AN883 Datasheet, PDF (1/4 Pages) Silicon Laboratories – LOW-COST IC LEVEL TRANSLATOR

AN883
LOW-COST I²C LEVEL TRANSLATOR
1. Introduction
This applications note discusses a low-cost circuit for I²C level translation. This circuit was developed for the
Si701x, Si702x, and Si703x humidity sensors but will work in many applications.
This circuit provides I²C level translation from a higher voltage supply, such as 5 V, to a lower voltage, supply such
as 1.8 or 3.3 V. In addition, the optional emitter follower circuit provides a low-voltage power supply rail from the
higher 5 V supply.
Note that some devices allow for higher voltage tolerance on I²C inputs. For example, the Si7034 has a 3.3 V
tolerant I²C interface, so the level translation is only required for 5 V I²C designs.
2. Circuit
The basic circuit is shown in Figure 1.
5V
Optionally replace with LDO
1.8V
U3
VCC ⁴
SCL ³
2
SDA
1
GND
R1
4.7K
R2
4.7K
R6
10K
R7
6.65K
D3
BAS16X
Q3
MMBT3904
R8
10K
R3
4.7K
R4
4.7K
D1
BAS40
D2
2
SCL
4 _SDA
U1
Si7034
6
NC
NC ³
C1
0.1uF
BAS40
Q2
MMBT3904
1.8V
R5
10K
Figure 1. Low-Cost I²C Level Translator Circuit
In this case, we are translating from 5 V to 1.8 V, and the I²C speed is assumed to be sufficiently slow for clock
stretching to not occur (i.e. less than 300 kHz for the Si701x, Si702x, and Si703x humidity sensors). In this case,
the SCL line is unidirectional.
Rev 0.1 1/15
Copyright © 2015 by Silicon Laboratories
AN883