Datasheet

BUS B
PCA9517
SDA SDAB
SDA
SCL
SCLB
SCL
EN
BUS A
3.3 V
SDAA
SCLA
V
CCA
V
CCB
10 kW
1.2 V
SLAVE
400 kHz
BUS
MASTER
400 kHz
10 kW
10 kW
10 kW
Not Recommended for New Designs
PCA9517
www.ti.com SCPS157D –DECEMBER 2007–REVISED MARCH 2012
APPLICATION INFORMATION
A typical application is shown in Figure 6. In this example, the system master is running on a 3.3-V I
2
C bus, and
the slave is connected to a 1.2-V bus. Both buses run at 400 kHz. Master devices can be placed on either bus.
The PCA9517 is 5-V tolerant, so it does not require any additional circuitry to translate between 0.9-V to 5.5-V
bus voltages and 2.7-V to 5.5-V bus voltages.
When the A side of the PCA9517 is pulled low by a driver on the I
2
C bus, a comparator detects the falling edge
when it goes below 0.3 V
CCA
and causes the internal driver on the B side to turn on, causing the B side to pull
down to about 0.5 V. When the B side of the PCA9517 falls, first a CMOS hysteresis-type input detects the
falling edge and causes the internal driver on the A side to turn on and pull the A-side pin down to ground. In
order to illustrate what would be seen in a typical application, refer to Figure 8 and Figure 9. If the bus master in
Figure 6 were to write to the slave through the PCA9517, waveforms shown in Figure 8 would be observed on
the A bus. This looks like a normal I
2
C transmission, except that the high level may be as low as 0.9 V, and the
turn on and turn off of the acknowledge signals are slightly delayed.
On the B-side bus of the PCA9517, the clock and data lines would have a positive offset from ground equal to
the V
OL
of the PCA9517. After the eighth clock pulse, the data line is pulled to the V
OL
of the slave device, which
is very close to ground in this example. At the end of the acknowledge, the level rises only to the low level set by
the driver in the PCA9517 for a short delay, while the A-bus side rises above 0.3 V
CCA
and then continues high.
Figure 6. Typical Application
Copyright © 2007–2012, Texas Instruments Incorporated Submit Documentation Feedback 9
Product Folder Links: PCA9517