TPS22981

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SLVSBM6B – DECEMBER 2012 – REVISED NOVEMBER 2015

7 Detailed Description

7.1 Overview

TPS22981 is a power mux designed for Thunderbolt™ and Thunderbolt II™ applications (based on the Mini

DisplayPort connector). Thunderbolt and Thunderbolt II provide options for different voltage levels to be supplied

to an external Thunderbolt cable, and on to a device or host connected on the far end of that cable. Thunderbolt

and Thunderbolt II initiate operation with a nominal 3.3-V voltage (3-V to 3.6-V range is supported by TPS22981),

but can be configured through the interface protocol to enable a high-voltage mode (TPS22981 supports the

range of 4.5 V to 19.8 V). In operation, transition from the 3.3-V mode to the high-voltage mode requires that

system brownout not occur. The TPS22981 achieves this by enabling the high-voltage path (when a high-voltage

input is available and HV_EN is asserted) and monitoring for reverse current though the low-voltage switch back

to V3P3. When reverse current is detected, the low-voltage path is disabled. Similarly, when switching from high

voltage back to low voltage, it is normally undesirable for the system output voltage to brownout. TPS22981

avoids brownout by breaking the high-voltage connection and discharging the output until it reaches

approximately 3.3 V, at which point the low-voltage path is enabled to avoid excessive droop of the output

voltage. However, if the output voltage (on the OUT pins) is loaded, the output voltage may transition to 0 V

before returning to 3.3 V (see Transition Delays).

TPS22981 also provides resistor-controlled current limiting, undervoltage lockout (UVLO), and thermal protection.

The high-voltage path on TPS22981 may be current limited to two independently controlled current-limiting

levels, with the current-limiting level selected through the S0 input pin. A system host processor may be alerted

to fault conditions with the FAULTZ pin (see Table 3).

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