8.3.1.1 PP5V Current Limit

The current through PP5V to VBUS current limit may be dynamically selected to support 1.5-A or 3-A operation via EN0 and EN1. An external resistance to GND on IREF terminal is required to set the bias current for accurate current limit operation.

Under overload conditions, the internal current-limit regulator limits the output current to the selected current limit setting, I_{LIM_PP5V}, where I_{LIM_PP5V} is I_{LIM_PP5V_1P5} or I_{LIM_PP5V_3P0}, as shown in the PP5V Power Switch Characteristics table. When an overload condition is present, the device maintains a constant output current, with the output voltage determined by (I_{LIM_PP5V} x R_LOAD ). Two possible overload conditions can occur. The first overload condition occurs when either: 1) PP5V input voltage is first applied, PP5V source path is enabled (EN1_EN0 = 10b or EN1_EN0 = 11b), and a short circuit is presented (load which draws I_OUT > I_{LIM_PP5V}), or 2) PP5V input voltage is present and the PP5V source path is enabled into a short circuit. The output voltage is held near zero potential with respect to ground and the TPS6602x ramps the output current to I_{LIM_PP5V}. The TPS6602x limits the current to I_{LIM_PP5V} until the overload condition is removed or the device begins to thermal cycle. This is demonstrated in Figure 31 where the device was enabled into a short, and subsequently cycles current off and on as the thermal protection engages.

The second condition is when an overload occurs while the PP5V source path is enabled and fully turned on. The device responds to the overload condition within time t_{OS_PP5V} (see Figure 10) when the specified overload (per Electrical Characteristics) is applied. The response speed and shape vary with the overload level, input circuit and rate of application. The current-limit response varies between simply settling to I_{LIM_PP5V} or turning off and a controlled return to I_{LIM_PP5V}. Similar to the previous case, the TPS6602x limits the current to I_{LIM_PP5V} until the overload condition is removed or the device begins to thermal cycle. The TPS6602x thermal cycles if an overload condition is present long enough to activate thermal limiting in any of the above cases. This is due to the relatively large power dissipation [(V_PP5V – V_VBUS) x I_{LIM_PP5V}] elevating the junction temperature. The PP5V source path turns off when its temperature reaches its thermal shutdown temperature of TSD_PP5V_R while in current limit. The PP5V source path remains off until its temperature cools to TSD_PP5V_F and then re-enables automatically.