SN74LVCH8T245_16 Datasheet, PDF (17/33 Pages) Texas Instruments – 8-BIT Dual-Supply Bus Transceiver

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SN74LVCH8T245
SCES637B – AUGUST 2005 – REVISED FEBRUARY 2016
10 Power Supply Recommendations
The output-enable (OE) input circuit is designed so that it is supplied by V_CCA and when the OE input is high, all
outputs are placed in the high-impedance state. To ensure the high-impedance state of the outputs during power
up or power down, the OE input pin must be tied to V_CCA through a pullup resistor and must not be enabled until
V_CCA and V_CCB are fully ramped and stable. The minimum value of the pullup resistor to V_CCA is determined by
the current-sinking capability of the driver.
V_CCA or V_CCB can be powered up first. If the SN74LVCH8T245 is powered up in a permanently enabled state
(for example OE is always kept low), pullup resistors are recommended at the input. This ensures proper, glitch-
free, power-up. See Designing with SN4LVCXT245 and SN74LVCHXT245 Family of Direction Controlled Voltage
Translators/Level-Shifters (SLVA746). In addition, the OE pin may be shorted to GND if the application does not
require use of the high-impedance state at any time.
11 Layout
11.1 Layout Guidelines
To ensure reliability of the device, TI recommends the following common printed-circuit board layout guidelines.
• Bypass capacitors should be used on power supplies.
• Short trace lengths should be used to avoid excessive loading.
• Placing pads on the signal paths for loading capacitors or pullup resistors helps adjust rise and fall times of
signals depending on the system requirements.
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