User's Manual

NXP Semiconductors
UM10301
User Manual PCF85x3, PCA8565 and PCF2123, PCA2125
UM10301_1 © NXP B.V. 2008. All rights reserved.
User manual Rev. 01 — 23 December 2008 41 of 52
b
r
P
C
t
R
⋅
=
8473.0
(max)
002aac883
C
b
(pF)
0 600400200
8
12
4
16
20
R
p(max)
(kΩ)
0
(1)
(2)
(3)
(1) Standard-mode
(2) Fast-mode
(3) Fast-mode Plus
Fig 17. R
p(max)
as a function of bus capacitance
Below R
p(max)
is calculated for both Standard-mode and Fast-mode I
2
C bus. The result
has been rounded down to E6 standard values.
400 kHz I
2
C bus: Ω=
⋅⋅
⋅
=
⋅
=
−
−
−
k
C
t
R
b
r
kHzP
22
109.148473.0
10300
8473.0
12
9
400
100 kHz I
2
C bus: Ω=
⋅⋅
⋅
=
⋅
=
−
−
−
k
C
t
R
b
r
kHzP
68
109.148473.0
101
8473.0
12
6
100
Two examples of an application diagram are shown in
Fig 18 and Fig 19. In these
examples the
INT output is left unused. If used, a pull-up to V
DD
is required.
The first example is using PCF8563 (
Fig 18), the second example is using PCA2125
(
Fig 19). In both examples the optional backup supply is realized using a 1 F capacitor.