SN74LVC2T45-Q1 Datasheet, PDF (16/23 Pages) Texas Instruments – DUAL-BIT DUAL-SUPPLY BUS TRANSCEIVER WITH CONFIGURABLE VOLTAGE TRANSLATION AND 3-STATE OUTPUTS

SN74LVC2T45-Q1
SCES818 – SEPTEMBER 2010
APPLICATION INFORMATION
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Figure 3 shows the SN74LVC2T45-Q1 being used in a bidirectional logic level-shifting application. Since the
SN74LVC2T45-Q1 does not have an output-enable (OE) pin, the system designer should take precautions to
avoid bus contention between SYSTEM-1 and SYSTEM-2 when changing directions.
V_CC1
I/O-1
V_CC1
Pullup/Down
or Bus Hold⁽¹⁾
1
8
2
7
3
6
4
5
V_CC2
Pullup/Down
or Bus Hold⁽¹⁾
V_CC2
I/O-2
DIR CTRL
SYSTEM-1
SYSTEM-2
The following table shows data transmission from SYSTEM-1 to SYSTEM-2 and then from SYSTEM-2 to
SYSTEM-1.
STATE DIR CTRL
1
H
2
H
I/O-1
Out
Hi-Z
3
L
Hi-Z
4
L
In
I/O-2
In
Hi-Z
Hi-Z
Out
DESCRIPTION
SYSTEM-1 data to SYSTEM-2
SYSTEM-2 is getting ready to send data to SYSTEM-1. I/O-1 and I/O-2 are disabled. The
bus-line state depends on pullup or pulldown.⁽¹⁾
DIR bit is flipped. I/O-1 and I/O-2 still are disabled. The bus-line state depends on pullup or
pulldown. ⁽¹⁾
SYSTEM-2 data to SYSTEM-1
(1) SYSTEM-1 and SYSTEM-2 must use the same conditions, i.e., both pullup or both pulldown.
Figure 3. Bidirectional Logic Level-Shifting Application
Enable Times
Calculate the enable times for the SN74LVC2T45-Q1 using the following formulas:
• t_PZH (DIR to A) = t_PLZ (DIR to B) + t_PLH (B to A)
• t_PZL (DIR to A) = t_PHZ (DIR to B) + t_PHL (B to A)
• t_PZH (DIR to B) = t_PLZ (DIR to A) + t_PLH (A to B)
• t_PZL (DIR to B) = t_PHZ (DIR to A) + t_PHL (A to B)
In a bidirectional application, these enable times provide the maximum delay from the time the DIR bit is
switched until an output is expected. For example, if the SN74LVC2T45-Q1 initially is transmitting from A to B,
then the DIR bit is switched; the B port of the device must be disabled before presenting it with an input. After the
B port has been disabled, an input signal applied to it appears on the corresponding A port after the specified
propagation delay.
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