Datasheet

Power Up
Enable and Disable
Pullup or Pulldown Resistors on I/O Lines
TXS0108E
www.ti.com ..................................................................................................................................... SCES642B – DECEMBER 2007 – REVISED SEPTEMBER 2008
(P1) for a short-duration and this speeds up the low-to-high transition. Similarly, during a falling edge, when
transmitting data from B to A, the One-Shot (OS2) turns on NMOS transistor (N1) for a short-duration and this
speeds up the high-to-low transition. The A-port edge-rate accelerator consists of one-shots OS1 and OS2,
Transistors P1 and N1 components and form the edge-rate accelerator and serves to rapidly force the A port
high or low when a corresponding transition is detected on the B port.
During operation, ensure that V
CCA
≤ V
CCB
at all times. During power-up sequencing, V
CCA
≥ V
CCB
does not
damage the device, so any power supply can be ramped up first.
The TXS0108E has an OE input that is used to disable the device by setting OE low, which places all I/Os in the
Hi-Z state. The disable time (t
dis
) indicates the delay between the time when OE goes low and when the outputs
actually get disabled (Hi-Z). The enable time (t
en
) indicates the amount of time the user must allow for the
one-shot circuitry to become operational after OE is taken high.
Each A-port I/O has a pull-up resistor (R
pua
) to V
CCA
and each B-port I/O has a pull-up resistor (R
pub
) to V
CCB
.
R
pua
and R
pub
have a value of 40 k Ω when the output is driving low. R
pua
and R
pub
have a value of 4 k Ω when the
output is driving high. R
pua
and R
pub
are disabled when OE = Low.
Copyright © 2007 – 2008, Texas Instruments Incorporated Submit Documentation Feedback 13
Product Folder Link(s): TXS0108E