8.3.1 Architecture

The TXS0101 architecture (see Figure 10) does not require a direction-control signal to control the direction of data flow from A to B or from B to A.

Figure 10. Architecture of a TXS01xx Cell

Each A-port I/O has an internal 10 kΩ pullup resistor to V_CCA, and each B-port I/O has an internal 10 kΩ pullup resistor to V_CCB. The output one-shots detect rising edges on the A or B ports. During a rising edge, the one-shot turns on the PMOS transistors (T1,T2) for a short duration, which speeds up the low-to-high transition.

8.3.2 Input Driver Requirements

The fall time (t_fA, t_fB) of a signal depends on the output impedance of the external device driving the data I/Os of the TXS0101. Similarly, the t_PHL and max data rates also depend on the output impedance of the external driver. The values for t_fA, t_fB, t_PHL, and maximum data rates in the data sheet assume that the output impedance of the external driver is less than 50 Ω.

8.3.3 Power Up

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.

8.3.4 Enable and Disable

The TXS0101 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.

8.3.5 Pullup or Pulldown Resistors on I/O Lines

Each A-port I/O has an internal 10 kΩ pullup resistor to V_CCA, and each B-port I/O has an internal 10 kΩ pullup resistor to V_CCB. If a smaller value of pullup resistor is required, an external resistor must be added from the I/O to V_CCA or V_CCB (in parallel with the internal 10 kΩ resistors).