TPS54428: OCP adjustment

Shidara,

TPS54428 uses valley detect current limit.  That is the current at the end of the off time.  The actual load current will be one half of the peak to peak inductor current above that, so increasing the inductor value will lower the effective load current limit.  See this blog:

TPS54428 is designed to be used with specific output inductor values, see table two in the datasheet.  It should be safe too increase the value by one standard value, i.e. if 2.2 uH is recommended, then 3.3 uF should work.  If you increase the inductor value, I would recommend using an output capacitance towards the lower end of the range to keep the LC product within range.

Hi Shidara, 

The device has the OCP function, typical value is 5.3A low side (with min of 4.6A and max of 6.8A). So the average current based on typical value is 5.3A+(Ipp/2). Ipp is determined by the inductance, input and output voltage. What is the Ipp you calculated based on equation 5 in the TPS54428 datasheet (I guess VIN, VOUT) and what it is the max average current (Load) in your system? you can play with the inductor value to reduce the peak to peak current, however, you need to make sure to follow the recommended values per the datasheet (table 2) for stability and also the inductor saturation current rating must be greater than the calculated peak current and the RMS or heating current rating must be greater than the calculated RMS current.

Here are some tips on the layout of the PCB for best thermal performance:

• Exposed pad of device must be connected to PGND with solder.
• For better heat dissipation, topside area adjacent to the TPS54428 should be filled with ground as much as possible to dissipate heat.
• The bottom-side area directly below the IC should a dedicated ground area. It should be directly connected to the thermal pad using vias as shown. The ground area should be as large as practical. Additional internal layers can be dedicated as ground planes and connected to vias as well.

Thanks!

Tahar Allag