The start-up and adjust logic imposes certain operating modes on the load-share controller during start-up, fault, and disable conditions. Under these circumstances the information obtainable by the error amplifier of the UCC29002 device may not be sufficient to make the correct output voltage adjustment, therefore the adjust amplifier may be forced to a known state. Additionally, the LS bus driver of UCC29002 device is disabled during these conditions.

The start-up and adjust logic in the UCC29002-1 is different than that in the UCC29002 and UCC39002. The behavior of the UCC29002, UCC39002, and UCC29002-1 are identical for LS bus fault and disable conditions. However for the initial start-up condition, the UCC29002-1 behavior is different from the other devices and this difference is discussed in the following paragraphs.

The UCC29002 and UCC39002 devices have a defined start-up mode which is active as long as V_CSO of the module that is starting up is less than 80% of the voltage on the LS pin. Because the output current of the starting module is low compared to the currents of the other modules in the system (represented by V_LS), the start-up mode logic disables the LS Bus Driver by the disconnect switch and applies 3V to the Adjust amplifier noninverting input to sink the maximum current through the adjust resistor. This operating mode causes the starting module to very quickly engage in sharing the load current because its output is adjusted to a sufficiently high voltage immediately at turn-on. Start-up mode is exited as soon as V_CSO exceeds 80% of V_LS, and the load-share bus driver and the adjust amplifier revert to normal operation.

In contrast, the UCC29002-1 device has some of the start-up logic disabled and has no defined start-up mode. Specifically, the UCC29002-1 does not apply 3V to the Adjust amplifier regardless of V_CSO level at any time and the LS bus driver is not disabled at start-up. The Adjust amplifier current rises as V_EAO rises. This difference allows the starting module with UCC29002-1 to engage its load-sharing at a slower rate. The UCC29002-1 version may be preferable for applications where the disturbance of rapid load-sharing start-up may be undesireable.

In cases of detecting the VDD bias voltage less than the minimum operating level, external disabling of the controller using the CS+ and CS− pins, or detecting an LS-bus fault condition, all three versions UCC29002, UCC39002, and UCC29002-1 act to disconnect the LS Bus Driver and ground the Adjust amplifier input.