Recently we have about eight PTH04070WAD modules permanently damaged one after another during working in our device where they provide supply voltages for Xilinx FPGA and CPLD, Ethernet PHU, DDR SDRAM and some other minor circuits. The device consists of three PTH04070WAD modules supplied with +5 V from external stabilized power supply unit and provides 1.2, 2.5, and 3.3 V outputs. The modules got damaged one at a time on in couples without any obvious reason for us. Before being damaged they work correctly for a considerably long period of several days. The way by which we use PTH04070WADs meets the recommendations given in the data sheet with the only exception that we use considerably large output capacitance of 3000 uF in order to provide supply for our circuits during a short period after the external +5 V is switched off for safe termination and storing variables in non-volatile memory. Damaging of the modules results in switching the external supply unit into current-limiting mode or in some cases in disappearing of the output voltage of the module. The output of the external supply unit has transient voltage suppression circuit which prevents possible pikes and over-voltage. Could you tell us possible reasons of such a behavior and means of correcting it.
Vladimir :
PTH04070W absolute maximum output capacitance is 560uF.This includes the 200uF ceramic capacitors.
The minimum ESR of the total output capacitors is 7mΩ. This is published in the product specification.When 3000uF capacitance is located on the output, the dv/dt will over stress the PTH04070W.
The PTH04070W inhibit pin for -on-off control, if used,must not be connected to any other pull-up component or any other module. The inhibit can be controlled with an open drain discrete transistor. This inhibit pin transistor must be dedicated to each PTH04070W . It cannot share this inhibit control pin with any other PTH04070W or module.
My e-mail contact is tguerin@ti.com if you want to discuss the details of this application
Tom