US223

Preliminary

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

5 of 7

www.unisonic.com.tw

QW-R129-022.a

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APPLICATION INFORMATION(Cont.)

Power Dissipation

The UTC US223’s junction temperature varies depending the several factors such as the load, PCB layout,

ambient temperature and package type. The output pin of UTC US223 can deliver the current of up to

2.5A(US223AH/AL) , 2A(US223BH/BL), 1.5A(US223CH/CL) and 0.8A(US223DH/DL) over the full operating junction

temperature range. However, at higher ambient temperature the maximum output current must be derated to ensure

the junction temperature does not exceed 100°C. With all possible conditions, the junction temperature must be

within the range specified under operating conditions. Power dissipation is determined by the output current and the

2

Although the devices are rated for 2.5A, 2A, 1.5A and 0.8A of output current, but the application may limit the

amount of output current based on the total power dissipation and the ambient temperature. The final operating

junction temperature for any set of conditions is calculated as follows:

Universal Serial Bus (USB) & Power Distribution

The USB’s goal is to be enabled device from different vendors to interoperate in an open architecture. The USB

is characterized incorporating ease of use for the end user, a wide range of workloads and applications, robustness,

synergy with the PC industry, and low-cost implementation. In addition, the benefits of the USB contain

self-identifying peripherals, dynamically attachable and reconfigurable peripherals, multiple connections (support for

concurrent operation of many devices), support physical devices up to 127, and compatibility with PC Plug-and-Play

architecture.

Each USB system has one USB host, and the USB connects USB devices with a USB host. USB devices can be

classified either as hubs, which provide additional attachment points to the USB, or as functions, which provide

capabilities to the system (for example, a digital joystick). Then the hub devices are classified as either bus-power

hubs or self-powered Hubs.

Self-powered hub power for the internal functions and downstream ports does not come from the USB, although

the USB interface may draw up to 100mA from its upstream connect, to allow the interface to function when the

remainder of the hub is powered down. The hub must be able to supply up to 500mA on all of its external

downstream ports. Over-current protection devices such as fuses and PTC resistors (also called poly fuse or

polyswitch) have slow trip times, high on-resistance, and lack the necessary circuitry for USB-required fault reporting.

A bus-powered hub draws all of the power to any internal functions and downstream ports from the USB connector

power pins. The hub may draw current as high as 500mA from the upstream device. External ports in a bus-powered

hub can supply up to 100mA per port, with a maximum of four external ports.

In order to protect the hubs to operating on the faults conditions, the faster trip time of the UTC US223 power

distribution can make it. For meeting voltage regulation and fault notification requirements, low on-resistance and

internal fault-reporting circuitry are required.

Furthermore, because the devices are power switches, they provide the designer of self-powered hubs flexibility

to turn off power to output ports. The devices have controlled rise and fall times to provide the needed inrush current

limiting required for the bus-powered hub power switch compared to a normal MOSFFT.

Supply Filter/Bypass Capacitor

To prevent input voltage droop occurs during hot-plug condition, a 1uF low-ESR ceramic capacitor located

the input. Furthermore, without the bypass capacitor, an output short may cause sufficient ringing on the input (from

source lead inductance) to destroy the internal control circuitry. The input transient’s value must be not higher than

the absolute maximum supply voltage ( 6.5V) even for a short duration.