UNTB0102

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CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

15 of 16

www.unisonic.com.tw

QW-R140-031.a



DETAILED DESCRIPTION

Overview

The architecture of the UNTB0102 is shown in Figure 1. The device does not require an extra input signal to

control the direction of data flow from A to B or from B to A. In a static state, the output drivers of the UNTB0102 can

maintain a defined output level, but the output architecture is designed to be weak, so that they can be overdriven by

an external driver when data on the bus starts flowing in the opposite direction. The output of one-shot circuits detect

rising or falling edges on the A or B ports. During a rising edge, the one-shot circuits turn on the PMOS transistors

(T1, T3) for a short duration, accelerating the LOW-to-HIGH transition. Similarly, during a falling edge, the one-shot

circuits turn on the NMOS transistors (T2, T4) for a short duration, accelerating the HIGH-to-LOW transition. During

output transitions the typical output impedance is 70 Ω at VCCO=1.2V to 1.8V,50Ω at VCCO=1.8V to 3.3V and 40Ω at

VCCO=3.3V to 5.0V.

Figure 1. Architecture of UNTB0102 I/O Cell

Power-up

During operation VCCA must never be higher than VCCB, however during power-up VCCA ≥ VCCB does not damage

the device, so either power supply can be ramped up first. There is no special power-up sequencing required. The

UNTB0102

includes circuitry that disables all output ports when either VCCA or VCCB is switched off.

Enable and Disable

An output enable input (OE) is used to disable the device. Setting OE=LOW causes all I/Os to assume the

high-impedance OFF-state. The disable time (tdis with no external load) indicates the delay between when OE goes

LOW and when outputs actually become disabled. The enable time (ten) indicates the amount of time the user must

allow

for one one-shot circuitry to become operational after OE is taken HIGH. To ensure the high-impedance OFF-state

during power-up or power-down, pin OE should be tied to GND through a pull-down resistor, the minimum value of

the resistor is determined by the current-sourcing capability of the driver.

Pull-up or Pull-down Resistors on I/O Lines

As mentioned previously the UNTB0102 is designed with low static drive strength to drive capacitive loads of up to

70pF. To avoid output contention issues, any pull-up or pull-down resistors used must be above 50kΩ. For this

reason the UNTB0102 is not recommended for use in open drain driver applications such as 1-Wire or I

2C-bus. For

these applications, the level translator is recommended.