for an I2C bus must not exceed 400 pF for standard-mode or fast-mode
operation. The bus capacitance can be approximated by adding the capacitance of the TCA9554A, Ci for SCL or
Cio for SDA, the capacitance of wires/connections/traces, and the capacitance of additional slaves on the bus.
9.2.3 Application Curves
25
Standard-mode
Fast-mode
20
15
10
5
0
0 50 100 150
Standard-mode
(fSCL= 100 kHz, tr = 1 µs)
200 250 300 350 400 450
Cb (pF)
D008
Fast-mode
(fSCL= 400 kHz, tr= 300 ns)
Figure 37. Maximum Pull-Up resistance (Rp(max)) vs Bus
Capacitance (Cb)
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
VCC > 2V
VCC <= 2
0
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
D009
VOL = 0.2*VCC, IOL = 2 mA when VCC ⤠2 V
VOL = 0.4 V, IOL = 3 mA when VCC > 2 V
Figure 38. Minimum Pull-Up Resistance (Rp(min)) vs Pull-Up
Reference Voltage (VCC)
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