FOUR-PORT USB HUB POWER CONTROLLERS
SLVS287A – SEPTEMBER 2000 – REVISED FEBRUARY 2001
POST OFFICE BOX 655303
• DALLAS, TEXAS 75265
Thermal protection prevents damage to the IC when heavy-overload or short-circuit faults are present for
extended periods. The faults force the TPS2070 and TPS2071 into constant-current mode at first, 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 TPS2070 and TPS2071 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 rises. Once the die
temperature rises to approximately 140
°C, the internal thermal-sense circuitry determines which power switch
is in an overcurrent condition and turns only that power switch off, thus isolating the fault without interrupting
operation of the adjacent power switch. If the die temperature exceeds the first thermal trip point of 140
°C, the device turns off. The OC output is asserted (active low) when overtemperature or
undervoltage lockout (UVLO)
An undervoltage lockout ensures that the device (LDO and switches) is in the off state at power up. The UVLO
will also keep the device from being turned on until the power supply has reached the start threshold (see
undervoltage lockout table), even if the switches are enabled. The UVLO will activate whenever the input
voltage falls below the stop threshold as defined in the undervoltage lockout table. This facilitates the design
of hot-insertion systems where it is not possible to turn off the power switches before input power is removed.
Upon reinsertion, the power switches will be turned on with a controlled rise time to reduce EMI and voltage
self-power to bus-power or bus-power to self-power transition
An autoswitching function between bus-powered mode and self-powered mode is a feature of the TPS2070 and
TPS2071. When this feature is enabled (BP_DIS is inactive) and SP is removed or applied, a transition will be
initiated. The transition sequence begins with the internal LDO being turned off and its external capacitance
discharged. Any enabled switches are also turned off and the external capacitors discharged. Once the LDO
and switch outputs are low, the internal logic will turn the LDO back on. This entire sequence occurs whenever
power to the SP input is removed or applied, regardless of the source of power, i.e., an external power supply
or the use of the external regulator.