TCA9617A Datasheet, PDF (8/17 Pages) Texas Instruments – LEVEL-TRANSLATING FM+ I2C BUS REPEATER

TCA9617A
SCPS244 – JUNE 2013
www.ti.com
B-side Pedestal
Figure 5 depicts the pedestal on the B side of the device. At point 1 in Figure 5 the slave device is driving the B-
side low. As the slave releases and the B-side rises, it will only be allowed to rise to 0.5 V until the A-side rises
above 0.3V_CCA. This effect is called the pedestal. Once this threshold is crossed the B-side will continue to rise to
V_CCB.
Due to nature of the B-side pedestal and the static offset voltage, there will be a slight overshoot (point 2) as the
B-side rises from the V_OL of the B-side driver to the 0.5 V offset. The TCA9617A is designed to control this
behavior provided the system is designed with RCs greater than 20 ns. Note that care should be taken to limit
the pull-up strength when devices with rise time accelerators are present on the B side. Excessive overshoot on
the B-side pedestal may cause devices with rise time accelerators to trip prematurely if the accelerator
thresholds are below 0.3 V_CCB.
2
1
Figure 5. B-side Pedestal
B-side Inverted Pedestal
To decrease the propagation delay of the TCA9617A, an inverted pedestal (Figure 6) is used on the B side of the
device. When the A side of the Bus drives to 0.7 V_CCA the B side driver will turn on. This will drive the B-side to 0
V for a short period (point 1) and then the B-side will rise to the static offset voltage of 0.5 V (point 2). This
design allows the B-side to drive to logic low much faster than simply driving to the static offset as driving to the
static offset voltage requires that the fall time be slowed to prevent ringing.
2
1
Figure 6. B-side Inverted Pedestal
8
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