LM5088: Positive and negative power supplies with same Non-Synchronous Buck Controller

Zain,

I don't see the schematic attached.

Can you please re-send.

Thanks!

Best Regards,

Ankit Gupta

Application Engineer

Please find attached schematic.

2134.Schematic.pdf

one more thing for information, thermal pad of +22.8 V supply is connected with ground while thermal pad of -22.8 V is connected to -22.8 V. 

Hi Zain,

The inverting buck-boost (IBB) design has an effective input voltage of Vin + Vout, so the bias supply LD) sees a larger voltage, thus increasing IC dissipation. Also, the IBB configuration has a different duty cycle, so check the conduction loss in the high-side FET with the BSC340 80V FET.

you can use the LM5088 quickstart calculator to check your design. Note that there should be an input cap from Vin to -Vout placed close to the FET and diode to complete the high-frequency switching loop. See app note snva856 for more detail.

Regards,

Tim

www.ti.com/lit/snva856

Hi Tim,

Thanks for your reply. That was very helpful.

* -22.8 V Supply

Inductor, Mosfet and diode in -22.8 V supply are according to app note snva856. But we missed the input cap from Vin to -Vout (placed close to the FET and diode). We did the rework to place this cap (floating in air) but still our inductor heats up to 100 C @ 2A load (this works fine @ 0.3 A load).Other component in -22.8 V supply are under 60 C. Also the value of COMP pin components and RAMP pin components are slightly different. So what is your suggestion on that?

* +22.8 V Supply

This supply is working good. All components temperature is under 60 C @ 4A load.

Regards

Zain