SCES643I November 2006 – December 2024 TXB0108
ADVANCE INFORMATION
Refer to the PDF data sheet for device specific package drawings
To begin the design process, determine the following:
• Input voltage range
- Use the supply voltage of the device that is driving the TXB0108 device to determine the input voltage range. For a valid logic high the value must exceed the VIH of the input port. For a valid logic low, the value must be less than the VIL of the input port.
• Output voltage range
- Use the supply voltage of the device that the TXB0108 device is driving to determine the output voltage range.
- Do not recommend having the external pullup or pulldown resistors. If mandatory, it is recommended the value should be larger than 50 kΩ.
• An external pulldown or pullup resistor decreases the output VOH and VOL. Use the below equations to draft estimate the VOH and VOL as a result of an external pulldown and pullup resistor.
VOH = VCCx × RPD / (RPD + 4.5 kΩ)
VOL = VCCx × 4.5kΩ / (RPU + 4.5 kΩ)
Where:
• VCCx is the output port supply voltage on either VCCA or VCCB
• RPD is the value of the external pull down resistor
• RPU is the value of the external pull up resistor
• 4.5 kΩ is the counting the variation of the serial resistor 4 kΩ in the I/O line. Refer to the Effects of external pullup and pulldown resistors on TXB application note