FXMAR2102 Datasheet, PDF (7/16 Pages) Fairchild Semiconductor – Dual-Supply, 2-Bit Voltage Translator / Isolator for I2C Applications

V_OL vs. I_OL
The I²C specification mandates a maximum V_IL (I_OL of
3mA) of V_CC • 0.3 and a maximum V_OL of 0.4V. If there
is
of
a master on
1.65V and a
the A
slave
port of
on the
an I²C translator
I²C translator B
with
port
a V_CC
with a
V_CC of 3.3V, the maximum V_IL of the master is (1.65V x
0.3) 495mV. The slave could legally transmit a valid
logic LOW of 0.4V to the master.
If the I²C translator’s channel resistance is too high, the
voltage drop across the translator could present a V_IL to
the master greater than 495mV. To complicate matters,
the I²C specification states that 6mA of I_OL is
recommended for bus capacitances approaching
I4^{20C0ptFra.nMsloartoer.IO}T^L hinecrIe²Caseasppthliecavtioolntagbeenderofitps
across
when
the
I²C
translators exhibit low V_OL performance. Figure 6
depicts typical FXMAR2102 V_OL performance vs. the
competition, given a 0.4V V_IL.
0.65
0.6
0.55
0.5
0.45
0.4
0
V_OL: FXMAR2102 vs. Device B, V_IL = 0.4V
Device B
V_IL = 0.4V
FXMAR2102
V_IL = 0.4V
2
4
6
8
10
I_OL (mA):
Figure 6. Device Comparison
© 2011 Fairchild Semiconductor Corporation
FXMAR2102 • Rev. 1.0.0
7
www.fairchildsemi.com