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| TCA9534_16 Datasheet, PDF (25/38 Pages) Texas Instruments – Low Voltage 8-Bit I2C and SMBUS Low-Power I/O Expander with Interrupt Output and Configuration Registers | |||
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Typical Application (continued)
TCA9534
SCPS197B â SEPTEMBER 2014 â REVISED NOVEMBER 2016
3.3 V
5V
VCC
LED
LEDx
Figure 35. Device Supplied by a Lower Voltage
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 as shown in Equation 5.
Rp(min)
=
VCC
- VOL(max)
IOL
(5)
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 as shown in Equation 6.
Rp(max)
=
tr
0.8473 ´ Cb
(6)
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 TCA9534, 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 36. 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 37. Minimum Pull-Up Resistance (Rp(min)) vs Pull-Up
Reference Voltage (VCC)
Copyright © 2014â2016, Texas Instruments Incorporated
Product Folder Links: TCA9534
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