TPS2047, TPS2057

TRIPLE CURRENT-LIMITED POWER-DISTRIBUTION SWITCHES

SLVS194 – APRIL 1999

18

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

APPLICATION INFORMATION

thermal protection

Thermal protection prevents damage to the IC when heavy-overload or short-circuit faults are present for

extended periods of time. The faults force the TPS2047 and TPS2057 into constant current mode, which causes

the voltage across the high-side switch to increase; under short-circuit conditions, the voltage across the switch

is equal to the input voltage. The increased dissipation causes the junction temperature to rise to high levels.

The protection circuit senses the junction temperature of the switch and shuts it off. Hysteresis is built into the

thermal sense circuit, and after the device has cooled approximately 20 degrees, the switch turns back on. The

switch continues to cycle in this manner until the load fault or input power is removed.

The TPS2047 and TPS2057 implement a dual thermal trip to allow fully independent operation of the power

distribution switches. In an overcurrent or short-circuit condition the junction temperature will rise. Once the die

temperature rises to approximately 140

°C, the internal thermal sense circuitry checks which power switch is

in an overcurrent condition and turns that power switch off, thus isolating the fault without interrupting operation

of the adjacent power switch. Should the die temperature exceed the first thermal trip point of 140

°C and reach

160

°C, both switches turn off. The OC open-drain output is asserted (active low) when overtemperature or

overcurrent occurs.

undervoltage lockout (UVLO)

An undervoltage lockout ensures that the power switch is in the off state at power up. Whenever the input voltage

falls below approximately 2 V, the power switch will be quickly turned off. This facilitates the design of

hot-insertion systems where it is not possible to turn off the power switch before input power is removed. The

UVLO will also keep the switch from being turned on until the power supply has reached at least 2 V, even if

the switch is enabled. Upon reinsertion, the power switch will be turned on with a controlled rise time to reduce

EMI and voltage overshoots.

Universal Serial Bus (USB) applications

The universal serial bus (USB) interface is a 12-Mb/s, or 1.5-Mb/s, multiplexed serial bus designed for

low-to-medium bandwidth PC peripherals (e.g., keyboards, printers, scanners, and mice). The four-wire USB

interface is conceived for dynamic attach-detach (hot plug-unplug) of peripherals. Two lines are provided for

differential data, and two lines are provided for 5-V power distribution.

USB data is a 3.3-V level signal, but power is distributed at 5 V to allow for voltage drops in cases where power

is distributed through more than one hub across long cables. Each function must provide its own regulated 3.3 V

from the 5-V input or its own internal power supply.

The USB specification defines the following five classes of devices, each differentiated by power-consumption

requirements:

D Hosts/self-powered hubs (SPH)

D Bus-powered hubs (BPH)

D Low-power, bus-powered functions

D High-power, bus-powered functions

D Self-powered functions

Bus-powered hubs distribute data and power to downstream functions. The TPS2047 and TPS2057 can

provide power-distribution solutions for many of these classes of devices.